I bent a rod on a 283 chevy when doing a start after a rebuild. Turned out the head gasket did not seal fully on one cylinder and radiator fluid (water in your case) got into the cylinder overnight. Of course, is was on the last of 8 cylinders to fire, so when physics took over ( water does NOT compress), the piston cycled up and bend the rod like a soft pretzel. Enough to have it knock against the bottom of the block.. Knocked like someone was whacking it with a sledge hammer.


Don't suppose you have a similar situation??

ps - new rod, no problems for many thousands of miles until the 57 got shortened by a drunk.