964 cylinder head modification

Patronus · 10:32 AM

We all know the 964 cylinder head & barrel upgrade which involves buying new barrels to accept a CE-ring and then machining the heads to accept the new barrels.
I've heard of people machining a groove into the old barrel which I believe is not a good idea because you end up with very little meat on either side of the groove, so you weaken the barrel. But I have a question: why not simply machine the cylinder head to accept the CE ring (in the cylinder head instead of the barrel) and keep the barrels intact? Even if the cylinder head then flexes a little bit in time, thereby creating a minute gap (because this gap is really minute), the CE ring will keep everything sealed. Or is the resulting mating surface then too small to be reliable?

prschmn · 03-17-2012, 12:28 PM

I've always been a bit ambivalent about that. 930s ran around tens of thousands with problem with nothing besides the buildup of deposits to help them seal. Personally I havent seen problems assuming surfaces are flat and correctly assembled. My 2 cents.

uwanna · 03-17-2012, 12:56 PM

Quote:

Originally Posted by prschmn

I've always been a bit ambivalent about that. 930s ran around tens of thousands with problem with nothing besides the buildup of deposits to help them seal. Personally I havent seen problems assuming surfaces are flat and correctly assembled. My 2 cents.

I agree with your assesment. Some of the early 964s had the cylinder/head oil leak problem, but most didn't. PAG claims only 20-30% had the problem. I have had a 1990 964 motor in my '80SC since 1992 and never have had a hint of a leak! Like they say "If it ain't broke, don't fix it" Then again I may just be one of the lucky ones!

Patronus · 03-17-2012, 01:34 PM

The engine of my previous 964 was rebuilt by an ex-OPC engine builder and he knew the 964 pretty well. He said, unless I sit with excessive cash, I don't need to buy new barrels and machine the heads. We fought hard about this because obviously I've been reading about this for decades (and he's been rebuilding 964 motors for decades). He assured me that when the barrel and head surfaces are properly lapped there won't be any leaks. He was quite passionate about this, and I took a chance and followed his advice. Well, all I can say is that I ended up with a bone dry engine. Not a drop of oil anywhere - and I drove the car hard in hot and cold conditions.

But now I am getting another 964 and need to rebuild the engine. So I am wondering about these things all over again.

ozzygus · 02-17-2015, 11:14 PM

Just wondering I've got leaky barrels on my 964. pretyy bad oil coming from all of them. is it possible to just pull it apart & replace all seals & gaskets with out rebuilding the engine (piston & rings ect) as it runs perfect with great compression in all cylinders.

prschmn · 02-18-2015, 04:48 AM

Theres no reason you cant just do a reseal without replacing everything depends
on what kind of shape things are in. Just be aware that besides the cylinder base o-rings the case bolt rings are suspect too. And of course valve guides may well
be bad. Kind of a waste to do a reseal without at least checking that stuff.

mikedsilva · 04-21-2016, 05:44 AM

how did you go with this ozzygus?

john walker's workshop · 04-21-2016, 06:50 AM

The trick to using a CE ring on 964 cylinders is to machine the contact surface from the outside until you can slip on a standard late 964 CE ring. There's no groove, just narrowed up from the outside. The depth of the cut is important, obviously, so the ring can have some crush.

mikedsilva · 04-21-2016, 01:13 PM

John, this is the first time I've heard of doing that. Wouldn't that give less surface contact area between the head and the cylinder?

john walker's workshop · 04-21-2016, 02:22 PM

Done lots of them that way. No comebacks yet. You still get about the same as an SC. On an SC, the surface outside the CE doesn't contact the head as tight as the inside surface, due to the way it was originally machined.