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Lycoming IO-360 Engine leak escalated quickly

AttackPilot64

Well Known Member
My Lycoming IO-360 Has 500hrs since a top end overhaul. The last 2 weeks I have been getting a lot of leaking in random places. After spending a bunch of cash on gaskets. A prop seal oil return lines ect, it was STILL leaking.I even cleaned my crankcase breather line. When I got home yesterday from my flight from FL I figured what the heck let me compression check my engine... #3 cylinder 10/80! After sweeping up my tears i opened her up and found this! Had 3 holes in my piston and it melted a ring completely ! Man I am so thankful nothing bad happened in flight. I still had all my horsepower,fuel flow, my CHT and EGT's were all normal indicating.i had not even a HINT That something was wrong. (Minus some oil on my engine cowling) That goes to show you the abuse these Lycoming can take and still fly. As for me, I pulled the whole engine and will be doing an overhaul. You can't put a price on safety. i sure hope santa can help me out this Christmas.
 
Yes but what caused the broken ring land? Piston failure or detonation?

Assembly - day one. It looks like the ring was likely broken 500 hrs ago and wore away the land, it doesn't look fractured. The clue (to me) is the other end of the broken ring wear area. The piece moved up and down in there until it wore a wide slot and eroded the land away a little at a time. I have seen a lot of pistons with broken rings looked just like this.

The top of the piston and the edges of the crown look way to crisp for detonation or preignition to have initiated the failure. I think a look at the cylinder wall will show significant scoring due to the ring section rotating. I would have expected to have it making iron in the oil, but the oil ring was doing double duty for a long time. It seems high crankcase pressure from the progression caused the oil leaks.

Nothing is certain, but quite high probability that this is where it started.

The Voyager engine that broke the wooden prop was torn down to modify it for the aluminum CS prop. My memory is bad on the hours, but it had a broken top ring and ran perfectly fine. If that prop had not broken the engine might not have made the world voyage. Maybe the history records will say how many hours it had. The builder at TCM was an outstanding engine guy, it happens. No shame on the builder.
 
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Yes but what caused the broken ring land? Piston failure or detonation?

When a ring lands breaks, it is often after extended, significant detonation or pre-ignition (the P/T doesn't need to be extended, based upon severity). The ring land breaks, because it is the weak point in the piston assembly opposing the greater than designed force from above. Excess cylinder pressure produces both excess downward force AND excess pressure (i.e. friction) on the ring pressing into the cylinder wall.

In normally aspirated engines, I believe it is uncommon to see broken ring lands without some other evidence of excessive cylinder pressure (i.e. detonation / pre-ignition) damage. In this case, as Bill pointed out, the ring land didn't break, it was worn away. In the case I described above, a portion of the upper ring land usually breaks clean off and additional damage is shown as that part bangs around the cylinder environment for many thousand cycles until it is small enough to fit through the open exhaust valve.

I should also add that the most common cause of ring land damage is due directly to heat and not really the pressure itself. Excess heat from the detonation, P/I, etc. (usually due to destruction of boundary layer) causes the ring to expand beyond the level accounted for with the ring gap. Once the gap is gone, additional heat makes it tighter and tighter and the first thing to give is the upper ring land when the friction gets too high. This is the reason that turbo engines run larger ring gaps.

Larry
 
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Engine

I am running 1 electric (Emag ) and one Bendix. I think I agree with you guys on its been wearing for hours. I am going to tear the engine down completely and rebuild her from the ground up.
 
I agree with BillL's assessment. I have seen exactly the same thing in my volvo B-20 with 11:1 compression. Piston ring breaks, then wears a wedge-shaped opening in the ring groove. In my case, I found it on a disassembly to put stock pistons back in before the wedge broke through to the crown, or it would have no doubt looked a lot like the OP pictures.
 
So the cylinder was still making normal power and CHT and EGT was normal with almost no compression?

That is certainly possible as I too had the same experience a few years ago. I have an IO-360A1A in my -8 and during a routine compression check I found my #3 cylinder at 10/80. And just like the OP, I had no indication of power loss, CHT, or EGT changes. If there were, it certainly wasn't obvious. In my case, the cause of the compression loss was a crack starting at both sides of the top spark plug hole and continuing halfway around the circumference of the cylinder! I don't know how many hours or minutes it could have gone before blowing the top off. After putting on a freshly overhauled cylinder, I did notice a very slight power increase, but no real changes in CHT and EGT. Takes a lickin' and keeps on tickin'!
 
Attackpilot: I think Emag has two ignition advance curves available. How much timing advance did you have? Also, what do you have for an engine monitor?
 
So the cylinder was still making normal power and CHT and EGT was normal with almost no compression?

You shouldn't closely correlate leak-down results with compression. A leak-down test (mistakenly referred to as a compression test in the aviation industry) only measures static leakage and can only be used as a guideline for cylinder health. 10/80 doesn't mean no compression. If you put a real compression gauge (measuring dynamic compression levels) on the cylinder and crank it over, you'll find plenty of pressure to fire the charge. Power level will be reduced somewhat, however, due to the lower pressure produced.

The 80 point scale is set to provide diagnostic guidance and is not an absolute compression range. 10/80 correlates to a low enough compression level that the cylinder is in need of repair, but not necessarily that it is not functioning.

Larry
 
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Engine

That's correct I have a dynon skyview system and of course Cht and EGT probes in every cylnder/exhaust. The only thing abnormal was mabye a 15 degree rise in CHT. Mabye I landed just in time but even after I landed I pulled my cowling and wiped the engine down and we did another run up to try and identify the leak. No abnormal sounds Cht or EGT on the ground run. The only reason I even elected to do a compression test was because it looked as if the engine was leaking out of the base of the other 3 cylnders. I figured the case was over pressurized.
I have already torn the engine completely down ( fearing the worst) but everything looks to be in great condition.no metal in the Sump or anything! I plan on cleaning everything up and inspecting evething to ensure everything is within limits.
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
 
Mag question

Cardinal flyer , I currently had the A jumper wire on my P-Mag. With the V40 software the give you up to 34 degrees.
 
Two lines of thought here. One, the "might as well, we're this close anyway", go ahead and send the items to be inspected. Number two, if you were buying this engine for your plane, which engine would you prefer, xxxx hours total time, 500 hours SMOH, 0 hours STOH with new cylinders or this engine, xxxx Total Time, 0 hours SMOH with new cylinders. Dan from Reno
 
Why oilleak?

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

LeRoy Johnston RV-6A Esperanza 1100 hrs
 
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.
 
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. :eek:
 
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.
 
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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.
 
Let me try to explain

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. :eek:

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
 
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.
 
Engine

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.
 
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