THROW THE UNDERDRIVE PULLEY OUT!!!!!

Yes im yelling. That is unless you want to do this again...

 

That UD pulley is going to be on the receiving end of a hate-fueled sledge hammer so that it can never hurt anyone again

 

Hahahahaha

Please document this.

Those under drives do not dampen the harmonics and are very well known to snap chains.

 

It wont, thats a myth. Many race cars dont use balancers period dont see them having problems. IF it was true then that chain is the biggest Kmart pos ever made

 

Sigh.

 

Update: It was the bolts that hold the timing gear to the camshaft. They sheared right off.

 

seeing the oil pump is on the crank snout, he had oil flow until the crank stopped turning

 

under drive pulley bad on a LS2 no likey, this is common knowledge

 

I would still reuse the short block. Replace any bent valves. Replace camshaft, gears and timing chain. Replace oil pump. New HB since you have it apart.

 

Doesn't sound plausible, I don't think the bolts sheared off and causing the valves to contact the cylinders, I think something else failed that caused the valves to contact the pistons that sheared the bolts off.

 

That's what I ended up doing. Reused the pistons and replaced cam, timing setup, and all the valves. Will be reinstalling the motor this week

 

I assumed one or more of the bolts backed out partially and allowed the gear to rock back and forth slightly each time torque is applied, eventually causing failure. What else could cause valve contact besides the timing chain breaking? (it didnt break)

 

I'd clean up the pistons and make sure there are no sharp edges on those contact points. New heads, cam and valvetrain and keep on trucking.

 

I doubt downshifting at 50 did the damage. If you downshifted and dumped the clutch you more than likely speeded up whatever was about to happen.

 

If you haven't already, get the ARP timing gear bolts and put a little bit of blue LocTite on them when installing.

 

Loose cam gear bolts makes a little more sense, On these motors, is the timing gear pegged to the camshaft or any other way to create slop in the valve train? Failed lifters, failed valve springs, how much thread was left on the cam bolts when they sheared? It may be difficult to find the exact cause.

I would give long and hard thought to replacing the pistons showing valve contact especially if you are going to use the car as more than a grocery-getter. They will have been weakened at the contact points. In the days when spark-knock was more of an issue, you would see divots taken out of the top of the pistons and they would eventually fail. In modern times we have systems that automagically retard timing when detonation is sensed, but I wouldn't want to rely on something to save my weakened pistons. Replacing them may not be too difficult of a job if you can get the motor high enough to remove the oil pan. With the pan off, it is just a matter of loosening the rod cap and tapping the piston/rod out. I did this on my '67 small block to repair a rod knock only it turned out to be a short term fix as the real issue was with the crank shaft.

Looking at your pistons, do you use a Catch can?

Since you are looking at a new head/cam package, this is a great opportunity to increase compression (another reason to replace damaged pistons!) with new heads and a higher performance cam just in time for summer.