Air­Cooled Engine Technology Roth 9 th Ch16 Bearings, Shafts, Valves Pages 303 ­ 336 Air­Cooled Engine Technology 1. 4 cycle engines have more parts, & require more __________________ than 2 cycle engines. Maintenance TLC Knowledge Air­Cooled Engine Technology 2. The ____________________ _______ attaches the piston to the crankshaft. Push Rod Connecting Rod Lightening Rod Air­Cooled Engine Technology 3. The connecting rod lower end can be either split or can be one­piece. ________________ bearings with smooth, sliding surfaces are usually used on the lower end of a split connecting rod. Friction Fractional Anti­Friction Air­Cooled Engine Technology 4. The diameter across the parting surfaces of a precision insert bearing is slightly larger than the rod & cap diameter. This condition is called bearing ____________. It gives tight contact and good heat transfer. Spread Crush Clearance Air­Cooled Engine Technology 5. The built­in design feature of precision insert ends protruding slightly above the parting surface of the connecting rod & cap is called bearing ______________. Crush height may be only .0005” ­ .002” Spread Crush Clearance Air­Cooled Engine Technology 6. Removable, _____________ insert bearings are so named because of exact size & fit. Semi­ Friction Precision Anti­Friction Air­Cooled Engine Technology 7. Precision insert bearing halves are prevented from turning in the rod and rod cap with ______________ tabs on the parting edge of each insert. The tabs fit into slots in the rod halves. (or in the block for mains) Locating Tab Air­Cooled Engine Technology 8. Connecting rods & caps as well as bearing halves must be kept in _____________ pairs if being reused. (wear­mated) Matched Matched Matched Air­Cooled Engine Technology 9. Needle, roller, and ball bearings are in the category of ________ ­ _______________ bearings. Sub­Friction Fractional Anti­Friction Air­Cooled Engine Technology 10. Antifriction bearings (balls, rollers, needles) can be held in roller _________ (races) or be loose (uncaged). Zoos Cages Barns Air­Cooled Engine Technology Air­Cooled Engine Technology 11. ______________ plates are often used to prevent rod nuts or bolts from loosening in service. Prevailing torque nuts or Loctiteä thread locking compound can also be used to prevent loosening. Locking Washer Tectonic Air­Cooled Engine Technology 12. Always use a _______ wrench to get the exact tightness of connecting rod, cylinder head, and flywheel fasteners. Torque specifications are found in manufacturers’ service manuals & charts. Ratchet Metric Torque Air­Cooled Engine Technology Air­Cooled Engine Technology 13. The _________________ converts the reciprocating motion of the piston into rotary motion which is used, or “taken off “ at the Power Take Off (PTO) end of the shaft. (cast or forged) Crankpin PTO Magneto Crankshaft Camshaft Balance Shaft Air­Cooled Engine Technology 14. The crankshaft ______ is the offset portion measured from the centerline of the main bearing journals to the centerline of the connecting rod (crankpin) journal. (offset x 2 = stroke) Throw Centerline Counterweight Air­Cooled Engine Technology Air­Cooled Engine Technology 15. ________________ are used on crankshafts to help offset the unbalance created by the force of the reciprocating mass (con rod, piston, & crankpin). Even though this works well, some manufacturers also use additional, gear driven counterbalance shafts & weights inside the crankcase. Counterweights Camshaft Lobes Helical Gears Air­Cooled Engine Technology A counterbalance system would offset the side thrust of the counterweights Air­Cooled Engine Technology 16. Crankshaft __________ bearings can be of the Rod sleeve, bushing, roller, tapered roller, or ball design. Cam Main Air­Cooled Engine Technology PTO Magneto Air­Cooled Engine Technology 17. Some crankshaft _____ _______ (axial play) is needed to allow room for lubrication & expansion. Manufacturers’ specifications for end play vary from about .002” to .027”. Measure it with a dial indicator. End Play Wiggle Room Vibration Space Air­Cooled Engine Technology 18.Undersize wear & taper on any crankshaft journal surface .010” should not exceed ______”. If so, discard it. .001” .0001” Air­Cooled Engine Technology 19. Bearing ________________ is the space between a bearing bore (hole) and journal (shaft surface). This space is often called the “oil clearance” of the bearing. If it exceeds the .002” ­ .005” tolerance on an engine, a connecting rod “double knock” will occur & oil pressure is lowered. Clearance Thrust Radial Play Air­Cooled Engine Technology 20. ___________________ ® is a special, compressible plastic material used to measure oil clearance between assembled, torqued components. It is considered a consumable tool because it can only be used one time. Plastigage ® Feeler Gauge Paper Towel Air­Cooled Engine Technology 21. Plastigage ® cannot be used on bushings or sleeve bearings. Journal outside ______________ (O.D.) are measured and compared to bearing bore _____________ diameters (I.D.) to determine oil clearance. Diameter, Inside