I wouldnt be surprized if a valvespring or rocker arm broke causing this, but what can I conclude of a valve that dropped on the piston and took the motor out on its way.

FYI, motor is an NA 427, lightweight forged. Valves are stock, double springs, small cam, and stock rocker arms.

- friends car -

 

Bad spring or too much pressure on the stock valve from the spring.
If it's a 06+Z06 head then the exhaust valves are known to break.

 

is it indeed a Z06, except its an 09, had an oil pump failure early this year that killed the bearings, and this is the second time it blows up...

Does ths have anything to do with improperly torquing the rocker arms? we figured out they were over torqued and loosened them a bit, but that was about 6,000KMs ago.

damn, well never figure out if it broke or the real cause the engine is a mess right now and is a complete waste, poor guy.

 

Um, just how much did you loosen them?

 

they were torqued to about 55pounds, loosened them to 30ish.

 

Cause and effect. Was it an exhaust or intake?

Not sure what your failure mode is. You say you lost an oil pump earlier on. Lack of lubrication on the valve guides can cause a valve to stick as it heats up. Lack of lubrication can also cause the various metal components to gall. Valve guides can gall and eventualy cause the valve to hang up.

As far as torque goes, you cannot get a true torque value loosening something. The final movement on any bolt, nut or plug must be in the tightening motion. If not, it will continue to loosen. On a 55 foot pound joint, something as minimal as 10 foot pounds in the loosening rotation can completely relax a joint 100%.

 

I didn't knoiw that was possible at all, we obviously loosen then retorque the bolts to 30pounds ft.



I

 

Have you taken the valvecovers off yet? If those little rocker bolts were torqued to 55ft-lbs, I'm a little suspicious of their integrity under operation. I've seen the lash caps come off, and the steel rocker tip completely eats away the titanium valve tip until the valve dropped, COMPLETELY destroying the engine.





Pretty cool, huh? I just have this sneaking suspicion something similar may have happened.

 

Uh I think the stockers are supposed to be 22ft lbs...

 

The same thing happened to my LS-1 last year.
The 921 Comp springs were improperly shimmed and I believe
valve floating around 6800 rpms caused a collision
with the piston and valve.

 

They are...but some aftermarket bolts torque to 30ft-lbs, Yella Terra's, I believe, torque to 30ft-lbs.

My point being that if a bolt, which is supposed to be torqued to 22ft-lbs, is tightend to more than double that, it may have stretched or even cracked the bolt holding the rocker down. The bolts should never have been re-used.

 

usually when a valve dropped it's because a spring broke

 

That or maybe a broken retainer or keeper. I've seen a few where the top of the valve stem let loose

 

ill try to get a few pics of the motor, lets see if that helps us guess what happened because im really curious/dissapointed and dont want to blame anyone YET.

 

as promised.

Can we guess what happened from those pics?

 

Wow, it even damaged the block. Look at the bright side... the intake manifold, valley cover, front accessories and everything from the flywheel / flexplate back is good....

OK, I'm going to cry now.

 

WOW....That makes me want to cry!!! Did you break an intake and exhaust valve?

Look at the cracks in the sleeve and the aluminum block. That will not make a nice coffee table!

 

Wow that’s pretty bad, went to the garage yesterday but the car wasn’t there just make me wanna
Give your friend my condolences and and to the people that worked on the car.

 

Oh look, another cracked LS7 block...

What does the other side of the cylinder head look like? Any broken springs?

 

^ So your telling me that dropping a valve typically doesn't result in a cracked block??