Oddjob

Unfortunately no fireworks to watch. We really were not immediately aware of what happened, just a thump noise and kind of a tug on the car. We both first thought it had blown a tire.

Couple pics of the head and oil pan (low res/quality - taken with a phone camera). Pics of the con-rod and block didnt turn out well enough to show very much. Cylinders 1-4 in sequence (#1 is the broken cylinder, #4 has the burned valve).

early85944

Wow and I thought my motor looked bad after it threw a rod

Oddjob

I will get some better pics of the piston, the girdle and the little selection of bits that used to be a connecting rod. I found the damge amazing/horrifying.

The wrist pin was basically pulled out of the piston, the piston skirts are mostly gone, about 2-3" of the rod is missing. The oil scrapper ring was imbedded down the side of the piston (the only place the skirt wasnt broken off). The piston itself was coined/deformed by being jacked into the cylinder at an angle.

What I find really amazing is that the engine still needed to be shut off - with #1 gone, and no compression on #4, it was still running on two cylinders...

JEC_31

Odd that the wristpin is pulled DOWN out of the piston. Usually it's smashed up through the top when the piston gets hammered downwards by the detonation much faster than the rod can move.

But all rules are off when the grenade goes off. Perhaps a detonation event broke the rings and jammed the piston in the bore, then the rod (with wristpin) tore down out of the piston and flailed itself to pieces in the resulting trainwreck -while the engine kept running (which is also shocking!).

CSI: 951 motors

tyro

Simply a guess on my part, but 1-3 look clean. Did you find any signs that coolant may have been in #1?

Oddjob

Yes, it is odd. The wrist pin busted out of the piston downward (which would indicate that the piston hungup on the downward stroke and the crank motion pulled the wrist pin through the stationary piston, also breaking the rod(?).

But, the oil scraper ring is imbedded in the piston skirt below the ring land, which indicates the piston was travelling upwards when it jacked and stuck in the bore. The upper rod section, still attached to the wrist pin, is bent/folded over.

Another unknown - one of the two rod nuts on the crank/rod cap was off. The nut was in the pan. The stud was intact, and the nut threads were ok (although the nut was squished), so it unscrewed itself.... ?

And where is the connection between this and the burned vavle? The two events had to be nearly simultaneous.

Oddjob

Our first thought when looking at the head and pistons, it was running very lean - but I wanted some more opinions.

The headgasket did not appear to show any leakage/burn marks on it. There was a little coolant that leaked out of the motor when it blew. A little coolant was in the oil puddle under the engine, and also on the belly pan. But I did not see where the water jacket had been cracked. No additional scoring in the bores - I would expect if there was enough coolant getting into the cylinders to cause serious damage, you would see some pretty rough scoring on the walls?

tyro

Not sure. True hydrolock in an engine is a violent end.

Let's just say a little coolant got in each cylinder, more in #1. Then what happens? I don't know.

Where were you on the track? Just though turn 3 if I remember right.