i'm running two steel spur gears and two hardend and vented clutch bells and i run the piss out of them. one set of them is on the stock F4.1 and the other is on my K4.6HO and that motor is a torque monster. i had my 4.1 slide over (forgot to check bolts i felt like a retard) and loosen the mesh but didn't hurt the spur or the cb