Lycoming IO-360 Engine leak escalated quickly

AttackPilot64 · #1 11-20-2016, 06:38 AM

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.

AttackPilot64 · #2 11-20-2016, 06:44 AM

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Steve Melton · #3 11-20-2016, 07:34 AM

I think the suspended boy has and eye on it.

Appears to be impact damage on the piston.

BillL · #4 11-20-2016, 07:39 AM

Root cause - broken ring on top end assembly.

Walt · #5 11-20-2016, 07:45 AM

A very good article on detonation and preignition:
http://www.contactmagazine.com/Issue...ineBasics.html

Curious as to what type of fuel and ignition you are running?

Walt · #6 11-20-2016, 07:47 AM

Quote:

Originally Posted by BillL

Root cause - broken ring on top end assembly.

Yes but what caused the broken ring land? Piston failure or detonation?

BillL · #7 11-20-2016, 08:02 AM

Quote:

Originally Posted by Walt

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.

lr172 · #8 11-20-2016, 08:57 AM

Quote:

Originally Posted by Walt

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

AttackPilot64 · #9 11-20-2016, 09:27 AM

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.

scsmith · #10 11-20-2016, 06:35 PM

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.