RESTRICTED Report No. NA-5629 ENGINE-- SECTION 11

Figure 144—PD-12K6 filler neck. The lower panel is fitted with a door for forced to the spray nozzle, which sprays the charge ground heating and propane priming, and has an evenly across the face of the . Fuel is opening containing a reinforced bushing for prevented from leaking into the engine by the insertion and support of the engine starting crank. spring-controlled discharge nozzle, which is closed when the nozzle fuel pressure is less than 4 Ibs./sq. 5. Engine Exhaust in. The engine exhaust is discharged from the 2 ex- haust ports in each through an individual b. COMPONENT UNITS—The carburetor is com- exhaust stack for each cylinder. The design of the prised of the following 5 separate units, each with its exhaust stacks incorporates a combination of flame own individual function: dampening and jet propulsion features. The stacks (1) — The throttle unit follows are constructed of corrosion- and heat-resisting conventional carburetor lines incorporating a stainless steel. throttle, a venturi tube system for developing suction, and a group of impact tubes for collecting 6. Carburetor the average entrance pressure. a. GENERAL—The airplane is equipped with a (2) AUTOMATIC MIXTURE CONTROL UNIT— Bendix Stromberg injection carburetor (see Figure This unit consists of a sealed metallic bellows, re- 144) fitted with a double diaphragm acceleration sponsive to variations in temperature and pressure, pump. This type of carburetor has a closed fuel sys- which operates a contoured valve. The automatic tem from fuel pump to discharge nozzle. Fuel is mixture control serves to maintain the correct fuel- delivered to the carburetor by the engine fuel pump air mixture ratio in the carburetor when operating at about 16 Ibs./sq. in. pressure. It is metered under conditions of varying air temperature and according to the mass airflow rate as registered by pressure such as result from changes in altitude. the venturi tube and automatic mixture control unit, (3) REGULATOR—The regulator unit auto- and is then matically adjusts the fuel pressure across the metering [ 187 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

[ 188 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 jets and, therefore, the fuel flow in proportion to the altitudes by gradually opening the throttle as the alti- mass airflow through the throttle body. The unit is tude is increased and smoothly closing the throttle made up of an air diaphragm, a fuel diaphragm, and during descent, thus maintaining the required mani- a balanced fuel valve, all mounted on one stem. Fuel fold pressure during climbing and diving. This device enters through a strainer, passes through the relieves the pilot of the necessity of making balanced valve to one side of the fuel diaphragm carburetor throttle corrections to maintain required chamber and then to the jets in the fuel control unit. manifold pressure during ascent or descent. The pilot A vapor separator is provided in the strainer can change the manifold pressure at any time by chamber to prevent vapor from entering the manually operating the cockpit throttle lever just as if regulator. there were no automatic regulator. The regulator merely maintains automatically the manifold pressure (4) FUEL CONTROL—This unit, attached di- selected by the pilot. As the regulator functions, the rectly to the regulator, contains the metering jets, a carburetor throttle is actuated by hydraulic pressure fuel head enrichment valve, an idle metering valve, supplied by the engine oil pressure and is regulated and a manually operated mixture selector valve. The by the supercharger air pressure. unit is designed so that metering jets and other variables may be selected to fit the mixture ratio 8. Carburetor Air Scoop and Heating requirements of the engine under all operating Duct conditions. The fuel head enrichment valve is The carburetor air scoop consists of an air intake operated by a diaphragm which obtains its operating duct built integral with the top engine cowling and an force from the difference between the metered and elbow duct mounted by means of a flexible joint to unmetered fuel pressures. As the mass airflow to the the carburetor intake. There are two types of air in- engine increases, the pressure of the fuel delivered take ducts, either of which may be installed on the to the fuel control unit increases proportionately, airplane. One, a lightweight duct, supplies only thereby causing the enrichment valve to open. The rammed, unfiltered air: the other is equipped with a idle valve is mechanically connected to the throttle retractable filter which can be operated in flight by and controls the mixture throughout the idle range of the pilot (see b, below). Both types of ducts may speeds. The manual mixture control provides full easily be interchanged by removing and replacing the rich, automatic rich, automatic lean, and idle cutoff top cowling. Provisions are made on all airplanes for positions. the installation of a carburetor heating duct (see Fig- (5) SPRAY NOZZLE AND ACCELERATING ure 145). PUMP—The spray nozzle is mounted on the rear supercharger housing to spray the fuel into the a. ELBOW DUCT—The carburetor air scoop elbow supercharger entrance. Combined with the spray contains a cold and hot air door operated manually nozzle is a double diaphragm acceleration pump from the cockpit. If the cold air intake duct becomes automatically operated by vacuum. When the obstructed because of icing conditions, the spring- throttle is opened, an accelerating discharge is loaded hot air door will open automatically as the sprayed into the air stream through a separate result of suction existing in the carburetor intake. discharge nozzle as well as through the regular spray This duct is held rigid by cowl formers riveted to the nozzle. A spring-operated valve and 2 diaphragms upper section of the duct and by braces attached to are required to produce this action. the engine mount. A drain line to eliminate any water or refuse which may accumulate in the air scoop 7. Automatic Manifold intake duct extends from the forward part of the Pressure Regulator elbow to the lower section of the engine accessory A Delco-Remy automatic manifold pressure regu- compartment. lator is mounted on the left side of the accessory case next to the carburetor. The regulator is b. RETRACTABLE FILTER—This installation connected to the carburetor throttle for the purpose consists of a hinged air filter which can be raised or of maintaining within a few inches of mercury a lowered by the pilot, a door in the upper cowl skin to selected manifold pressure, independent of altitude, admit unrammed air, and a lower fairing door to up to the critical altitude for the selected power assure a smooth flow of air through the scoop when condition. After the pilot moves the throttle control the filter is retracted. The mechanism is operated to obtain the desired manifold pressure, the regulator manually by means of rods and bellcranks. Two drain will automatically compensate for the differences in lines extend from the air scoop duct to the cowl skin. air density at various [ 189 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

[ 190 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

(1) OPERATION—When the filter is raised, the throttle arm and is adjusted to the throttle position top door opens inward and the lower door hinges for take-off. In case the pilot requires more than downward simultaneously. Rammed air entering the take-off power, he may pull up the spring-loaded scoop is thus closed off, and unrammed air passes release lever on the throttle arm and draw from the through the filter to the carburetor. engine the power reserved for war emergency. The (2) FILTER RETRACTED—When the filter is propeller control lever is connected to the propeller lowered, the top door closes tightly and the lower governor by means of a flexible Arens control. door hinges upward so that the lower door and the Push-pull levers with flexible cables operate the top of the filter are on the same horizontal plane. retractable filter, the carburetor air doors, and the Rammed air entering the scoop has a free flow over carburetor heating door. the top of the filter to the elbow. 11. Propeller c. CARBURETOR HEATING DUCT—This duct ex- The airplane is equipped with a Curtiss three-blade, tends from the air scoop elbow to a door located directly aft of the left rear exhaust stack. The door is built integral with the side cowl former and is opened by means of a flexible cable. When the door is open, the hot engine exhaust gases travel through the duct to a U-shaped adapter built around the air scoop elbow. Passing into the elbow through a num- ber of small holes, the engine exhaust is utilized to warm the carburetor induction system.

9. Magneto and Distributors A Bendix Scintilla double magneto, mounted on the upper end of the engine case just forward of the 2 distributors, provides true double ignition from a single unit. Four sparks are produced in each coil for Figure 147—Propeller Detail Diagram every revolution of the magneto drive shaft. The high-tension current from the coils is distributed to 2 10-foot 9-inch diameter, electric, constant-speed independent sets of spark plugs through the 2 dis- propeller. A reversible electric motor mounted in the tributor heads, which are driven at speed. propeller hub serves to control the propeller blade Since the magneto gives 4 sparks per revolution, it is angles. The electric energy required for operating driven at 1-1/2 crankshaft speed for the 12 cylinders. the motor is taken from the airplane power supply The right distributor supplies the high-tension spark and passes through a set of brushes, mounted in a to all the exhaust plugs, and the left distributor sup- housing attached to the engine nose, to slip rings plies the spark to all the intake plugs. Their rotors fixed to the rear of the propeller hub. From the slip are adjustable for timing to the proper plugs, and the rings, the electric energy passes through connector rotor speed is 1/2 to 1. The magneto and distributors leads in the hub to leads in the speed reducer, and are timed by using the No. 1 left cylinder. The firing thence to the motor. The motor changes the blade order is 1L, 2R, 5L, 4R, 3L, 1R, 6L, 5R, 2L, 3R, 4L, angles through a two-stage planetary-type speed 6R. reducer which drives a master bevel gear. This gear meshes with a bevel gear attached to the shank of 10. Engine Controls each blade. Thus, depending upon the direction of The engine control quadrant is mounted on the rotation of the motor, the angle of the blades is left upper longeron in the cockpit. The throttle increased or decreased. A brake is attached to the control lever is interconnected by rods and front end of the electric motor for the purpose of bellcranks to the automatic manifold pressure stopping its rotation the moment the pitch-changing regulator, and the mixture control lever is current is cut off. The brake also provides a definite interconnected in the same manner to the carburetor. lock which holds the blades in a fixed position when A throttle stop (see Figure 146) is bolted to the no angle change is desired. upper longeron across the path of the

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of operation as engine power, airplane speed, and air density.

13. Propeller Spinner The spinner is a streamlined fairing installed around the propeller hub for the purpose of cutting down wind resistance. It consists of two sections dynamically balanced in the process of fabrication. The aft section of the spinner is secured with bolts to the back side of the propeller hub adapter before the propeller is installed. The forward section is then bolted to the bulkhead of the aft section and can be removed for access to the propeller operating mechanism in the hub. A hole in the nose of the forward section, created in the process of fabrication, is closed with a butadiene plug (NA 73- 44029) of 60 Shore hardness.

14. Engine Drain Box A drain box (see Figure 149) bolted to the lower

Figure 148—Propeller Governor

Switches in the hub end of the power unit limit the low and high blade angles of the flight range. These switches are cam operated and are connected to their respective motor leads.

12. Propeller Governor A spring-loaded, centrifugal-type proportional governor with an oil servo mechanism is mounted on a pad at the forward end of the engine. Basically, the governor is a single-pole, double-throw switch placed in the propeller circuit and operated automatically by the flyweight forces, which are affected by variations in governor speed. The RPM setting of the governor is varied by a cockpit control lever connected to the governor control lever by means of a flexible push-pull Arens control. A take- Figure 149—Engine Drain Box off RPM limit arm having an adjustable stop screw is pinned to the governor control lever. The purpose cowling former in the accessory compartment of the governor is to maintain the engine at a set receives the combined drainage of the various constant speed by changing the propeller blade accessory compartment drain lines. An overboard angle to correct for such varying conditions line leads from the drain box to the radiator access cover.

[ 192 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 OPERATING INSTRUCTIONS

15. Engine (10) Set fuel booster pump switch, located on the pilot's switch panel, to ON. Fuel pressure gage a. STARTING ENGINE—The sequence of opera- should indicate 10 Ibs./sq. in. shortly after booster tions listed below should be followed when starting pump is turned on. the engine. (11) Prime engine 3 to 4 strokes when cold, (1) Turn ignition switch to OFF. one when warm. The priming system is (2) Turn generator disconnect switch to ON. independent of the carburetor, and caution must be (3) Pull propeller through several turns if en- exercised not to overprime engine in view of the gine has been idle for more than 2 hours. extreme effectiveness of the priming system. No (4) Place carburetor air. control in the COLD priming action nor fuel discharge is accomplished position. by pumping the throttle. After priming, ascertain that primer is locked in the OFF position. (12) Set propeller selector switch in AUTO CONSTANT SPEED and push propeller circuit- breaker button to ascertain that electrical circuit to propeller governor is complete. Raise the safety guard over the selector switch. (13) Uncover switch by pulling hinge cover upward. Press starter switch to the ENERGIZE position; when the flywheel has reached the maximum speed, press the switch upward to CRANK position to engage starter with the engine. An electrical socket on the right side of the fuselage aft of the pilot's cockpit may be used for connecting an external power supply. A starter crank and extension stowed in the right wheel well may be removed by loosening the wing

Figure 150—Engine and Propeller Controls

(5) Set throttle approximately 3/4 inch open. (6) Set mixture control at IDLE CUT OFF. (7) Set the propeller control at full INCREASE RPM (low pitch) position. (8) Turn the main system fuel selector valve to left: auxiliary system off. (9) See that all personnel are clear of propeller; then turn ignition switch to the BOTH position.

Figure 151—Starter Crank Installed

[ 193 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 nut on the clamp around the arm of the crank. The extension tube is removed by twisting up and pulling outward. To crank engine by hand, insert crank and extension through hole in lower aft engine cowl and into the funnel-shaped starter attachment. (See Figure 151.) (14) As engine starts, move mixture control to AUTO RICH. If engine does not start after one or two turns, move mixture control forward and then back to IDLE CUT OFF. (15) Should engine stop, return mixture control to IDLE CUT OFF position immediately to avoid flooding engine with fuel.

