Yes most use a square drive. I have been but am switching to the round. I like the Acutec struts. The hole drive train is stronger and lighter than the square set up. When I did use the square I would make the shaft long enough to push on the engine ellimanting the need for thrust washers on the stub shaft. Worked really well. I only had the flywheel issue once. doing what I posted got rid of that problem. I generally turn down the flywheels anyway to lighten them up. The lighter they are the quicker the jump to max rpm. Less rotating mass = more hp.
Mike is correct. I noticed this several years back that the flywheel cone would wear into the inner race of the small bearing. There is very little clearance between the flywheel and crankcase. There are three options to fix this problem: (1) Releave flywheel on a lathe (2) Shim the flywheel cone between it and the bearing or (3) buy a new cone and change it after every other crank bearing change. Cones are cheap===$9.00
