Old style 964 cylinders and Heads
 

I have decided to stick with the early cylinders on my 1990 964 engine and not to have the fire ring mod done for my engine rebuild as they were showing no signs of leakage previously . The sealing faces have been kept clear of scratches marks etc , they have been lightly sand blasted during the cleaning up and look to be still good .

What I would like to know if someone can help me out are they good to go or should I as a matter of course lap the cylinders to the heads with grinding paste to ensure seal . Or is this a bad idea as the cylinder is not flat and has a run out bevel to help sealing . They look pretty flat to me . Thanks

I'm interested to see what feedback you get on this. I have been getting my shop ready to do an engine drop on my 964 to fix its massive oil leaking from the through bolts, and have been contemplating what to do about the cylinder-head joints.

Anyone? Or a link to good advice would be handy.

There is no need to lap the cylinder to head joint.
The problem with the early design is that the head "bends" at the sealing joint and nothing short of a support flange will cure that. I did a bunch of those engines under warranty back in the 90s and every one of them leaked prior to replacement. If yours is not leaking, you have a rare example.

Thanks Henry , I hear what you are saying , if I have to strip again in the future its not the end of the world ,its a summertime weekend car mainly and I enjoy working on it .I am sure it will be a lot easier and quicker second time round !

Henry-thank you for sharing your incredible amount of expertise. How did you fix the head "bending" problem?

On early 964 heads there is a ceramic insert in the exhaust port designed to control exhaust heat. The design of this insert makes the head casting very narrow around this port. When the head bolts are tightened, this narrow /thin area allows the head to bend between the studs creating an area where the cylinder will not seal. The only cure is to support the head around the studs. The factory repaired this flaw by machining the head flat and adding a reinforcement flange to the cylinder casting. The "new" cylinders have this modification. The only way that I know of the combat this flaw and still use the early cylinders is to make a plate that surrounds the cylinder spigot replicating the later cylinder and machine the head flat. It's doable but rather half *ssed. The best thing is to source later cylinders and repair the problem properly.

Ken , info@911vintageparts.com (760) 731-4911 may have good used late style cylinders that make to conversion relatively painless.

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