Lycoming IO-360 Engine leak escalated quickly

[Lote]

I am unclear as to why this condition results in oil leakage?

LeRoy Johnston RV-6A Esperanza 1100 hrs

[Krynn]

Originally Posted by Lote

I am unclear as to why this condition results in oil leakage?

The damaged ring/piston caused excess pressure inside the crankcase, which in turn caused oil to force it's way past various seals.

[Lote]

Very helpful--thanks.

LeRoy Johnston RV-6A Esperanza 110 hours

[sblack]

Would a borescope inspection of the cylinder wall have caught this early? I mean 50 hrs before this would there have been substantial marks on the wall? How long would it take to bash a piston into such a sad state?

I am not trying to be critical of the OPer, I am just wondering what one can do to catch something like this before it becomes catastrophic. And I am very glad it was discovered on the ground - kudos for deciding to do a compression check. Amazing that the engine still developed full power. The symptoms it was showing seem to be all out of proportion to how pooched the piston really was.

I would be curious to know if there is other collateral damage in the engine, metal in the screen or filter etc? Could it be that the engine could be returned to service with just a new jug? I can understand why the OPer wants to rebuild everything, but there are risks associated with that as well - infant mortality. If after a teardown to verify that the journals are all good and there is no crud anywhere and no damage to the other jugs, a new jug might be the safer option.

Mike Busch has written that engines with 40/80 compression still develop full power. Now this thing with 10/80 was also flying ok. That is amazing.

Thanks for posting - a real eye opener for sure.

[sblack]

Originally Posted by Krynn

The damaged ring/piston caused excess pressure inside the crankcase, which in turn caused oil to force it's way past various seals.

well I think there is normally high pressure in the case, every time the piston comes down. But if you are missing a big chunk of ring it would go right by the piston and out the exhaust. That happens to some degree as engines wear. I don't see why the broken ring would cause any MORE pressure in the case. It is supposed to be creating a seal. How can a broken ring seal more?

Caveat Emptor I am not an engine guru so I could be dead wrong.

[sblack]

Originally Posted by AttackPilot64

My next questions is I have 500 hrs on the engine SMOH I went ahead and ordered new Cylnders pistons ect I planned on ordering new bearings for the bottom end but do you guys think I should send the crankshaft and cam off for inspections. They have 500hrs since last time they were sent off. All the gears were replaced last overhaul and they look to be in great condition. I plan on spending next day or 2 mic ing and cleaning parts. If Ishould send them off who do you guys recommend ? I want to get her back together as soon as I can

I would expect that any damage to the crank journals and bearings would be obvious. You can mic it yourself. Theoretically, if there has been good oil flow to the crank the wear might be almost nil. Do you know what the journal measurements were at last overhaul? Good quality pics sent to a knowledgeable engine person will get you some useful feedback.

My C90 was torn down 300 hrs after a new crank because of oil pump issues. I was putting on 4 new jugs (much older than 300 hrs) and I figured there was no point putting new jugs on a junk case since I had no provenance on the lower end. The journals and bearings were virtually new - no visible wear. If there is always oil there, no cold starts etc, then there is no metal to metal contact. Inspect first and I think the proper way forward will be obvious. If you got bits throughout the engine and especially in the bearings it will be visible as scratches. If you have metal in the screen and filter that is going to make you want to check everything very carefully - cam, lifters, oil pump etc etc. It might cost you, but you still have your airplane and you are not in the hospital so it's all good. Good luck.

[rapid_ascent]

My engine knowledge is very limited but I'm curious if the oil filter was checked for metal at the oil changes. Aren't these changrs required every 100 hours? I'm trying to understand how to detect such problems at an earlier stage.

[Mark Burns]

Originally Posted by sblack

well I think there is normally high pressure in the case, every time the piston comes down. But if you are missing a big chunk of ring it would go right by the piston and out the exhaust. That happens to some degree as engines wear. I don't see why the broken ring would cause any MORE pressure in the case. It is supposed to be creating a seal. How can a broken ring seal more?

Caveat Emptor I am not an engine guru so I could be dead wrong.

Scott,
As one piston retracts, another is extending. Any crankcase air pumping is cancelled out.
There will be some wind, but no "crankcase" pressure generated by just the pistons stroking.

A broken ring allows combustion gases (high pressure) to leak INTO the crankcase causing an overall increase in crankcase pressure.

Hope this helps,
Mark

[sblack]

Originally Posted by Mark Burns

Scott,
As one piston retracts, another is extending. Any crankcase air pumping is cancelled out.
There will be some wind, but no "crankcase" pressure generated by just the pistons stroking.

A broken ring allows combustion gases (high pressure) to leak INTO the crankcase causing an overall increase in crankcase pressure.

Hope this helps,
Mark

Ah. Makes sense. Thx.

[AttackPilot64]

Thanks for all the replies, I have been doing oil and filter changes every 50 hrs. I do cut the oil filter after the change to inspect. There has never been anything that would cause concern.(other than a little high iron content on my oil analysis) I have since inspected all other journals gears pieces ect and can't find ANY scratches or anything out of limits.the oil screen and sump had some slight sparkling in the oil and ONE little peice in the oil screen. I have chosen to send of the steel parts crank rods and cam for inspection since I'm waiting on new cylnders. The other 3 cylnders look immaculate. (I will post some pics) I will most likely just sell them since I ordered new ones.
Perhaps I could have caught this by doing a bore scope during my annual inspections. Mabye I would have seen the scarring the ring was causing in the jug. From now on it will be on my conditional checklist. I think I would have been A ok just replacing a JUG and driving on but, It's a peice of mind for me to make sure things are perfect on the bottom end.