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Unusual oil leak source

airguy

Unrepentant fanboy
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I have been chasing a very minor but persistent oil leak on my IO360 in my 9A, and from the apparent location of it I was becoming concerned that I might have a cracked cylinder barrel. So today I took the time to thoroughly degrease the engine, making a respectable mess on the floor in the process, and then did a high power runup until my cylinder temps starting getting pretty warm. I shutdown and did the black light trick, and found my leak.

The picture below is of the #4 exhaust valve pushrod guide tube. A couple years ago I had dropped a cordless screwdriver onto it and dented it slightly - I made certain then that it did not contact the pushrod, and deemed it operable and kept going with it. Sometime later it developed a crack on that same impact spot, and that's where my minor oil leak has been coming from.
 

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I had the same thing happen. Dented one of the tubes taking out a spark plug. So I rotated the dent down so it looked pretty. Thought I had a valve cover leak for months then it got really bad. I read an article on Kitplanes about oil leaks and found it. Dent turned into a crack. BTW it was a Superior tube. They certainly seem softer than the Lycoming tubes.
 
Actually, this is pretty common, especially with older engines. Mechanics tend to get a little careless with spark plug wrenches and hit the extremely thin-walled tubes, creating dents…then cracks. I’ve seen it a number of times!

paul
 
A long time ago, some of these tubes were made of plastic. You can tell by thumping it with your finger against an aluminum one. Over time, the plastic will get brittle and crack.
 
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