Note: Operation of the engine at low RPM or idling speeds should be avoided as much as Figure 152—Carburetor Air Filter Control possible. Low engine operating speeds permit oil to accumulate on the electrodes because of filtered unrammed air: push the control in to obtain low temperatures and excess fuel deposits. unaltered rammed air. b. CARBURETOR AIR—Two carburetor air con- b. STOPPING ENGINE trol handles (see Figure 153) are located on the left (1) Idle engine at 600-800 RPM to cool: then side of the instrument panel. Both controls are of the accelerate to 1200 RPM and move mixture control push-pull type. Pull the cold air control (No. 1) out to IDLE CUT OFF position. The throttle should to obtain nonrammed air: push the control in to ob- then be pushed forward. tain cold rammed air. Pull the hot air control (No. 2) (2) Turn ignition switch OFF after engine out to heat the carburetor: push the control in to shut ceases firing. Allow mixture control to remain in off . Ordinarily the carburetor heat IDLE CUT OFF position as a precaution against control will be in the cold position during ground accidental starting. operation of the engine. However, during extended (3) Turn all switches and fuel selectors OFF. ground operation and before take-off, full carburetor air heat should be applied under icing conditions. Note: Stopping the engine by shutting off the fuel When ice is eliminated, maintain a carburetor air tank valves may allow vapor to be pumped into the temperature of 15° C to 30° C (50° F to 86° F). regulator, and is not recommended. 17. Propeller c. OIL DILUTION — Before stopping the engine The propeller governor control lever is located when a cold weather start is anticipated, hold the oil on the control quadrant, and the propeller dilution valve control ON for approximately 4 min- SELECTOR S'WITCH (see Figure 154) is on the utes with the engine running at 800-1000 RPM, and left side of pilot's switch panel. By moving the stop the engine by moving the mixture control to selector switch, the propeller may be controlled for IDLE CUT OFF position. Turn the ignition switch optional automatic constant speed operation, fixed OFF, continuing to hold the oil dilution valve pitch, or manual selection. The manual control control switch ON until the engine stops. Turn the positions of the switch lever are marked DEC RPM dilution switch and fuel tank selector valves OFF. and INC RPM. Contact is maintained only while the For complete information on oil dilution refer to switch is held in these respective positions: when Section 21, Paragraph 10b. released, the switch returns to FIXED PITCH. Thus the manual control is a means by which propeller 16. Carburetor Air Scoop and Heat pitch may be adjusted to obtain any desired RPM Controls with precision. A spring-loaded guard moves the a. RETRACTABLE FILTER—The filter control switch to AUTO CONSTANT SPEED when swung (see Figure 152) is located on the right side of the upward. A circuit breaker at the right of the selector instrument panel. Pull the control handle out to switch is used to cut off the power in case of obtain overload.

[ 194 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 REMOVAL AND DISASSEMBLY

18. Engine

To remove the engine from the airplane, follow the general procedure outlined below:

a. Take off all removable cowl panels. Remove accessory panels first and disconnect the retractable filter control if the filter is installed. b. Drain oil and coolant systems. c. Remove the propeller and spinner. (See Para- graph 20.) d. Disconnect engine controls as follows: (1) Disconnect Arens control from propeller governor and from engine support bracket. (2) Disconnect flexible control cable from car- buretor air scoop elbow, and control which operates carburetor heating door. Figure 154—Propeller Control Switches sary fuel, oil, coolant, hydraulic, vacuum, and drain lines. f. Disconnect electrical wiring at power panels. Disconnect wiring at propeller relay box and at booster coil box on right engine mount.

Note: Refer to Section 24, Figure 285, for a com- plete list of engine disconnect points and their locations.

g. Remove nose ring cowling, cowling formers, and braces. To do this, disconnect the generator blast tube, and the lines to the coolant tank and engine drain box. Remove carburetor air filter elbow and carburetor heating duct.

Figure 153—Carburetor Air Control (3) Disconnect throttle and mixture control rods at jackshaft assembly and at manifold pressure regulator and carburetor. e. Disconnect at the firewall or remove all neces-

Figure 155—Hoisting Complete Power Plant

[ 195 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 h. Fasten a hoist to the engine mount lugs and 20. Propeller and Spinner propeller shaft (see Figure 155), and take up enough slack on hoist to disconnect the 4 bolts which hold Refer to Figure 165 for identification of the engine mount to the firewall. Place the engine on a various units referred to in the following instructions stand. for removing the propeller and spinner: i. Remove engine mount from engine by taking a. Run propeller to maximum low pitch. out the 10 bolts which extend through shock support b. Remove access door on right side of nose ring housings (see Figure 162). The support housings cowling and, working through the aperture, proceed may be removed by unscrewing lockwired nuts from as follows: studs attached to engine block. (1) Release the 2 latches that hold the slip ring j. Remove the various accessory units from their brush assembly to the housing and remove the brush mounting flanges and disassemble engine as assembly. Damage will occur if propeller is required. removed with brushes in position. (2) Remove front section of spinner from rear 19. Complete Power Plant Unit section (see Figure 157). An extension wrench with The entire power plant section of the airplane a 1/2 - inch socket may be inserted through the may be removed at the firewall and mounted on a lightening holes in rear spinner sections when fixed structure for disassembly, and another power propeller is rotated manually to proper positions. plant unit substituted in its place. To remove the power

Figure 157—Propeller Installed— Spinner Removed Figure 156—Removing Propeller Spinner plant section it is first necessary to take off the pro- Note: It may be necessary to pry off the front spin- peller (see Paragraph 20). Next remove the ner section. Handle the spinner carefully during accessory compartment cowling and the cowl removal. formers which attach to the firewall. Disconnect at the firewall all engine controls, all electrical wiring, c. Remove spinner centering ring by detaching and the fuel, oil, coolant, vacuum, and hydraulic the 3 bolts which hold it to adapter plate on back of lines. A hoisting sling may then be attached to the power unit. engine mount lugs and propeller shaft. When the 4 d. Remove the power unit, neoprene seal, and firewall mounting bolts are removed, the power grease seal. plant unit may be hoisted from the airplane. [ 196 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 e. Rotate each blade until gear teeth are down be- cowl former at the right side of the air scoop elbow. hind bulkhead of hub. Disconnect the booster coil junction box from the f. Remove locking pin assembly. underside of the cowl former to the right of the air g. Remove locking sleeve. scoop. Disconnect the carburetor air control rod h. Insert a 3-1/2 - foot bar completely through from the actuating arm and the bracket on the left propeller shaft and loosen nut, using a force of 250 side of the air scoop elbow assembly. Loosen and to 300 Ibs. Do not hammer on bar. Attach a sling remove the 2 air scoop adjustable braces (at the rear and hoist (or support the propeller if a hoist is not of the scoop elbow) that extend to the engine mount available) and remove the snap ring, front cone, on each side. Remove the 4 bolts and 2 countersunk propeller shaft retaining nut, grease seal and screws in the 2 cowl former joints at each side of the spreader. Install a thread protector. carburetor air scoop elbow assembly. Remove the bolts securing the air scoop elbow assembly to the Note: If a hoist is available, it is not necessary to upper adapter ring and lift off the air scoop elbow remove the nut, snap ring, or front cone from the assembly. propeller hub. b. To remove the neoprene adapter, take out all the screws securing the lower adapter ring to the These parts are so arranged that as the retaining carburetor and lift off the adapter. Care should be nut is backed off it pulls the propeller with it, until exercised at all times to prevent anything from the nut reaches the end of the propeller shaft thread. falling into the supercharger section. Removing the When employing this procedure, a suitable hoist is neoprene adapter provides access to the 7 nuts that necessary to support properly the weight of the pro- secure the carburetor to the adapter. peller and prevent damage to the shaft threads. c. Seven 3/8 - inch studs secure the carburetor to i. Slide propeller off shaft, being careful not to the adapter. These studs are tapped into the adapter damage rear cone seat or shaft. Place propeller on a casting and extend up and through the throttle unit. smooth, clean surface. The nuts which hold the carburetor to the adapter fit j. Remove rear spinner section by taking out the into recesses so that the top of the nuts are below the 9 bolts which hold it to the propeller slinger ring level of the top flange of the throttle unit. adapter. Disconnect the fuel spray nozzle line at the k. Remove rear cone and any shims that may carburetor and loosen the sealing nut at the spray have been installed at assembly. nozzle so that the line can be swung back out of the 1. If desired, remove locking adapter from end of way. Disconnect the fuel hose which goes to the propeller shaft. carburetor. Disconnect the oil dilution and fuel m. The anti-icer slinger spout and the brush box pressure line at the bottom of the carburetor. housing may be removed by detaching nuts which Disconnect the carburetor vent line at the vapor hold them to the engine studs. separator fitting. Disconnect the mixture and throttle control rods at the carburetor actuating arms. 21. Carburetor Remove the safety wire and the carburetor hold- To gain access to the carburetor for removal, take down nuts and lift the carburetor from the studs: be off the upper engine cowl panel containing the for- careful not to damage any of the lines or protrusions ward section of the air scoop, and the upper engine near the carburetor. As soon as the carburetor has accessory compartment cowl panel. Disconnect the been removed, cover the entrance to the retractable filter control before removing the top supercharger. Cover all open lines with tape or other cowl. Disconnect the carburetor heating duct from suitable material when the openings are to be the air scoop elbow. Then proceed as follows: exposed for any length of time.

a. Disconnect the manifold pressure and primer 22. Exhaust Stacks lines at the unions just forward of the air scoop, and To remove the exhaust stacks, take off the top remove the 2 clips that secure these lines to the cowl and the two side cowl panels. Remove the engine lower and upper shroud sheets and the upper shroud supporting tube. Detach the nuts which hold the exhaust stack to the engine and remove the stacks, gaskets, and backing sheets.

[ 197 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 23. Cleaning Engine Parts while the inner race is being rotated. If the slightest a. STEEL PARTS—All steel parts such as gears, evidence of roughness is found, the bearing should shafts, rods, etc., can be cleaned with any one of the be replaced. Inspect the roller or ball cages for following materials: evidence of loose rivets or feathering of the cage Trichlorethylene Vapors from wear. Gasoline (unleaded) c. LUBRICATION — Serviceable bearings will re- Mineral Spirits quire only a coating of engine oil. They should then If the parts are not to be inspected or refinished be wrapped in oiled or waxed paper until they are to immediately after being cleaned with be installed. Do not remove the lubricant from these trichlorethylene vapors, they should be given a light bearings before installation unless there is reason to coating of oil to prevent corrosion. Clear, unleaded believe that dirt or grit is present in the bearing. gasoline or a solution of No. 10 Mineral Spirits mixed with an equal part of Apcothinner may be 25. used as alternative cleaners if trichlorethylene is not a. SPARK PLUGS—The reconditioning of spark available. No. 10 Mineral Spirits and Apcothinner plugs is a duty of the overhaul shop or depot, and are both products of the Anderson-Pritchard Oil the plug manufacturer's equipment should be used in Corp., Oklahoma City, Oklahoma. cleaning, repairing, and testing the plugs. Spark b. ALUMINUM AND MAGNESIUM PARTS —— All plugs should be adjusted to .012-inch clearance for castings such as accessory housing, crankcases, either mica or ceramic plug installations at regular coolant pump bodies, etc., are cleaned by spraying a maintenance periods. The core of spark plugs should 50-50 mixture of No. 10 Mineral Spirits and be tightened between 350 and 400 inch-pounds Apcothinner (see a, above). torque. b. DISTRIBUTORS CAUTION: The flash point of this mixture is 100° (1) Minor blemishes in distributor heads or F, and should not be used near any open flame or parts may be dressed up by using a fine grade of where excessive heat is present. sandpaper. These blemishes do not affect the heads either mechanically or electrically. After dressing 24. Antifriction Bearings up, apply a light coating of engine oil and wipe dry a. CLEANING—When ball and roller bearings are with a clean cloth. removed for inspection, clean them with a grease (2) In service, when a distributor has been solvent. It is not sufficient merely to wash the operating under moist conditions, a film of nitric bearing in the cleaning solution until all grease is acid may be found under the heads. This film has removed; the bearing must also be blown with air to the property of attracting moisture, causing ignition remove any foreign matter. The bearing must not, malfunctioning. Normal cleaning, even with carbon however, be permitted to spin in the air, because tet-rachloride, does not remove the nitric acid film, damage might result from the bearing running dry. and in such cases the distributor heads and parts or the bearing might disintegrate and injure should be cleaned with acetone. Treat the affected personnel. The air line used for cleaning bearings parts with engine oil after they have dried. should have a separator to remove any water. (3) When the brass distributor rotor fingers be- b. INSPECTION—When the bearings are free from come pitted sufficiently to require grinding, it is per- all dirt and grit and thoroughly dry, inspect for missible to grind as far as the scribed line on the roughness of balls and races, and for both radial and finger. When the scribed line is ground off, it will be lateral wear. Roughness can best be detected by necessary to discard the rotor and replace it with a grasping the outer race with one hand and slowly new one. For this reason, the grinding on the rotor rotating the inner race with the other hand while finger should be held to a minimum. exerting a side pressure. Both sides of the races (4) Extreme care should be taken when secur- should be checked in this manner for lateral ing the distributor heads. Before tightening the roughness. Radial roughness can be detected by securing screws, make sure that the head rests holding the bearing as described above, except that squarely and is fully seated on the distributor drive the pressure will be exerted radially housing mounting flange. Do not tighten the 3 screws too tightly.

