Whittle key stock to fit with a file. Height will be total depth of key way in
flywheel and crankshaft or slightly less. Length and profile will be file to fit.
As long as key ways ok this should work. KEY only locates relative position of
flywheel to crankshaft. The lock up of taper between flywheel and crankshaft
is created by proper torque of flywheel nut. Taper should not have any lube
as the lockup is between dry surfaces.
If taper surfaces are scored or uneven, they can be "lapped" to mesh using
valve grinding compound...a process requiring patience. Remove all traces of
grinding compound when done. Old school technique.
Do not over torque (splits hub) or under torque (tears up key)
In addition to being part of magneto ignition, the flywheel absorbs, stores and releases energy so power of engine is smoother. This means flywheel is under forces that
lead and follow the crankshaft...if flywheel torque is insufficient the key takes
a beating and may fail or batter the key ways in both crankshaft and flywheel
Windy,but, important details.
A small vise to hold key while filing is very helpful.