Trackday engine failure...mystery solved...or is it?!

[AlexG40]

So, today I took the engine out of the G expecting to see a head gasket blown between two cylinders.  Instead I found this:







So, a few minutes with a valve spring compressor and we get a lovely view like this:



Answers on a postcard as to how that happened...

[liam]

cambelt slipped maybe?

[cheys03]

Bugger

Can only think that the cambelt or a vernier pulley slipped really, or that for some reason the valves were sticky or slow to close
Was it at high revs when it started to show symptoms? I assume it has done a few hundred/thousand trouble-free miles since any prior work e.g cambelt etc?

[AlexG40]

4 years n 20k since rebuild. Drove fine in the morning, started making a noise then gradually got louder then bang. Gonna check the crank pulley is not spinning. No vernier so it's not that. Hmmmm

[Andy]

Fucking hell!

Was the water pump tight and tensioning the cambelt correctly? Any signs of damage to the belt? Are there any signs of debris in the tappets?

[AlexG40]

All good Andy and belt looks brand new. Timing belt covered too.

[cheys03]

Was the timing still ok before disassembly?
Oil and pressure ok?

[hayesey]

ouch. that's not good.  I can only think the cambelt has slipped.  I guess that noise was valves hitting pistons then

[AlexG40]

Well, this is a case of logic winning through. Talking to Yoof yesterday we agreed that the timing being out was the only explanation, what couldn't be explained without guessing was why. Timing belt slipping is the obvious guess but there were no obvious telltales, no teeth missing, no bits of rubber etc, in fact everything looked brand new.  I said that in theory the only thing that would have caused the gradual failure would be a pulley loose. However as we all know there are keys to prevent this on both of the vital pulleys. However, I never touched the crank pulley when I did the engine for the car so I was curious to see if anything was missing. This is what I found:



So, mystery finally solved.

[Yoof]

Bingo!

Debris in the woodruff keyway when the crank pulley was bolted on it my guess, either that or overtorqued.

PITA either way!

[cheys03]

oh....there goes my 'sticky valves' theory
Bloody hell. Bizarre failure

[PeteG40]

more common on g60s as the bottom bolt comes loose.

Did you use a new bolt? or did you not touch this?  they are single use stretch bolt

[AlexG40]

Never touched it Pete. Wish I had now, as you know it would have been replaced with gen all pukka torqued.

[Boris]

Man that sucks.  I'm still a little confused as to the cause from that pic though, is that a part of one of the teeth or a bit of debris that was between them?

[AlexG40]

It's the woodruff key on the pulley that has failed.