knock,knock who's there?

[bwanacandu]

okay, i'm stumped. bought a dupor, flat top piston, installed my used arc rod w/new bearing, fly wheel, 18lb springs,jet,etc. when i spin the engine by hand(without the plug,of course), i have a knock. pulled the head- off-no knock. it appears to be coming from the vacinity of the cam,i think. any thoughts on this?could it be(hopefully) lash between cam gear and crank gear? help a dummy out,huh?

 

[minidragbike]

If nothing is hitting it could be the compression release on the lobe and lifter contact. This is just a guess unless I had it in my own hands.