PLUGGING THE HEAD GASKET DIKE

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PLUGGING THE HEAD GASKET DIKE BY THOMAS MARCY Doing a competent head gasket failure diagnosis and repair today calls for more than sticking a finger in a leaking dike.

1 PLUGGING THE HEAD GASKET DIKE BY THOMAS MARCY Doing a competent head gasket failure diagnosis and repair today calls for more than sticking a finger in a leaking dike. To be sure, some shops do stick one finger into this job by simply replacing the gasket, only to have to do the same repair again (and again!) to the same vehicle. Truth is, modern bimetal engines are more prone to springing leaks around the head gasket area than older ones. When trying to nail a failed head gasket in today s automobiles, know that there can be several areas of dike failure. The first symptom is coolant loss. Though it would seem that finding fluid is as easy as counting your fingers, a leak site may be difficult to locate. To tackle this problem, first turn the engine off, then check the coolant quality and quantity. Examine the reservoir or overflow bottle. If the coolant level is low, take a quick look underhood for leaks. Next, remove the radiator cap carefully, to prevent burns. If coolant boils as you open the cap slightly, wait for the engine to cool before proceeding. Once the cap is safely removed, see if the coolant has a muddy, rusty or gray appearance. If this discoloration is evident, corrosion and boiling may be breaching the dike. Also check the coolant mix. An improper mix can cause head gasket failure from overheating. If this is the case, don t just replace the head gasket; inspect the head and block and service the entire cooling system. Now pressure-test the system for an extended period. During this test, carefully check the radiator and hoses, looking for bulging or signs of aging. While the system is pressurized, also look for coolant leaks at the water pump gasket, shaft and bearing. Examine the cooling fan and belts, as well, and check the head gasket seams between the block and head. If a pressure loss occurs during the test, also don t forget to eyeball the heater core for leakage inside the passenger compartment. But don t confuse coolant with the plain water that can drip from a clogged evaporator drain. Next, raise the vehicle on a lift and check the cooling system core plugs. If the vehicle is so equipped, also inspect the engine block heater for leaks. Now, lower the vehicle and check the engine oil dipstick. Look for a milky residue of coolant in the oil. Be careful here, though. Short drives can build slight crankcase condensation that can mimic coolant leakage. Ask the owner about his driving habits before condemning the head gasket. With the pressure gauge still attached, start the engine and watch the gauge needle. If pressure rises rapidly beyond the cap rating, shut down the engine quickly to prevent injury or further radiator, gasket or hose damage. Note that high-compression leakage 34 August 2001

Head gasket work abounds for those willing to stem the tide of leaky pressures. Here s what you can do to ensure that your shop plugs these leakers effectively and permanently.

2 Head gasket work abounds for those willing to stem the tide of leaky pressures. Here s what you can do to ensure that your shop plugs these leakers effectively and permanently. can burst cooling system components, and is a signal that the head gasket has failed. It s a good idea to use a combustion leak tester to confirm your pressure test results. This tool gets inserted into the radiator neck with the engine running and uses a special chemical that changes color when combustion gases are present in the coolant. Compression Path You can also trace head gasket compression loss by doing a compression test or a power balance test. If coolant loss is significant, the affected cylinder will usually misfire. But remember, some engines may not lose coolant until heated to operating temperature. For an engine with a suspected compression leak, also consider that the loss may travel to an adjacent cylinder. If the leak is between cylinders, compression will be equally low in both. Once you perform the above tests, you should have a pretty good idea where the gasket leak is located. But not always. For example, a carbureted V6 leak we plugged recently lost coolant into the cylinders, but leaked from the corner port of the intake manifold gasket. Although the coolant loss blew out the spark plug hole when the engine was cranked, apparently indicating the dike had blown in the cylinder, disassembly proved otherwise. The coolant leak entered through that cylinder s air stream. In this case, the loss was major, but it may be difficult to trace, since coolant is consumed in combustion. One tip-off is sometimes found in allowing the vehicle to sit for an extended period with test pressure applied to the cooling system. Also remember that if coolant finds its way into the exhaust, the oxygen sensor may be affected. Drain the Pond After your diagnosis is made, drain the cooling system and remove the head, then strip it for service. Thoroughly clean the combustion chambers and all component parts. Use a fine-wire brush to remove carbon deposits. Now check finish and flatness. For head gaskets to seal properly, the surface finish and flatness of the head and block must be within limits. Also, cylinder head warp should be within specified tolerances. As a rule of thumb, with cast-iron components and a conventional head gasket, both surfaces need a finish having a 30 to 110 Ra rating, with 60 to 100 Ra preferred. With aluminum heads mounted on cast-iron blocks, 30 to 60 Ra is recommended, with 50 to 60 Ra preferred. But if you re working on a late-model vehicle having an engine with MLS (multilayer steel) head gaskets, follow the gasket maker s specs. Many of these engines require a very smooth, shiny finish less than 30 Ra. August

Next, lay a heavy straightedge across the head gasket surface and use a feeler gauge to make sure that the head has neither convex nor concave distortion.

