Cometic head gasket sizes

[GTX]

Hi gurus,

I'm considering putting in an MLS gasket, but got confused. My engine is not over bored and has a standard factory cylinder size (85mm). Cometic manual states the following:

Eclipse 90-99 4G63 89-92 DOHC 16V 2.0L 1997cc - 85.5mm MLS .051 C4233-051
Galant 89-92, EVO 1-3 92-95
86mm MLS .051 - C4234-051
87mm MLS .051 - C4235-051

It is not clear which gasket fits the default size bore. What do I need to put into mine if I have 6-bolt engine. I'm not sure where the engine came from (bought it separately), Galant or Eclipse. The only thing I know it is a standard default size, did not need to machine it.

Thanks,
A

 

[tektic]

85.5mm

If your gasket ain't broke don't fix it.
If you do it anyway make sure you read up on mls surface prep and get yourself some arp studs.

 

[prove_it]

The gasket is .5mm bigger on all gaskets since the gasket can't be inline with the cylinder bore or the fire ring would be destroyed. That's why it's listed at 85.5mm.

 

[GTX]

I have the head re-done and re-surfaced. Have a new graphite gasket, but considering an MLS one, as I have been told these engines prone to head gasket failures if you crank HPs. Have new non-ARP studs, but not planning to run more than 350HPs

 

[prove_it]

All the MLS offers over the OEM composite is knock resistance. The composite will fail during long knock events. MLS will hold back knock, but is picky about the surface prep. It's also easier to clean up I suppose.

 

[tektic]

You have new bolts sir. Studs are an aftermarket replacement.

 

[GTX]

You are right! Bolts! BTW: what benefit the stud gives over the bolt? Just the fact that the threads in the block are stressed less?

 

[prove_it]

The forces applied along the fastener are more equalized at both ends, versus just one end of the bolt. Studs are an engineers idea, bolts are the accountants choice.

 

[GTX]

Hmm.. interesting observation. I was under impression that studs are used when the block is made out of aluminum alloy. You tighten the lower end once and it stays there put. You use the upper part of the stud for fastening. The nut has lesser lengths of the thread than the bolts thread, so I wonder if you could tighten the nut with factory specs, eh?

 

[Coltsfan]

The nuts and studs are very strong, and can be tightened more than the factory bolts. As for surface prep, you need a smoother mirror like finish to use the MLS gasket, and you would be taking a decent size risk if you don't have the block deck surfaced to match.

 

[prove_it]

Quoting GTX:
Hmm.. interesting observation. I was under impression that studs are used when the block is made out of aluminum alloy. You tighten the lower end once and it stays there put. You use the upper part of the stud for fastening. The nut has lesser lengths of the thread than the bolts thread, so I wonder if you could tighten the nut with factory specs, eh?



No, that's not how studs are installed or used. You only finger tighten the stud itself. Once you tighten the nut, the torque is applied evenly across both ends of the stud which results in more engaged thread. This allows the higher than OE torque and clamping force.

Never torque a stud then tighten the nut, that is how you will snap studs in the hole and wanna die.

 

[GTX]

Thanks guys! You are so helpfull!!