F4i Engine Failure

[VFR750R]

My guess would be failed pin bosses, and/or wristpin clip coming out allowing pin to move over and fail pin boss still holding pin. After a few cycles like that, which with the piston being thrown up at TDC knocks valves off stems during overlap. The hole in the piston is from the small end of the rod once the pin came out.

[Pete M]

Nothing on that engine looks like detonation or pre-ignition related damage... The thing just bashed itself whilst moving at a few hundred strokes a second.

You can probably tell what happened to cylinder 2 by looking at the others. Cylinder 1 looks to have been bashing in the squish area, just not to the point of failure.

[Wesley]

I don't think the wrist-pin can back out within the bore - not enough room if I recall correctly. (which I may not)

It looks like you dropped a valve, and as it bounced around inside it smashed the rest of them up so they broke off as they tried to reseat, and got smashed into place by the approaching piston.

The amount of chipped up aluminum in the chamber suggest the valve head (probably the leftmost exhaust, by the looks of it) bounced around for a good bit before being lodged there.

It's hard to believe there wasn't any preignition though, but the piston crown is a really weird place for it to start. I would expect the valve relief eyebrows to be melted off first, not the rounded part of the piston. Though I guess if it was starting from the sparkplug (which is likely, it being steel) it would impact the piston crown first.

I think the valve head may have just punctured the crown and contacted the wrist pin enough to crack the shoulders for the pin bore, so it separated on the next induction stroke.

I don't know, but I think post-mortems are fun! Even though it means you blew up something expensive.

Don't know if we put up our post-california explosion pics, that was an impressive piece of work.

[Lexusteck]

Hey Erich, did you photograph the dyne motor failure this summer. Looks kind of familiar.

[Bill Kunst]

Is it me, or does cylinder one have aluminum on the exhaust valves?

[Pete Marsh]

It is a bit hard to see from the pics but the rod and piston, indeed the entire reciprocating assembly is still fine. The reason the hole is in the middle of the piston is it is thick enough elsewhere to ram the valve down a port instead. The damadge to no.1 is due to ingesting bits of no.2 that were blown into the intake system. Same for the oil in the other cylinders.
14500 rpm is the stock bike rev limit but we do run less piston to valve clearence than the bike. The engine has done more than this before and was actually at 14300 rpm when it blew. It blew right on a large bump in the road and our feeling is the sudden MAP change from the throtle moving on the bump plus possibly some unfortunate timing of an extra vertical G or so took it over the edge.
There is no sign of detonation and the engine is not knock limited on 98 RON anyway, this is not a factor.

Pete.

[neil trama]

That was a valve failure probably caused by valve float.
The damage in adjacent cylinders is schrapnel from the second failure i.e. piston material.
Neil