Originally Posted by 1QwkSport2.5r

You will likely need to remove the prop driver and manically push the collet up against the front bearing. I had a flywheel come loose on a Picco buggy engine that wouldn't tighten up (had the same axial movement in/out as you describe) just by tightening the crankshaft nut. I had to remove the flywheel and collet and re-set the collet. Pulling on the crank when putting the collet on works best.