SEALING IN QUALITY BY TOM NASH Stop the ‘head’-scratching over head gasket replacement with some useful information to help make sure the engine is sealed tight the first time.
ylinder head gasket re- vising gaskets to successfully seal bimet- placement has given al engines has become a challenge for many a technician night- gasket companies. Gasket makers have mares. If not done prop- developed a wide variety of gasket de- Properly position a new head erly the first time, the signs, many invented for one specific gasket to avoid blocking the flow vehicle surely will make application, to overcome these prob- of coolant and oil. Always refer an unscheduled return trip to your lems. Some engines present a unique to the instructions and dia- shop. If the correct gasket isn’t used, combination of problems, making them grams packaged with the gasket Cproper techniques aren’t followed or even more difficult to seal effectively. to avoid installation problems. proper inspection isn’t done, the seal Photo courtesy Fel-Pro courtesy Photo won’t be right. Difficult Engines to Seal The head gasket must seal combus- GM’s 2.3L Quad 4, Chrysler’s 2.2 and block. The more times the engine is tion pressures up to 1000 psi in gaso- 2.5L and Honda’s 1.3 and 1.5L engines started and warmed up, the faster the line engines and up to 7200 psi in tur- are the ones that present gasket mak- deterioration. bocharged diesel engines. In addition, ers with the biggest challenge. Let’s Fel-Pro’s method of solving this the head gasket must withstand tem- take ’em one by one: problem is with its PermaTorque gas- peratures in excess of 2000°F. Given GM’s 2.3L Quad 4 engine. This ket, a “no-retorque” design. The appli- this severe environment, even the engine’s bimetal construction, high op- cation for the Quad 4 has stainless- slightest fault in a gasket will eventually erating temperatures and tight toler- steel armored fire rings and silicone result in its failure. ances created head gasket failures that beads top and bottom around the fluid The emergence of bimetal engines— resulted in the telltale white exhaust openings, and it’s coated with Teflon which use different metallurgical com- smoke of coolant being vaporized. on both sides. The result is a sealing binations of engine block and cylinder Since the coefficients of expansion design that allows the surfaces to slide head materials—has further complicat- for the cast-iron engine block and the on either side of the gasket while ed the situation. Most bimetal engines aluminum cylinder head are different, maintaining a seal that will contain in service today consist of a cast-iron the potential for trouble starts the mo- pressurized hot gases, coolant and oil. block with an aluminum cylinder head. ment the engine is fired up. The head Chrysler’s 2.2L & 2.5L. In these Since different metals and alloys ex- gasket can be literally “scrubbed” apart engines, small radiators and air trapped pand and contract at different rates, de- when the head expands faster than the in the cooling system can contribute to
38 August 2002 “hot spots,” which cause engine castings nation of epoxy coating topped with sil- graphite clinched to a perforated steel to expand unevenly, excessively com- icone helps ensure a secure seal at the core and a stainless-steel flange. A pressing the cylinder head gasket. metal-to-metal interface between the thicker gauge metal flange at the com- When these engines cool and the cast- gasket and the block. The graphite fac- bustion chamber improves the torque ings contract, the head gasket may be ing material is also coated to provide a retention in this most critical area. unable to recover its normal size and tight seal at the cylinder head. shape. And if that wasn’t enough, large Honda’s 1.3L & 1.5L. These en- Causes of Gasket Failure core holes in the casting contribute to gines present a different kind of prob- Here are some of the causes of gas- head flex and the engine is prone to lem. The so-called “siamese” exhaust ket failure that must be recognized detonation. All these elements combine valves on these engines create local- and understood in order to correct to allow combustion gases to leak. Even- ized heating that can cause head gasket the problem: tually, the leaking gases burn the gasket damage if the cooling system isn’t op- Hot Spots. A hot spot causes metal facing material, causing gasket failure. erating at peak efficiency. Poor coolant in a small area of the head and/or block Corteco’s answer to this problem is circulation can eventually lead to com- to expand excessively. This expansion its White Gasket technology, which us- bustion leakage between cylinders. can crush and damage the head gasket. es two layers of graphite facing materi- Victor Reinz’s solution is the Ni- As a result, the gasket may leak, erode al with a double steel armor envelope troseal replacement head gasket, and/or eventually burn through. to prevent crushing. A special combi- which is composed of Teflon-coated If a head gasket is replaced without
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coolant is added in order to provide even cooling. The thermostat some- times blocks the air, leaving pockets in the upper block and/or heads. In other cases, the configuration of the cooling system itself makes it difficult to re- move air. With air in the system, coolant does not circulate properly, so the engine doesn’t cool evenly. Air trapped in the system can often be found in the heater core. Little or no output from the heater when the engine is warm is a good indicator of air trapped in the system. Check the overall condition of the
