Head gasket failure

·         What, including detonation, leads to head gasket failure?

Detonation; what you can’t hear will still hurt you.. Or, if it runs on gas but sounds like a diesel, have your camera ready..

We’re discussing internal combustion engines not dynamite so, in context, detonation is defined as: “a premature spontaneous burning of a fuel-air mixture inside an internal-combustion engine”. Detonation is the result of a second flame front that ignites as a result of; rapidly increasing pressure from the compression stroke and ignition of the spark induced flame front.  Detonation occurs after the spark plug fires (as opposed to pre-ignition which occurs.. well, prior to ignition) and the resultant spike in pressure delivers a blow to the ascending piston and combustion chamber so severe that you can hear it in the driver’s seat (open headers can make it tough to hear but the damage is still happening). The effect of detonation is very similar to whacking the piston with a sledgehammer as it approaches TDC, except that the impact is more widely distributed. If allowed to continue, detonation will eventually lead to component failure, how soon depends upon the engine output per cubic inch. High horsepower-per-cubic-inch engines develop higher combustion pressures and in turn, deliver a harder ‘hit’ under detonation. Therefore, most readers of this article won’t have much time to ‘detect and correct’ before something blows up, or out. Though it may seem odd for a head gasket manufacturer to say, the preferred component to fail is the head gasket. Why? Because it’s cheaper than pistons, rods, crankshafts, cylinder heads or blocks. In this case the head gasket acts as a fuse. Learn to read your head gaskets, it’s the closest you’ll ever get to having your engine talk to you, “Houston.. we have a problem..”

Cleanliness is next to..

You might be surprised at some of the samples we have received from customers asking “why did it fail?” Then again, if you’ve been around racing for a while, you may not be surprised at all. I have seen head gaskets with sawdust, sand and actual small rocks embedded in them, as well as the remains of facing material from the previous head gasket. The aircraft industry has an acronym that’s suitable here; FOD, Foreign Object Damage. Like leaving a wrench in the lifter valley, rocks in the combustion seal are not ok, chaos will ensue. So, as Momma taught us: let’s be clean when we’re doin’ our duty. Use a residue-free solvent such as aerosol brake cleaner and a clean rag on the head and block sealing surfaces before assembly.

Hot Stuff..

Aside from the obvious, (poor machine work, dirt & debris on the sealing surface, uneven surfaces) a composite performance head gasket will fail from excessive temperature. Sometimes it’s difficult to determine which happened first, the high temperature or the gasket failure, regardless, it is imperative to find the culprit. High temperature can be caused by: detonation, plugged coolant system, inadequate radiator or fan(s) incomplete coolant filling or low water pump volume. A few really sharp engine builders have recently been able to add some insight about heat related head gasket failures. In short; the coolant temperature gauge may not be telling the whole story. If coolant filling is incomplete or flow (velocity) is too low, localized hot spots may develop around the combustion chamber. These ‘hot spots’ can cause the coolant to boil locally which in turn damages the head gasket. The kicker is; this localized boiling event can take place while the overall system temperature is registering at or near normal. The way to combat this is to have a water pump that moves A LOT of water and some electric water pumps are not up to the task. 

Ryan Hunter

SCE Gaskets, Inc.