Bad starter clutch.. nope just a loose alternator rotor bolt?

[Guest]

My 1978 GS750 seemed to have a bad starter clutch...

But once I pulled the alternator cover, i noticed the alternator rotor bolt (which goes into the crank) was suspiciously loose, and the clutch seemed ok.

So I pulled the alternator rotor off to see how things look, and the clutch looks good, but it looks like the alternator rotor was slipping on the shaft because I saw some scoring and some very fine metal between the surfaces.

So my questions is this:

Why is the shaft/rotor not keyed to prevent the rotor from slipping on the shaft?

Is it simply a friction fit which depends on the rotor bolt which must be tight?
Why did mine loosen up suddenly?

Do I just torque it down with some lock tight and a nice lock washer and expect it to be fixed?

[GregT]

In sequence...
Because the rotor position on the crank isn't critical it doesn't need a key.
Yes, a taper shaft which is done up tight can transmit much more force than required here.
It happens...hot/cold changes, a sudden deceleration...
No lock washer, Loctite only on the outer - head - end portion of the threads. And use a rattle gun if you have access to one.

I say Loctite only on the outer - head- end portion of the threads. Anyone who has tried to remove a rotor bolt where there is excessive loctite set inside the hollow shaft will understand why...The bolt is longer than required and loctite on the inner disengaged threads simply won't wind out.

[dano]

Ok, thanks for the thoughts GregT.

I hadn't considered how the taper factored in, but now I see how that would increase the force between the mating surfaces and prevent slippage.
Thanks for the tips on the Loctite as well.