[David2159]

Yes I have a service manual but it is not clear on this. How can I hold the sprocket still while unscrewing the bolts?

[Aspired]

Have you tried to use an air tool - usually that work since it spins it out before it turns it. Don't use an air rachet but a impact should do it if you can get at it safely.

Didi you remove the timing chain yet? That might hold enough tension also it you stuff it in gear and use a breaker bar and hit it quick.

Hope this help but be careful!

[toomuchtodofriday]

The lower cam mark has a 7mm allen wrench that holds the crank you just need someone to hold it or have the motor out of the frame when you do it, also works for re-assembily and remember loctite.