[ 198 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

WARNING: If the distributor head has been washed in gasoline, be certain that it is thoroughly dry before installation so as to avoid any possible explosion of qasoline vapors.

c. MAGNETO—The magneto requires very little attention in service beyond proper lubrication and weekly inspection of the contact breaker. When in- specting the contact points, the main breaker spring should not be moved beyond 1/16-inch clearance between the movable and stationary contact points. Further tension of the main breaker spring caused by moving it beyond this point will result in weakening of the main spring.

Note: Do not disassemble the magneto unless fa- cilities are available for recharging the magnet. Each time the rotating magnet is removed, it must be recharged or the magneto will not function properly.

26. Replacement of Intake Manifold Gaskets

Note: Intake manifold gaskets can be removed STUD TIGHTENING SEQUENCE without disturbing the rubber manifold connections or removing any section of the manifold proper. Figure 158—Tightening Cylinder Hold- a. Using an Allison No. 2140-29 service down Nuts wrench, remove the cap screws in the top of the manifold flange, and loosen the nuts in the manifold b. Tighten by turning the nut through an angle of bottom flange just enough to free the gasket. 90° to 110°. c. Cotter each nut after final tightening. Note: The gaskets are made with slotted lower holes to allow their removal from the studs. 28. Bracket Stud Nuts b. Install new gaskets and tighten evenly so as These nuts should not be tightened excessively, not to damage the manifold flange. as high-temperature strains will result, causing c. When loosening the cap screws and nuts, it possible breakage of the studs. The correct should be determined if improper tightening was procedure for tightening the rocker arm bracket stud responsible for the gasket leak. If not, loosen the nuts is as follows: hose connection clamps at the tee and remove the a. Be sure that lobes are down on each manifold from the engine. Check the mounting bracket assembly before starting each tightening surface of the manifold on a surface plate for operation. evidence of distortion, and lap if necessary. b. Tighten all nuts down firmly so as to seat brackets, and cap on cylinder head bosses with cam 27. Cylinder Hold-down Nuts lobes in the proper position. At specified periods (see "25-Hour Inspection" c. Starting at bracket No. 1 and continuing in Paragraph 51), the cylinder hold-down nuts through in order on brackets containing camshaft should be inspected for tightness. The nuts are bearings (brackets Nos, 1, 3, 5, 7, 9, 11, and 12), tightened as follows: follow this procedure: Loosen one nut, and then a. Loosen the nut: then turn the nut down so that either turn it down finger-tight or pull it down it just makes contact with the boss but does not load lightly with a wrench—whichever is required to the stud. Loosen only one nut on a block at a time. have the nut make contact with the rocker arm bracket and the [ 199 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 lower face of the bracket make contact with the f. Inspect the cone seats in the hub. If metal has mounting boss. From this position, tighten to 65° to been picked up from rear cone, it should be cleaned 85° angularity, and cotter in place. Then loosen and out and the seat lapped with a fixture made for that tighten the other nut on bracket No. 1 in the same purpose. manner before proceeding with bracket No. 3, and g. The slip ring brushes should have no frayed or so on until the stud nuts of all brackets containing broken leads and should slide freely in holder. camshaft bearings have been tightened. h. Inspect propeller shaft seal and spreader for d. Following the same procedure as outlined deterioration. above, tighten the stud nuts of brackets not equipped i. Inspect propeller shaft nut locking adapter and with camshaft bearings to 55° to 70° angularity, lockpin assembly for wear and damage. Make sure starting at bracket No. 2 and continuing in order, that plungers are operating freely. one nut at a time, with brackets Nos. 4, 6, 8, and 10, cottering each nut in place. 30. Carburetor e. Tighten stud nuts of the locating camshaft The carburetor requires little attention between bearing cap from a finger-tight position to 30° to 50° overhauls. The regulator and fuel control units may angularity, and cotter in place. be drained through plugs in the bottom. The fuel strainer in the regulator body may be removed for CAUTION: The engine must be cold when the cyl- cleaning by unscrewing a single bolt. The fuel inder hold-down and rocker arm stud nuts are supply line does not have to be disconnected to tightened. clean the strainer. Be sure the strainer is put in the strainer housing with the recessed end (into which 29. Propeller the spring fits) toward the outside or housing cover. After disassembly, all of the propeller parts should be inspected in accordance with the following WARNING: Never use compressed air to blow out outline, and necessary repairs and replacements the carburetor or assembled units. made. Before inspection, the parts should be cleaned thoroughly and oiled to prevent oxidation. • Do not flush the carburetor With carbon telra- chloride. CAUTION: Do not use gasoline containing tetra- • To prevent damage to the diaphragms, use clean ethyl in cleaning the propeller parts. gasoline and new 100% paraffin-base light motor oil for cleaning and flushing. a. The hub, retaining nuts, gears, gear pins, and all other moving steel parts should be inspected by 31. Propeller Governor means of the Magnaflux method. a. SLUDGE REMOVAL—Any sludge entering the b. All bearings should be inspected for possible governor should be flushed out in order to prevent it damage, wear, or roughness. from collecting in and around the servo cylinder, relief valve, pressure pump, and other portions of Note: If it is found necessary to replace a single the governor control system; such a condition could bearing of a set of blade bearings, the entire set must cause the system to become inoperative. To flush be replaced. The bearings in each individual stack sludge from the governor, move the control lever are matched for and O.D.: consequently, it is back and forth with a smooth, continuous, not too necessary to return the stack to the manufacturer for fast motion, without stopping at the extreme satisfactory matching of a single replacement bear- positions of the lever. The lever should be moved ing. back and forth about ten times. This will pump clean c. All gears must be inspected for excessively oil through the system and remove the sludge worn or damaged teeth. through the oil outlet line. d. All threads shall be free of nicks, distortions, b. VIBRATION—Vibration may often be attributed wire edges, and roughness. to a hunting or surging governor. This is a condition e. All parts on which the plating is worn or cor- created by a faulty pressure relief valve, roded must be replated.

[ 200 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 dirty contact points, foreign material in the oil, a underspeeding, referred to as hunting, may exist. If galled metering valve or the like. If the oil pressure this condition exists, it is best to remove the to and from the servo is not constant or fluc- governor and replace it with one that is known to be tuates, a condition of successive overspeeding and accurate, or test the defective unit on a test bench.

REPLACEMENTS

32. Propeller Brushes a. SLIP RING BRUSHES—The brushes in the slip ring brush assembly are inscribed on the side with an arrow pointing toward the end of each brush. When the point of wear of a brush reaches the tip of the arrow or beyond, the brush must be replaced. b. MOTOR BRUSHES—If a propeller motor brush is less than 5/16 inch in length, replace the brush and spring assembly.

33. Spark Plugs The spark plugs recommended by the manufac- turer for use in this engine are the Champion C-34S and the AC-LS85. Use only solid copper gaskets.

34. Rubber Engine Mount Bushings If the rubber bushings in the engine mount shock support housing show signs of deterioration, they must be replaced. Evidence of excess oil or fuel on the rubber should warrant very close inspection of Figure 159—Engine Mount Shock these bushings. The bushings can be tested for Support Housings deterioration by pressing a piece of stiff wire with a blunt end against the rubber. If the wire should enter this engine are Allison Part No. 40751-E. The same the rubber 1/8 to 1/4 inch, the rubber has deteriorated gasket may be used as often as three times before to an extent that warrants replacement. being discarded, provided it is properly coated with graphite paint before each installation (see Paragraph 35. Exhaust Manifold Gaskets 41), and provided no defect occurs in the gasket itself The correct exhaust manifold gaskets for use on which would prohibit its further use. No gasket should be used more than three times.

ADJUSTMENTS

36. Valve Clearances and .020 inch for all exhaust valves. (See Figure a. When adjusting valves, make sure that the 161.) If adjustment is necessary, loosen the locknut engine is thoroughly cool, 10° C to 50° C (50° F to and back off or turn down the valve adjusting screw 122° F). In order to check the valve clearances, first as required. When retightening the locknut, be remove the valve covers and rotate the propeller careful not to turn the adjusting screw. shaft so that the cam roller is on the heel or base circle of the cam for the particular valve being CAUTION: Draw adjusting screw locknuts tight checked. with a service wrench, but do not strike the wrench b. Use a feeler gage between the valve stem tip with any object. and the valve adjusting screw ball end. The proper c. After tightening the locknut, the clearance valve clearance when cold is .015 inch for all intake, should be checked again. All clearances which are

[ 201 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 found to be below the proper amount should be reset to the proper figure. Reset all intake valves with clearances exceeding .017 inch, and reset exhaust valves with clearances exceeding .022 inch. Also turn the engine several revolutions and recheck clearance. Reset if clearance is incorrect. d. Items affecting adjustment of valve clearances: Concentricity of cam roller Oil film or foreign matter between end of valve stem and Condition of feeler gage — burred edge — Cleanliness Judgment and methods used by personnel e. When checking valve clearances, if any are found to have opened up to .025 inch or more for the exhaust and .020 inch or more for the intake, remove the adjusting screw and examine the ball ends for abnormal wear or breaks. Otherwise, the adjusting screws need not be removed between Figure 161—Valve Tappet Clearances overhauls.

ASSEMBLY AND INSTALLATION

37. Engine recesses in the sides of the engine mount line up a. Screw 4 studs (NA 73-31936) into each with the shock support housings. Attach the engine mounting pad on the engine (see Figure 162). Slip mount to the shock support housings, using the the fore and aft shock support housings onto the studs bolts, nuts, washers, and cotters indicated in Figure and secure them with AN310-6 nuts: then lockwire. 162. Place the end plates (J1269-2) and snubbing washers b. Hoist engine and engine mount into position (Jl269-3) in position at the top and bottom of the for attachment to firewall. shock support housings, and slide the left and right c. Bolt engine mount to upper longeron and engine mount beams into position so that the lower frame fittings as illustrated in Figure 162. Details C and D. Shim with washers as necessary. Bolts should be tightened to a tension of 2600 to 2700 inch-pounds ( see Figure 160). d. Connect the following lines:

Fuel lines (indicated by red band) Oil lines (yellow band) Coolant lines (white, black, and white bands) Hydraulic lines (light-blue, yellow, and light-blue bands) Vacuum lines (white and light-green bands) Propeller anti-icer line (red and white bands)

Note: Refer to Section 24, Figure 285, for a com- plete list of engine-to-firewall connections and their locations.

e. Install engine nose ring and cowling formers (see Figure 164). Install carburetor air scoop elbow, f. Connect electrical wiring at the power panels, Figure 160—Tightening Engine Mount to propeller relay, and booster coil box. Firewall [ 202 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

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g. Connect oil breather lines, coolant tank lines, and lines to engine drain box. h. Connect engine controls as follows: (1) Connect the throttle and mixture control rods at jackshaft assembly and at carburetor and manifold pressure regulator. Adjust linkage so that there is 1/8 - inch spring-back at quadrant. (2) Connect flexible control cable to carburetor air scoop elbow hot and cold air doors, and the control to carburetor heating duct. (3) Connect Arens control to propeller governor. Fasten engine support bracket (NA 73-44015) and eyebolt (NA 73-44034) to the control. With ad- justment screw on governor lever against the stop, there should be 1/8 -inch spring-back at control quadrant. i. Install propeller and spinner (see Paragraph 39). j. Check all connections and install removable cowl panels. If retractable filter scoop is used, install top panel first and then connect retractable filter control.

