After waiting 2 weeks for a .3 mm crank shim. I'm finally on to the build. One thing I was glad I checked was the water pump impeller clearance. It was slightly proud and touching the outer case half. There were minor scuff marks from before, and looked like the aluminium ridged up on the case a bit. So i took emery cloth and blended it back down. There were marks on the impeller as well. From what I see, it looks like the engine momentarily locked up. (the bad crank bearings from the previous owner.) And the counter balance shaft was thrust forth, (Due to the way the gears mesh. From the cbs's ((counter balance shafts)) centrifugal inertia.) Therefor the impeller was shoved into the outer case impeller housing. After all, the only thing retaining the bearing on the counterbalance shaft is that flimsy stamped steel bearing retainer plate. So one would surmise, that such a scenario, (bad crank bearings, or even a blown top end) could lead to other catastrophic failures that are left undetected, just waiting to rear its ugly head. Just an FYI
No this did not happen here, but for someone that blew a top end? You might want to dig deeper into your top end failure.

 

I've seen my share of blow 350/400 engines over the years but not to the extent that the counter balancer had shifted.Never had a bent retainer plate holding the counter balance in place. If anything the counter balancer gear could possibly move a little under force or shock since it's pressed on but the rest of the body and shaft would be intact and in place.Problem on the water pump cavity could be that it could move inward or outward because of that small single bearing if the 4 nuts holding the water pump housing in place were not fully tightened. That could cause it to suck in air causing excessive heat and cavitation.Anyone that just does a top end takes a big chance on the 350/400 engines and I wouldn't guarantee a partial rebuild at the shop. Way too may parts that could wear and need to be addressed beside the three cranks bearings,rod,lower rod bearing and crank seals.