There was a service bulletin to the effect that the flywheel on the small keyed 40 horse was made with a slight difference in the taper and those models should not be lapped. It explained that the key was only their to locate the flywheel and said flywheel was held in place by the hub gripping the shaft when the proper 105 foot pounds of torque is applied by the flywheel nut. If less torque is used the key will shear requiring the flywheel and crankshaft be replaced. That said, i have lapped a few, but was careful to use more lapping compound on the upper part of the taper.