3 PLUGGING THE HEAD GASKET DIKE This 5.2-liter Chrysler cylinder head was claimed to have blown a gasket. As a result, it sat in the customer s truck bed for winter traction, but upon disassembly, the rocker arm covers hid no water or sludge formation. Next, lay a heavy straightedge across the head gasket surface and use a feeler gauge to make sure that the head has neither convex nor concave distortion. Generally, cast-iron heads in V8, V6 or inline 4-cylinder engines can tolerate distortion up to.003 inch (.076mm). With long inline 6-cylinder heads, distortion of.006 inch (.152mm) is the limit. Checking across the gasket surface should reveal no more than a.002-inch (.05mm) variation. Because of aluminum s greater expansion rate, hold aluminum heads to tighter tolerances, with no variations beyond.002 inch (.05mm) in any area or direction. With all heads, allow no sudden surface deflections exceeding.001 inch in any direction, especially checking around the outer corner wall areas. Over the Top Check OHC cylinder heads for true in two ways first, the gasket surface, then cam bore straightness. Often, if the head warps, both go awry. Also consider that machining the gasket surface lowers the cam centerline toward the block. That means the head sits on the block with valve clearances lessened and the cam drive sprocket centerline lowered. The sprocket timing cover may also need altering. When stripping the head for machining, remove any shaft(s), followers, rocker arms, balls and nuts. Keep these parts together, according to their corresponding valves. If needed, Photos: Thomas Marcy use an appropriate valve spring compressor to disassemble each valve, spring, retainer and keys, and keep these parts in order, too. If reused, they should go back into the same cylinder locations. Next, use a good solvent to clean each valve stem, and clean the guides with a soft-wire hole brush. Fit each cleaned valve back into its guide and check the guide clearances. Examine the valves for pits or tip wear. Have your machine shop replace burned, corroded or bent valves. Check all valve springs and any vibration dampeners. As part of a head overhaul, order new valve seals. Lastly, check the springs for square. You should typically replace any spring where vertical distortion exceeds 1 16 inch. Most machine shops follow the vehicle manufacturer s tolerances for maximum material removal. Be aware that on V6 and V8 engines, the intake manifold may have to be milled to provide for proper manifold gasket fit. Deck Surface Checks Now use a straightedge and feeler gauge to check for block deck warpage. Use the same method as Water in the intake ports, but no coolant. Is this an example of an intake manifold leak or a crack made by freezing? Neither! This water accumulated through the 5.2 s open intake manifold while the engine was riding in the pickup bed. 36 August 2001

If warpage is excessive or gross side-toside differences exist in V-style engines, schedule the block for deck resurfacing, provided the deck height reading allows for it.

4 Was this damage caused by a leak in the head gasket or a crack in the head? Make sure you look closely, and use a crack detector spray to be sure. A small crack can burst the dam of an otherwise coolant-tight head. when checking the head surface. If warpage is excessive or gross side-toside differences exist in V-style engines, schedule the block for deck resurfacing, provided the deck height reading allows for it. Remember, deck height is measured from the crankshaft centerline to the block head gasket surface. While the head is being straightened or machined, check the rocker arms for scoring, cracks or wear. Correct minor wear on the valve contact point using light grinding, but replace the arm if damage is excessive. If the vehicle is so equipped, check the rocker shaft for wear or damage. On heads having ball & stud-mounted rocker arms, check the balls, studs and nuts. If a stud is worn, replace it. Some studs thread into the head, while others simply press into place. ply a gasket-removing compound or general-purpose degreaser, or clean the gasket surfaces using a soft brush. Do not use a drill and abrasive pad or wire brush! While a head may have been resurfaced at a machine shop, never assume cleanliness. Resurfacing Getting a Grip Make sure your hands are clean when doing head gasket work, and keep the head clean after it s serviced. Remember, gasket surface debris can form a path for leaks, damage the new gasket or harm the surface of the head or engine deck. To ensure that the job goes well, apusually removes debris, but sometimes ground and sanded gasket surfaces can pick up debris. Ordinary soap and water works well for a final head cleaning. After cleaning, place the completely restored head on a clean workbench. Now check the block bolt holes. Dirty or deformed threads can reduce clamping forces. To ensure accurate torquing, run a bottom tap fully into each head bolt hole to make sure the threads are clean. Also check hole depth to ensure that the bolts don t bottom. Chamfer the edges of each hole so block metal doesn t pull above the deck surface when the bolts are tightened. Finally, clean all holes to remove any debris and make sure no liquid resides there. (A liquid-filled hole can crack a block!) Think about sealer usage. Under no circumstances should you use any type of shellac, chemical sealer or adhesive on a conventional nonasbestos or graphite head gasket. These gaskets have a solid or perforated steel layer faced on both sides with a soft material. The core provides strength while the soft facing material allows for proper sealing. Many gaskets have additional antifriction coatings to resist shearing forces in bimetal engines. Others, Head gasket failure often occurs at the corner of the head, where the coolant passage routes close to the wall. The dike gets pretty thin here. August

However, on certain late-model engines (especially those with MLS head gaskets), some engine makers specify the use of a sealer. Always follow the gasket maker s guidelines concerning sealer types.

