Annoying oil leak

[jnisley]

That plug is in the Lycoming governor drive adapter, not the governor itself. Remove it, clean the thread thoroughly and reinstall the plug with thread sealand and torque it per the Lycoming manual.

Clarence

My mechanic did this and it solved the problem!

[James Stiles]

I've been fighting a pesky oil leak on our '62 M20C in the same location or very near to that adapter drive plug mentioned a few posts back. Was never sure if it was the plug or the gasketed joint between the adapter and the gov'r. It got to the point that during the recent annual I took all accessories off, including the gov'r. and drive adapter and meticulously cleaned and re-sealed all the surfaces only to start up right after the annual and find the leak again. This time I pinpointed its location using a borescope (It's so easy to access that area of the Mooney you know... : ). There was s drip forming at the gov'r. base and drive adapter flange hanging off one of the lower flange stud/nut. It was the one closest to the adpater drive pipe plug. I removed the gov'r. and drive adapter again and could find no anomolies and found all gaskets and sealing surfaces were in perfect condition. Took the governor in for a flush, reseal and bench test (it passed all test parameters) just to be safe, then took the drive adapter over to Custom Airmotive in Tulsa to ask about why there was a helicoil inserted in the 1/8 pipe plug hole on the gov'r. drive adapter where there is about 200+ psi present during engine operation. My thoughts were that we apply sealant to the OD threads on a pipe plug but what if the helicoil threads were themselves seeping oil between the insert threads OD and the alum. adapter body?? I was told that it's not uncommon to see NPT helicoil inserts in that drive adapter and that the mecahnical fit of the insert to the cut threads in the alum. adapter body is such that when the pipe plug is installed there is virtually no way for oil to seep by the insert thread to alum body engagement. They then relayed to me that there has been a probelm leak for some time on several model -D Lycomings, most notably Cardinals but Mooneys also, with rear gov'r mounts. They said the fix was to install the Lycoming alum. spacer plate and additional gasket to that joint. What ever that Lycoming engineered fix does it fixed the oil leak issue according to many of the -D engine drivers. I bought the spacer and all new gaskets and will try that fix after I confirm and get comfortable with the drive engagement clearance by the addition of another gasket and .040" alum. spacer. I'll let you know how it works out. Oh, and of course I'm sealing the heck out of that plug when I put it back in!