Nagging oil leak at front seal
 

I have a 78 930 engine, just rebuilt, with a problematic oil leak at the front seal (that's the flywheel end). The seal was replaced during the rebuild with no drama or problem. When I started the engine a couple weeks ago, I found a leak from behind the flywheel. I pulled the engine, replaced the seal again, reinstalled the engine on the dyno, and found I still have a leak. The original seal was a dark red color, and came with the Reinz gasket kit. It was installed dry. The new seal is black, reportedly better (though I don't recall the brand), and it was put in with a sealing compound around the outside circumference. The leak is significant -- it's dripping two or three drops per minute when the engine is running (no dripping when it's not running). The install on this round was done with a tool that keeps the seal outboard a bit from the "home" position in the groove; the original seal had been located deeper in the groove. The new seal appears to have made no difference in the rate of leak. Red assembly lube was used on the seal lip/crankshaft interface this time around -- and within a few minutes of running, I found red-colored oil leaking from behind the flywheel again. This leads me to believe that the oil is leaking from between the crankshaft and seal.

The engine was pulled again, the area cleaned up and put back on the dyno. It was cranked (but not started), for about 5 minutes. Oil pressure during that time was about 40 psi. No leak. The crankcase was pressurized with air at 4 psi for 15 minutes. Engine pulled again: No leak.

I don't know what's going on. Does anyone have any suggestions as to what may be wrong and how I might fix this?

Are you sure it's the seal? Could it be from the breather on top of the engine? I had to use some sealant on the hose that attaches to this breather to stop it leaking on my 1977 930.

Re: Nagging oil leak at front seal
 

Dang, Rob! That's a lot of times to pull and re-install the engine! As for the seal, after doing much research when I was doing the clutch on my 930, I learned that the BLACK seal is the one to stay away from. The dark brown Reinz seal (OEM) is the one you want. It's made from the Vitton material. I actually got a black one with a clutch kit that I purchased and the seal was made by Federated Mogul. I bought the brown one from Pelican. Are you sure there's nothing wrong with the actual sealing surface on the case itself? A knick or ding? Is the surface around the crank perfect?

The crank seal land may have too much run out relative to the case seal bore for the sealing lip to follow and seal. Have you checked this? During the rebuild was the case bore checked?

Could there be a tiny burr or imperfection on the crank that's maybe cutting the seal on installation?

Man-oh-man...I was thinking this, but didn't want to go there yet! If this is the case and it were my rebuild and car, I'd have a neighbor come over and quickly lower the floor jack with me under the rear of the car with the wheels removed! I can only endure so much "fun"! I hope it's minor...start small and work up to the BIG-O!

This is one example why a trial assembly with plastic-gage can be helpful. Everything can be to spec in terms of size and calculated clearances but still not be on a common axis.

Folks,

Thanks for your ideas. It's this thought that I am most worried about, though I've never heard of this happening:

The crank seal land may have too much run out relative to the case seal bore for the sealing lip to follow and seal. Have you checked this? During the rebuild was the case bore checked?

More facts:
The case was professionally verified by a real pro. The assembly of the bottom end was done by him as well, in my presence. The crank is 0/0; the case was not line bored. Bearings were new. The surface of the crank does not appear to have a nick on it, nor does the outer sealing surface of the case. There's no chance of the breather cap above being the source - it's clearly totally dry. The oil is coming from the seal...

The engine pulls haven't been that labor intensive yet. The first install was in the car, just to get the engine running. It was pulled anyway, to go on the dyno. We pulled it back a couple times from the dyno, after the seal replacement, to check it out. But it's soon going to take a toll.

I can't imagine how the seal could be off center relative to the crank. None of those surfaces have been altered during the rebuild. It worked fine with no leaks before the engine work. But at this point, something seems amiss, and I don't know what it is.

I don't think plasitigage would have helped here. This engine was set up with bore gauges and each bearing clearance was verified on each journal. As far as I know, no stones were left unturuned. But then again, it leaks...

Thanks again for your thoughts, guys. If there are any more ideas, let me know. If/when I find the problem, I'll let you know.

What about the case sealing hardware in that area? Are they torqued properly? I think there are three fasteners: one above the crank seal and two below.

Was the run out of the crank checked?

The front to back play/movement of the crank...correct?

As far as I know, all critical dimensions of the crank were checked; straighteness, runout, bearing journal diameters, etc. The case was also checked in all important ways -- especially bore alignment (which didn't need to be altered, and spigot height (which was indexed off the crankshaft centerline and was altered to bring all six spigots to the same height).

So, I'm perplexed. Obviously, something's wrong. Even if there were some mismatch between crank centerline and the seal bore, how far could it be off? The seal has a flexible lip that should accommodate some misalignment.

I'll keep looking.

Some links to read:
http://forums.pelicanparts.com/911-engine-rebuilding-forum/191031-rear-main-seal.html?highlight=seal
http://forums.pelicanparts.com/showthread.php?s=&threadid=167287&highlight=main+s eal

I just spoke with the crank/case machinist. He suggested putting a dab of silicone sealer on the aluminum oil plug on the end of the crankshaft (that's in the vicinity of the bolt circle). He has seen those leak, and when they leak, it acts just like a seal. Apparently, during the crankshaft cleaning process, the seal around that plug can be disturbed, and it can leak. I will certainly give that a try. He said that the seal around the 9 bolt cranks is very robust and rarely leaks or has a problem. It's a good idea to clean that plug with brake cleaner, put a dab of silicone over it, and bolt on the flywheel. Let's hope that's it.

A picture would be great!

What oil pressure were you running? There should not be much if any pressure on that seal but the oil does have to drain back by way of the two drain holes in the case, I know on some engines porsche enlarged these holes to help drain the oil from this area..

Sand_man,

I don't think I have a picture of that detail. If you look at the end of the crankshaft in the photos od the threads you posted (thank you for those, by the way), you'll see a small aluminum plug in the midst of the bolt circle. I have a 9 bolt crank, but I think the appearance is equivalent.

cgarr,

My oil pressure is normal -- approximately 85 psi cold at 3000 rpm, and about 60 psi when hot at 3000 rpm. You're right -- there should be no oil pressure directly on that seal. But if there's a leak at the crankshaft oil gallery plug, now we have full oil pressure acting on it. And that plug is beyond the seal, so it would tend to leak right out as it is doing. The oil plug has now had a dab of silicone RTV applied to it (and the flyweel has been bolted on over it). We will check this weekend to see if this has solved the problem.

Best of luck, Rob! I'm hoping this is it! Please let us know!

Jeff

I just did mine last night, its should look something like this?

http://www.gruppeb.org/users/upload/images/crankend.jpg

Funny, I know that the Porsche crank is a complicated part, (as is the case itself) but I didn't even notice that plug when I went through dissassebly on my engine. I'll be sure it gets looked at during assembly! My crank was cleaned extensively during the machining process. I guess it can't hurt to hit it with a dab of something!