38. Power Plant Unit Figure 163—Propeller Brush and Slip Ring For engine installation, the engine and mount may Alignment be attached to a fixed structure and the accessories A between the face of the thrust nut and the center installed before the complete power plant unit is in- of the forward brush, and the distance B between the stalled at the firewall. center of the front slip ring and the rear cone, which should be held firmly in the hub. If the difference 39. Propeller, Power Unit, and Spinner between A and B is greater than .040 inch, shim be- hind the rear cone or brush housing as required. a. INSTALLATION OF PROPELLER (See Figure 165) (4) Install rear cone on shaft. (5) Place propeller shaft locking adapter in end (1) Check thrust nut on the enginefortightness. of shaft. (6) Clean thoroughly and coat the threads of Clean shaft threads and splines thoroughly, removing the propeller shaft and the propeller shaft nut with a all nicks, burrs, and galls from shaft and face of the mixture of 70 % white lead and 30% lubricating oil thrust nut. Carefully check if threads on the shaft are by volume. Apply a light coating of engine lubricat- burred or pulled. ing oil to splines. The rear cone should be left dry. (2) Remove the nuts (and spacers or spacer ring (7) Place propeller on a stand and turnblades to if provided) from brush housing mounting studs on the low pitch mark on the blade index (see Figure nose of engine and place brush housing on the studs. 168). Adjust anti-icer nozzles on slinger ring so that Replace, tighten, and secure the nuts. they will feed fluid into collector cups on each blade. Note: Except for the purpose of measuring for brush (8) Bolt rear spinner section to slinger ring location as described below, the brush assembly must adapter, using nine AN4-6A bolts, B985-24-63 be left out of the housing until the propeller has been washers, and AC365-428 nuts. installed. (9) Rotate each blade until gear teeth are down behind bulkhead of the hub to allow enough clear- (3) In order to predetermine the location of the ance for front cone and nut to be installed. brush contact on the slip rings, it is necessary to measure as shown in Figure 163. Measure the distance Note: To avoid the possibility of damaging the propeller shaft threads while installing the propeller, it is desirable to use a thread protector.

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(10) Screw thread protector onto shaft, Note: Whenever the power unit is operated and the tightening only by hand. electrical contact is not made through the slip rings, (11) Being careful not to damage the shaft or the mechanical stop must be removed to eliminate rear cone seat, locate and slide propeller halfway possibility of damaging the speed reducer housing. back on shaft. (12) Remove thread protector. (2) The cam may be rotated to the correct (13) Install grease seal and spreader. position by introducing a current through the two (14) Install nut, front cone, and retaining snap proper contacts on the face of the power unit. To ring. prevent unnecessary burning of the contact points, the leads should be held firmly to the side of the Note: New cones may come in one piece, in which contact, and contact made at the battery. case it will be necessary to saw the halves apart and carefully remove the metal left in the split. Note: The power unit splined shaft has a master or index spline which is indicated by an etched mark (15) Slide propeller back on shaft and on its inner diameter. The power gear is marked in carefully start nut on the threads of the propeller increments of 1°. Etched lines or a decal-comania on shaft. Tighten nut with a force of 250 to 300 pounds the blade gear sleeve indicate the blade angle when on a 3-1/2 -foot bar placed through holes in the nut. aligned with the index on the front of each blade Hammering on the bar is unnecessary and should be socket. The low angle setting is 23°. avoided. (16) To make a final check of the brush align- ment on the slip rings, apply a light coating of Prus- sian blue on the ends of the slip ring brushes and place them in the housing. Rotate the propeller back and forth slightly to remove the brush assembly. The brush track should be in the approximate center of the slip rings and not closer than .020 inch to the slip ring insulators. Shim behind either the rear cone or the brush housing as required to obtain proper alignment. When the alignment is satisfactory, clean the brushes and slip rings and install the brush as- sembly, locking the latches with safety pins. (17) Fit the locking sleeve to the adapter inside the propeller shaft nut, so that a lockpin hole lines up with a hole in the nut. If the holes do not line up on the first application, remove the locking sleeve and change its position on the adapter until the holes are in alignment. Place the lockpin assembly in position and release the lockpin. Note that it passes through both the locking sleeve and Figure 166—Limit Switches propeller shaft nut. (3) Replace power gear assembly, having b. INSTALLATION OF POWER UNIT master spline in line with the 23° mark on the (1) Before installing the power unit, check to power gear (see Figure 167). Replace the 3 see that the low limit switch arm is just riding on the attaching screws and snap ring. low limit segment of the cam (see Figure 166). To (4) Fasten spinner centering ring to forward make this check, remove the power gear and adapter face of power unit adapter plate with three AN7- plate from the power unit by removing the 3 attach- 10A bolts, B985-29-28-63 washers, and AC365- ing screws and the snap ring at the end of the power 720 nuts. unit splined shaft. (5) Rotate blade assembly until index on blade gear sleeve indicates 23°, the desired low blade angle.

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a. Lower carburetor on the studs and allow it to slip into place, exercising care not to damage the threads or bend the studs. Next place the proper washers and nuts on the studs and tighten uniformly and securely into place. Then safety wire these 7 nuts. Before the next step is taken, place a clean rag or other suitable cover over the carburetor venturi. Connect the spray nozzle fuel line at the carburetor, making sure the gasket is in good condition. Tighten and safety wire the packing nut on the spray nozzle assembly. Connect fuel hose to the carburetor fitting. Connect the oil dilution and fuel pressure line to the Y fitting at the bottom of the carburetor. Connect the boost control throttle link and mixture control rod to the corresponding carburetor actuating arms. b. Inspect neoprene adapter gasket for damage or deterioration. Position the adapter, secure it with the drilled fillister head screws, and lockwire. c. Position air scoop elbow, making sure cowl Figure 167—Indexing of Power Gear former joints line up. Fasten elbow to upper adapter (6) Coat gears with an approved grease. Make ring with screws, and lockwire. Bolt cowl formers certain that propeller shaft nut seal is in place in the bottom of power gear, and that neoprene ring seal is in place on adapter plate. (7) Clean contact points on face of the hub, and place power unit on the hub. Push unit hard against hub so that power gear meshes with blade gears. Secure unit with the 6 attaching bolts and lockwire them. (8) Completely fill hub with grease according to instructions contained in Section 3. (9) Install mechanical stop and safety. The zero on the mechanical stop must be adjacent to the zero on the speed reducer housing, and serial numbers on the mechanical stop and the power unit must be identical. (10) Fasten front spinner section to rear spinner section by fitting them together so that studs and holes coincide. Working through propeller brush access door, secure the two sections with six Figure 168—Indexing of Blade AC365-524 nuts and AN960-516 washers. into place and connect the air scoop elbow

adjustable braces. Connect carburetor air control rod 40. Carburetor to the bracket and the actuating arm on left side of Before installing carburetor, make sure that there air scoop elbow. Bolt booster coil junction box to is no foreign matter of any kind lodged in the super- underside of the cowl former to the right of air charger section. Check the gasket on the scoop. Connect manifold pressure and primer lines supercharger flange for damage or deterioration, and at their respective unions just forward of air scoop, if necessary, replace the gasket. Then install and clip these two lines to cowl former at right side carburetor as follows: of air scoop elbow.

[ 208 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 d. Install upper engine cowl panel and connect Figure 169), omitting the nuts where the 3 clamps retractable filter control. Install carburetor heating for the upper shroud support tube attach. Gaskets duct to air scoop elbow. If air scoop elbow does not should be installed with the raised bead away from line up properly with air scoop or carburetor heating cylinder block. Tighten nuts evenly to avoid distort- duct, readjust it with the adjustable braces. When ing gaskets. carburetor has been removed or drained for any pur- d. Assemble upper shroud plate and support tube, pose, it must be refilled. Replace top accessory cowl but do not tighten clamps. panel. e. Put this assembly in place and tighten all nuts securely on exhaust stack studs. 41. Exhaust Stacks f. Adjust upper shroud to correct position and a. Before installation of the stacks, clean the tighten clamps securely. mounting face of each exhaust port thoroughly and g. Install lower shroud sheets to backing plates examine all studs for looseness. and to upper shroud support tube clamps. Connect b. Paint both sides of the gaskets with a mixture upper and lower shrouds with three AN3-32A bolts, of electric furnace graphite and mineral oil mixed to B1070-10-88 spacers, AN970-3 washers, and a consistency suitable for application with a brush. AC365-1032 Boots nuts. c. Install backing plates, gaskets and stacks (see

Figure 169—Installation of Exhaust Stacks

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[ 210 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 42. Spark Plugs a. Place right shield (35A4544) inside slotted a. When installing spark plugs place a solid end of cylinder (NA 73-43033), and insert long end copper gasket (Part No. 40A888-718-968-080) of bolt assembly (NA 73-43036) through hole in between the spark plug and cylinder, except where a shield. Slide a spacer (NA 73-43038) onto bolt thermocouple gasket (Part No. 35A2037) is used, in assembly, and fit left shield (NA 73-43035) into which case no other gasket is required. cylinder so that tabs on shield fit into slots provided for them in cylinder. CAUTION: Do not install or tighten spark plugs b. Fasten this assembly to quadrant support when the engine is hot, as thread seizure with bracket (NA 73-43026) with an AN310-4 nut and subsequent damage to the spark plug shell and cotter pin. To do this, the quadrant support bracket cylinder bushing may result. must be detached from the upper longeron. b. Lubricate threads of plugs lightly, using spark c. Insert throttle and mixture control levers plug thread lubricant Spec. 3578. The lubricant through slot in upper longeron and fit lower end of should be stirred thoroughly prior to use. Apply only each lever over cylinder, assembling them with the a light coating of lubricant on the shell threads and correct discs and spacers (see Figure 170). none on the cylinder bushing threads. Any lubricant Assemble all levers, discs, and spacers with a thin which may have been deposited on the firing end of film of grease, Spec. AN-G-3. the plug must be completely removed before d. Place propeller control lever and spacer (NA installation of the plug. 73-43024) over cylinder, and fit the 068707 spring c. Draw down spark plugs firmly with a wrench over short end of bolt assembly. having 10-inch leverage. A torque of approximately e. Install plate (NA 73-43032), name plate (NA 480 in.-lbs. is sufficient and should not be exceeded. 97-43030), friction adjusting knob and ring lock. The two plates are connected to support bracket with 43. Engine Control Quadrant screws on forward end and with a screw, spacer, and nut on aft end. The engine control quadrant assembly (NA 97- f. Bolt support bracket to upper longeron, install 43005) must be completely disassembled prior to upper name plate, and connect throttle, mixture and installation in order to fit the throttle and mixture propeller controls, making certain controls have 1/8 control levers in the slot provided for them in the -inch spring-back at the quadrant. upper longeron. Use the following assembly pro- cedure, and refer to Figure 170:

FINAL TEST AFTER ASSEMBLY

44. Testing Engine Note: It is necessary to observe the a. Warm up the engine at approximately 1000 to reading immediately after switching to single 1200 RPM until the oil temperature shows a definite magneto operation, before the automatic boost increase and the oil pressure remains steady when control has had time to compensate for the RPM throttle is opened. If oil pressure does not reach 60 drop. Ibs./sq. in. within 30 seconds, stop engine and d. With engine turning 2200 RPM, hold propel- investigate. ler selector switch in DECREASE RPM until a decrease of approximately 200 RPM is noted. Then b. Refer to the engine limitation plate on right- hold selector switch in INCREASE RPM until hand longeron for oil pressure, oil temperature, original engine speed is resumed. This test shows coolant temperature, and fuel pressure. that pitch changing mechanism is working properly. Place selector switch in AUTO CONSTANT c. Press propeller selector switch to the FIXED SPEED and pull governor control lever back until a PITCH position and, by moving it to INCREASE reduction of not more than 200 RPM is noted. At RPM, raise the engine speed to 2200 RPM at 30 in. this RPM, the propeller should hold the engine at a Hg manifold pressure. Check each magneto for a steady speed without surges or other irregularities. maximum loss of 80 RPM. Return governor control lever to the full INCREASE RPM setting. If propeller is

[ 211 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 operating properly, the engine will resume its original run with this adjustment for at least 15 seconds, watching the tachometer and the manifold pressure speed. gage. If the engine speed has increased, this will

cause a corresponding decrease in manifold WARNING: In testing operation of the propeller. do pressure, and demonstrate that the mixture now not decrease RPM by more than 200. Further decrease being delivered to the engine is more neatly of is liable to damage the engine. proper strength. c. Still without moving the throttle, repeat this e. Set propeller governor control lever at full process using several different notches until the one INCREASE RPM and selector switch at AUTO CON- is found where the engine speed is the highest and STANT SPEED. Open throttle to obtain 2400 RPM the manifold pressure is the lowest. and note manifold pressure. With this fixed throttle and d. With the idle mixture adjustment set in the manifold pressure setting, vary engine speed from 2400 notch giving the best operation, reset idle speed RPM to 2200 RPM by moving propeller governor adjustment to return idling RPM to 650. control lever toward DECREASE RPM. The manifold e. Repeat procedures a, b, c, and d to determine if pressure should remain constant within one in. Hg. the original mixture adjustment is still correct for the f. Check the OFF position of the ignition switch to new throttle adjustment. In some cases, it may be assure proper connection of ground wires. This check found necessary to repeat this process even a third should be made at end of the engine warm-up period with propeller in full low pitch and engine turning over approximately 700 RPM. The switch should be turned to the OFF position momentarily (2 or 3 seconds is ample) to note whether or not the engine stops firing, and then immediately return to the BOTH position. If the engine does not cease firing when the switches are placed in the OFF position, it will be necessary to stop the engine by moving the mixture control to the IDLE CUT OFF position.

