how did the valves bend?

[spec guy]

I am working on a 944 turbo. The timing marks all lined up as we started the dismantle. We found what looks like 5 valve marks on number 2/3 and 4 pistons. THE QUESTION. Did the driver overrev the thing or might there be some other way to bend valves while keeping in time??? broken cam woodrif key ?? any thoughts

[Arizona_928]

teeth missing from the timing belt?
broken woodruff key is uncommon, but could be a result of overrev...

[chally72]

There are several posts on here about valve collision without timing belt failure.

For example, one of the causes was a loosened bolt in the cam tower that collided with the valvetrain, stopped it until the piston hit it, and then got knocked out of the way. The timing belt stretched and then snapped back into place, with seemingly nothing wrong.

[Rasta Monsta]

How do you know the damage happened with the motor in time?

[333pg333]

Belt skip? How was the motor running prior to teardown? Did it suddenly run crap and sound bad therefore you took the head off, or did you just discover it afterwards?

[dmdirks]

In an overrev condition, say due to the driver downshifting into second instead of fourth, the valves will float open. When this happens it is more common to find bent exhaust valves. This is because on the exhaust stroke, the piston 'chases' the exhaust valve shut, unlike the intake stroke, where the intake valve opens as the piston goes down.

[M44/41]

No Chance of over rev IMO, sheared woodruff key you would of been detected COZ ITS NOT A PARTIAL FAIL.... belt slip could be masked by dishonest PO....or you messed up? Don't kill me but thats an option too.

[dmdirks]

How could there be no chance of over-rev? It happens all the time in 944-Spec racing- the driver is going 100+ in 5th, misses 4th and goes into second instead. The rev limiter in the DME does not work in this situation.

[Jrboulder]

How could there be no chance of over-rev? It happens all the time in 944-Spec racing- the driver is going 100+ in 5th, misses 4th and goes into second instead. The rev limiter in the DME does not work in this situation.

haha!
If you tried to go from 5th to 2nd going 100 in my car the gearbox would put up quite a fight. My friends dad has over reved the same Z4 twice.

Jackson

[krystar]

another more common one is missing 3-4 upshift and going into 2.

[Capt Squid]

I agree with the the others that it could of been an over rev by shifting into the wrong gear. As dmdirks stated, not uncommon among the 944 Spec racers. I did my valve bending by shifting from 3rd to 4th in a high G curve. It went into 2nd and the tach pegged.