Threaded boss in engine case… what’s it for?

[47U]

Location reference… the tube is the oil dipstick and the #3 cylinder rear baffle, O-360-A1D.

I was looking for the source of a small oil leak (you can see it accumulated on the baffle) and noticed this threaded boss in the crankcase.  Looks to be 1/4” course threads.  I looked through the Lycoming parts book but didn’t find anything.  Ideas?  Anyone?

Oh, the oil leak was a rocker box oil drain tube… all good now.

[RLCarter]

Really surprised no one has replied, so here’s my 0.03¢ (inflation)

Hard to tell from your photo…. It looks like it’s plugged off? It’s common in manufacturing to have a plugged hole from a cross drilling operation but they are generally NPT (National Pipe Thread) and an 1/8” NPT is fine thread. It could used on a different variant within that engine family and/or a different aircraft. 

I’d find another “C” of the same vintage and look to see if anything is attached there

[Raymond J1]

 

This tapped hole is present on many cranckcases, it measures 1" deep, made to receive a 1/4 x 3/8" screw. Used for fixing the rear cooling baffle by some, it is not used on Mooney.

Edited February 12, 2023 by Raymond J1

[Guest]

10 minutes ago, Raymond J1 said:

 

This tapped hole is present on many cranckcases, it measures 1" deep, made to receive a 1/4 x 3/8" screw. Used for fixing the rear cooling baffle by some, it is not used on Mooney.

Exactly what it is, a baffle attachment point.

[47U]

Thanks JR and Doc…