Oil Leak at Cylinder Through Bolt

[wyoflyboy]

Hello all!

I have been seeing some oil leaking around a cylinder through bolt on cylinder #6. How should I address this leak? From what I have read, this is fairly common in O300's?

Thanks in advance for your help!

[Metal Master]

Recently had a friends Swift with a C-125 which uses the same cylinders as C-145 or O-300. He had a leak that initially we thought was coming from one of the through bolts. After several cleanings and re-runs of the engine we found that the cylinder flange was cracked at the cylinder. Upon removing the cylinder, we found that the crack ran up inside the cylinder and then spiderwebbed about 3/4” of an inch. The cylinder was scrap. In 50 years of aircraft maintenance I had never seen this before. Neither I nor the engine shop I work with could explain how this could happen.
Jim

[wyoflyboy]

Recently had a friends Swift with a C-125 which uses the same cylinders as C-145 or O-300. He had a leak that initially we thought was coming from one of the through bolts. After several cleanings and re-runs of the engine we found that the cylinder flange was cracked at the cylinder. Upon removing the cylinder, we found that the crack ran up inside the cylinder and then spiderwebbed about 3/4” of an inch. The cylinder was scrap. In 50 years of aircraft maintenance I had never seen this before. Neither I nor the engine shop I work with could explain how this could happen.
Jim

Jim,

Yikes! That sounds scary!

I hope that is not the case with my issue. I have 6 Millennium Cylinders with around 100 hours on them, so I hope that isn't the issue.

Thanks for the information!

[GAHorn]

Sometimes a cylinder change-out can shift a thru-bolt and dislodge or move the O-ring at the case-split and that can allow oil to seep.
I fixed such a leak on one of my engines by removing the base-nut, cleaning thoroughly with electronic aerosol cleaner (Which also quick-dries the area) then forcing Permatex #2 into the stud/cyl interface and placing a tightly-fitted O-ring onto the bolt-shaft before running the nut back down and tightening it.
I did this following the same procedure on the left/fwd engine-mount strut after one of the mechanics I worked with reminded me that some of these stud also penetrate all the way into the oil-sump area. His technique worked in that instance so I did it again on the cyl thru-bolt.

It is not a procedure that anyone approved but me but it’s not leaked there for the last 6 years now. (Not saying anything about the other leaks on that engine.)

[wyoflyboy]

George,

Thank you very much for the information. Sounds like it would be worth a shot to try. The leak is primarily an annoyance at this point, but I would like to try to stop them if at all possible. It seems to like marking its territory!