Photo courtesy Fel-Pro courtesy Photo cooling system. Make sure the thermo- A proper head gasket replacement job requires that warping and distortion stat, cooling fans, belts and hoses are in be corrected. Use a straightedge and feeler gauge to measure the surfaces good working condition. Check the of the head and block. Straighten or resurface the casting as necessary. hose clamps on the intake side of the water pump to ensure air is not being finding the cause of the hot spot, the the damaged spot, then compare the sucked into the system. replacement gasket will eventually fail, reading to other areas of the gasket. Consult a service manual to deter- too. Hot spots also cause additional If you find evidence of crushing, ex- mine cooling system capacity and stress to the head itself, resulting in amine the corresponding surfaces on make sure the full volume of coolant is cracking or warping. the head and block for damage. Use a added. The manual will also help you Hot spots have an even more dra- straightedge and feeler gauge to check locate any bleeder valve(s) and will list matic effect if the operating tempera- for flatness. If either surface is dam- any special refilling procedures that tures rise above normal. A severe over- aged or out-of-flatness, it must be are required. Front-drive cars and heating incident can cause castings to resurfaced to assure proper sealing minivans are more prone to having air distort permanently. when a new gasket is installed. trapped in the system because the The excessive crushing caused by Cooling System Problems. Air heater core may sit higher than the en- hot spots leaves head gaskets measur- pockets in the cooling system can gine. In some cases, it may be neces- ably thinner in the damaged area. Ex- cause head gaskets to fail. They can be sary to remove one of the heater hoses amine the failed gasket, using a mi- formed while coolant is being added. to let air escape from the core. crometer to measure its thickness in Air must escape from the engine as the Coolant-Related Problems. Sometimes coolant can be problemati- cal for head gaskets in bimetal engines. Corrosion inhibitors are added to many coolants to protect all types of metals. In bimetal engines, these addi- tives eventually form aluminum salts, which can form a coating on the radia- tor tubes, reducing cooling efficiency and possibly leading to gasket failure. A thorough flushing is called for in this case. In extreme cases of plugging or deterioration, radiator replacement may be the only answer. Replacing a radiator at the first sign of a problem is usually cheaper and easier than doing a head gasket job after the engine dam- age has been done. Casting Motion. This is the result Corteco’s White Gasket technology uses an epoxy, which surrounds the of the cylinder head trying to lift away graphite-based gasket, topped with silicone. This design provides excellent from the block under the pressure of sealing of rough surfaces and accommodates cold seals. compression and combustion. This
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thinner than the block and the physical law that heat rises. Although severely warped heads must be replaced, some minor warping can be removed by clamping and heat- ing the head. This technique is recom- mended only for technicians with ex- perience in cylinder head work. Mini- mal warping and distortion can also be corrected by resurfacing. First, inspect the cylinder head and engine block for flatness. Place a straightedge lengthwise on the head or block and, using a feeler gauge, check for warping between the head and straightedge. The total maximum lengthwise out-of-flatness of head and block combined should not exceed Fel-Pro’s PermaTorque head gasket distributes the pressure and heat evenly .003 inch for 3-cylinder and V6 en- to avoid detonation problems and lessen the effects of “scrubbing.” gines, .004 inch for 4-cylinder and V8 engines and .006 for Straight Sixes. pressure stretches the head bolts and problem in bimetal engines. The dif- The total allowed widthwise out-of- allows minuscule movement of the ference in thermal conductivity be- flatness of head and block combined block and/or head away from the gas- tween the block and the cylinder head should not exceed .002 inch. Remem- ket. This releasing and retightening on causes distortion that results in a side- ber to inspect both the engine block the gasket causes it to deteriorate over to-side motion. This scrubbing action and cylinder head and to combine the time. causes abrasion and shearing to the readings for tolerances. If the cylinder head bolts are not gasket, ending in gasket failure. Again, torqued to specs, the deterioration oc- proper head bolt tightening sequence Proper Surface Finish curs sooner. Loose bolts allow too and torque are the answer to minimize For head gaskets to seal properly, the much casting motion, and bolts that this effect. engine block and cylinder head must are overtorqued can be stretched be- Out-of-Flatness. Warping and dis- have the proper surface finish. A rough yond their tolerance. Using the correct tortion are problems inherent with alu- surface provides more grip for the gas- torque and tightening sequence will minum cylinder heads because of the ket, but causes abrasion and deteriora- minimize the casting motion effect. high thermal conductivity of alu- tion as the engine expands and con- Scrubbing. Scrubbing is a common minum, the head being smaller and tracts from heating and cooling. A smooth surface allows movement be- tween the head and gasket, which is essential on engines with iron blocks and aluminum heads. However, if the surface is too smooth, it may not pro- vide enough grip to hold the gasket in place. Bimetal engines may use multi- layer steel gaskets that require an al- most mirrorlike finish on the metal surfaces. Surface finish must match engine materials and head gasket design. Fin- ish is measured in microinches (mil- lionths of an inch), which is usually ex- pressed as the root mean square (RMS) or roughness average (Ra) of the hills and valleys of the surface.
