There is no MHG that is plug-and-play...proper prep is the key to installing a MHG. The Cometic is a very good MHG, but here are a few things you need to do:
- You check the head for warpage with a machinist straight edge and a set of feeler gauges...0.1mm (0.0039") is the max. The TRSM tells how to do it. A hardness test on the head is highly recommended.
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Both the head and block have to be re-surfaced to the RA spec required for the MHG used. 50 RA max is the spec for a Cometic...you want the lowest RA on both the head and block the machine shop equipment is capable of. (Seven M...you got lucky on your block)
- The proper thickness of the MHG is determined by how much material is removed from the head/block. The stock thickness is 1.0mm...there is .039" per 1.0mm...you can do the math
Cometic will make a MHG to the thickness you need.
- You DO NOT want to use any type of spray coating on a new MHG. They come pre-coated with a very thin layer for the initial seal. Cometic specifically warns not to do this. Spray coatings can turn the factory pre-coat into goo. (Seven M...that's twice for you...buy a lottery ticket ASAP) If you re-use a MHG, then using a spray coating is fine...basically you are replacing the factory coating.
- The Cometic MHG uses rivets to hold the MHG together...any rivet that touches the surface of the head must be removed prior to install or you risk a bad seal.
- Using ARP hardware, use the torque spec included in the box...studs vs bolts are different.
- When the block is decked, the front plate has to be machined as well so it doesn't stick up on top. This will prevent a seal as well. Make sure you use RTV per the TRSM on the top of the front plate, otherwise you will have an oil leak.
