Engine block failure

I replaced the head gasket on a gen 3 about 2K miles ago. Yesterday, the block developed a serious crack...Maybe an inch wide near the water pump. Is there something that I might have gotten wrong during cylinder head installation to cause this. I'm pretty sure the bolt torque values and sequence was correct. The engine code originally was for cylinder 1 misfire although the problem only happened on early morning startups. Cylinder 1 also had some polishing on opposite sides while the 2, 3, and 4 had uniform cross hatching from the factory. I believe the original misfire was from coolant collecting in that cylinder. I'm wondering whether the coolant in the cylinder could cause an over pressure situation that would create a small crack...although I didn't notice any visible ones. Curiously, cylinder 1 had the best compression numbers.

 

There were no DTCs and it seemed to run normally. But, it did have pronounced polishing on opposite sides of the number 1 cylinder wall. I would think a bent connecting rod would cause that as well. Also, that cylinder had better compression than 2, 3, and 4. I will try to get pics. My belief is that the coolant was leaking into the cylinder during engine cool down. The amount of coolant deposited would vary depending on piston position after shut down.

 

The bolts last used were new from Felpro...installed and torqued only once. The engine block failed in the lower area near cylinder 1, between the dipstick and water pump. I don't see how previously torqued bolts or even overtorqued bolts would cause this. The idea of a bent rod from continued use after gasket failure...with the high pressure created on startup by coolant in a cylinder...seems much more likely. No coolant was lost in the several housand miles between head gasket replacement and block failure.

Bottom line is if I knew the vertical polishing in cylinder 1 was an indication of a bent rod, there's no way I would have put the engine back together without replacing the connecting rod. The bent rod theory also explains the increased compression in that cylinder before and after repair. Nothing related to the head can explain the two symptoms known before complete failure.

 

This is the front of the block looking down between dipstick and water pump. Dipstick is yellow out of focus near top.

 

I see where the confusion is. I did re-use one set of bolts on the advice of the Felpro tack people. The coolant accumulation was prior to my work on the car. Coolant lost after I worked on it went into the crankcase, not the cylinders. I didn't feel good about having reused the bolts but another issue came up when I failed to seal the coolant passage in the timing chain cover. Anyway, I installed a new bolt set after that. There was no coolant loss after I fixed the RTV problem in the timing cover and put the last new set of bolts in. However, I believe the connectingcylinder. Was present from start to finish based on the issues I mentioned earlier.

 

I used RTV Ultra Black on the water pump flange. The existing pump was reused. I might have put antiseize on the bolts but not sure on that.

 

It's not mine but I've been told that never happened. The failure was apparently quite sudden and it sounded like things were bouncing between the engine and the road surface.

I would imagine that the hydraulic pressure developed when coolant accumulated in an engine cylinder is compressed through the exhaust valves into the manifold is quite high. High enough to bend a rod and maybe even fatigue or crack the block. But, if that's what happened, there were no symptoms except for the increased compression in that cylinder and the vertical polishing on opposite sides of the cylinder walls.

This is the only motor I've seen with uniform compression across 3 cylinders and dramatically higher compression in 1 cylinder.