I fitted a nice rebuilt engine today, all went well, fired up after a few turns and idled no probs, really quiet and smooth....
After a few mins of running top end starts knocking really loudly, like when you've just fitted a new set of lifters and they havent filled with oil yet.

Doesnt really do it on idle (but you can tell the sound is there), more when you accelerate and back off.
The car runs fine other than this, so I cant figure it??!!

Needles to say after 2 miles of it not quietening down it's back on the drive, didnt want to risk anymore running like this.

Engine has done about 600 miles since the full rebuild, only parts that were not changed where crank, rods & pistons everything else is new!

Any ideas?