IO360 Oil leak at cylinder jug base

[Majorpayne317641]

I recently noticed some Oil dripping off my cowl so I pulled it to inspect. The #2 and #3 have a good amount of oil seeping from their bases that has made its way all over the bottom of the engine/exhaust/engine cowling. Any ideas? The engine has about 1100hrs. Nothing shows abnormal in CHTs, EGTs, fuel flow rates or power. Oil consumption was about 1 to no more than 2 quarts per 40hrs. I'm now at 2 quarts in 30hrs which explains the leaking. Can the o rings really just go bad? Or is there something else going on? The engine was zeroed back in 2012.

[Secondwind]

Are you sure it's the cylinder bases leaking or is it the oil return connector hoses from the rocker boxes? Those hoses will get hard and leak with time.

[lr172]

The base O ring is a pretty uncommon place for oil leaks. When mine appeared to leak from that area, it was actually the push rod tube seals that were the source, just hard to see the oil on the top side of the Cyl. Another area is leaking from the through studs in the case. That will appear as though the base gasket is leaking, as the oil comes out around the stud and then drips down the base flange. This is more common when the cases do not have sleeves to prevent case movement, though most have no idea if they are in the case or not.

Bad oil return hoses leak from the same area, but generally don't leave oil on the cyl flange. But that really depends upon air flow and how well the baffles seal. In a well organized baffle, air is flowing from the cyl base to the oil return tube, not the other way. Leakage from the spinner area can change the direction though.

Larry

[airguy]

+1 on the pushrod tubes - I've been fighting a persistent small leak on my #4 exhaust.

[Ironflight]

For those with leaks at the inboard end of the pushrod tubes, the Lycoming school instructor taught us to turn the (green) seals inside out before installation, and they work better…..

[Bavafa]

#2 and #3 cylinders share the same thru bolt. While it is very unlikely, it is a good idea to check the torque on those nuts.

[lr172]

Originally Posted by Bavafa

#2 and #3 cylinders share the same thru bolt. While it is very unlikely, it is a good idea to check the torque on those nuts.

While that is a good idea, they don't leak due to insufficient torque. They are interference fit bolts and excessive case movement causes wear between the stud and case hole. Once you get a thou or two of clearance between the stud and the case, they leak, unless the case was retrofitted for o-rings at the web joints where the through studs pass. That said, I believe these are slow leaks. If the OP is getting pooled oil in the cowling it is probably not from the through studs.

Larry

[Majorpayne317641]

Thank you for all of your responses. My A&P IA looked it over today and said the oil is so bad all over the bottom of the engine it is hard to tell where exactly the leak is starting from. I put about 44hrs of tach time since the last oil change and since I saw inside the cowling, which was dry then.

He told me to clean off all the oil from the engine and preform a ground run to warm the oil and find the source of the leak. I hope that this amount of oil is too much for a thru bolt leak. I didn't build the plane so I don't know if the baffling is sealed perfectly. I thought seeing some Oil at the base above the cylinders was a bad sign. I didn't notice any oil leaking from the push rod tube though. Here are 2 pics but they don't really reveal much other than the amount of oil. One pic is of the #2 and the other of the #3 from the bottom looking up.

[abwaldal@gmail.com]

Wow, it looks like you need a case of brake cleaner to get all the oil off that mess. Ya, I know people use Stoddard solvent and all kind of cheap stuff. But, my money goes to the large cans of brake cleaner, electrical cleaner or the like.
Dries virtually clean and dry and fast.
You really need a black light and a dark hangar after you wash it to within a an 1/8" of it's life.
Most oil will glow green when hit with a black light. I use Phillips 20/50 and it is so green you could put cows out to pasture on it. When I started using a black light, I actually bought some oil leak detector dye. It is still on a shelf in my hangar somewhere.
I made the lucky mistake of shining the light on just plain oil.
Clean, clean clean, then look for leaks/weeps. Start engine for a few minutes and look again. Repeat and then repeat.
The black light trick has found the smallest of leaks.
Your luck will probably be just as good as mine after. Art

[Majorpayne317641]

I think I will hit it first with Carbon X stain remover first to get the dripping oil off, then I will use brake cleaner like was recommended in the previous post. I will definitely try the black light trick, I just ordered one on Amazon.