WARNING: After the engine stops, do not touch the propeller until the difficulty has been found and corrected, as the engine may start or kick over and cause death or serious injury.

45. Idling Adjustment Adjustment of the idle mixture screw on the car- buretor should never be made on either a cold or hot engine. If the engine has been run up and is quite hot, allow it to idle for 5 minutes before attempting to set the idle adjustment. The engine should be idled at Figure 171—Adjusting Idle Link approximately 1000 RPM for this cooling period. Refer to Figure 144 in conjunction with the instructions time to ensure proper engine operation. The throttle outlined below. should be opened and closed between each a. Set idle speed adjustment in the position which adjustment. gives an idling speed of 650 RPM with the throttle stop f. In case the engine operation is apparently the arm against the adjustment stop. Note manifold same in any of the several notches, the adjustment pressure. screw should be placed in the leanest of these b. Leaving the throttle set in this position, loosen notches. idle mixture adjustment lockscrew and move idle mix- Note: Under no circumstances should the idle mix- ture adjustment one notch toward the lean side, which ture adjustment screw be leaned beyond the point of is counterclockwise facing the carburetor from the rear. maximum speed. Such action may result in poor Open and close the throttle and allow engine to engine acceleration. [ 212 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 g. In case there is insufficient travel of the idle mixture adjustment to obtain the correct idle mixture (see Figure 171). idle link (1) should be disconnected from screw eye (8) by removing link bolt (6). The screw eye (8) should then be screwed into threaded bushing (9) if leaner mixtures are required, or screwed out of the bushing if richer mixtures are desired. One revolution of the screw eye is equivalent to approxi- mately 13 notches of mixture adjustment indicator (12). The idle link (1) should be reconnected with extreme care to be certain that the various parts are in their correct positions. The 4 plain washers (4) should be in the positions shown. The spring wave washer (2) must be carefully placed so that it fits over the outside diameter of bushing (3) and so it is next to screw eye (8). The castle nut (5) must be tightened enough to allow the yoke of idle link (1) and plain washers (4) to clamp bushing (3) tightly in place so it cannot move on bolt (6). If castle nut (5) is not tightened sufficiently, the clearance between the inside diameter of bushing (3) over the outside diameter of bolt (6) Figure 172—Top Dead Center will allow enough play in the linkage to cause inconsistent engine idling. Note: The No. 6L piston must be located at T.D. C. h. After the idle is properly adjusted, tighten and on the intake stroke (intake valves beginning to lockwire the idle mixture adjustment lockscrew. open). e. Remove distributor housing covers, and lift 46. Checking Valve, Magneto, and each distributor head from its pilot. Each head is Distributor Timing secured by 3 flange screws. f. Check timing of valves, magneto, and distrib- Engine timing should be checked by using a magneto utor in the order listed below. type timing disc, Allison No. 2380, and a top dead Cyl. center indicator, Allison No. 2057. Operation Affected Read on Disc Reading Exh. Valve Closing No. 6L Inner Fig. 26° :± 2° after T.D.C. Note: The degrees calibrated on the timing disc *Exh. Mag. indicate degrees of crankshaft travel. There are two Breaker No.lL Inner Fig. 34° before T.D.C. *Intake Mag. scales of degrees on the disc. The inner scale is used Breaker No.lL Inner Fig. 28° before T.D.C. for left bank timing, and the outer scale is used for Exh. Valve Closing No. 5R Outer Fig. 26° ± 2° after T.D.C. right bank timing. *With engine set at these values, check the location of the distributor finger. The leading edge of the finger should be 3/32 inch past the distributor housing flange mark. a. Set tappet clearances (see Paragraph 36). b. Install top dead center indicator in No. 6L intake WARNING: Always rotate the engine in the di- spark plug bushing. rection of propeller rotation before making a c. Remove magneto cover and cam screw. Slip reading, to ensure that all backlash has been taken timing disc on magneto housing, install pointer—in- up. dexing its step with the step on the magneto cam— and secure with the special screw. 47. Checking Magneto and Distributor Timing d. Locate No. 6L piston in top dead center, using Without Timing Disc or T.D.C. Finder both the top dead center indicator and the timing disc for accuracy (see Figure 172). Then rotate the timing a. The engine is designed with 60° between the disc on the magneto housing until pointer aligns with right and left cylinder banks, and the exhaust valve T.D.C. indications for the left bank (inner diameter gradations), Tighten clamping screw.

[ 213 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 closing position of a designated cylinder of the right (5) If these checks fail to disclose the reason bank after top dead center gives the correct for roughness, one further check may be made: Take crankshaft and piston position before top dead a propeller from an airplane of the same type, which center for the firing of No. 1 left cylinder. is operating properly, and install, and test this propeller on the airplane which has been operating b. The exhaust (right) and intake (left) distrib- roughly. If the substitute propeller is also rough, it is utors have only one index timing mark (No. 1 left almost certain that the trouble is not caused by the cylinder) on the distributor head mounting flanges. propeller. Therefore, the correct exhaust valve closing position of the right bank cylinder on its relative exhaust b. ENGINE SURGING OR HUNTING—This condi- stroke to the No. 1 left cylinder on firing stroke must tion is defined as the failure of the engine to run at a be obtained to arrive at the ignition firing degree constant RPM. before top dead center of No. 1 left cylinder. (1) Should surging occur when the propeller is c. In this right bank exhaust valve closing posi- operating in AUTO CONSTANT SPEED, it may be tion, the crankshaft throw has traveled 26° past top caused by either faulty engine operation or faulty dead center of the right bank—thus 26° from 60° propeller control operation. To determine which results in a crankshaft and piston position of 34° system is malfunctioning, operate the propeller in before top dead center of the left bank. This 34° fixed pitch. If the surging stops during this B.T.C. is the exhaust magneto and distributor rotor operation, check the propeller automatic control firing position. system. If the surging continues, the trouble is almost certain to be located somewhere other than in Note: This procedure is intended the propeller controls. primarily for the checking of the magneto and (2) Surging may be caused by the points of an distributor rotors, and will indicate the timing within improperly adjusted relay chattering as the result of ±2° only, because of the tolerance of vibration. Inspect the relay, measuring the contact ±2° of crankshaft travel. In emergency, the timing of point gap and the gap between the outer edge of the either the magneto points or distributor rotors within armature head and the upper transverse arm. The this ±2° limit will be satisfactory. former gap should be .080 inch to .100 inch: the latter should be at least .008 inch when the armature 48. Testing Propeller stem is held solidly against the coil housing. If the propeller is not operating properly, the (3) Inspect the governor contact points for cause can usually be determined by making the proper adjustment. following tests: (4) Check the tachometer for proper operation. a. ROUGH OPERATION—If this condition exists, (5) If the surging exists only at take-off, the first check the engine. A malfunctioning engine is condition may be caused by the engine. very often the cause of rough propeller operation. If, (6) Check the brake clearance (see "50-Hour however, this condition is being caused by the Inspection" in Paragraph 51) and make certain the propeller, it is usually because of the propeller brake is operating properly. blades and not the propeller operating mechanism. (7) Make the checks suggested in c, immedi- ately below. (1) Examine the blades and blade cuffs closely c. SLUGGISH OPERATION—Sluggish operation to see if they have been badly scarred or damaged. exists when the propeller responds slowly to control Determine the extent of any possible damage and changes, and will cause a hunting condition in the refer the blade to the proper agency for repair. propeller control system. (2) Check the blade angle to make certain (1) If this condition exists at take-off, check blades are all at the same angle. the battery. Since most of the airplane electrical ap- (3) Check blades for track to make certain pliances are in use at take-off, the electrical power they are not bent. All blades must be within ±1/16 output of the battery available to the propeller motor inch of one another. may be greatly reduced, thereby causing sluggish (4) Check propeller for balance on a knife operation of the propeller motor. edge balancing stand. (2) Check generator for proper current rating output.

[ 214 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11

(3) Check blade bearings for damage or rough- qage and locked into the correct position. These ad- ness. justable stops must not be changed from their (4) Check brake operation and brake clearance. original setting. (5) Check wiring for loose connections.

(6) See that slip ring assembly and brushes are (4) Push the cockpit throttle lever forward as free of grease and oil. far as it will go (full OPEN position). When the (7) With the engine not running, operate the hand pressure is released from the lever, there propeller manually in both directions. If it fails to should be a gap of 1/8 inch between the cockpit operate normally, check the pitch changing mecha- throttle lever and the stop at the OPEN end of the nism for a binding condition. throttle quadrant. (8) If none of these checks reveal the (5) With the cockpit throttle lever in the full difficulty, replace the governor. OPEN position, check the regulator unit to see that Note: Refer to Section 16 for propeller system the throttle pivoting crank lever is against its front wiring diagrams and for further information on adjustable stop. If the throttle pivoting crank lever testing the propeller electrical circuit. on the rear of the regulator does not contact its front

adjustable stop when the cockpit throttle lever is set 49. Testing Manifold Pressure Regulator in the full OPEN position, adjust the linkage between the regulator unit and the cockpit throttle a. TEST WITH ENGINE NOT RUNNING lever. If this linkage is adjusted, be sure to recheck (1) Check carburetor mixture control linkage to the closed throttle gap (see Paragraph 49a). see that all 4 mixture control positions are obtain- able in accordance with markings on the cockpit b. TEST WITH ENGINE RUNNING control quadrant. (1) When all of the above checks have been (2) Pull back cockpit throttle lever as far as it completed, the regulator should function will go (fully closed position). When hand pressure satisfactorily at all engine speeds with only a few on the lever is released, there should be a gap of 1/8 minor adjustments and is ready for an operation inch to 1/4 inch between the cockpit throttle lever check. Tie the airplane to the ground or place a and the stop at the CLOSED end of the throttle chock at each main wheel and start the engine (see quadrant. Paragraph 15). (3) With cockpit throttle lever in the CLOSED (2) Set the adjustable carburetor idle stop (see position, make the following checks at the regulator Paragraph 45) in the required position. unit: (3) Set the adjustable throttle stop on the con- (a) Check the carburetor adjustable idle stop trol quadrant (see Paragraph 50). to see that it is set at ZERO (butterfly valve closed) (4) Check the maximum (war emergency) and that the stop on the carburetor throttle lever is in manifold pressure obtainable, by lifting the throttle contact with the adjustable idle stop. If they are not stop release lever (see Figure 146) and advancing in contact, adjust the linkage, as outlined in Para- the cockpit throttle lever to the full OPEN position. graph 50 below, to bring these stops into contact. At this position, the maximum manifold pressure (b) Check the gap between the throttle piv- should be approximately 57 in. Hg absolute. oting crank lever and its gear adjustable stop on the rear of the regulator unit. This gap, or cushion, WARNING: Do not operate the engine at maxi- should be .015 inch to .032 inch while the carburetor mum manifold pressure longer than a few seconds. throttle stop lever is in contact with the adjustable idle stop. Adjust the link rod between the carburetor (5) If approximately 57 in. Hg absolute mani- throttle lever and the regulator differential lever to fold pressure is obtained, the regulator unit is oper- provide this gap. ating, since the maximum manifold pressure obtain-

able by direct linkage, through manual operation, is CAUTION: The throttle pivoting crank lever front only approximately 52 in. Hg manifold pressure at and rear adjustable stops are set with a sea level. Therefore, maximum (war emergency) manifold pressure can be obtained only through the operation of the regulator unit.

