Stopped up to a friends house yesterday to help him break in his new engine, and had big troubles. Looking for possible clues that might help.

Its a 10 to 1 360, flat tops, basic bottom end, has Magnum R/T heads (cast iron), and hydralic flat tappet cam (i do not know the specs, but it too is mild mannered-- around .500 lift).

3 minutes into break in at 2000 rpm, a dreadful noise started and he hit the key off immediatly. We pulled the valve covers didn't see any thing that caught our eye as we rotated the motor over by hand, ended up putting it together, tried starting it again. It ran quiet for about 30 seconds and the noise returned---again key off right away.

Well, to make a long story short, #4 intake pushrod got bent. then we noticed #4 intake valve hanging open a bit, around half lift. Tried tapping it with a hammer and no movement at all--its stuck. Rolled #4 piston to BDC and used a bore scope to look in and looks like no piston damage, or it at most it just got tagged (older bore scope, was a little hard to see), but the valve relief notches appeared to be ok and the piston top seemed ok too. Could not get it to bend enough to see the condition of the valve.

Sooo, assuming the valve isnt bent (although i am not ruling it out), what do you think would hang the valve open and seize it that quick? It has plenty of retainer to guide clearance on it in case anyone was wondering. Plenty of oil on top of the motor, everything was running great untill this happened.

The heads are not pulled off yet, not sure when they will be as he is pretty dejected right now about it. Were actually going to just pull the engine back out and put it on a stand when he is ready to work on it again.