When was the last time you used a chisel on a cylinder head? In the cast-iron, asbestos gasket days, a head gasket job could involve everything from carpenter’s tools to two-by-fours wrapped in emery cloth. Modern engines are a different story. Thin-wall castings, aluminum alloys, minimal clamping forces and high compression all conspire to make sealing modern engines difficult. Multi-layer steel gaskets are a solution, but like all critical gaskets, MLS needs careful block deck and head surface care to achieve a tight seal. It’s not rocket science, but attention to detail is important. How do you improve your chances of no-comeback success? Start with the obvious but overlooked factor: your eyes. Examine the head on a well-lit bench and don’t be afraid to use magnification to spot small defects. Add extra lighting under the hood and wash the block deck well, removing all traces of gasket material and dowels. Look for evidence of inappropriate use of a gasket sealing compound from a previous job, especially on a MLS gasket. If there’s “hi-tack” everywhere, was another tech trying to get around a more serious problem? The old gasket also tells a story. Use light and magnification to find signs of detonation or preignition as well as trouble around siamesed cylinders. If you’re reinstalling the original head without machining, consider penetrant crack detection spray and UV light as a value-added service procedure that can spot trouble before investing time and money on a bad casting. It’s best to have the head checked and resurfaced at a competent machine shop, but regardless of the shop’s reputation, wash down the head’s mating surface and check the surface finish. Low-cost reference comparators are available to help gauge the finish visually. Going with a belt sander? It is possible to get the correct finish with the carpenter’s tool and the right abrasive, but sanding won’t correct a bowed or warped mating surface. If the head has been resurfaced, it is possible to have excessive compression, valve interference problems, or bottomed head bolts after assembly. A good idea is to check the availability of spacer shims for the particular engine and if they’re not available, remind the machinist where necessary that if the head requires heavy resurfacing, it’s beyond repair.
Little things count in head gasket service. How about the bolt holes? The almost imperceptible ridge around a bolt holed hammered by combustion and expansion forces can have definite consequences, as can loose or missing dowels. Chasing threads is a given, along with thorough cleaning of bolt holes and ideally, slight chamfering of the hole at the deck to prevent threads from pulling into the mating surface when torquing.
At the other end of the bolt, deburring of the hardened washer is a good idea, as is inspection of the pocket in the head. Debris here will ‘cock’ the bolt and cause erratic torque readings and clamping forces.
Torque-to-yield bolts should not be reused and the new bolts should be brought up to torque gradually, in multiple steps. How many? Five is not too many, especially for alloy heads that can take a “set” if torqued unevenly. TTY bolts stretch during installation, so don’t retorque. Use an angle gauge for final tightening. If you’re re-using standard bolts, dress the threads and be sure to install the correct bolts into the correct holes. Don’t forget to use sealer on bolts that penetrate water jackets, and lube on dry hole threads.
There are more service tips for head gaskets than can be covered in any one article, but cleanliness, common sense and a quality attitude go a long way towards a reliable, “no comeback” seal.
FOUR TIPS FOR A BETTER SEAL
Here are four useful head gasket tips, courtesy of Fel-Pro
1. Most Ford “V”-type engines have directional head gaskets. Always follow the “Front” marking, even if the gasket appears to be flipped over.
2. The webbed area between cylinder combustion seals is non-directional, and may face either the block or head.
3. Water temperature gauges are average reading, and won’t give an accurate sense of cylinder head temperatures.
4. Not all holes lead somewhere. Core sand holes in heads and well as intake manifold coolant port block offs may seem to be dead ends, but it’s quite normal. If you’re in doubt, look at the old gasket.
HEAD GASKET HINTS AND THE FORD 3.8 V-6
Marty Novil, director of static sealing for Corteco, has done considerable research on sealing the tough ones, and has recommendations for block deck and head surface preparation before installation of a new head gasket:
“If they go at the block like ‘Roto-Rooter’ or with a 3-M pad, they run the risk of chamfering the edges near the combustion chamber. They won’t get a combustion seal, and they can ruin an area of line seal on an MLS head gasket, where you won’t get the full impression of the embossed areas. I warn about quick jobs where they don’t even remove the head from the engine. They lift it up, slide a head gasket in and put it back together. Even with the right MLS gasket and the right coating, without the right service procedure, it can be a problem.”
Should you use a spray? According to Novil, “I’d go for a spray, and use a thin, even coating, then handle it carefully afterwards. I’d use a spray designed for the purpose. The big issue is, what is the interaction between the solvents in the spray and the rubber on the gaskets? If you have a very hard, fully cured rubber like the Japanese use, there’s likely no problem. If you have a semi-cured coating used on some good aftermarket gaskets, I’d be worried about spraying those.”
And the Ford 3.8 V6? Many in the industry point to the head casting as weak, allowing head motion and distortion. Novil notes that the service procedure has to match the engine spec and requires extra care to clamp this engine: “Ford stated out with non TTY bolts, then they went to TTY, and changed the torque spec. We use a graphite gasket, as well as many of our competitors. But just because we have the right gasket doesn’t mean its going to last a long time. A head gasket isn’t going to solve basic engine problems, and in the case of the 3.8, there are some bad gaskets out there.”