SEALING. Cylinder head gasket replacement IN QUALITY

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1 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. Cylinder head gasket replacement has given many a technician nightmares. If not done properly the first time, the vehicle surely will make an unscheduled return trip to your shop. If the correct gasket isn t used, proper techniques aren t followed or proper inspection isn t done, the seal won t be right. The head gasket must seal combustion pressures up to 1000 psi in gasoline engines and up to 7200 psi in turbocharged diesel engines. In addition, the head gasket must withstand temperatures in excess of 2000 F. Given this severe environment, even the slightest fault in a gasket will eventually result in its failure. The emergence of bimetal engines which use different metallurgical combinations of engine block and cylinder head materials has further complicated the situation. Most bimetal engines in service today consist of a cast-iron block with an aluminum cylinder head. Since different metals and alloys expand and contract at different rates, devising gaskets to successfully seal bimetal engines has become a challenge for gasket companies. Gasket makers have developed a wide variety of gasket designs, many invented for one specific application, to overcome these problems. Some engines present a unique combination of problems, making them even more difficult to seal effectively. Difficult Engines to Seal GM s 2.3L Quad 4, Chrysler s 2.2 and 2.5L and Honda s 1.3 and 1.5L engines are the ones that present gasket makers with the biggest challenge. Let s take em one by one: GM s 2.3L Quad 4 engine. This engine s bimetal construction, high operating temperatures and tight tolerances created head gasket failures that resulted in the telltale white exhaust smoke of coolant being vaporized. Since the coefficients of expansion for the cast-iron engine block and the aluminum cylinder head are different, the potential for trouble starts the moment the engine is fired up. The head gasket can be literally scrubbed apart when the head expands faster than the Photo courtesy Fel-Pro Properly position a new head gasket to avoid blocking the flow of coolant and oil. Always refer to the instructions and diagrams packaged with the gasket to avoid installation problems. block. The more times the engine is started and warmed up, the faster the deterioration. Fel-Pro s method of solving this problem is with its PermaTorque gasket, a no-retorque design. The application for the Quad 4 has stainlesssteel armored fire rings and silicone beads top and bottom around the fluid openings, and it s coated with Teflon on both sides. The result is a sealing design that allows the surfaces to slide on either side of the gasket while maintaining a seal that will contain pressurized hot gases, coolant and oil. Chrysler s 2.2L & 2.5L. In these engines, small radiators and air trapped in the cooling system can contribute to 38 August 2002

2 hot spots, which cause engine castings to expand unevenly, excessively compressing the cylinder head gasket. When these engines cool and the castings contract, the head gasket may be unable to recover its normal size and shape. And if that wasn t enough, large core holes in the casting contribute to head flex and the engine is prone to detonation. All these elements combine to allow combustion gases to leak. Eventually, the leaking gases burn the gasket facing material, causing gasket failure. Corteco s answer to this problem is its White Gasket technology, which uses two layers of graphite facing material with a double steel armor envelope to prevent crushing. A special combination of epoxy coating topped with silicone helps ensure a secure seal at the metal-to-metal interface between the gasket and the block. The graphite facing material is also coated to provide a tight seal at the cylinder head. Honda s 1.3L & 1.5L. These engines present a different kind of problem. The so-called siamese exhaust valves on these engines create localized heating that can cause head gasket damage if the cooling system isn t operating at peak efficiency. Poor coolant circulation can eventually lead to combustion leakage between cylinders. Victor Reinz s solution is the Nitroseal replacement head gasket, which is composed of Teflon-coated graphite clinched to a perforated steel core and a stainless-steel flange. A thicker gauge metal flange at the combustion chamber improves the torque retention in this most critical area. Causes of Gasket Failure Here are some of the causes of gasket failure that must be recognized and understood in order to correct the problem: Hot Spots. A hot spot causes metal in a small area of the head and/or block to expand excessively. This expansion can crush and damage the head gasket. As a result, the gasket may leak, erode and/or eventually burn through. If a head gasket is replaced without August

