What happened to my head ? How to analyze a failed head gasket

BY JERRY ROSENQUIST

So, you’ve kicked out a head gasket. Now what to do? Throw on another one and hope for the best? Change brands? Add some gasket fix in a can perhaps? The best approach is to determine why the gasket failed in the first place. Like reading spark plugs to see how the cylinders are firing, examining a head gasket can do much the same. Different gasket designs can fail for different reasons. What follows generally applies to composition , but the same techniques can also be applied to MLS gaskets.

CARBON TRACKS Carbon tracking behind the combustion seal is a definite sign of combustion leakage. If the combustion seal is working properly, any carbon build up will end in a distinct line where the head and block come in contact with each other. If this line is “fuzzy” or there are streaks, the seal is leaking to some degree. Reasons for carbon tracks include insufficient clamping force on the gasket, out of flat surfaces, bending of the head or block, or high pressure overcoming the clamping force. Fixes include insuring proper bolt tightening and lubrication procedures, surfacing the head or block, Figure 1. The combustion leakage removed the coating proper ignition timing and air/fuel ratio. Head or on this MLS head gasket. block bending is generally a result of excessively milled surfaces, or inherently weak castings.

HEAT DISCOLORATION Heat discoloration changes the normally shiny appearance of the armor used on a composition gasket to a bluish/black color. This can easily be determined by attempting to scrape it off with a fingernail. If it comes off, it is carbon tracking; if it doesn’t, it is caused by excessive localized heat. If the gasket is an MLS design, the coating will show streaks or burn marks. This heat occurs adjacent to exhaust valves or in areas of insufficient coolant flow. As the coolant hits the very hot exhaust bowl area, it flashes to steam and any heat transfer from the casting to the coolant stops. It won’t Figure 2. Good example of distorted diameter.

60 JULY-SEPT 2016 engine professional FAILED HEAD GASKET BY JERRY ROSENQUIST

Figure 3. This engine overheated with obvious results. show-up on a temperature gauge because it is only in localized areas. Fixes include insuring the overall coolant flow, reducing exhaust gas temperature through tuning, and making sure the cooling system is operating properly. Designed to bring the technical portion of an ARMOR NOSE DEFORMATION Deformation of the nose of the armor is a classic AERA convention to sign of detonation. The extreme cylinder pressure your region of the country, caused by the detonation pinches the armor material, as if grabbed by a pair of pliers. If you are having saving you long travel times detonation problems it must be corrected or you are and expenses. in for a very expensive rebuild. • Gain knowledge and network with other ELONGATED GASKET BORE DIAMETERS engine professionals Measuring the bore diameter of a used gasket can be a good way to identify detonation. Measure all the • Meet with leading manufacturers of gasket bores in a 12 o’clock to 6 o’clock direction. If engine building/rebuilding tools, supplies, any of them are more than .010 - .020” large than services, parts and machinery others then that cylinder has had higher cylinder pressure than the other cylinders. I have examined For the current conference schedule, go to: gaskets that looked fine except that one or two of www.aera.org/conferences the bores were stretched .060 - .080” large than the others. The combustion seals did not blow out but the pressure was so high it lifted the head and stretched the seal.

ARMOR CRACKS Armor cracks are a sign of dynamic motion of the . The entire head or sometimes just specific areas of the head move rapidly in a vertical direction. This flexes the armor back and forth at THE SOURCE FOR INFORMATION a frequency equal to the rate of combustion cycles 500 coventry lane, suite 180 per second. Armor cracks are generally caused by crystal lake, il 60014 weak castings, insufficient clamping force holding the Phone or 815-526-7600 head down, excessively milled surfaces and abnormal 888-326-2372 combustion pressure. Fax 888-329-2372 or 815-526-7601 Fixes include insuring proper bolt tightening and www.aera.org lubrication procedures, reducing the friction at the bolt head or threads, using different heads or block, and tuning. facebook.com/aeraep twitter.com/aeraep (continued)

62 JULY-SEPT 2016 engine professional FAILED HEAD GASKET BY JERRY ROSENQUIST

RECOVERED THICKNESSES OF USED GASKETS coolant will migrate across or through the facing The ideal gasket installation will provide material. If the clamp load is sufficient and perfectly even loading across the entire gasket. evenly distributed, the impression left around the In reality, head and block bending can be severe coolant holes in the head and block will be even enough that the compression of the gasket can and distinct. Any seepage will leave a “fuzzy” vary as much as .004”. When it gets this high it outline or trail around the holes. The cures for is difficult to seal combustion and coolant; gasket coolant leaks include increasing the bolt torque, failure is imminent. Mapping a used gasket is resurfacing or replacing the heads or block and an extremely valuable evaluation procedure. sometimes, although most gasket manufacturers don’t recommend it, applying a sealer to the Jerry was with Fel-Pro Wipe off the used gasket and trace the outline for 31 years. He was on a piece of paper. Measure the thickness of the gasket may help. responsible for creating, gasket body within ¼” of every bolt hole and at designing and maintaining a point midway between bolt holes. Also, try to In summary, the following areas need to be the High Performance and Marine product lines. He find an area of the gasket body that has not been closely examined when inspecting a used head gasket: worked extensively with compressed and measure the thickness there. NASCAR, NHRA, Indy, sprint The compressed areas should be .003-.004” and short track engine 1. Is the outline of the coolant ports distinct on thinner than the uncompressed areas, and all builders. He was Chief the gasket? Engineer for the Fel-Pro compressed thicknesses should be within .001- aftermarket for ten years, .002” of each other. 2. Are the armors clean and shiny? retiring in 2010. He received nine US patents for various 3. Do all the gasket bores measure COOLANT SEAL gasket applications including approximately the same? many high performance Coolant leaks are caused by insufficient designs. compression of the body of the gasket. Each 4. Are the body thicknesses within .001- .002” gasket is designed for a certain amount of clamp across the whole gasket? load for a positive seal around coolant ports. If 5. Does the nose of the armor still have a nice this load is too low or the flanges are bending the radius?n

64 JULY-SEPT 2016 engine professional