I've got the dreaded absorber gear wheel (on the engine output shaft) rivet failure, so I'm going in to see if I can do something about it.

I'm up to removing the bell housing, almost. I've removed the clutch housing and then realised I needed it to clamp the engine in position with the help of a broom handle so I can loosen the bolt holding the alternator dog drive in. So I put clutch housing back on, tightened it back up with the big nut, spacer and o-ring, but when I try to loosen the nut on the dog drive the whole engine turns, even though the clutch housing is staying still.

What am I doing wrong? Any ideas?

The answer is to wedge something (in this case a spanner) between the dogwheel and an adjacent bell housing flange.

good find rickety ...lots o luck on the repair mate ...

use an air wrench to spin the nut off, it wont turn the motor.