A friend had 39 Merc, took the car to a small garage to rebuild the engine, they brought the block to another shop to be bore, the block had tin sleeves, that shop was'nt to bright, they started to bore with a boring bar, the chips came out with a long string, so they honed the .040 thick sleeves with a Sunnen CK10 automatic honing machine to .030. The engine had the iron piston, they replaced them with heavy aluminum pistons. The first small shop built the engine and installed them in 39 Merc, it run good but had a vibration, they asked me to lissen to it, I told them at this point I'd pull the Clutch and PP and have check it for balance, the balance good so they stripped the engine, and had it all balance, the balance man had to do alot to the crank on account the aluminum pistons was alot heaver than steel pistons. Walt