Examining Gasket Failures

A careful examination of every component and joint during disassembly reveals considerable information about the engine's operation. This examination certainly includes the head gasket. Handling it on disassembly must be done with extreme care, to preserve evidence of pending failures or even of correct function. A five-power magnifying glass, a strong light, and a micrometer will aid inspection.

Combustion leakage

Examine the armor of the gasket for signs of leakage, as evidenced by streaks across the armor or a fuzzy edge at the line where the gasket contacts the block or head Streaks are pending failures. If the lines of contact is distinct and no streaks are apparent, the seal is working well. If otherwise, look toward increasing clamp-up on the head.

Dings in the armor

Virtually the only possibility for banging up the armor band of the gasket is detonation. This is not a gasket-related problem, but the evidence of the gasket suggests that the engine control system is not working at optimum.

Cracks in the armor

If the armor cracks, one must look at how the armor band can flex up and down. This can occur only if the head moves up and down with combustion pressure. The relaxing and clamping applied to the gasket's armor can create fatigue crack in short order in a piece of material never intended to be fatigue resistant. Look for solutions in the area of deck stiffness and clamp-up force.

Diameter changes in the armor

If detonation is allowed to pound on the gaskets yet doesnt completely fracture the armor band, you can bet the bore diameter will be a bit bigger than when it was created. Measure and record the before-and-after dimensions. If changes in excess of 0.005 inch are noted, look for other signs to corroberate the presence of detonation.

Thickness variation

If the cylinder head and block were infinitely stiff and all fasteners absolutely equal in tension, postmortem examination would disclose a gasket of uniform thickness. if these conditions do not exist, evidence of local problems can be deduced from variations of thickness across the gasket. Check thickness in an area within 0.25 inch of the head fasteners. They should be equal within 0.002 inch. Spaces between fasteners ought not to be more than 0.004 inch thicker than those next to the fasteners.These variations reveal problems with deck stiffness or consistancy of head fastener tension. In persuing fixes, aim at getting all thickness variations within 0.002-0.003 inch. this may dictate fastener torque changes for each fastener. Where a section is thicker, try an extra 5 foot-pounds of torque at that fastener, and where thinner, relax the torque by 5. Also, where a thicker gasket section is found, look for localized deformations in the block and head coinciding with that section of the gasket.

Heat discoloration of the armor

If the armor band shows a bluish-black color that won't scrape off with a fingernail, something is running too hot. Likely the coolant flow around the exhaust port area is not quite adequate. For fixes, one needs to consult a professional engine builder.

Coolant sealing

Each coolant transfer port must be examined for equal compression and migration of coolant across the gasket. seepage will leave uneven or fuzzy outlines around the coolant port. Look for local deformations in the deck surfaces and consider the ports proximity to a fastener that could receive a slightly higher torquing. As a last resort, use a sealant locally around the port.

The above information is taken from articles by Jerry Rosenquist, of Fel-Pro