I doubt you'd crush the stem (or hub as maxtorque calls it in their partslist)
I haven't tried of course, but it's at least highly unlikely ...
I mean sure with a -what 16UNF?- thread you can add a metric ton of force and theoretically crush everything..
BUT if you're not getting a 3ft lever on the wrench locking the piston BTDC
I'd say you'd have a hard time trying to do so
Maxtorque SS clutches are no racing priced clutches (I paid 25 bucks)
and DO NOT have a built in key..
funny enough, I have it on my desk (since I lost the dang snapring )
litteraly within arm's reach at this very moment...
trust me.. no built in key, and it's certainly cheap (as in low price, not as in bad quality!!)
You're right.. ideal way of rotational locking is a cut keyway, no doubt about it!
but Honda Cranks I've seen have been hardened..
cutting a keyway will be quite a task in the homeshop.
slipping with the angle grinder and cutting into the crank case cover would be
way more hassle and way harder to fix than a slipping clutch stem because of a improper tightened nut, don't you think?
(especially since the key sit's inboard on an outboard mounted clutch.. close to the crankcase)
And if you remove the crankshaft to cut the keyway...
you could as well just replace it with a keyed 3/4" shaft replacing an hour of labour with ten bucks of monetary units
'sid