Oil leak after rebuild

wilson234 · 07-30-2015, 07:39 PM

Just installed 964 1989 engine after taking it down all the way except splitting the cases. Installed new head studs, new case through bolts seals essentially all new seals. etc. I'm getting a slow leak after idling engine for 5 minutes right between the case and cylinders about middle engine from drivers side. I'm just curious if I could expect once the car is actually driven and temp cycled either the case through seals or base gasket seal on the cylinder would settle in a stop the leak. Well that's where I think the leak is coming from. It's an 89 so it has the heads that are without gasket, and before the car had the bottom skid plate so I was not aware exactly where the or existing leaks were coming from

RedCoupe · 07-31-2015, 05:34 AM

Did you pull the cylinders and change the o-rings on the cylinder bases? Also there was a batch of early 964 cases that had the through-bolt pockets machined too deep on one of the crankcase halves. The factory used a more shallow washer on that side and stuffed one o-ring on top of another to seal the bolt on the deeper side. Hopefully, your engine isn't one of those. There is a Porsche TSB with the engine numbers of the affected engines. But, in any event, the through bolts seem to be one of the 964's favorite leaking places.

wilson234 · 07-31-2015, 08:15 PM

Yes I replaced oring at cylinder base with new seal. If my case happens to be one of these errors would I see two oring seals on the case bolts? I did not see more than one orings on either side of the case through bolts. Replace two oring seals for each case through bolts with Viton green orings from host. Any idea if heat and time running engine conform new orings to help seal from oil leaks? The new orings are like doughnuts, the old ones were like cylinder shape from being compressed for 25 years. Hoping a few heat cycles will allow new Viton seals to expand?

RedCoupe · 07-31-2015, 08:44 PM

If your engine is a 1989 (k series) it wouldn't be one of the ones with the bad machining. I found the TSB and the problem engines are all L series: 62L11289-62L11307, 62L12581-62L12801, and 62L51104-62L51140. As far as static o-rings improving their sealing with time and heat cycling, I've never experienced anything like that. In my experience, they either seal right from the start, or they start leaking pretty quickly after assembly, usually because they were somehow damaged during assembly. But, that's just my experience. YMMV.

alexeskin · 08-13-2020, 12:32 AM

Hello, all. I am in Honolulu, and I tackled with the guidance and assistance of an air cooled very experienced mechanic, a Complete Reseal on my 1990 C2 964. It had 48K miles, we did a compression check prior to strip down and all cylinders were ok. I had replaced gaskets and o rings to stop leaks at common offending areas, but the cylinder base gaskets on 2 cylinders were leaking badly. So, we tore down, but didn't split the case. The cylinders were clean, still had factory honing. I ended up with 2 broken lower stud bolts and the 2 base gaskets were broken. So, we cleaned everything up, resealed the gaskets with the green Viton and also the clear Molykote Dow Corning 111 compound to those base gaskets. After replacing all 24 stud bolts, and a 3 angle grind valve job, replaced exhaust side brass guides, teflon seals, put it all back together. I am experiencing still an oil leak from the base of 1 maybe 2 cylinders at those new base gaskets......??!!! We were super careful on re installation not to crimp or bugger them back into the case. I have the early heads without the top head gasket. We decided to keep it original, and it wasn't leaking from the heads before, only the base of cylinders. And that is what is still the issue, my heads are not leaking, just the base of 2 or 1 cylinders on drivers' side..

Does anyone have any recommendations on perhaps a stop to the offending leakers?!! Besides an engine out and re attempt!!!

I am planning on doing an oil change soon and remove and replace t
he oil line that goes from the oil tank, routes along lower rear part of engine and flexes and then up to the engine. That line got dented on the re install, so got a new one and will replace during the oil change.

Was wondering if anyone had tried to put in any stop leak for a gasket leak? I know its sort of sacrilegious to put in some foreign fix a leak crap in the oil, but I am willing to see if maybe there is some good German or Japanese product that in small form finds small areas that can try to stop oil from passing by? Anyone? Bueller??

Well, thanks in advance..

Alex in Hawaii Kai..

brighton911 · 08-15-2020, 03:43 AM

Sorry to hear of your troubles Alex & Wilson. You have nothing to lose waiting a bit to see if the leak stops but I doubt it will make a difference. "Stop leak" act upon rubber parts to swell them slightly, they are more suited to a tired engine with seals gone hard with age. Not the news you want to hear but I think your only recourse to re-do the job(s)