Finally found out what was causing the engine 'knock'.... number 10 cylinder piston apparently broke which seems to have caused the rod to break right at the top of the crank journal end. No idea why this happened. It wasn't an oiling issue as the rod bearing actually looked pretty good. No signs of overheating due to lack of oiling. I'm thinking it may have dropped a valve or valve seat on startup which took out the piston which jammed everything up and snapped the rod. Crazy!