[ 215 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 50. Throttle Stop Adjustment WARNING: Do not hold the control at this setting To set the adjustable throttle stop on the control more than 15 seconds. quadrant, place a chock at each main wheel and start the engine (see Paragraph 15). When the engine has f. Move throttle against stop and check for a man- warmed up, proceed as follows: ifold pressure of 52 in. Hg and 3000 RPM. a. Loosen bolts that secure throttle stop so that it g. If above readings are not obtained, readjust the can slide fore and aft. stop. It is possible that vibration of the aircraft will b. Place propeller selector switch in AUTO CON- cause stop to creep from determined setting when STANT SPEED. loosened. c. Place propeller control lever in full h. After obtaining proper adjustment, set the INCREASE RPM. throttle by means of the linkage so that there is a 1/8 d. Place mixture control in AUTO RICH. -inch spring-back at the full forward and aft e. Move throttle forward slowly until 52 in. Hg positions. manifold pressure is obtained at 3000 RPM, and i. Make certain that the lockwire break-through tighten throttle stop so that it contacts release lever seal is in place and unbroken. at this setting. PERIODIC INSPECTION

51. General (4) Inspect engine cowling panels for general The inspection and maintenance procedures out- condition, correct fit, and security. Check air scoop lined below are to be considered minimum require- opening for presence of foreign matter. See that ments only. Local authority should not hesitate to starter handle and extension are securely stowed. increase the scope and frequency of these (5) Check the throttle, mixture, carburetor air, inspections whenever local conditions, peculiarities carburetor filter, and carburetor heat controls for full of equipment. or abnormal usage warrant such throw and ease of operation. action. For more complete information regarding (6) Check propeller circuit-breaker switch. these periodic inspections, refer to Section 3. (7) Check propeller control lever (see Paragraph Paragraph 12b, "Nature and Extent of Periodic 43d). Inspections." (8) Check manual control positions of propeller SELECTOR SWITCH, noting an increase or decrease PREFLIGHT of RPM. Check operation of the limit switches by (1) The engine should always be warmed up on changing the pitch with the manual switch in both the ground until proper lubrication and engine oper- directions until the limit switches operate. ation for the take-off and flight are assured. See Paragraph 15 for instructions on starting engine; see AFTER FLIGHT Paragraph 44 for testing engine. If a heavy, viscous After each flight, inspect the throttle control lever oil is indicated by oil pressure that is too high, or by stop to determine if the lockwire seal is broken, oil pressure that fluctuates or falls back when the which would indicate that war emergency power has engine RPM is increased, the dilution switch may be been used. If war emergency power has been used, pushed ON to dilute the oil and correct this make the following engine inspections prior to condition. If dilution is used during the warm-up, release of the airplane for further flight: close observation of oil pressure will be necessary during the time of dilution and through the (1) Remove and inspect the Cuno filter for the remainder of the warm-up to determine whether or presence of metal particles. not the oil has been overdiluted. Overdilution results (2) Remove the oil drain plugs and examine the in low oil pressure and is to be avoided. oil for metal particle contamination. (2) Inspect fuel pressure gage to see that it main- (3) Remove the valve covers and check the valve tains a pressure of 12 to 16 Ibs./sq. in. (3) Check generator and electric switches.

[ 216 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 clearances. Check the rocker arm bearing bracket (11) See that propeller is properly installed and studs. Check valve springs for breakage. Turn the all exposed screws, bolts, and pins are tight and engine by hand to check for blow-by at the valves. safetied. (4) If war emergency power has been used for an (12) Examine the exterior of all parts of the pro- extended period, replace all spark plugs with a new peller for cracks, bends, nicks, and other damage. or reconditioned set. The entire leading edge, trailing edge, and tip (5) Visually inspect the engine and engine mount portion of each blade should be continually checked for cracked structures. Check the supercharger inlet to guard against development of cracks. A for evidence of chafing by the supercharger magnifying glass will facilitate this work. When in impeller. This is usually indicated by peeled or doubt as to the extent or seriousness of apparent scorched paint on the supercharger inlet elbow. cracks, aluminum alloy blades should be given a local etching. Watch especially for longitudinal (6) Evidence of erratic operation or engine mal- cracks. functioning which ordinary maintenance cannot (13) See that all exposed surfaces of propeller are remedy will be considered sufficient cause for thoroughly coated with clean engine oil. If airplane engine replacement. has been operated near salt water, propeller should be washed thoroughly with fresh water and dried Note: Close coordination between the pilot, crew before the oil coating is applied. chief, and engineering officer will be required to (14) Inspect propeller spinner for general keep an accurate record of the amount of time any condition and security of attachment. engine has operated at War Emergency Rating conditions. When 5 hours of such operating time has 25 HOUR accumulated, the engine should be pulled for (1) Inspect elbow terminals and shielded plugs teardown inspection and reconditioning. for security. When tightening the elbow assemblies, the barrel must not be loosened. DAILY (2) Wash engine completely, taking care that no (1) Inspect high-tension ignition leads for evi- cleaning fluid enters the generator, starter, or any dence of burning as a result of leaks in the exhaust other electrical equipment. system. Inspect ignition harness. (3) Check reduction gear housing, supercharger (2) Check for evidence that the engine is throwing housing, and all accessory housings of the motor for oil. general condition and security. (3) Inspect the engine-to-engine-mount bolts and (4) Clean carburetor fuel strainer. The fuel sup- the engine-mount-to-fuselage attachment bolts for ply line does not have to be disconnected. security and correct safetying. (5) After replacing carburetor strainer, and while (4) Inspect all drain plugs and access doors for strainer is filled with air, disconnect the flexible proper safetying and security. hose in vent line at carburetor. Then apply fuel pressure at approximately 14 Ibs./sq. in. with the (5) If the Cuno oil strainer is clogged, remove and electric booster pump. and observe the action of the clean it with a solvent until it turns freely. vapor eliminator. It should be possible to notice the (6) Check that intake manifold pipes are securely rush of air being expelled, and then ceasing when attached. Make certain that the gaskets and the hose the fuel level raises the float and shuts off the vent connections do not leak. passage. There should be no fuel flow from the vent (7) Inspect exhaust stack flanges for security. line other than just a few drops, which is normal (8) Examine engine-driven accessories for general seepage. condition and security of attachment. (6) Check carburetor attachment bolts and air (9) Inspect carburetor and fuel line connections scoop elbow nuts for tightness. for fuel leakage, paying particular attention to drain (7) Check ignition ground and booster connec- plugs and passage plugs, and the parting surfaces tions. between the regulator castings. (8) Inspect and lubricate engine controls. Check (10) Inspect all safety wiring on carburetor. linkage, rods, bellcranks, etc. Refer to Figure 146 for locations. (9) Check engine idling. (See Paragraph 45.)

[ 217 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 (10) Check supercharger vent for free air (12) Lubricate propeller hub with grease, AAF passage. Remove vent and blow through it to see if Spec. 3581, Grade AA, using a pressure gun on the it is open. Clean and reinstall. zerk fitting located on speed reducer housing just (11) Check supercharger scroll drain for open forward of front hub face. Apply grease until the passage. This drain, on the right-hand side of the hub is full: this will be indicated by a flow of grease scroll, can be checked by taking off the line at the from the relief fitting. drain fitting. Open mixture control to FULL RICH (13) Check oil level in the propeller speed and operate fuel pump for approximately one minute reducer by removing filler plug near front of to see whether fuel drains out. housing, and rotating propeller until plug opening is (12) Check front and rear engine breathers for approximately 20° below horizontal when the free venting—passage through packing wool. airplane is at a ground angle of approximately 12°, (13) Visually inspect condition of all flexible and 8° below horizontal when the airplane is conduits running to propeller governor unit at points leveled. The oil in the speed reducer should then be where damage might occur. at plug opening. If not, fill gear assembly at this (14) Visually inspect the condition and security point with AAF Spec. 3563 oil. of propeller governor Arens control. Inspect cockpit (14) Remove propeller brush assembly from control lever to determine that it has at least 1/8 - housing by releasing the 2 latches. Wipe slip rings inch spring-back from full forward position. Adjust by holding a cloth against them while the propeller control if necessary, but do not adjust stop screw on is being rotated, and inspect slip rings for wear. the governor, as it is already set to provide take-off Clean oil and carbon dust from brush holder and RPM. brushes with a clean, dry rag or brush, and make certain that brushes slide freely in the holder. Check 50 HOUR length of brushes (see Paragraph 32) and replace if (1) Inspect ignition shielding for proper anchor- necessary. age and security of the union nuts and tube brackets. (2) Inspect fuel intake system for broken studs. Note: Do not clean propeller slip ring brushes with Check lines for leaks or damage. solvent. (3) Check exhaust stacks and studs for looseness. (15) Remove propeller motor cover. Inspect gen- (4) Examine engine cowling support brackets for eral condition of motor: terminals and wire connec- general condition and security. tions. tightness and condition of brush riggings. (5) Clean and check carburetor and carburetor Check brake clearance by inserting a feeler gage nozzle assembly (see Paragraph 30). between the inner ring of end shield assembly and (6) Grease mixture control latch mechanism with the rear brake plate. Clearance should be between Spec. VV-G-681 medium grease. Lubricate throttle .010 inch and .020 inch. Clearance adjustments may shaft bushing with machine gun oil, Spec. 2-27. be obtained by adding or removing shims under (7) Inspect valve mechanism as follows: front brake plate. (a) Check condition of cylinder head cover (16) Check automatic manifold pressure gasket. regulator for proper mounting and security of (b) Check for broken springs. attachment, and for proper attachment of manifold (c) Check valve clearances: when necessary, pressure, oil pressure, and drain lines. Inspect for make adjustments (see Paragraph 36). excessive oil leakage at servo piston rod. In event of (8) Inspect ignition distributors and rotors (see excessive oil leakage, replace the unit. Paragraph 25b). (9) Test spark plugs; clean and regap if Note: A small amount of oil seepage at the servo necessary. piston rod may be encountered. However, it should (10) Check cylinder hold-down nuts and rocker not exceed one drop per minute at normal tem- arm studs (see Paragraphs 27 and 28). perature. 71.1 ° C (160° F), and normal pressure (50 (11) Check propeller hub and retaining nut for Ibs./sq. in.) . looseness on shaft. If repeated tightening of 100 HOUR propeller hub retaining nut is necessary to maintain (1) Replace all spark plugs with new or recondi- proper tightness, remove propeller and investigate. tioned plugs of an approved type.

[ 218 ] RESTRICTED RESTRICTED Report No. NA-5629 ENGINE--PROPELLER SECTION 11 (2) Remove all 4 primer fittings on top of the connections, making sure that none is loose and that intake manifolds and check for clogging. Clean and there is no possibility of the terminals touching each replace. other. Replace relay in the box. (3) Check high-tension leads from magneto to distributors. ENGINE CHANGE (4) Check the 2 magneto breaker points for pitting. (1) Engines will be changed and overhauled Replace if necessary. after approximately 300 hours of running time (5) Check high-tension leads in the magneto. unless malfunction or failure of an engine part Leads should have 1/8 - inch spring-back when occurs prior to this time. When an engine is changed, accomplish all special instructions and placed in the magneto. maintenance work prescribed by technical (6) Remove distributor heads. Check carbon brush instructions to be done at engine change. Inspect the and spring for free movement. Brush holes can be 10 Lord mounts for general condition and security cleaned out by using emery cloth. (see Paragraph 34). (7) Remove and clean distributor rotors [see Par- (2) When replacement pumps are available, re- agraph 25b, (3)]. place all accessory pumps except those with less (8) If oil is found in the distributor heads, check oil than 100 hours since last overhaul. This includes drains from the distributor for clogging. electric motor-driven pumps, fuel, oil, hydraulic, (9) Check ignition booster for operation by turning coolant, vacuum, and similar power-driven units. ignition switches ON and engaging starter. (3) Whenever a new or newly overhauled engine (10) Check propeller governor contact points on is installed, ground test the installation for approxi- both decrease and increase RPM's. If points are bad, mately 30 minutes, during which time the operation replace the governor. of the engine, engine instruments, and related acces- (11) Ground check the operation of the automatic sories will be thoroughly checked for proper manifold pressure regulator as outlined in Paragraph functioning. Do not exceed maximum cylinder and 49. oil temperatures. Warm-up speeds from 800 to 1000 (12) Check rubber pad on forward end of the car- RPM are recommended. Operation at rated speeds buretor air scoop elbow for deterioration. and manifold pressures will be limited to short (13) Remove contact switch cover from propeller bursts sufficient only to determine instrument readings and to confirm engine acceleration. Clean governor. Inspect condition of the contacts and see all removable oil screens. At the completion of the that wire leads are securely attached. Thoroughly ground test, a flight test for one hour will be made at clean contact assemblies with cleaning solvent or reduced power and full mixture. After a careful gasoline, and remove any oil that may have inspection for evidence of failure or malfunctioning, accumulated in the switch compartment. While another flight test of approximately two hours will contact points will not require dressing, their be made at reduced power with full rich mixture. All contacting surfaces should be cleaned with crocus removable oil screens will be cleaned at the end of cloth or fine sandpaper. Place not more than one drop the flight test. of light lubricating oil on upper end of shaft which Note: At the end of the first 5-hour flying time of a supports center contact assembly. Replace cover. new or overhauled engine, the cylinder block hold- (14) Partially remove propeller governor relay from down nuts should be inspected for tightness (see its box and inspect for proper mating of contact Paragraph 27). In general, the nuts will be points and sufficient contact point pressure. somewhat loose because of settling of the cylinder blocks and compression of gasket paste on the Note: The contact point material is Elkonite, which cylinder barrel bearing plates or shims. is rather hard and does not require dressing or polishing. The discoloration and fine pit marks which 25 HOURS AFTER ENGINE CHANGE develop on the surface are normal characteristics of (1) Make a complete detailed inspection and ad- justment of valve mechanism, checking condition of this material and do not affect its conductivity. valve springs and cylinder head cover gasket. See

Paragraph 36 for information on valve adjustment. Make sure armature floats freely on its pivot pin. (2) Check propeller shaft thrust bearing nut. Sub- Lubricate if necessary with a small quantity of oil or sequent tightening will be at the discretion of the semifluid lubricant. Examine all terminals and wire engineering officer in charge, or at any time that the nuts are found to be loose.