Photo courtesy Fel-Pro courtesy Photo Most cast-iron heads should be fin- A surface comparator like this one can be held up to the head or block to vi- ished to 60 to 125 RMS or 54 to 113 sually compare the sealing surface finish to the samples on the tool. Improp- Ra microinches. A range of 80 to 100 er sealing surface finishing is a guaranteed comeback. Ra is recommended. Aluminum heads
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the original specification. Most shims are .020 inch thick, but other sizes may be available, depending on the block. Torque-to-Yield (TTY) Bolts Torque-to-yield is a method used by some engine manufacturers to tighten cylinder head bolts by stretching them beyond their yield point. These bolts will not return to their original length when removed. The TTY system re- sults in more uniform clamping force on the cylinder head for proper sealing of the head gasket. Some manufactur- ers caution against reusing these bolts, while others have specific instructions for their reuse. The Nitroseal replacement head gasket from Victor Reinz consists of a Teflon- Most gasket makers recommend coated graphite layer clinched to a perforated steel core. A stainless-steel replacing TTY bolts with the new gas- flange surrounds each cylinder to inhibit combustion leakage. ket. Some TTY bolts are made for one use only, and tightening them be- using layered gaskets should be fin- This can cause such problems as me- yond the yield point a second time ished to 22 RMS (20 Ra). These speci- chanical interference of the valves and may create a weakness, causing the fications allow enough roughness to pistons, detonation or valve timing re- bolt to break under usage, resulting grip the gasket and enough smooth- tardation in overhead-cam engines. in gasket failure. Using new TTY ness to avoid damaging it. The corrective method here is to add a bolts helps eliminate the possibility of Once the head has been checked spacer shim between the head gasket broken bolts, leakage and comeback and corrected for flatness, the final fin- and the block to raise the head up to repairs. Always consult the gasket set ishing is achieved by using a rotary broach, milling machine, surface 14 Steps to ‘No-Comeback’ Gasket Replacement grinder or belt sander. Milling ma- chines and surface grinders provide emember these tips when doing a cylinder head gasket replacement. the most precise finishes. If a belt RThey’ll help ensure a done-right-the-first-time job: sander is used, the head must be 1. Properly diagnose the cause of gasket failure. The cause of the gasket turned often to obtain a crosshatch failure must be determined and corrected before or during the replacement pattern, since parallel scratches could procedure. Otherwise, the replacement gasket will fail from the same cause. lead to leaks. Hand-sanding is not rec- 2. Allow the engine to cool completely before removing the head. Cylinder heads tend to warp if they’re removed while still hot, espe- ommended, because it’s not precise cially those made of aluminum. Heat expands metal, making bolts more and can leave high and low spots that difficult to remove and prone to breakage. Working on a cool engine also the head gasket may not be able to fill. avoids burned body parts. During finishing, the surface must 3. Remove the head bolts in reverse sequence. Loosen and remove the be measured frequently using either a bolts in the proper torque sequence to minimize the possibility of warping. profilometer (a hand-held electronic 4. Inspect the old gasket. Check for wear and damage. It provides meter with a diamond stylus that’s clues to problems that need to be corrected prior to the installation of the dragged across the head to measure the new gasket. Look for burned, discolored or missing material. surface texture) or a comparator gauge 5. Clean all sealing surfaces. All foreign matter such as old gasket materi- (a metal card with samples of finishes al, carbon and rust should be removed. A chemical solvent can be used to soft- en caked-on material. On steel and iron surfaces, a scraper or wire brush can be created by the various finishing tech- used. Use a nonmetallic scraper on aluminum surfaces to avoid damage. niques—milling broach, grinder and 6. Check for out-of-flatness. Inspect the cylinder head and engine sander). The comparator gauge is held block for out-of-flatness using a straightedge and feeler gauge. Correct any up to the head to visually compare the warping and distortion before you install a new gasket. head surface to the samples. 7. Prepare the sealing surface properly. Make sure you properly fin- ish the sealing surfaces for the engine block, cylinder head and gasket com- Adding Shims bination according to the gasket maker’s instructions. Improper sealing sur- Occasionally, a technician may have to face finishing is a guaranteed comeback. machine a cylinder head that’s already 8. Read the instructions with the new gasket. Gasket makers know been machined one or more times.
