Good old fitting skills or using a file carefully, and then fine sandpaper.
Don’t just file to tolerance and then sand, as more likely than not, you will end up with a clearance fit!
Leave at least 10-15 thou on the key before sanding.
Still used loctite 660 (shake before use) and primer 7240.

If the key gets badly galled, then it is too tight; the use of ‘engineers blue’ will also help highlight any high spots, on the key or keyway.
Also check gear keyways as well as the crankshaft keyway for damage, you may need to lightly deburr the edges, with a grinding stone, but don’t take masses off as this results in reducing the key contact area, and increases point loading.
The crankshaft keyway can be lightly cleaned with a diamond burr; again don’t go mad.

The sanding of the key will help to reduce the likelyhood of galling when placing gears over shaft with key fitted.
Either use standard key steel or 316 (A4) stainless steel.
Filing stainless, do this carefully if using stainless as the key will work harden, then filing will become substantially more difficult.

With either key steel or stainless key steel, use a hack saw and files DO NOT USE POWER TOOLS, except if using a milling machine / lathe, as this uses cold cutting.
Hot cutting will end up work hardening the steel and causing embrittlement.
De-stressing stainless is an arduous task.

Keysteel (mild) can be bought on Amazon and Stainless / mild on eBay, in 6” or 12” lengths.
Not the cheapest, but I don’t have room for a 6m length of keysteel in the house!
Ideally buy 8x7mm key steel, otherwise just get 8x8mm.


>>Make sure the surfaces are clean after you have checked transition clearance fitment.

>>Apply primer to both surfaces and allow to dry (key and key way; and keyway in gears if necessary)

>>Apply loctite 660 (after shaking) to key and keyway (and keyways in gears if necessary).

>>Then fit lockwasher and torque up crankshaft nut to 120Nm.