Possible crankcase leak and mystery hole - IO-540

[Tassie]

My BPE IO-540 has been performing really well for 18 months now, but on a recent inspection I noticed some black sooty/coke like material on the engine block just behind the #5 cylinder. The material was not oily, and rubbed off easily with a bit of diluted iso-propyl alcohol on a rag. I can't really figure out where the material came from. The pressure relief valve is not leaking, and the black stuff didn't seem to be anything like oil. There's also nothing below this area, where an oil leak would go due to gravity (and cooling airflow). So I'm thinking this must be leaking crank-case fumes. The engine is fitted with an ASA air/oil separator, the reed valve unit is welded to the exhaust pipe and is not coked up. The separator oil return goes back into the case.

My question - there is a threaded hole just near the base of the pressure relief valve, and by the paint in the threads it is clear there has never been a plug in this hole. I've never noticed it before, and I can't find any reference to it in the Lycoming manuals. I've marked the hole in question in the attached photo. What is this hole for, and should there be a plug in it?

 

[eatonair]

My BPE IO-540 has been performing really well for 18 months now, but on a recent inspection I noticed some black sooty/coke like material on the engine block just behind the #5 cylinder. The material was not oily, and rubbed off easily with a bit of diluted iso-propyl alcohol on a rag. I can't really figure out where the material came from. The pressure relief valve is not leaking, and the black stuff didn't seem to be anything like oil. There's also nothing below this area, where an oil leak would go due to gravity (and cooling airflow). So I'm thinking this must be leaking crank-case fumes. The engine is fitted with an ASA air/oil separator, the reed valve unit is welded to the exhaust pipe and is not coked up. The separator oil return goes back into the case.

My question - there is a threaded hole just near the base of the pressure relief valve, and by the paint in the threads it is clear there has never been a plug in this hole. I've never noticed it before, and I can't find any reference to it in the Lycoming manuals. I've marked the hole in question in the attached photo. What is this hole for, and should there be a plug in it?

I’m guessing the picture isn’t oriented top being up. Looks to me like thats just the machined/tapped hole for the accessory housing bolt. Common for lycoming in that area. Shouldn’t be an issue unless the gasket is leaking.
But I may be looking at the picture incorrectly.
Just my two cents.

Ray

 

[Tassie]

Thanks Ray. Top is up in the picture. Baffle around cylinder #5 is on the right. Part of the base of the oil pressure valve is visible (yellow). The accessory case on the left is obscured behind the (blue) engine mount which is a bit out-of-focus in the foreground.

 

[Aden Rich]

Confirming with Ray. Its the stub that holds the engine mount ear onto the case. It's just been machined through farther than others. My 540 does not have that but I doubt is affecting anything at all.

 

[DanH]

I noticed some black sooty/coke like material on the engine block just behind the #5 cylinder. The material was not oily, and rubbed off easily with a bit of diluted iso-propyl alcohol on a rag.

Look for aluminum on aluminum fretting wear.

 

[TASEsq]

Look for aluminum on aluminum fretting wear.

I was wondering if checking the torque on the cylinder nuts was a good idea? Could this be some paint which was incorrectly applied under the cylinder and has worn away?

 

[lr172]

anything coming from the engine, including C/C vapors will leave the tell tale oily residue; It maybe be crusty from dirt, but when you wipe it off, you notice the oilly nature. If black/dark grey, dry soot (comes off on finger still dry and very light), I would be looking for an exhaust leak in that area. That area is near the #5 flange. Possibly debris from aluminum fretting, though it would need to be pretty substantial if it is being deposited on the crankcase.

 

[lr172]

anything coming from the engine, including C/C vapors will leave the tell tale oily residue; It maybe be crusty from dirt, but when you wipe it off, you notice the oilly nature. If black/dark grey, dry soot (comes off on finger still dry and very light), I would be looking for an exhaust leak in that area. That area is near the #5 flange. Possibly debris from aluminum fretting, though it would need to be pretty substantial if it is being deposited on the crankcase.

You are looking for a failed gasket on #5 or a crack in/near the weld where the tube attaches to the flange. Cooling air blows the exh gas aft and settles on the case. There should be other signs closer to the leak.