[prateroad]

Old thread but I bought a 71 C50 someone had put a 400 smallblock in it. It sounded good running but when I timed it right, it started knocking. PO had retarded timing so it would labor and not knock for the sale. I thought it was a 350 until further investigation verified the 400 which is externally balanced by the front damper and the flywheel. I don't think GM made a flywheel for a 400 in a medium duty truck. It was shaking itself apart, I do believe. Put a 350 in it. Also found out on another C50 that you shoudn't use a regular pickup 350 engine for a C50 because it doesn't have the steel crank. That big flywheel and the torque load put on it broke the crank just inside the engine at the last journal. Might save someone some headache knowing what I didn't know then.