When is an oil leak too much?

[helitim]

Just finished a top on my J model I0 360 A3B6D. Initial leak check showed a few drops from around the #3 cylinder. Break-in flight consumed 3/4 quart of oil in 2.1hrs of hard running per S.I. 1427. After shutdown, I noticed the leak had just enough oil to flow out from under the cowling and streaked down the right hand side of the fuselage about 18-24 inches long and a small amount was on the right side of the nose gear door. After pulling the cowling, I cleaned the area thoroughly, put some talcum powder over the area and did a static run up. It appeared to be coming from the vertical area between the thru bolts on the back of the #3 cylinder. I then pulled the cylinder off carefully, replaced the cylinder base gasket with another new one, thoroughly cleaned the mating surfaces again and reassembled the engine.

Initial ground run looked dry. Once around the pattern revealed one drop of oil slowly running from the same spot. Then did a 2.3 hr non-stop high powered flight just in case the rings hadn't already seated on the first long flight. Got back home and noticed an equivalent of maybe 15 or 20 drops of oil anywhere from 12 to 24 inch long drip lines from the right side of the cowling and down the fuselage. It only took about 10 seconds to clean it off. The engine still has mineral oil in it at present.

Now to most pilots and mechanics this may not sound like much of leak. My question to the group is, when is a leak too much? How do you quantify when a leak should be repaired and when you should just live with it ?

Thank you,

Tim

[carusoam]

Leaks aren't normal...

Depending on the source, some are easier to fix than others...

Determine what it is, go about getting it fixed.

Was the leak existing prior to the TOH?

Cracked parts of the block can be a pain.

Hopefully, it is an easy fix....

Good luck,

-a-

[helitim]

No, the leak did not exist prior to the top. During the initial teardown, I did notice what appeared to be a small amount of RTV on the gasket. The previous repair station may have known about the leak and this was their only solution short of more money/ work.

[orionflt]

oil could be coming from one of the thru bolts, if the o ring on the bolt is worn releasing the tension by pulling the cylinder could allow the o ring to unseat. 

 

Brian

[N601RX]

The oring usually does a good job of sealing the cylinder to the case, unless there is a nick on the case.  A loose leaking throughbolt is a lot more common. Oversized bolts are available.

[1964-M20E]

I’m experiencing this but on #2 right now.  I did just what you did remove the cylinder replaced the O-rings and other seals.  I went on a 4 hour flight looks like we slowed ti down but maybe not completely stopped it.  My next step will be to use oversized thought bolts since I believe that is where the problems lies.

 

There is another thread discussing this somewhat.

 

http://mooneyspace.com/topic/8051-lycoming-io-360-a1a-oil-film/

 

Ly-con will machine a recess in the case for an O-ring on the through bolts where the cylinder mates to the case but that requires total engine disassembly.  I’m not sure why they could not have a setup wilt a tool that could do it in place one the through bolt was removed seems simple and my brother who is a machinist said it would not be a problem.  We even discussed a relief machined on the cylinder base for an O-ring as an alternate but alas no STC.

[N601RX]

I have some oversized bolts if anyone needs them. When I rebuilt the engine a couple of years ago I had the case machined to use hollow dowls for alignment and orings for sealing. I then purchased a set of stock sized bolts, the oversized ones were quite pricy.