Inliners International Forums General Discussion Engines chevy 250 Smoking, can anyone help?

Hi there, i just bought a 64 chevy belair, somone put a later model 250-6 in the car, the motor runs very strong but i have a smoking problem!

I will start it up and it wont smoke until about 5 minutes after it warms up a little bit, then lets out a big cloud. then it will clear out and when i rev it up a bit, when i let off the gas it lets out a puff.

Or when im idling and nail the gas at take off it puffs a cloud too.

Its bright white smoke and smells like oil..
How can i tell if its valve seals or rings?

Again the motor runs strong, i would like to atleast get the summer out of the car, but it dosent look good,.
thanks for all your help!
Jason