The International Cessna 170 Association

Can oil pressure set too high cause oil leakage past the seals at the starter shafts on an O-300 engine?

No, there is no pressurized oil supplied to the starter shaft.

And there is no way to "set" your oil pressure on a Continental. Unlike a Lycoming you should not be putting washers under the HIGH pressure relief valve. It is just that a high pressure relief, it will not set minimum pressure.

These Continental engines were built with a drop of oil hanging on the end of the starter shaft.

The starter had both oil seals replaced about 10 hours ago by Aerotech of Louisville. Because of the oil leakage getting down onto the
alternator, I sent starter and adapter plate still together off to Aerotech of Louisville. They said the starter was "full of oil". They miked
the shafts and said they were OK. Said it's very unusual for both seals to leak at once.

They also said that things inside the accessory case are lubed just by splashing, which I knew. Their conclusion was that the excessive leakage
must be caused by oil pressure too high, causing a mist of slightly pressurized oil inside the accessory case. I'm planning to get my mechanic
to hook in an accurate oil pressure gauge when the starter comes back from Louisville tomorrow.

Check your crankcase vent so as not to build pressure in the block.

John

Aerotech is a good outfit...but they are accessory people... not necessarily engine lube specialists.

John Hess's recommendation is a good one, but high crankcase pressures are not likely the issue either or you'd have alternator and magnetos full of oil as well. The oil filler cap has a gasket on it and the dipstick (oil gauge rod) MAY have an O-ring.... which would both give indications of high crankcase pressures/blow-by.

In other words, high oil pressure and ordinary crankcase pressures are not the cause of starter oil leaks. Leaking oil seals are. There were 3 (?) different designs for that starter adapter, and therefore 3 different seals, … and the correct seal must be used. I'll try to find the article that provided that info and publish it, but I believe it was Neal over at the 120/140 Assoc'n. Steve Grimsley also wrote an article in one of the Flypaper/170 News issues. I'll research it and get back to you.

Thanks, George.

OK... Go to the Members Only page of this website and download the First Quarter, 2013 The 170 News http://cessna170.org/forums/membersOnly ... ws1Q13.pdf

Steve's article will be found therein. Here is Steve's article only: As for new seals that also leak... it is a common error for oil seals to be installed in reverse. In the case of generator, alternator (ie, things attached to the accy case) the oil seals should be faced to keep oil IN THE ENGINE...not in the accessory as may be the usual case. I've seen experienced shops sometimes make this error, usually when the carburetor guy fills in for the starter guy when the starter guy is on vacation.

OK, I read Mr. Grimsley's article. Near the end he says: "However, leaks around the upper seal will put crankcase oil inside the
starter motor which could cause poor electrical contact." Unless I'm missing something, I would think it would be leaks around
the lower seal that would put oil into the starter motor.

In any case, I'm assuming that Aerotech of Louisville will install the seals and bushings correctly. And I think they switched to a
different adapter case. My mechanic glued the gasket between the starter adapter and the accessories case. So I spent a lot of
time scraping gasket material off both surfaces. I asked Aerotech about that, and they advised installing the new gasket dry.
I'm for that - even if it leaks, replacing it will be much easier if it isn't glued into place.

Mr. Grimsley had it right - it would indeed be the upper seal leaking that would allow oil to migrate into the starter.
I was thinking wrong about how it was set up.

The starter and adapter plate with new seals and bushings are now back from Louisville, and I'm keeping my fingers crossed about oil leaks.
Unfortunately, it looks like you'd have to remove the adapter plate with the starter to see if oil was leaking into the starter.

Yesterday I reinstalled the starter and flew for an hour. No leaks! I have no idea what was wrong with the first set of seals Aerotech of Louisville installed.