44 August 2002 instructions and OEM specifications for TTY information on your particu- lar head bolt requirements. Head Gaskets Requiring Retorquing Some cylinder head gasket designs re- quire that they be retorqued after run- ning the engine to bring it up to oper- ating temperature. While cast-iron block and head combinations can be retorqued while still hot, bimetal en- gines should be allowed to cool before the procedure is begun. Some gaskets even require a third tightening after a certain running time or mileage. Con- sult the gasket set instructions for the correct information. Victor Reinz is developing the next generation of cylinder head gaskets. These Most gasket makers have service so-called “smart” gaskets will go beyond sealing combustion, lubricant and hotlines or websites to help with gasket coolant. They’ll become an integral part of the engine management system. installation problems. When in doubt about how to proceed, contact the gas- called “smart” head gaskets, nectors, converters and sensors. ket company for the proper procedure. equipped with miniature tempera- Temperature sensors will monitor ture, pressure and flow-rate sensors, hot spots in the engine and alert the Future Technology that will provide the engine ECU cooling system to boost operation of What does the future hold for cylin- with real-time, reliable information the water pump and therefore the per- der head gasket technology? The about engine operation. These gas- formance of the cooling system. Flow- folks at Victor Reinz are looking at so- kets will include the signal lines, con- rate sensors will provide coolant flow information to the cooling system as well. Pressure sensors will monitor the combustion pressure and have the ca- the special tricks and techniques involved in removing and installing their pacity to detect the onset of engine gaskets. They create gaskets for specific engine applications. Take advan- knock. With this real-time information, tage of their R&D and don’t guess. the engine ECU can improve the com- 9. Ensure the proper fit of the gasket. Pay close attention to the correct bustion process, which in turn leads to fit of bolt holes and water and lubrication ports. Many head gaskets have a reduced emissions, better fuel econo- “top” and “bottom.” Compare the new gasket to the old one. Using the wrong gasket often causes gasket failure and could lead to engine damage. my and higher performance. 10. Position the new gasket properly. Improper positioning of cylin- Back to Basics der head gaskets can alter or block the flow of coolant or oil, leading to cooling problems or serious engine damage. Many gaskets are designed to Until the day comes when “smart” meter the flow of fluids and may not exactly match the openings on the cylinder head gaskets monitor the block or head. Always give special attention to the installation instructions critical factors that lead to gasket fail- and diagrams packaged with the gasket. ure, technicians will just have to 11. Replace all torque-to-yield bolts. Since TTY bolts are generally avoid costly comebacks by doing it made not to be reinstalled, using new TTY bolts helps eliminate the possi- right the first time. Remember the bility of broken bolts, leakage and comeback repairs. basics, be aware of bimetal engine 12. Install the head bolts in the proper torque sequence. Engine manufacturers specify a particular tightening order and torque, based on combinations and read the instruc- the materials and design of the engine block and cylinder head, to ensure tions in the gasket set; you’ll sleep a precise clamping of the gasket to seal the engine. lot better knowing that all-day gasket 13. Inspect for leaks. When the head gasket installation is complete, job won’t come back to haunt you. inspect the sealing areas to confirm your installation was done properly. Run the engine and inspect it again. Visit www.motor.com to 14. Retorque the head bolts, if specified. Some older cylinder head download a free copy of this gasket designs require that they be retorqued after the engine is brought article. Copies are also available up to operating temperature. Consult the gasket set instructions for the by sending $3 for each copy to: correct information. Fulfillment Dept., MOTOR Magazine, 5600 Crooks Rd., Troy, MI 48098.
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