3 SEALING IN QUALITY A proper head gasket replacement job requires that warping and distortion be corrected. Use a straightedge and feeler gauge to measure the surfaces of the head and block. Straighten or resurface the casting as necessary. finding the cause of the hot spot, the replacement gasket will eventually fail, too. Hot spots also cause additional stress to the head itself, resulting in cracking or warping. Hot spots have an even more dramatic effect if the operating temperatures rise above normal. A severe overheating incident can cause castings to distort permanently. The excessive crushing caused by hot spots leaves head gaskets measurably thinner in the damaged area. Examine the failed gasket, using a micrometer to measure its thickness in the damaged spot, then compare the reading to other areas of the gasket. If you find evidence of crushing, examine the corresponding surfaces on the head and block for damage. Use a straightedge and feeler gauge to check for flatness. If either surface is damaged or out-of-flatness, it must be resurfaced to assure proper sealing when a new gasket is installed. Cooling System Problems. Air pockets in the cooling system can cause head gaskets to fail. They can be formed while coolant is being added. Air must escape from the engine as the Corteco s White Gasket technology uses an epoxy, which surrounds the graphite-based gasket, topped with silicone. This design provides excellent sealing of rough surfaces and accommodates cold seals. Photo courtesy Fel-Pro coolant is added in order to provide even cooling. The thermostat sometimes 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 remove 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 cooling system. Make sure the thermostat, cooling fans, belts and hoses are in good working condition. Check the hose clamps on the intake side of the water pump to ensure air is not being sucked into the system. Consult a service manual to determine cooling system capacity and make sure the full volume of coolant is added. The manual will also help you locate any bleeder valve(s) and will list any special refilling procedures that are required. Front-drive cars and minivans are more prone to having air trapped in the system because the heater core may sit higher than the engine. In some cases, it may be necessary to remove one of the heater hoses to let air escape from the core. Coolant-Related Problems. Sometimes coolant can be problematical for head gaskets in bimetal engines. Corrosion inhibitors are added to many coolants to protect all types of metals. In bimetal engines, these additives eventually form aluminum salts, which can form a coating on the radiator 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 damage has been done. Casting Motion. This is the result of the cylinder head trying to lift away from the block under the pressure of compression and combustion. This 40 August 2002

4 SEALING IN QUALITY Fel-Pro s PermaTorque head gasket distributes the pressure and heat evenly to avoid detonation problems and lessen the effects of scrubbing. pressure stretches the head bolts and allows minuscule movement of the block and/or head away from the gasket. This releasing and retightening on the gasket causes it to deteriorate over time. If the cylinder head bolts are not torqued to specs, the deterioration occurs sooner. Loose bolts allow too much casting motion, and bolts that are overtorqued can be stretched beyond their tolerance. Using the correct torque and tightening sequence will minimize the casting motion effect. Scrubbing. Scrubbing is a common problem in bimetal engines. The difference in thermal conductivity between the block and the cylinder head causes distortion that results in a sideto-side motion. This scrubbing action causes abrasion and shearing to the gasket, ending in gasket failure. Again, proper head bolt tightening sequence and torque are the answer to minimize this effect. Out-of-Flatness. Warping and distortion are problems inherent with aluminum cylinder heads because of the high thermal conductivity of aluminum, the head being smaller and A surface comparator like this one can be held up to the head or block to visually compare the sealing surface finish to the samples on the tool. Improper sealing surface finishing is a guaranteed comeback. Photo courtesy Fel-Pro 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 heating the head. This technique is recommended only for technicians with experience in cylinder head work. Minimal 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.003 inch for 3-cylinder and V6 engines,.004 inch for 4-cylinder and V8 engines and.006 for Straight Sixes. The total allowed widthwise out-offlatness of head and block combined should not exceed.002 inch. Remember to inspect both the engine block and cylinder head and to combine the readings for tolerances. Proper Surface Finish For head gaskets to seal properly, the engine block and cylinder head must have the proper surface finish. A rough surface provides more grip for the gasket, but causes abrasion and deterioration as the engine expands and contracts from heating and cooling. A smooth surface allows movement between 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 provide enough grip to hold the gasket in place. Bimetal engines may use multilayer steel gaskets that require an almost mirrorlike finish on the metal surfaces. Surface finish must match engine materials and head gasket design. Finish is measured in microinches (millionths of an inch), which is usually expressed as the root mean square (RMS) or roughness average (Ra) of the hills and valleys of the surface. Most cast-iron heads should be finished to 60 to 125 RMS or 54 to 113 Ra microinches. A range of 80 to 100 Ra is recommended. Aluminum heads 42 August 2002

