Nope. None of those, so far as I can see. Weird!

This looks just like that. It's an MoD recon, so I guess they used good parts? But yes, good question, was there a failure from the ring groove root?

It's +40 on first quick measurement. No real wear, can't catch anything with a fingernail.... Its an MoD engine, so there won't have been any cost cutting with the bits. It's obvious that one quadrant had failed long before the rest though.....

I shall do that I think. I'm assuming the big-end bolts are reusable..... ?

It's been running quite rich judging by the plugs/crowns/valves.

Looking at the piston, it seems like one quadrant has been fractured at the top ring groove for some time before the final failure. See the pics below.

OK Forensics Team - tell me what you make of this:- 1: Bore is OK I believe. :) 2: Bottom end is OK I believe. 3:Engine spins freely. 4: Self-tappers & claw hammers work to extract piston crowns (it wasn't tight). 5 Measure up and new piston time! For your delight and amusement:

Indeed - but very low usage and no audible pinking. Any thoughts on what the timing should be for worst case Tesco unleaded?

Yeah, I was thinking that. It should be smack on standard, whatever that is, but I shall check. If it's been detonating/over advanced I'll replace all four pistons, but at the moment I don't see any evidence for that. The dizzy is reputable, new-ish, and electronic. Weird. Unleaded BTW.

See below! Conrod seems fine.

Nope, no melting or any other classic stuff. The rest have a little coke build-up and nothing else, and there is almost no discernible bore wear or a lip that might catch. When I get the piston out I'll know more....

UPDATE ! Having finally found the time to get the sump cover off, I now find that the piston is detached at the top, and the gudgeon pin is still attached to a ring of aluminium. Bottom end appears undamaged. Pics to follow..... Any suggestions as to why?

Exactly the plan. That's why I asked how thick the crown is. Or a long drift from the bottom. Your next dramatic instalment is tomorrow.......

I'm still excavating. Trust me to find a new failure mode.....

OK, I've got the piston knocked back down 3/4" and the bore up top looks ok. I now need to cobble some sort of puller. Does anyone know how thick the piston crown is?

B series Morris Oxford, Leeds to Teesside once with a crank which came out in two pieces.

:vb-bouncy3::vb-bouncy3::vb-devil2::vb-bouncy3:

I wonder what the conrod was doing....

Weird, innit? It still ran. I'll have another session later and get the bottom end exposed.

It's a voyage of discovery..... o_O