Primary Chain tention

If the sleeve gear bushes are worn, then as you squeeze the top and bottom runs of the final drive chain, you will see the tension of the primary chain move through the inspection hole. There will always be some movement apparent. The tendency is for the gearbox to move backwards. The gearbox mounting bolts need to be done up to about 80 Ft/lbs (both of them) any less is not enough.

Can these bushes be changed by just removing the primary side?

No as the clutch needs to come off

How much of the gearbox needs removing to get the old bushes out?

Most of it, there won't be much left, the camplate can stay in and the camplate pivot.

This is more likely caused by you doing the tensioning sequence correctly, its in the manual but get it wrong and the first ride will get the gearbox being pulled backwards by the main chain as that exerts a greater force and a tight primary.

Tension is of course the wrong term - it should be slackness. Pedantry over. When adjusting the primary chain slackness, I place a boot hard on the rear chain to tension it. This will attempt to pull the gearbox backwards. I then adjust the primary chain slackness followed by the rear chain slackness. The primary chain will now maintain its set slackness, but it's always worth a further check after the first ride.

dear Peter,

We have all been here and majority have earned T-shirt.

Think of ot like this; Rear wheel adjusters job is to stop wheel moving forward, just like a bicycle, However gearbox adjusters job is to stop gearbox being pulled back - effectively it needs to be set pushing forwards taking up play in bolt holes etc which are currently allowing your gearbox to float. This is because final drive tension is much greater than primary tension when under load - all that mechanical advantage stuff.

So try Gordons method - With gearbox bolts just slack stand on lower run of rear chain to pull gearbox back, Tighten top gearbox bolt till it just bites, now use adjuster to push gearbox forwards till primary tension is ok. then big spanner tighten gearbox bolts, finally adjust rear wheel position if needed.

Have fun

Martin.

The key is in what Martin says, always finish the job by using the adjuster to push the gearbox forward so that when the back chain tries to move the gearbox back all the slack is already taken up.

I used to slightly overtighten the primary on my Commando to start with, then push it forward with the adjuster as described to get the right slack in the chain. It's the adjuster that keeps the 'box where it is and hence maintains slack, not the through bolt.

I can't agree with that Ian. The adjuster is to adjust the tension/slack and the grip of the top and bottom bolts clamping the gearbox is what holds it in that position. Once tight You could remove the adjuster and go without it. That is what the 75 Ft/Lbs is doing. Some people fit a second adjuster when fitting a belt drive. The issue here is that the belt drive is less tolerant of the two pulleys being out of alignment. Two adjusters allow for for more accurate alignment of the two pulleys. Peter's fix was to do the bolts up properly.

I'm not sure.... My understanding is that the bolt (and of course the bottom pivot, although that's less critical) needed to be tight in order to stop the gearbox twisting in the engine plates. Its function in stopping the box sliding backwards depends only on friction, whereas my method gives a proper location and stops all backwards movement.

I remember when I had my Commando (for 20 years) there being discussion about this in RH and elsewhere and ISTR (but am probably wrong) that it was Tim Stevens who explained all this.

Anyway, whatever works for you......