With the new motor the bike definitely ran better, vibrations were lower although the bike was still reluctant to move off and there was possibly a gear change issue. However rotating the rear wheel showed the there was a nasty grinding noise and an apparent wobble. All of this suggested that the rear wheel needs to come out for checking.
First step was to detach the rear brake actuating arm. Unscrew the adjuster and pull the rod out of the brake arm.
Remove and detach the rear brake torque arm by removing the split pin and nut.
Just to note the spacer fitted on the rhs of the bike between rear hub and swinging arm.
Loosen the rear axe- smaller nut
Using 2 spanners remove the nut from the rhs
Spacer and nut will drop off.
The axle can be tapped out towards the left. The wheel can then be pulled to the right and off the cush rubber sprocket carrier drive.
If using a bike stand you need to make sure the bike is far enough back to let the wheel drop out from under the mudguard. If not using a bike lift, then the bike will probably need to be raised using a block under the centre stand.
Having removed the wheel I reinserted the axle and tested the rotation out of the bike. The wheel appears to spin true so the explanation for the wobbling in position must lie elsewhere. I did find that the sprocket carrier was stiff and noisy to turn- grating on the chain covers. It was clearly necessary to remove the sprocket and the first step is to remove the chain covers. Each is only 2 screws and the upper lifts off first.
Note how the chain covers fit together, the upper cover clipping over the lower at front, rear and back.
The sprocket carrier is held by the 17mm hollow centre nut on the stub axle below the shock absorber.
Remove the chain by unfastening the split link. The sprocket carrier can be tapped out once the chain has been removed. The assembly was pretty solid and there was no rotation around the bearing. The sleeve penetrating the oil seal also seemed stuck
The sprocket carrier didnt look to be in great condition. I couldnt push the stub axle out so I used a press to push out the assembly. The oil seal came out first with ita centre piece. The seal had clearly failed and was split.
The sprocket carrier was full of shredded oil seal
... and the bearing was rusted onto the stub axle- there was no rotation the bearing was totally siezed. I tapped the bearing off the stub axle.
... and cleaned the components up.
Rebuilding
You will need a double-shielded bearing 6203 ZZ or drs and a 27x40x6 nitrile oil seal. Reassembly is pretty straight forward- tap the bearing onto the stub axle up to the ridge and then tap the assembly into the sprocket carrier hub. Take care you get it the right way round - the threaded part of the stub axle goes towards the outside. Lube the oil seal inner lip and slip it over the threaded part of the stub axle and tap it home. Insert the spacer disc.
I did all this but when I checked rotation by inserting the axle I was disappointed. I had expected a smooth and silent turn. Instead the wobble was still there accompanied by a grating sound. At this point examination showed that the stub axle had play inside the bearing so it would appear that running whilst siezed had worn the stub axle. I'll have to disassemble and rebuild with the new part. Note to self- probably best to always order a new stub axle when siezure is apparent.
Second note to self the new stub axle slipped in easily- possibly easier than the old, and showed just as much play inside the bearing as the old part. However when assembled with the axle and wheel there is little if any play in the wheel itself and it spins silently and freely. Ive concluded that a certain play between stub and sprocket carrier bearing is permissible.
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