hey erik: Forgot cam info, it's a stock replacement for a 283 power pack. (since this was a stock rebuild we went with a kit from federal mogul to keep it simple). On our other '57 we had a replica 270 hp dual four barrel 283. Went alot fancier with this one and it would pull 6000 rpm all day long. Our rod clearance on that one was .012. From other builders, it seems most feel .010-.012 for a bone stock motor is fine. I do agree with you that when you get into heavy hot rodding that you may want to change clearances around to suit that particular build up. I've heard of alot of crazy clearances that seem to work for people. By the way the crank and rods were checked by two different machinists. I'm not a professional builder so I asked for alot of help on the second rebuild. That's why this problem is so frustrating. (I'm not the sole person rebuilding it, and it still smokes!). this problem has begun to stump our best mechanics and machinists in our town. I didn't have the guage to do a correct leak down test, so today mike lent me his guage for the test because he's dying to know what it is too. (Mike and the shop he works at are excellent on figuring out the wierd problems people have with cars). Not a problem, but Mike told me years ago a lady had an idler arm replaced on her car and came back mad because her engine wouldn't idle right! The shop I guess had a heck of a time explaining it to the lady. Later