Engine problems

[UK Pete]

What the F---K would cause the piston  to disintegrate in this kawasaki engine, the conrod went straight through the front and back of the barrel totally trashing the whole engine, it wasnt through lack of oil or seizure

[K2-K6]

Oooh that has kinda recked it Pete! not much to be saved from that.

If lubrication was ok then I'd guess your'e looking at material / fatigue failure around the gudgeon pin bosses to let go and release all the bits.

Once took apart a Yam DT400 that was making a very odd noise and the piston was in the process of failing in that the gudgeon pin area was cracking away from the crown but stayed together (wouldn't have lasted much longer) but you could see that the edge of the cracks where lightly polished as they weren't still connected.

If you don't know the history of it, possible that it's been revved hard and effectively used the life of the piston sooner rather than later.

What was the bore and rings like? if worn they would also add to piston stress as lowered compression will arrest the piston less effectively and rely more on the con-rod.

[UK Pete]

The barrel had no wear ridge at the top so i guess the bore was in ok condition,  bit hard to tell with the rings, but they are still on what is left of the piston, even one of the gear cogs has snapped

[florence]

I'm not certain but possibly this is what that red line thing on the rev-counter is for?  You may find the engine will now be difficult to start, especially on cold mornings.

[matthewmosse]

I bought a bmw sidecar outfit cheap because it had done a similar thing- in that case I think the con rod had let go, piston clearences etc were good on that one, good way to tell piston condition at a glance might well be to look if there are burnt deposits down the side of the piston, below the rings. Looks like that piston may well need replacement............. Either over revved or faulty piston?

[hector2800]

Piston top would much lighter colour if it had got too hot so I'm with florence it's been over revved, although I would have expected some valve damage in the piston top if that were the case.

[Seamus]

Looks like a two stroke problem, piston has completely failed, not running weak judging by the colour of things. You have ruled out lubrication, as above over revving or fatigue of the piston. How about detonation from incorrect timing?
Did'nt drop a gear or two by mistake instead of changing up?

[K2-K6]

From what can be seen in the pictures it just doesn't seem to show any temperature effects i.e. detonation / lean running. Looks like the rod was intact so getting that off the hook, just looks like the structure of the piston failed.

Nice subtle humour there Florence, that made me laugh.

[rigwit]

looks like pist and broke again, im in the gudgeon pin lands failing as in pic 3 you can see clear shear fatigue and they are the only shiney bit showing as well -------tough luck on that mb a recycle job project for early dark nights