So i was cleaning out the engine that i had just bought off a guy on this site. The engine seem to flow very smoothly and with out any problem. I took out the sleeve and Pistion to make sure there was no damage and put it all back together. The problem that i am having is when hits dead top center there seems to be slack. The rod seems to click before the piston goes back down. Is this normal or should the engine be flowing smoothing through the whole process. It does it will the head on, with the head off or will glow plug in.

PLEASEHELP.......

THANKS