Oil leaking - any ideas?

A cracked crankcase, or damage on the crankshaft where the seal is?

Also a lot of mechanics damage the seal during installation.

Peter wrote:

A cracked crankcase, or damage on the crankshaft where the seal is?

Yes, probably… worst case, but fortunately still on warranty (as all the recent repair efforts).
Seal – not so probable, after three different efforts… one must have been successful, one would think.

Surface finish on the crankshaft is important, this service bulletin local copy may be worth looking over, if you haven’t already. One trick on some engines (I have no experience with large Continentals) is to install the seal at a slightly different axial location than the previous seal, to move the seal lip to a slightly different location on the shaft. If there are alternate STC approved seals, they may also be worth looking at, for the same or similar reasons.

Multiple leaks alas are typical with old hoses, engines, components. It took me about 2 years to sort all of mine.

well the engine is as new, given that we have had all hoses etc renewed when it was disassembled last year…
The angle with the angle – I’ll follow up on that ! Thanks

For all, this is not the issue, as I have a McCauley prop.
Currently we’re checking if the crankcase may be overpressurized due to either a clogged breather tube or other sources.

See here.

This is becoming pretty mysterious.

Established facts are so far:

• The crankcase is not overpressured. The breather tube is free, and there is no oil residue coming out at the end; I assume there would be oil coming out if there’d be pressure in the case, no ?
• Dip stick cap gasket is tight, all other gaskets as well,
• Cylinders have been boroscoped, all have compression >60, are dry inside, no apparent issues with the piston rings,
• Oil filter gasket is tight
• Prop is a McCauley and the issue eddsPeter has mentioned doesn’t apply
• Crankcase seal has been replaced three times now, last by a mechanic of the well renowned engine overhaul firm in Denmark
• Leak is between the crankcase and top of crankshaft, and – mysteriously – even when the engine is not running.

According to the Danish firm, the crankshaft has been measured and was within limits. Well, obviously, it must have been, there is not radial play, only axial play.
It’s not so much oil that I cannot fly. The engine runs smoothly and all data are normal. Its just – annoying and, to an extent, nagging in the back of the head….

Maintenance guys, engine guys, myself, and all, have pretty much done everything imaginable and quite frankly, we’re at our wit’s end a bit…

So – ideas are appreciated ;)

How can you have a leak there on a stationary engine, when the oil should be way down in the sump?