06 Yz 450 post rebuild ?'s

So I just had the bike apart all summer. I had to do a complete motor rebuild, and now that the top end is clacking( it kinda sounds like piston slap in an old 2 stroke) when it is at idle but as soon as it is under load it is going away. I have run the motor for only 15 min and then this sound started. So I promptly shut it down and had it pulled apart to investigate. Now the bike is back together and the sound was gone until it had run in for another 5 min of run time. Any ideas or similar experiences ? Thanks for your input.....:thumbsup:

I had this problem with my YZ250, the power was good but clacked really bad at idle. It was the lower rod bearing. I replaced with new wiseco crank set.

It turned out to be the wrist pin circlip was not getting seated correctly and was causing the piston to make the noise......

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