piston damage (new pictures)

[billfish]

Removed piston today and this is what I found. see attached pictures.

[tubman]

Ouch! I guess the guys were right. What does the cylinders wall look like?

[RalphM]

I'd be worried about where the rest of the ring went. There's a lot missing it looks like. Did it all go out the exhaust?

[billfish]

Cylinder walls look good except for a few miner scratches. I guess the missing piece of ring went out the exhaust. It's not in the pan where else could it be?

[40 Deluxe]

No surprise here! Used to see a lot of identical damage back in the day.

[JWL]

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That looks pretty conclusive. Some of the marks on the piston appear to be longer than the opening would allow to pass. Obviously not. Thanks for the pictures.

[51 MERC-CT]

Wonder if the ring may have broken into several small segments and then spit them out of the opening one by one.

[WestCoast]

seeing how many pits in the top of piston, I agree the ring broke into a lot of small pieces and went out thru the exhaust valve, check valve to make sure its not bent or the valve seat is not damaged

[chap52]

Sure looks familiar...refer post #20
I was also amazed, and felt very blessed not to find any collateral damage to the cylinder or valve.

[Kahuna]

Would something like that occur during installation?
Or, as a result of something else?

[Bluebell]

I imagine many reasons. Just a few;
Ring clearance wrong (end, side)
Not removing a ridge properly (sounds like not this engine)
careless insertion of piston and breaking ring on assembly.(to me, most likely)
Detonation.
Overheating (ring partly welding to bore causing it to break) may have done thousands of miles with no obvious problem since.

We can guess endlesly, but at the end of the day, something was out of spec.

[FritzJr]

A common cause of broken top rings is from having the ring hit the ridge at the top of the cylinder. If an engine is babied for many miles and never taken to high revs, the ridge will be in a certain place. If that engine is then run at much higher revs, the higher stresses will allow the piston to go much higher in the bore. The top ring then hits the ridge and breaks ring and/or piston.

[billfish]

I've had this car for 2 and 1/2 years. That head was off 10 months ago for inspection and the piston was fine, no damage visible. The former owner tells me the heads were not removed during the 20 years he had the car. I've put about 4,000 miles on the car since I bought it. It always ran fine but the compression was slowly dropping. Some exhaust valves were leaking and in the process of doing a valve job I discovered this problem. The pistons look original and the block has never been re-bored. I am assuming this is normal wear and tear.

[billfish]

It seemed strange to me but there is very little ridge in the cylinders and this cylinder had almost no ridge and the piston came out easily without using a ridge remover.

[40 Deluxe]

Originally Posted by billfish

I've had this car for 2 and 1/2 years. That head was off 10 months ago for inspection and the piston was fine, no damage visible.

10 months ago that broken ring could have been within .010" of breaking through and you would never see it!

[51 MERC-CT]

Originally Posted by billfish

It seemed strange to me but there is very little ridge in the cylinders and this cylinder had almost no ridge and the piston came out easily without using a ridge remover.

If the ring was broken in that cylinder shortly after assembly (or even before or during assembly) in that cylinder, that would explain why there was less ridge in that cylinder where it was expected to be. (less or no spring pressure)

[billfish]

51 MERC
Your explanation sounds like a real possibility. I found an original piston and will hone the cylinder, fit it up with new rings and new rod bearings and give it a go. I know I should do a complete rebuild but at 73 I'm pushing my luck going this far.
Bill

[51 MERC-CT]

Originally Posted by billfish

51 MERC
Your explanation sounds like a real possibility. I found an original piston and will hone the cylinder, fit it up with new rings and new rod bearings and give it a go. I know I should do a complete rebuild but at 73 I'm pushing my luck going this far.
Bill

I've got 10 years on Ya' and I remember back in the day that's the way it would have been done. Can remember standing in a grease pit and watching one or two (as required) crankshaft rod journals being ground while still in the car.

[Bluebell]

Billfish, Try to get the weights the same. same model piston and wrist pin?
Also What sort of hone will you be using? If there is any sort of ridge left in that bore, have the top ring groove moved down by machining the top groove for a spacer. The groove is widened on both faces (top and bottom) then a steel spacer goes in above the ring. This lowers the top ring down, slightly off the ridge.

[billfish]

After initial startup with smooth quite operation the cylinder with replaced piston has developed a knock. The knock only occurs after engine sits overnight and stops after a few minutes of warm-up. Knock also stops if that cylinder's plug wire is pulled off. Piston was replaced with new rings and a new rod bearing of standard size. Not sure if it is piston slap, rod bearing or something else. Like I said - engine runs and sounds great after about 3 to 4 minutes of warm-up.