5 SEALING IN QUALITY The Nitroseal replacement head gasket from Victor Reinz consists of a Tefloncoated graphite layer clinched to a perforated steel core. A stainless-steel flange surrounds each cylinder to inhibit combustion leakage. using layered gaskets should be finished to 22 RMS (20 Ra). These specifications allow enough roughness to grip the gasket and enough smoothness to avoid damaging it. Once the head has been checked and corrected for flatness, the final finishing is achieved by using a rotary broach, milling machine, surface grinder or belt sander. Milling machines and surface grinders provide the most precise finishes. If a belt sander is used, the head must be turned often to obtain a crosshatch pattern, since parallel scratches could lead to leaks. Hand-sanding is not recommended, because it s not precise and can leave high and low spots that the head gasket may not be able to fill. During finishing, the surface must be measured frequently using either a profilometer (a hand-held electronic meter with a diamond stylus that s dragged across the head to measure the surface texture) or a comparator gauge (a metal card with samples of finishes created by the various finishing techniques milling broach, grinder and sander). The comparator gauge is held up to the head to visually compare the head surface to the samples. Adding Shims Occasionally, a technician may have to machine a cylinder head that s already been machined one or more times. This can cause such problems as mechanical interference of the valves and pistons, detonation or valve timing retardation in overhead-cam engines. The corrective method here is to add a spacer shim between the head gasket and the block to raise the head up to 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 results in more uniform clamping force on the cylinder head for proper sealing of the head gasket. Some manufacturers caution against reusing these bolts, while others have specific instructions for their reuse. Most gasket makers recommend replacing TTY bolts with the new gasket. Some TTY bolts are made for one use only, and tightening them beyond the yield point a second time may create a weakness, causing the bolt to break under usage, resulting in gasket failure. Using new TTY bolts helps eliminate the possibility of broken bolts, leakage and comeback repairs. Always consult the gasket set 14 Steps to No-Comeback Gasket Replacement Remember these tips when doing a cylinder head gasket replacement. They ll help ensure a done-right-the-first-time job: 1. Properly diagnose the cause of gasket failure. The cause of the gasket failure must be determined and corrected before or during the replacement procedure. Otherwise, the replacement gasket will fail from the same cause. 2. Allow the engine to cool completely before removing the head. Cylinder heads tend to warp if they re removed while still hot, especially those made of aluminum. Heat expands metal, making bolts more difficult to remove and prone to breakage. Working on a cool engine also avoids burned body parts. 3. Remove the head bolts in reverse sequence. Loosen and remove the bolts in the proper torque sequence to minimize the possibility of warping. 4. Inspect the old gasket. Check for wear and damage. It provides clues to problems that need to be corrected prior to the installation of the new gasket. Look for burned, discolored or missing material. 5. Clean all sealing surfaces. All foreign matter such as old gasket material, carbon and rust should be removed. A chemical solvent can be used to soften caked-on material. On steel and iron surfaces, a scraper or wire brush can be used. Use a nonmetallic scraper on aluminum surfaces to avoid damage. 6. Check for out-of-flatness. Inspect the cylinder head and engine block for out-of-flatness using a straightedge and feeler gauge. Correct any warping and distortion before you install a new gasket. 7. Prepare the sealing surface properly. Make sure you properly finish the sealing surfaces for the engine block, cylinder head and gasket combination according to the gasket maker s instructions. Improper sealing surface finishing is a guaranteed comeback. 8. Read the instructions with the new gasket. Gasket makers know 44 August 2002

6 instructions and OEM specifications for TTY information on your particular head bolt requirements. Head Gaskets Requiring Retorquing Some cylinder head gasket designs require that they be retorqued after running the engine to bring it up to operating temperature. While cast-iron block and head combinations can be retorqued while still hot, bimetal engines should be allowed to cool before the procedure is begun. Some gaskets even require a third tightening after a certain running time or mileage. Consult the gasket set instructions for the correct information. Most gasket makers have service hotlines or websites to help with gasket installation problems. When in doubt about how to proceed, contact the gasket company for the proper procedure. the special tricks and techniques involved in removing and installing their gaskets. They create gaskets for specific engine applications. Take advantage of their R&D and don t guess. 9. Ensure the proper fit of the gasket. Pay close attention to the correct fit of bolt holes and water and lubrication ports. Many head gaskets have a 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. 10. Position the new gasket properly. Improper positioning of cylinder 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 meter the flow of fluids and may not exactly match the openings on the block or head. Always give special attention to the installation instructions and diagrams packaged with the gasket. 11. Replace all torque-to-yield bolts. Since TTY bolts are generally made not to be reinstalled, using new TTY bolts helps eliminate the possibility of broken bolts, leakage and comeback repairs. 12. Install the head bolts in the proper torque sequence. Engine manufacturers specify a particular tightening order and torque, based on the materials and design of the engine block and cylinder head, to ensure precise clamping of the gasket to seal the engine. 13. Inspect for leaks. When the head gasket installation is complete, inspect the sealing areas to confirm your installation was done properly. Run the engine and inspect it again. 14. Retorque the head bolts, if specified. Some older cylinder head gasket designs require that they be retorqued after the engine is brought up to operating temperature. Consult the gasket set instructions for the correct information. Victor Reinz is developing the next generation of cylinder head gaskets. These so-called smart gaskets will go beyond sealing combustion, lubricant and coolant. They ll become an integral part of the engine management system. Future Technology What does the future hold for cylinder head gasket technology? The folks at Victor Reinz are looking at socalled smart head gaskets, equipped with miniature temperature, pressure and flow-rate sensors, that will provide the engine ECU with real-time, reliable information about engine operation. These gaskets will include the signal lines, connectors, converters and sensors. Temperature sensors will monitor hot spots in the engine and alert the cooling system to boost operation of the water pump and therefore the performance of the cooling system. Flowrate sensors will provide coolant flow information to the cooling system as well. Pressure sensors will monitor the combustion pressure and have the capacity to detect the onset of engine knock. With this real-time information, the engine ECU can improve the combustion process, which in turn leads to reduced emissions, better fuel economy and higher performance. Back to Basics Until the day comes when smart cylinder head gaskets monitor the critical factors that lead to gasket failure, technicians will just have to avoid costly comebacks by doing it right the first time. Remember the basics, be aware of bimetal engine combinations and read the instructions in the gasket set; you ll sleep a lot better knowing that all-day gasket job won t come back to haunt you. Visit to download a free copy of this article. Copies are also available by sending $3 for each copy to: Fulfillment Dept., MOTOR Magazine, 5600 Crooks Rd., Troy, MI August