5 PLUGGING THE HEAD GASKET DIKE made for cast-iron engines, may come equipped with silicone sealing beads to provide better cold-engine sealing. Generally speaking, RTV silicone sealers should not be used when installing a cylinder head. However, on certain late-model engines (especially those with MLS head gaskets), some engine makers specify the use of a sealer. Always follow the gasket maker s guidelines concerning sealer types. Make sure you locate the head gasket properly on the block. Some have a top face marking, others do not. Check for right-side or left-side markings if the engine is a V-style. Don t proceed until you know the gasket is correctly placed and located. Many gaskets key over dowels in the block or head. Dropping the Sandbag When you place the head on the block and gasket, make sure the gasket remains in place and the head seats properly. Now check the fasteners. As mentioned, a good head gasket seal is dependent on proper pressure loading and torque. Ask yourself, What s the tightening sequence for this engine? All head bolts are torqued to recommended values in calculated steps and require tightening in a specific sequence. If the head bolts are to be reused, first make sure they re all in perfect condition, with clean, undamaged threads. Check that they re the correct length and not stretched. Wire-brush the threads and closely inspect each bolt. Replace any that are nicked, deformed or worn. For head bolts that screw into blind holes, lubricate the threads lightly with oil. Also, lightly lube the underside of the bolt heads. For head bolts that extend into a coolant jacket, coat the threads with a suitable sealer to prevent leakage. Torque-to-Yield Bolts Many modern engines use torque-toyield (TTY) head bolts. These stretch slightly when tightened, which provides improved head gasket sealing. You tighten the bolts to an initial torque, using the appropriate pattern. Then tighten to the additional amount. This last step is usually measured in degrees of bolt rotation. This final twist stretches the bolts and builds the elastic clamping force that provides even loading across the gasket surface. Because TTY head bolts are designed to stretch, many engine makers advise against reusing them, claiming that a prestretched bolt won t hold the same tension as before, which may lower clamping forces. Simply stated, all TTY bolts Always check the flatness of the head gasket mating surface with a heavy straightedge and a feeler gauge. Any excess warp here may indicate the need for machining and, on OHC setups, cam boss straightening. Cam bearing saddles usually follow head gasket surface warpage. Depending on your machine shop s recommendations, these may be bored and fitted with oversize bearing inserts. A competent machinist is a must here. August

PLUGGING THE HEAD GASKET DIKE A head gasket seal works best when the surface grip is correct. Here, a technician checks the smoothness of the finished grind, which is critical to a long-lasting seal.

The two outside layers are high-temper spring steel with a raised bead that provides combustion sealing.

6 PLUGGING THE HEAD GASKET DIKE A head gasket seal works best when the surface grip is correct. Here, a technician checks the smoothness of the finished grind, which is critical to a long-lasting seal. Always use a quality gasket when reassembling the head. This Victor-Reinz MLS gasket consists of three layers of steel, set up in a sandwich-type arrangement. The two outside layers are high-temper spring steel with a raised bead that provides combustion sealing. They re selectively screen-printed with a polymer coating, which provides the fluid seal needed to prevent coolant migration. The center layer provides the necessary gasket thickness. should be replaced when reinstalling a cylinder head. If you re installing head bolts on aluminum cylinder heads, use hardened steel washers beneath the heads and always position them with the chamfered side up. These washers distribute the clamping force and prevent metal galling. At some point you should ask yourself, Are the bolts now too long because of surface machining? Resurfacing a cylinder head decreases its height. Make sure the bolts don t bottom in blind holes. If this is a problem, you can use either hardened steel washers under the bolt heads to raise them up, or a thicker head gasket or gasket shim. If the head was machined to its maximum, a thicker gasket can restore proper head height and compression. Now tighten the head bolts using an accurate torque wrench. Normally, you ll use three to five steps to achieve the proper torque. Follow the recommended sequence and recheck torque on the last step. This final check ensures that no bolts were missed. If a bolt doesn t achieve and hold the specified torque, either it s stretched or the bolt threads pulled. If this happens, replace the bolt or repair the threads. With TTY head bolts, use a torque-to-angle (TTA) indicator to confirm your final step. Occasionally, a head gasket manufacturer will require additional bolt torquing after the engine runs to normal operating temperatures and then cools. In this case, set the final torque using the same bolt sequence as before, making sure the engine is cooled to ambient temperature! On some applications with these additional-torque head gaskets, you may need to retorque the bolts after a specified mileage or time interval. Check the gasket or engine maker s recommendations. Make sure all manifold gaskets are properly placed, using guide dowels, if necessary, to position the manifold. Install the bolts, then tighten the retaining bolts in the correct torque steps and sequence. Install the timing belt(s), making sure a change in head height did not adversely affect tensioning capability, and that the sprockets and timing marks are properly aligned. Replace hoses and belts as necessary and, lastly, refill the cooling system as recommended. As a final test, check the dike by pressure-testing the cooling system to ensure that it s leak-free. Make sure the reservoir holds the correct amount of coolant after the thermostat opens, and then road-test the vehicle to gauge engine performance and to make sure everything is okay. 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 2001

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