[ 219 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12

[ 220 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12

Section 12

FUEL SYSTEM

DESCRIPTION 1. General units in the fuel system are satisfactory for use with a. THE UNITS—The fuel system, including the aromatic fuels. main system and the auxiliary system, consists essentially of the following units: 2. Main Fuel Tanks Unit Location The pressure molded, main fuel tanks, manufac- Main Fuel Tanks (2)...... One in each wing tured by the Firestone Tire and Rubber Company of Selective Sump Valves (2) ...... Between the main tanks in the California, are of a self-sealing construction incor- centersection of the wing Strainer Right side of firewall, bottom porating an AAF approved aromatic-resistant liner. Booster Pump...... Left side of firewall, bottom Each main tank has a total fuel capacity of 90 U.S. Selector Valves (2)...... Inside of right and left wheel gallons (75 Imperial gallons). Small holes are pro- Recesses Fuel Pump...... Aft end of the engine vided in the extreme lower portion of the stiffening Drain Box...... Lower aft end of the engine baffles to permit fuel flow toward the sump when Propane Primer ...... Lower aft end of the engine the tank is nearly empty. A magnetic-type fuel gage Ferrying Tanks (2) ...... Bottom of the wings, outboard Combat Tanks (2) ...... Bottom of the wings, outboard is mounted on each tank. Each tank is provided with a long vent line which extends into the fuselage and b THE SYSTEM—The engine is supplied with fuel has its outlet at the wing fillet. from the two main self-sealing tanks in the wings and from the auxiliary tanks when they are installed. 3. Ferrying Tanks The regular fuel flow is from the main tanks, The droppable ferrying tanks are constructed of through the selective sump valves to the selector wood and have a fuel capacity of 150 U.S. gallons valve, through the fuel strainer and booster pump, (125 Imperial gallons) each. When carried, they are and on to the engine fuel pump and carburetor. installed on the bomb racks by means of two shackle When auxiliary tanks are used, the fuel from them fittings. Four sway brace fittings secure the tank. passes through the auxiliary system selector valve The tank fuel line is connected to the wing outlet by and on to the main fuel lines. The auxiliary tanks a rubber hose and a straight nipple which is installed consist of either droppable combat or ferrying tanks, in the underside of the wing forward of the bomb one mounted beneath each bomb rack. The main rack. Access to the fuel line within the tank is fuel lines are of the self-sealing type, and aluminum gained by the removal of the access door, which also tube lining is used at critical bends. The tanks are contains the filler cap. A vent line extends along the not interconnected, and it is necessary to switch top of the tank from the front to the rear. The filler from one tank to the other to provide smooth cap is at the front and top of the tank, and the drain operation of the engine. Sufficient feed to the engine plug is on the bottom of the tank. during steep climbs or dives is ensured by 2 outlet lines, 1 at the forward end and 1 at the aft end of 4. Combat Tanks each tank, interconnected by a selective sump ball- The droppable combat tanks may be installed on and-socket valve to a single line. Additional the bomb racks when neither ferrying tanks nor facilities for furnishing the engine with sufficient bombs are being carried. They are constructed of fuel when the fuel level becomes low are the thin metal template interlined with a pressed rubber bulkheads with flapper valves, located at the inboard covering, and contain a series of baffles inside. The end of each tank, which form a sump chamber over fuel flows through a strainer, which also acts as a the fuel outlet, and the booster pump installation. drain plug, located at the bottom of the tank. A vent The carburetor is of the type line extends from the top of the tank to the aft end. containing an idle cutoff device, and is equipped with a vapor line that extends to the left main fuel tank. All of the [ 221 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12 8. Engine Primer System a. An engine primer pump and operating handle are installed on the subpanel at the lower right side of the instrument panel. When priming operations are completed, the handle must be pushed in and turned clockwise to the OFF position. b. The distributor valve is located forward of the carburetor on top of the engine. From the distributor, four 1/16-inch lines run to the forward and aft ends of the intake manifolds.

1. ACCESS COVER 9. Propane Primer 2. FUEL GAGE A propane primer system is provided for priming 3. FILLER NECK the engine in extremely low temperatures. The plug 4. AUXILIARY WING TANK LINE for outside attachment is accessible through the 5. MAIN TANK VENT ground heating door of the engine accessory 6. AUXILIARY WING TANK VENT compartment cowling.

Figure 174—Main Self-sealing Tank 10. Carburetor

The filler cap is at the front and top of the tank. The The carburetor is a Stromberg Type PD-12K6 and is tanks have a capacity of 75 U.S. gallons (62.5 Im- mounted on the aft end of the engine; refer to Sec- perial gallons) each. tion 11 for further instructions.

5. Booster Pump The electric booster pump for the fuel system is a Type G 10, Model TFD-10,100 manufactured by the Thompson Products Company of Ohio. The control switch for the booster pump is on the right side of the switch panel below the instrument panel. The pump assembly consists of two units, a No. A-7025 motor and a Type TFD-2100 fuel pump. The relief valve, which is housed in a separate body, may be mounted in reverse position on the pump to permit change of rotation where this may be necessary. The booster pump may be used for either the main fuel system or the auxiliary fuel system by adjustment of the selector valve controls.

6. Fuel Pump An engine-driven fuel pump. Type G9, is mounted directly on the engine at the aft end. When the engine is being started, this pump is assisted by the booster pump.

7. Selector Valves

Two fuel selector valves, one located in each wheel Figure 175—Fuel Selector Valve Diagram recess, provide for control of the main fuel system and the auxiliary fuel system. The valves are manually operated by control handles located side by side on the cockpit floor, directly underneath the switch panel.

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Figure 177—Fuel Selector Valve Control Diagram

OPERATING INSTRUCTIONS

11. General a. Push in on the operating handle and rotate To operate the fuel system, proceed as follows: counterclockwise to unlock. a. Set the main fuel tank selector valve in the RIGHT b. Pull out and then push in on the handle. Prime or LEFT position. the engine in this way: 3 strokes when cold, and 1 b. Set the booster pump switch in the ON position stroke when warm. and then start the engine. c. Switch the selector valves of the main and WARNING: Caution must be used when priming the auxiliary systems to all positions to determine that engine, as overpriming constitutes a fire hazard. the systems are functioning properly. c. When finished with the priming operation, push 12. Engine Primer the handle in and turn clockwise to the OFF position.

To operate the engine primer, proceed as follows:

REMOVAL AND DISASSEMBLY

13. Main Fuel Tanks landing lamps, and at the jacking point in the center Prior to the removal of the tanks, the system should be of the wing at the wing attaching rib. The weight of drained as instructed in Section 3, Paragraph 13d. Jack the airplane should be supported at the center jack- the airplane at the wing jacking points on the lower ing point, with the outer jacking points being used surface of each wing section just inboard of the for balance only. After the jacking is completed, proceed as follows:

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SALVO position: both tanks will drop simultaneously.

15. Combat Tanks

The combat tanks are removed by the same method as used to release the ferrying tanks. (Refer to Paragraph 14 above.)

16. Booster Pump

To remove the booster pump, disconnect the 2 fuel lines, 1 from the strainer and 1 to the engine, Figure 178—Jacking Airplane for Fuel Tank and the 4 bolts at the firewall. Tape or plug the lines Removal to keep out dust or dirt.

17. Strainer

a. Remove fairing at lower wing attaching point. To remove the fuel strainer, disconnect the fuel b. Remove overflow line from the engine drain line from the selector valves, the fuel line to the box along the wing attaching point. booster pump, and the line from the primer. Then c. Remove forward scoop. remove the 2 bolts and spacers holding the strainer d. If left tank is being removed, disconnect to the bracket on the firewall. Tape or plug the lines carburetor vapor vent line adjacent to the left tank to keep out dust or dirt. gage. e. Remove the screws from the access cover prior 18. Fuel Pump to completely removing the cover; provide a stand to support the tank within the tank bay. Remove the intake, outlet, and drain lines, and the nuts f. Disconnect fuel and vent lines, and remove the that secure the pump to the engine. After the lines are removed, tape the ends to prevent dirt and dust from securing screws at filler neck and tank gage. entering. A cover should be installed to prevent dirt from entering the engine.

14. Ferrying Tanks 19. Fuel Selector Valves

Prior to the removal of the tanks, drain the system Remove all lines from the selector valve and tape as instructed in Section 3, Paragraph 13f. The fairing the lines to prevent dirt from entering. Disconnect on the tanks should be removed before removing the control rod that leads into the cockpit. Remove tanks. To remove the fairing, lower the tail fairing the nuts and bolts from the selector valve bracket and release the tension on the coil spring. Remove and remove the valve from the wheel recess. the hinge bolts on the tail fairing and then remove the screws and the wing nuts holding the front 20. Engine Primer System fairing to the tank. When removing the droppable tank while the airplane is on the ground, have a. CONTROL—Disconnect the lines that are attached available 2 racks or stands or some other means of to the primer on the forward side of the instrument support on which to set the tanks. Seven men are panel. Remove the 3 screws that hold the primer to the panel. required to remove the droppable tanks, one at the b. DISTRIBUTOR—Remove the 1/2 - inch stud bomb release control and three to hold each tank that holds the distributor unit in the proper position. when it drops. The tanks are released by placing the Remove all the T fittings from the manifolds. Install bomb control handle in the plugs in the manifolds to keep out dirt.

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Figure 179—Adjustment of Fuel Figure 180—Adjustment of Booster Pump Pressure Pump Pressure

MAINTENANCE REPAIRS

21. Booster Pump 22. Engine Primer Control

In case of faulty operation of the relief or by-pass Packing may be replaced without removing the valve, remove the valve assembly and inspect for primer from the instrument panel. Use only Parker foreign matter that may have lodged on the valve packing. First, switch the primer to the ON position, seat, valve, or valve stem guide. Wash the parts unscrew the packing cap, and then pull the entire thoroughly and check the valve stem and guide for piston out of its housing. Remove the handle screw, easy action. See that no foreign matter is imbedded handle spring, and the handle spring follower. Slip the in the Corprene facing of the by-pass valve, and that packing, cap packing follower, and the old packing the air vent line and vented plug are free from off the piston barrel. Replace the old packing with a obstructions. new packing and reassemble.

ADJUSTMENTS

23. Fuel Pump Relief Valve cockpit to check the fuel pressure gage, and one to Two men are required for this operation: one in the make the adjustment on the pump. With the engine operating at 2200 RPM, proceed as follows:

[ 229 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12 a. Break the safety on the pressure adjusting pump. To make adjustment, proceed as follows: screw locknut and loosen the locknut. a. Break the safety on the hex valve cap nut and b. Turn the pressure relief valve adjusting screw remove the hex cap. clockwise to increase, and counterclockwise to b. Turn the ignition switch to the BAT position decrease, the fuel pressure. and the booster pump switch to the ON position. Do c. When the fuel pressure gage reads 14 Ibs./sq. not start the engine. in., tighten the locknut on the adjusting screw, safety c. Pull the small lever from the slot and turn the locknut, and turn engine off. lever clockwise to increase, and counterclockwise to decrease, the pressure. 24. Booster Pump Relief Valve d. When the fuel pressure gage reads 10 Ibs./sq. Two men are required for this operation: one in in., replace the lever in the slot, turn the ignition the cockpit to turn on the switches and check the switch to OFF, and the booster pump switch to OFF. fuel pressure gage, and one to make the adjustment Replace the hex valve cap nut and safety. on the

TEST BEFORE INSTALLATION

25. Auxiliary Fuel Tanks pressure. The test is made with a mercury test stand Test the droppable fuel tanks with 2 Ibs. of air and an air shut-off valve to regulate the flow of air to the tank.

ASSEMBLY AND INSTALLATION

26. Main Fuel Tanks fuel line fitting and the rear end of the vent line. When installing the main fuel tanks, first place the Install the tanks so that the fitting will be bent forward end of the tank in the bay and let it rest on slightly outboard and the vent line will outlet on the the lower flange of the forward spar. Then connect outboard side when installed. the fuel and vent lines, position the tank fully in the (3) Inspect the drain plug to see that it is prop- fuel cell compartment, and install the cover with a erly installed and safety wired. Do not tighten drain sufficient number of screws to keep it in place. The plug excessively as this will crack the plastic next step is to secure the filler neck and tank gage to threaded insert in the boss. the upper surface of the tank bay. It is very (4) Inspect the flap to see that it is in the full important that the screws are not cross-threaded UP position. Raise the flap handle lock bar to a hori- when the tank covers are replaced. If the screws are zontal position and see that the peg on the bar is cross-threaded and enough pressure is applied, it is engaged in the hole on the quadrant housing. This very possible that the basket nut might be forced off lock bar stops the flap control handle at 20° so that the anchoring channel. If this happens at the forward the pilot cannot damage the flaps or the ferrying and outboard row of screws, it will be necessary to tanks by lowering the flaps more than the tank remove the cover to replace the nut. Then replace installation permits. the forward scoop, the engine drain box line, and the fairing at the lower wing attaching point. b. INSTALLATION (1) Open the bomb rack support hooks while 27. Ferrying Tanks the bomb control handle in the cockpit is being held in the SALVO position. Then return the control a. PREINSTALLATION PROCEDURE handle to the LOCK position. (1) Check the bomb racks for both electrical (2) Remove the plug from the wing fuel line and manual operation. outlet and install a nipple. The nipple provided has (2) Inspect the tank for possible damage. The no bead. right- and left-hand tanks are identical except for the (3) Install fuel hose on tank with two clamps.

