964 O-ring fix/update

[ChrisBennet]

I've looked through the posts and I *think* I understand what is required but maybe someone could confirm what the 964 cylinder head leak fix(es) are.

A) An O-ring is added to seal between the top of the cylinder and the head. Is the top of the cylinder grooved or is the outer edge just "notched" to trap an O-ring between the head and the cylinder?

B) The bottom of the cylinder has a groove machined in it and a matching groove is machined in the case. Or is the groove in the case and later addition?

thanks,
Chris

[ischmitz]

The cylinder base on 964 and 993 has an O-ring by default. Nothing needed here in terms of mods. To fix a head to cylinder leak on the earlier 964 you can cut a step into the cylinder to add a fire ring. Others have cut a groove into the head. Basically, you add a head gasket that is used on the Turbo's. Check here for an example http://forums.rennlist.com/rennforums/showthread.php?s=&threadid=111791

Ingo

[Bill Verburg]

The 964 uses a 2mm o-ring at the cylinder base, a groove is machined into the cyl.wall. These have been known to leak.

The RS used a wider 3.53mm o-ring w/ a groove machined into the block wall in addition to the cyl groove.

[ChrisBennet]

Originally posted by Bill Verburg
The 964 uses a 2mm o-ring at the cylinder base, a groove is machined into the cyl.wall. These have been known to leak.

The RS used a wider 3.53mm o-ring w/ a groove machined into the block wall in addition to the cyl groove.

Thanks Ingo and Bill.
Bill: Which RS; 964 or 993? I have the 964 manuals (an early edition of them) but I don't see anything on making the modification. Do you know a source for this info?
thanks,
Chris

[Bill Verburg]

The 993RS tech manual only makes the following comment
"Profile seal rings (quad rings) are fitted in the groove on the crankcase to provide additional sealing between the cylinders and crankcase."

here's the pic


Here is a pic of the stock 964 crankcase


and here is a pic of seals that have been blown out of the case


Some builders will apply Dow 730 as additional sealing.

Peter Dawe is the only one that I know for sure has the correct tools to do the case mod. Perhaps C. Garibaldi?

I don't even know if this is needed on a 3.6, but I have seen a lot of them leaking there.

[ChrisBennet]

Thanks Bill, that's a big help.
Is a "Profile seal rings (quad rings)" a square section O-ring?
Machining wise it doesn't look like a big deal. No more work than decking the spigot faces.

-Chris

[Bill Verburg]

Chris, I don't know.

here's a shot of my cyl base w/the groove.


These are 102mm bore w/ 109mm base

[WERK I]

Chris,
I'm using the C2 turbo cylinders on my 930 case. The case spigot bores were not modified by the previous owner and were not a source of leaks. The cylinder sealing rings are round viton and are not a square section type. I really have serious doubts about removing more material from the spigot base area. If you look at the sealing area around the head studs, it seems you need all the surface area you can find.

[pmajka]

[QUOTE=Bill Verburg;1249308]The 993RS tech manual only makes the following comment
"Profile seal rings (quad rings) are fitted in the groove on the crankcase to provide additional sealing between the cylinders and crankcase."

here's the pic


I am rebuilding my Andial 3.7L (based off the 3.8 spec) the case bore is 107mm. Do you know the PN for that O-ring? ( is the o-ring 110mm? )

Thanks in advance if any one reads this.

[dap930]

Chris,

A quad ring seal has a profile that looks like a miniature 4-leaf clover, so there are four sealing lobes. These are normally used for dynamic sealing applications such as piston seals for hydraulic cylinders.

[prschmn]

So I wondered at first about why a 12 year old thread would return-like a Phoenix.
Then I realized who had started it----

But those squirted out o-rings--only makes sense if the heads weren't torqued correctly.
If it were assembled correctly in the first place there is zero gap between the cylinder and
case hence the orings can't escape.

[pmajka]

Originally Posted by prschmn

So I wondered at first about why a 12 year old thread would return-like a Phoenix.
Then I realized who had started it----

But those squirted out o-rings--only makes sense if the heads weren't torqued correctly.
If it were assembled correctly in the first place there is zero gap between the cylinder and
case hence the orings can't escape.

My Andial is apart after 70Kmi, but it leaked at 10Kmi.

well, wondering if this part is correct. case bore is 107mm, groove depth is 1.56mm (estimated)

Cylinder Base O-Ring 99970502341 - Genuine Porsche - 999-705-023-41 | Pelican Parts

EDIT: my orings did not squirt out., just leaked like a sieve.