C85 Oil leak

[biggles120]

I am chasing an oil leak that appears to be on the join of the crank casing, lower section where the intake spider bolts to the case.

Other than removing the engine and splitting etc... are there any other methods of stopping this type of leak?

I know in the vintage car world there are additives that can be put in the oil, but I guess this is a no no in the aviation world...?

[Brian Hope]

Hi Paul, if you have a leak I'm afraid the answer is to solve it rather than stick some dodgy jollop in the engine - if that stopped the leak then you have to ask what other oil ways is it restricting or blocking.
However, I may be the bearer of bad news. These older engines have two studs that are located on the centre main bearing web on one half of the case, they come through the other side and bolt down with two cylinder base nuts. These studs can break off part of the web so that they are just two studs with a chunk of detached web on each stud, thus not actually pulling the centre section of the cases together, and leaving that job to the row of small nuts and bolts along the case flange. This then frets and you get leaks.
Later versions of C90 and the O-200 solved this by replacing the two centre studs with studs that pass right through the case, nutted down each side by cylinder base nuts.
I hope your leak is something much more innocent, it could be but, if it persists despite your efforts, be prepared to split the engine and find a replacement pair of cases (they are matched so no good just getting the half with the studs in).
Good luck. Brian

[biggles120]

Hi Brian​,

Is there a way of checking these studs with the engine in situ?

Cheers

Paul

[mikehallam]

Paul,

This I'm told by our ex resident Luscombe owners is an andemic 0-200- fault which in their case last winter was the simpler (!) one of the stud pulling its threads.

There is an approved remedy kit but it still requires engine out and split. Then failed stud hole is thread cut for a helicoil etc. & that's it.
They did some of the work themselves but one can get other engineering facilities to do it if you don't wish to explore personally.

Send me a PM and I'll let you have an e-mail address to ask them.

mike hallam at btinternet dot com

[Brian Hope]

Hi Mike, yes stripping a stud thread on a Continental is not uncommon, the issue I am talking about though is when the centre main bearing web actually breaks so that when you strip the engine you lift out the stud with a chunk of the main bearing web on the end of it. On the O-200, the web no longer has studs, it has through-bolts, each end of which also serves as cylinder base nuts.
I don't know how long my engine had the broken web, it was running fine, oil pressure was not perfect but was OK and it wasn't losing an excessive amount of oil but was always pretty messy. It was certainly an unpleasant surprise to lift out the studs with lumps of web attached. I bought a set of secondhand O-200 cases from Rollasons, which shows how long ago it was - the mid to late 1990s.
I don't think you can really check the studs in situ, I certainly don't recall noticing anything unusual when I was stripping the engine, such as loose hold down nuts or any movement of the studs, everything is still clamped together by the other case studs and the smaller nuts and bolts around the case flanges.
Clearly you need to be certain the oil is coming from the crankcase joint, it uses the old idea of a thread around the faces to seal it, rather than a gasket - fingers crossed it is just a leak from poor sealing - or better still it is coming from elsewhere, like the sump gasket, the pushrod tubes or a cylinder to case joint.
Rgds, Brian

[mikehallam]

Quite so Brian,

Just to indicate one alternative cause, & that an oil leak needn't always mean it's the worst case possible.

mike hallam.