964 Engine Rebuild Questions

[mrmoots]

Hi

This is my first time posting on this Forum. I came across it following an article in Total 911 about Ian Gray and his 964 Rebuild. Well done Ian, great article.

The time has come to contemplate at least a top end rebuild of my 1990 964 C2, with 82K on the clock. The oil leaks from the through bolts and barrel to crankcase junctions are getting worse and the leak down test figures are around 30%. Bubbles can be heard in the oil tank so the assumption of rings has been made. Oil pressure is still good hot and cold and I can hear no knocking noises.

I have had two respected independents look at the car in the recent month and both have diagnosed the same faults and near identical leak down results, so I am happy that I am not being flimflammed.

The estimates from both are comparable, but I am seriously thinking of doing the strip down and reassembly myself, then farming out the head rebuild, and any other specialist machine work.

Regardless if I do it or I get others to do it, I have a few questions that I would like to pose to a wider audience before I go any further.

1. My car is an early 1990, presumable with the early style head and barrel arrangement. There is no record in the service book that this has been changed under warranty, or by others. It has been mentioned that I could have the head and barrel machined to accommodate a larger seating surface and grove for the later head seal. But from what I understand at present, I thought that there is not enough material available for this. I have read a post on a forum somewhere where someone has had this done.

2. If I keep the early style head and barrels can I still use the later style 993 head bolts, or will these cause increased distortion of the head and lead to more leaks? Are the 993 studs Dilavar or steel? I have read that the Dilavar expands and contracts similar to the aluminium of the heads.

3. The through bolt seals are leaking badly and these cannot be replaced without stripping the barrels and heads off. But can they be replaced one at a time without fear of loosing the pinching effect of the crankcase half’s onto the main bearings? Or will a completed split of the crankcase be required to ensure that I don’t get a spun bearing when I start it all back up? Axl911`s post gives the impression that he replaced them without splitting the case. It does appear silly not to rebuild the bottom end whilst the engine is out, but other than a leaking main seal, it appears OK on the surface.

4. Fingers cross that the Nikasil finish and the barrels themselves are still OK and not badly ridged or worn through. Just as a passing thought, 3.8 barrels and pistons look to be similar price to new 3.6 items. If 3.8 barrels and pistons were used, does anything need to be done to accommodate them onto the original heads? I presume a lot of this will depend on the answer to question 1, above. Even if later heads were used or the early ones could be machined to accept a larger seating surface is the diameter not different that forms the combustion chamber?


Thank you in anticipation of any replies

[jackoporsche]

I can offer some information on the head vs. barrel dilemma. I have a very similar situation with my 62,000 mile '90 964. My oil leaks are from the same areas and my car has the early style barrels and needs head work due to worn exhaust valve guides. I have removed and disassembled the engine and am on my way back together. The route I chose with regard to the head gasket issue was to send the heads to Ollie's in Santa Ana for the guide and valve job. They can also mill the heads to accept a steel shim head gasket. No modifications necessary to the barrels, and they will send the gaskets back with the heads. They tell me this was the original fix from Porsche before new barrels came into play. The shim-type gaskets are a current Porsche part number, though I do not know it yet.

I chose to split the case to inspect my main and rod bearings and crank journals and to get a fresh bead of Loctite 574 between the halves, though I didn't see leaks at the seam. Since my goal is a car I can park in someone else's clean driveway, I'm all about the total reseal. I got the Reinz crankcase gasket set from Pelican which turned out to be a complete collection of all seals, washers, o-rings, and gaskets needed including front and rear crank seals. Hope this info is useful.

[shbop]

. The through bolt seals are leaking badly and these cannot be replaced without stripping the barrels and heads off. But can they be replaced one at a time without fear of loosing the pinching effect of the crankcase half’s onto the main bearings? Or will a completed split of the crankcase be required to ensure that I don’t get a spun bearing when I start it all back up? Axl911`s post gives the impression that he replaced them without splitting the case. It does appear silly not to rebuild the bottom end whilst the engine is out, but other than a leaking main seal, it appears OK on the surface.

I've been here a few times, and have always opted to split the case. I'm not saying you should, only that I've never been comfortable thinking, I should have. Probably lack of experience has pushed me in this direction. Anyway, good for a bump, and hopefully the 3.6 guys will chime-in and give you some solid advise.

[mrmoots]

shbop.

In hindsight, logic should prevail and for the additional outlay of bearings etc splitting the case is the best option. Would hate to do all this work then something else rears its ugly head at me.

jackoporsche

That’s really interesting about the machining of the head was a Porsche approved solution at first. I am based in the UK so need to find someone over hear that is capable of undertaking this or something similar