the 63 is up and running but with a noticable change since breakin. after a few hours on the motor I know have one or several tyapping noises much like a colapsed lifter. everything is brand new. the heads were milled and the crane roller rockers are 1.7 ratio. this coupled with the lift ont he 270 cam could be creating valve clearance problems in one or more cylinders. I can start by shimming the rockers. But why would the tapping start two or three hours after breakin and not be noticable at the start? Any other suggestions?