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of the front wing pads. All 4 sway brace bolts must not be more than finger-tight against the wing pads. Additional tightening will only preload the two main shackle fittings on the tank and might cause possible failure. Lock each adjustment bolt with its locknut. (7) The fuel hose may now be connected to the nipple in the wing. Apply light grease. Spec. VV-L- 791-2, to the nipple before attaching the hose. Use only one clamp to hold the hose on the nipple. (8) Fill the tank to the proper capacity of 150 U.S. gallons (125 Imperial gallons). If tank is per- mitted to stand for several hours before flight, drain out a small amount of fuel through the drain plug, retighten and safety plug, and refill tank with new fuel. This removes any water which may collect in the tank.

28. Ferrying Tank Wooden Fairing After the ferrying tank is hung, adjusted, and filled, proceed as follows to install the wood fairing: a. Place the front fairing around the tank, locating the 3/4 - inch hole over the peg at the upper front end of the tank. Engage the clevis bolts in the brackets on top of the tank, install the wing nuts on Figure 181—Main Fuel Tank Line Installation clevis bolts, and tighten and lock the wing nuts with safety wire. b. Raise the wooden handle off the peg screw on (4) Screw the 4 sway brace adjustment bolts the tail fairing, and turn handle forward so that the down into the sway bracket as far as possible. (5) Three men, 2 at the front and 1 at the rear of the tank, can now raise the tank into position and engage the shackles on the tank in the support hooks on the bomb rack. Raising the tank will cause the bomb rack hooks to snap shut. Check the rack through the inspection holes in the rack to be sure it is positively locked. (6) Tilt the tank until the dimension from the upper edge of the tank to the under surface of the wing opposite the rear outboard sway brace stud is approximately 4-1/4 inches, and the dimension opposite the rear inboard sway brace stud is approximately 1-3/4 inches. Raise the two rear sway brace studs until the top dowel portion enters the hole in the wing pad and the shoulder of the stud rests against the wing pad. This adjustment will make a gap between the side of the tank and the landing gear fairing at the closest point about 1 inch. Check the tank to eliminate side play in the rear studs before raising the front adjustment bolts. Raise the 2 front adjustment bolts until the heads of the Figure 182—Wood Fairing Installation bolts touch the dimpled portion [ 231 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12

[ 232 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12 steel strap is extended. Loosen the 2 screws on each tighten the hinge bracket screws as tightly as side of the tail fairing which hold the adjustable possible. This will cause the protruding metal teeth hinge point brackets. Then engage one end of the on the bracket to bite into the wood fairing and coil spring in slotted hole on the steel strap, and ensure that the hinge bracket will not slip. Raise the install the tail fairing on the tank, engaging the tail fairing to the up position and tighten the pivot forward end of the coil spring in the slotted hole in bolts snugly: then back them off one turn to permit the bracket on top of the tank. easy movement of the fairing. c. Install bolts through the adjustable hinge point e. Safety wire the heads of the pivot bolts and the brackets into the rear holes on the sides of the tank. hinge bracket screws together. Lower the tail fairing Shift fairing around until it fits snugly against the into the down position and while holding the fairing flap and within 1/4 inch around the rear end of the down with one hand, pull back on the wooden tank. Tighten the hinge bracket screws enough to handle on top of the tail fairing to put tension on the hold the bracket temporarily, then raise and lower coil spring. Snap the handle over the peg to lock in the tail fairing to check the operation. position. Raise the tail fairing slowly; do not let it d. When proper operation has been obtained, fly up. Install screws in the slotted holes on each side of the front fairing at the aft end.

Figure 184—Fuel Strainer and Booster Pump Installed

[ 233 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12 29. Combat Tanks pump sets properly and then install the nuts on the Install the combat tanks in the same manner as stud bolts, using washers if necessary. Inspect the that of the ferrying tanks. (Refer to Paragraph 28 inlet and outlet lines and the drain line for any dirt above.) that may have entered, and then install the lines. 30. Booster Pump 33. Selector Valves Place the booster pump on the firewall, install Locate the selector valve at the proper position. the 4 bolts and tighten to the proper tension. Install Inspect to see that the metal is not cracked at the the inlet and outlet lines after they have been bolt holes. When the selector valve is in position, inspected for any dirt that may have entered. install and tighten bolts. Connect the control rod that leads into the cockpit, and then install the lines after 31. Fuel Strainer inspecting them for cuts and dirt. Place the fuel strainer in the bracket on the firewall and install the 2 bolts and the spacers. 34. Engine Primer Inspect the inlet and outlet lines and the line from Insert the primer head into the instrument panel the primer for any dirt that may have entered, and from the front side, and install the screws. Do not then install the lines. apply too much tension on the screws, as they are made of brass and might strip. Then connect the 2 32. Fuel Pump lines on the front side of the panel. Install the pump to the engine pad. See that the

FINAL TEST AFTER ASSEMBLY

35. Main Fuel Tanks 36. General After the main tanks are installed, a pressure test Run up the engine, and switch the selector is made with a mercury test stand at a pressure of 2 valves to all of the tanks. Let the engine run on fuel Ibs. The test is made by connecting the line from the from each tank long enough to ensure that the test stand to the main fuel tank vent line at the system is free from dirt or water, and that the trailing edge of the wing. An air valve is used to selector valves are functioning properly. Shut off the regulate the air for proper pressure. The pressure engine, and inspect the system for leaks. If none are must be maintained for a period of 15 minutes. apparent and the repairs are satisfactory, replace the access cowling.

PERIODIC INSPECTION

37. General see that filler caps are properly secured. Before The inspection and maintenance procedures out- servicing tank with fuel, drain small amount of fuel lined below are to be considered minimum require- from each tank through the drain cocks to remove ments only. Local authority should not hesitate to any accumulation of water or foreign matter present increase the scope and frequency of these in the tank. See that drain cock is secure and inspections whenever local conditions, peculiarities properly safetied. of equipment, or abnormal usage warrant such action. For more complete information regarding CAUTION: The airplane must be grounded before these periodic inspections, refer to Section 3, filling the tanks. Paragraph 12b, "Nature and Extent of Periodic Inspections." (3) Rotate fuel cock control handle one com- plete revolution and note whether binding occurs at PREFLIGHT any point. Should any pronounced binding be indi- (1) Make a general examination of fuel system cated, connecting linkage should be checked for for obvious leaks. correct alignment. (2) Replenish fuel tanks when necessary and (4) During engine warm-up, test functioning

[ 234 ] RESTRICTED RESTRICTED Report No. NA-5629 FUEL SYSTEM SECTION 12 of all tanks by switching the fuel valve to each tank; at a pressure of 10 Ibs./sq.in. when the engine is not test each tank long enough to ensure that fuel from running. Check the electrical connection for security the tank has an opportunity to flow to the engine. on the booster pump. Proper performance of engine during this test will (2) Ascertain that engine primer does not leak ensure, as far as possible, that entire fuel system is when pressure is applied by means of the booster free from water and dirt, and is operating properly in pump. all selector valve positions. Fuel selector valve posi- (3) Remove screen from end of the fuel strainer tions must be determined by a click and feel and not and clean the screen in gasoline. Ascertain that inte- entirely by the setting indicated on the dial. rior of strainer is clean before reinstalling the strainer screen. DAILY (1) Inspect tank access doors on the bottom of the 50 HOUR wing for obvious leakage of fuel. (1) Make a detailed inspection of all fuel lines (2) Drain a small amount of fuel from drain cock and connections, except those within the tank bay, of the fuel strainer to remove any accumulated mois- for general condition and security. See that all lines ture and foreign matter. See that drain cock is secure are properly supported and are not touching any part and properly safetied. of the airplane in a manner likely to cause wear. (3) See that all drain plugs are properly secured (2) Inspect fuel vent relief valves for general con- and safetied. dition and correct operation. (4) Inspect all fuel lines for leaks, security of (3) Inspect fuel selector valve controls for anchorage, wear caused by vibration or chafing, general condition and security. Check for excessive dents, or cracks. Check all connections. backlash or drag, and see that connections to the (5) Examine fuel tank vent lines to see that they tank correspond to dial markings. are clear. (4) Completely drain the self-sealing main fuel (6) Check fuel quantity gages for correct func- cells. Refill tanks and compare quantity of fuel tioning and inspect for visible defects and security required to fill each tank to level of the filler neck of attachment. with the original capacity of the cell as reported on the filler cap. If the capacity of the tank is less than Note: The fuel gages are accurate only when the 95% of the original capacity, remove the cell and airplane is in the level flight position. inspect to determine the cause of the reduced capacity. (7) Inspect carburetor and fuel line connections for fuel leakage, paying particular attention to drain 100 HOUR plugs, passage plugs, and parting surfaces between (1) Remove the fuel tanks and inspect them thor- the regulator casting. oughly. Visually inspect the tanks, through fitting openings, and access doors by means of a light and 25 HOUR mirror. If no raised or blistered areas, loose seams, (1) Inspect vent opening plugs in the fuel pump or any other apparent defects are noted, the tanks and the booster pump by inserting appropriate sized may be returned to service. drill or wire into vent opening. Do not use an air (2) Check lines, hoses, and clamps within tank hose to blow out opening. Inspect pumps for leaks, bay for general condition and security. proper operation, and security of mounting. With (3) Remove fuel gages from the tanks and check engine operating at 2200 RPM, adjust relief valve rods, gears, and cocks for bends, damage, or deterio- on the engine-driven fuel pump to relieve at a ration. pressure of 14 Ibs./sq in. Adjust the booster pump to relieve MAJOR OVERHAUL

38. General Inspect the tanks and the fuel hose for deterioration Remove the tanks, the self-sealing fuel hose, and general condition. All special instructions and engine-driven fuel pump, fuel strainer, and booster maintenance work prescribed by technical pump. instructions should be accomplished at this period.

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1. Preinstallation Procedure SALVO position. Then return control handle to the a. Inasmuch as the combat tanks were not orig- LOCK position. inally designed for installation on the P-51A Air- (2) Remove plugs from the auxiliary fuel line plane, certain alterations must be made on each tank outlets in wings and install an AN844-12 elbow in in order to install it on the airplane. Refer to Figures left-hand wing outlet and an AN840-12 nipple in below while following procedure outlined below: right-hand wing outlet. (1) Disconnect the vent line from the fitting on the (3) Install line (NA 97-48894) on the left tank, forward end of the tank. Spread the clips holding the and line (NA 97-48895) on the right tank. These vent line to the tank and cut off the forward vent line lines are included in the loose equipment on the air- clip. plane. Install hose and clamps on the lines. (2) Reroute vent line and close the clips holding the line to tank. Then turn elbow to meet vent line, CAUTION: The slip fitting on the tank should not and connect the line. be made too tight around the line, as excessive (3) Place tape on the vent line and tie with safety tightness would prevent the line from slipping out if wire to the plate welded on the forward right-hand the tank is dropped in flight. side of the tank. (4) File forward side of front hanger fitting on the (4) Install the sway brace adapters on the bomb tank and round off aft corners of the fitting. racks. Make sure that the altered sway braces are in- (5) File cutouts in forward edge of front sway stalled on the forward end of the bomb racks and brace adapters only. Then paint filed areas with zinc that the cutouts are in the front. Screw the 4 sway chromate primer. brace adjustment pads up into the sway braces as far as possible. 2. Installation (5) Two men. one at the front and one at the a. When alterations on the tank have been com- rear, can now raise the tank into position and engage pleted, proceed as follows to install each tank: the shackles on the tank in the support hooks on the (1) Open bomb rack support hooks while the bomb bomb rack. Raising the tank will cause the bomb control handle in the cockpit is being held in rack hooks to snap shut. Check through the inspection holes in the rack to make sure it is positively locked. (6) Lower the front and rear sway brace pads on the inboard side until they just touch the tank. Lock the pads in place with the adjustment nuts. Then position the outboard sway brace pads against the tank and lock with the adjustment nuts. The fuel line may now be connected to the fitting in the wing.

FORWARD HANGER ON TANK

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