Originally Posted by techron
OK, as a retired mechanic i've always done cast iron head engines. the question i have is about head gaskets with aluminum heads. i have installed both composition head gaskets and have installed steel shim head gaskets with KW coppercoat sprayed on them and never had a failure. my questions are-
can you use a steel shim head gasket (.021) with aluminum heads?
should you spray them with KW copporcoat?
if not, which gaskets would you install and how? KW, non KW. i'm looking for gaskets of about .021 compressed height.
any tips about head gaskets (the thinner the better) with aluminum heads is wecome from you machine shop guys. or you old hotrodders with experience with aluminum heads on iron blocks. part #s for gaskets are welcome.
You've got two problems beside keeping hot gases in, that's aluminum moves a lot compared to iron so the head gasket has to decouple that or it busts up. The other is corrosion, so a stable non reactive metal and insulation coatings are needed.
My numeral uno choice is the Cometic MLS5325 for zero decked blocks to stock high blocks. This sucker is three layers of stainless steel with a flouroelastomer coating, they call it rubber, I call it Teflon. This guy is .040 thick.
Next comes some GM gaskets I have two faves and one all-right.
The faves are 14096405 stainless on one side and graphite impregnated composite on the other at only .028 thick. The other is 10105117 stainless foil on the outside and something synthetic on the inside this sandwich is also only .028 thick.
The so-so it's all-right is the 12557236 classic GM cast iron to aluminum sandwich .051 thick, comes from the old L98 'vette needs TLC with some re-torquing after initial use. Not bad, but you gotta remember to visit the head bolts.
Another very nice one is the FelPro FEL1094, now I never used this on a street engine only race so I have no experience as to how long this will keep a seal on a daily commuter that never gets the heads popped till something goes wrong. This gem is a stainless shim with a "rubber" coating on both sides. At only .015 inch thick it's great for helping pump up compression, it doesn't like warped parts, but then who does. It also demands a really smooth finish from the machinist.
Keep in mind you've gotta compute compression ratios piston to deck clearance with these things, a couple are pretty thick, a couple in the middle and one's mighty thin. So watching the ratio and also where the piston is at TDC to the squish/quench deck needs to be on one's mind.