Diameter, Outside Diameter, End Play Air­Cooled Engine Technology 22. Crankcase _______ prevent oil leakage from areas where the crankshaft or camshaft go through the sump cover or engine block casting. The knife edge of the sealing lip rubs lightly on the shaft. Walrus Penguins Seals Air­Cooled Engine Technology 23. The knife edge of the sealing lip and the small coil spring on the seal always face ____________the fluid being sealed. Seal protectors should be used anytime the crankshaft is slid through the seal. Toward Away From Doesn’t Matter Air­Cooled Engine Technology 24. Four stroke cycle engines use __________ valves to open & close the intake & exhaust ports. Poppet Reed Rotary Air­Cooled Engine Technology 25. Valve springs are held onto the valve stems with “____________” like retaining washers, pins through holes in the valve stems, collars & rotators and key­hole washers. “keepers” “holders” “sealants” Air­Cooled Engine Technology Air­Cooled Engine Technology 26. After cleaning a poppet valve with the wire wheel, inspect for: 1) eroded, cracked, or pitted valve FACES, heads, & stems; 2) a warped HEAD; 3) worn or improperly ground TIPS or STEMS; 4) BENT valve stems; 5) MARGIN less than 1/64”; and 6) partial SEATING. Air­Cooled Engine Technology Air­Cooled Engine Technology 27. Valve springs can loose their elasticity & become distorted. Check each spring for _______________ and proper length. Some shops also use a valve spring tension tester. squareness interference fit brand name Air­Cooled Engine Technology Air­Cooled Engine Technology 28. Lack of spring tension can cause “valve ________________” (also called “valve float”) which is an incomplete closing and sealing of the valves, especially during higher RPM operation. Butter Flutter Clutter Air­Cooled Engine Technology Face angles are either 46° or 31° Air­Cooled Engine Technology 29. Valve ________ align the stems so that the faces and seats seals contact each other properly. keepers guides Air­Cooled Engine Technology 30. Worn valve guides can be serviced by 1) rebushing; 2) replacing the whole __________ itself; or by 3) reaming the guide oversize and fitting it with a new valve with an oversized stem. Air­Cooled Engine Technology 31. Heavy carbon deposits on the intake valve can ____ the air/fuel mixture entering the combustion chamber. This reduces the power potential of the engine. Leaky valve stem seals, especially on an OHV engine, or a heavily pressurized crankcase can be the cause of such deposits. restrict agitate encourage Air­Cooled Engine Technology 32. A 45° valve face fits into a _____ degree seat. 46º , 31º A 30° valve face fits into a _____ degree seat. 90º , 60º 45º , 30º Air­Cooled Engine Technology 33. The 1º variation between seat & face angles is called _______________ fit. interference best practice obnoxious Air­Cooled Engine Technology Air­Cooled Engine Technology 34. Valve faces & seats can be cut with carbide ___________ or grinding ____________ to exact angles. Used valves and seats in fair condition can be hand lapped to guarantee good seating & sealing. bits, stones drills, reamers saws, wheels Air­Cooled Engine Technology Air­Cooled Engine Technology Air­Cooled Engine Technology Air­Cooled Engine Technology 35. A 3­angle, 46° seat would have a top cut of _____ degrees and a throat cut of _____ degrees. *** A 3­angle, 30° seat would have a top cut of 15° and a throat cut of either 45°or 60° *** Air­Cooled Engine Technology Air­Cooled Engine Technology The 3­Angle Valve Seat Throat Cut of 60º Top Cut of 30º Seat Cut of 46º Provides better flow of: Air & fuel into the chamber Exhaust out of the chamber Air­Cooled Engine Technology Air­Cooled Engine Technology Air­Cooled Engine Technology 36. Valve ________ measuring & service (if needed) Stem must always be done before any seat cutting is begun. Margin Guide Air­Cooled Engine Technology 37. Valve clearance (often called lash) refers to the space between the end of the stem and the end of the lifter (or rocker arm on OHV). It is measured with the valve closed & engine cold! Air­Cooled Engine Technology 38. Too ___________ valve clearance will hold the valve open when the stem heats up & expands. This reduces compression & power. Severe cases can even prevent a hot engine from running at all. Much Little Late Air­Cooled Engine Technology 39.Too _______ valve clearance will make the valves open a shorter distance & a shorter period of time. Lift is the term for distance they open. Duration is the term that describes the time they stay open. Much Little Late Lobe Height Lobe Base Height – Base = Lobe Lift Air­Cooled Engine Technology Lift of Lobe Lobe Height Base Diameter Air­Cooled Engine Technology 40. If engines don’t have adjustable tappets or rocker arms (OHV), Margin valve adjustment (setting the clearance) is done by grinding Face material off of the end of the valve ____________. Stem Measure w/ flat feeler gage. Air­Cooled Engine Technology 41. Of the 4 valve arrangements (LIFT), the valve in block or L­head & the _____________ valve (OHV) or I­head are the most common two.