Broken Piston rings

So under the heading of “the more I learn the less I know” can you guys now explain how piston rings break?
I’ve now removed the pistons from my injection engine and whilst most of the rings are stuck two pistons have broken top compression rings. The is nor scoring in the bores so assuming this discounts damage on assembly what causes them to break in service? They are broken in two. Not broken into many pieces.

In no particular order of likelyhood:
Ridge at the top of cylinder
Insufficient back clearance
Mishandled during installation
Excessive ring land clearance
Insufficient end gap
That’s all I can think of at the moment…

So Phil when the engine was rebuilt, what was done? Those pistons look like A&E’s are they?

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I don’t have the history of the engine. I’ll clean up this pistons tomorrow but I think they are AE. Will measure gaps and report back.

Do you know if these are the original pistons and rings? Any info on mileage? Very unlikely that Jaguar assembled the originals poorly. Insufficient end gap can do it if it was a rebuild. Are the broken ends polished, as if they had been rubbing together, or do they have a granular or porous appearance? If polished, they were broken when it was running, rough or granular, when you took it apart. If there is also no cylinder wall scoring, my guess is disassembly.

All good points, but if stock pistons/ rings, Id strongly consider the possibility of heavy detonation.

Excessive temperature, leading to thermal expansion of the ring, being contained in the bore, ends coming together, pushing each other, break would most likely occur 180 degrees across from the gap; i.e. insufficient end gap as has been said by David and Mike.

My engine seized due to a thrown chain guide rubber snagging the chains. It bent a rod and I found several broken compression rings. I can’t prove that caused the ring breakage but it seems likely. They definitely weren’t broken on installation 20 years ago because the compression was balanced, and there wasn’t a bunch of carbon on the cylinder walls, and the gap was within spec, at least it was 20 years ago.

Detonation Wiggie? Maybe. Blow up the pic of the pistons. You’re right!
Look at the erosion of the second piston just above the top ring.

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