3.8L cylinder to case seal - help needed!

[Moriartyhlms]

Does anybody know what the best method is for sealing the base of 3.8L Mahle machine-in conversion cylinders to the crankcase?

I'm in the middle of rebuilding the 3.6L engine from my 1990 C2, and got the pistons and cylinders installed last night, but now I have some doubts about what I've done. I stretched the standard gasket kit 3.6L green viton cylinder base o-rings to fit over my new 3.8L cylinders and just installed them dry. Neither my cylinders nor my case have o-ring grooves, the mating surfaces are flat.

Should I have used the larger diameter o-rings from the 993 3.8L euro-only RS engine?

Should I have used some kind of sealant on the o-rings; DC 111 or 55?

Or, because I don't have o-ring grooves, should I just have skipped the o-ring and used Threebond 1211 or Curil K2?

-Thanks
Sam

[Henry Schmidt]

Originally Posted by Moriartyhlms

Does anybody know what the best method is for sealing the base of 3.8L Mahle machine-in conversion cylinders to the crankcase?

I'm in the middle of rebuilding the 3.6L engine from my 1990 C2, and got the pistons and cylinders installed last night, but now I have some doubts about what I've done. I stretched the standard gasket kit 3.6L green viton cylinder base o-rings to fit over my new 3.8L cylinders and just installed them dry. Neither my cylinders nor my case have o-ring grooves, the mating surfaces are flat.

Should I have used the larger diameter o-rings from the 993 3.8L euro-only RS engine?

Should I have used some kind of sealant on the o-rings; DC 111 or 55?

Or, because I don't have o-ring grooves, should I just have skipped the o-ring and used Threebond 1211 or Curil K2?

-Thanks
Sam

In order to use the o-rings, the cylinders need a groove. If you have a groove (you stated you don't) then Dow 55 is correct. No groove means you can just seal it with Curil T or some other non-hardening sealant. The lack of an o-ring groove allows you to use a copper base gasket if needed to adjust deck height.

It is also possible to machine a groove in the case spigot to fit an o-ring on the inside. This technique can be expensive but very effective.

[Bill Verburg]

As Henry says the bigger base seal 110.72x3.53(vs stock 102x2) needs a groove machined into the case

It looks like this

[Steve@Rennsport]

Bill's pics show the right way to do this. We machine every case for the O-rings that gets the 102mm cylinders for this very reason.

[Moriartyhlms]

All, thank you very much for the guidance, this is exactly what I needed. Unfortunately, I should have sought this out a long time ago.

Can I get away with Just Curil-T and no o-rings or grooves? Otherwise, I'll have to tear everything down and go back to the machine shop. But I'll do it if I have to.

Thanks again.

[Steve@Rennsport]

The Curil-T may be worth a try, but I think sooner or later, you will machine the case for the O-ring grooves for a reliable seal.

Been there,...

[mamut]

It will never seal right, no matter what you put under the cyls., the only way to do it right is as recommended, machine the groove on the spigots, you will have leaks if you don't, the problem is that there is not enough surface area under the cyls. for the sealants to be effective, BDDT lots of times. Stef.

[Moriartyhlms]

All right, resolved to my fate. Gonna split the case for a third time and go back to the machine shop.

Can anybody give me the dimensioning for these o-ring grooves so I can shut up about it?

Thanks for the help.
-Sam

[mamut]

Call JB Racing, Mike has done a few for me, he should be able to give you that info.,cheers, Stef.