[rotorwrench]

My older brother pulled the heads off the motor in my old hand me down 1951 Merc back when he was in High School. He thought someone had sabotaged the motor by cramming it full of bailing wire and sand. It was just crap left over from the casting process at Ford. We took as much as we could get to out. I took the motor out not too long after that and did the usual tear down with a trip to the Redi-Strip shop. They had filters to catch the crap and protect his pump set up in the tank. He took more than a full size coffee can full of sand and core wire out of that block even after we had tried in vain to clean it. We had never had any trouble with overheating either. The guys on the vibrator table may have been in a hurry the day they shook the core material out of it back in 1950. From what I've seen, this is not all that unusual for an original block on the first overhaul.