LS3 Mystery

[davepl]

LS3 in a big lead sled. Ran great for a little bit, then started ticking. Then the ticking got louder.

Shop pulled the top end, didn't find anything, replaced the lifters, problem remained.

Cylinder 7's exhaust pipe looks a lot more blue than the others.

Upon teardown, it turns out that the ring ends butted and a piece of the crown is missing, which mercifully must have gone out the exhaust.

This is a brand new crate LS3, so I'm really surprised that the ring gap would be the aggressive.

My total guess is debris in the injector leaned that cylinder out, ran it way hot, that butted the ring gaps and popped the top off. But I've never seen a factory ring gap close up!

[71cadc10]

have seen several boosted stock engines, butt rings and tear the top or chunk of the top off the piston.
when the heads were off, how did they not see a piece of missing piston?

[davepl]

Odd I know, but it's the backmost piston and it's way under the cowl of this old car so I can see how they'd miss it changing lifters, even on an LS, if it was down in the bore at the time. Tiny piece too, and no damage to the bore other than they all seem awfully polished up.

[Wildkarde]

The ls engines especially the later ones, run pretty tight ring gaps. I think typical factory gap on the ls3 is .008-.012, doesn't take a lot of extra heat to make them expand too far.

[homemade87]

I have heard of this on the ls motors . Mostly on boosted engines . If the engine is sitting some what level the air can not escape the rear of the head unless it has the 4 corner steam vent . If the engine is at a 3 degree angle or more the air will migrate to the front steam lines and be removed . It could be the injector had a problem also . The # 7 is more prone to have problems for some reason and runs hotter .

Not to say this is or part of your problem , but may be something to consider if your engine is no at enough angle to remove the air from the rear of the head .