Rear Wheel and Sprocket Carrier

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.

Removing the motor

Well it pains me to say this, but even after all my efforts, this bike still runs like a bag of nails. It's quite hard to start requiring several kicks before it will run on smoothly and when it's cold at least, acceleration is very poor. I had always attributed this to a fuel supply problem or possibly a carburettor blockage. However, I changed the carburettor with it's integral fuel tap and fuel is flowing freely. I have also put in new jets, larger than those which were supplied with a pit bike carburettor and equivalent to those fitted in the usual Keihin unit. This hasn't helped. I've changed plug, I've changed the the coil, the CDI unit and the HT cap and none of this has really solved the problem. Certainly the bike is running better than when I first obtained it but equally certainly it's still not running correctly. Perhaps the most annoying feature is that it's got an awful lot of vibration and the top end is noisy. Since I am confident I have now dealt with all of the extraneous problems which might have lurked in the peripheral systems, I am now forced to consider that there may be something wrong with the motor itself. I know compression is fine, but some of the noise from the top end could be a rattling camchain. As adjustment on this bike is entirely automatic, this could mean that camchain is nearing the end of its life. It might have skipped a tooth or maybe replaced wrongly after a previous rebuild upsetting the valve timing. This might also account for the poor starting, poor power and excessive vibration. In any event it's looking to me like I need to do a top end strip to swap the camchain and ensure it's set correctly. I'd also like to remove the barrel and check the little end in case the tapping I'm hearing comes from there. 

Hopefully as a shortcut, I bought a used motor to compare with my horrible vibrating machine. Its in worse condition than my own externally, and compression is low too- but if it runs I can see if it has the same vibration and then probably "mix and match" to get one functional unit- either putting the crank from this one into my own, or swapping the piston, barrel and possibly the head onto this replacement bottom end?

The first step is to see if this one runs and that means fitting it. Its also necessary to remove my own motor if I'm going to swap its innards, so whichever way you look at it- removal is the first step.

Replacement motor- bought second hand- turns over but beyond that condition is unknown.

I removed the gear change lever

... and turned to the opposite side to remove the exhaust.

 I removed the exhaust mounting flange nuts from their studs.

And also the exhaust hanger from the frame. 

So that the exhaust could be finagled out.

I removed the bolts holding the carb inlet tube to the barrel as I'm leaving the carb in place. There seemed to be no gasket under this.

Turning to the opposite side I removed the sprocket cover (2 bolts only)

Followed by the sprocket retaining plate

 

Plate and bolts removed

I could then lift the sprocket and chain to one side. Note to self- this oil seal did require replacement so if working on this motor then this will need to be done.

I decided that I should remove the alternator cover to give more room - and because I may need to fit this to the replacement motor (see on). I disconnected the mysterious sprung push connection from the rear of the alternator cover to the body (neutral inicator switch)

... and disconnected the battery at the earth terminal.

I unclipped the HT lead from its clip on the barrel as this will also stay with the bike.

Unclipping HT lead

The carburettor drain hose is clipped to the motor so I slipped this off the carburettor spigot

Carb drain hose slipped off carb spigot.

The rear brake lever is spring mounted with its return spring attached to the nipple-shaped end of one of the rear motor-retaining bolt- so I unclipped this.

Rear brake pedal spring (large) and rear brake light switch spring (smaller) attached to the frame. Note the pedal return spring attaches to the nipple-shaped end of the rear engine mounting bolt. 

Pedal return spring removed-

Identify the opposite end of this bolt (situated above and to the rear of the  final drive sprocket and fit a socket on that. Use a spanner to hold the nipple-bolt whilst loosening the opposite side.

Holding the nipple bolt whilst the bolt itself is undone from the opposite side.

And remove the nut and washer from the rhs of the bike.

Nut and washer removed from the rhs.

The upper mounting bolt doubles as the leg-shield retainer so remove the chromed dome nuts and leg-shield mounting plates- and then unscrew the mounting bolt itself from the rhs.

Nut unscrewed from upper engine mounting bolt

You can then tap the upper bolt through towards the lhs, and let the motor drop- pivoting around the rear bolt.  I placed some wooden packing underneath. You can then tap out the rear bolt itself.

Tapping out rear mounting bolt.

The motor can then drop free of the frame.

At this stage I found a couple of wiring connections that I should have disconnected first- luckily the wooden packing prevented the motor from dropping too far and so none of these connections were strained. 

Firstly this bike has a separate dedicated green wire earth connection for the starter motor. This isn't shown on the wiring diagrams but it attaches to the back of the starter motor itself.

Green starter earth wire

This was removed by unscrewing one of the starter bolts 

Green starter motor earth disconnected at the eye terminal.

Secondly there is a black PVC-coated wire bundle emerging from the alternator cover.

Alternator cover connecting wire bundle.

On this bike the black pvc coated wire bundle from the alternator cover terminates in a multiplug. The metal wire harness clip can be bent back and released allowing the multiplug to be unclipped.

Unclipped.

Unclipping the alternator cover connecting mutiplug- note the black wire with its bullet connector situated alongside and behind. Behind this black wire you can also just see the starter motor 2-pin multiplug which also requires disconnection- see on.

There is also a black wire bullet connection which needs to be unpopped before the alternator cover is free.

Alternator cover connections unclipped- the alternator cover is now free to be removed.

Finally, there is also a second, 2-pin multiplug connection at the same point in the frame which runs to the starter motor itself and which is just visible in the picture above- this also has to be unclipped to allow the motor to come out of the frame.

Overall there are a few obvious wiring differences between the new and old bike motors. Unfortunately none of these are identified on the wiring diagram I have from the Haynes manual. 

Firstly- the separate green-wire earth for the starter has already been mentioned. The older motor relied on engine crankcase connections for this earth path. The green wire is simple to reinstate and should present no problems. 

The starter on my bike is also connected via a 2-pin multiplug (again not shown in the diagrams) whereas the older motor has only a single pin inside the plug (see below). Obviously, this will not connect to a 2-pin fastener in the bike when I install the older motor and so I'll need to investigate what these extra wires are actually for.

Starter motor single pin connector on the older replacement motor

There are also differences in the alternator cover plate connections- The older bike has 6 spade connectors ...

Older motor to be fitted as replacement- alternator output plate consists of 6 spade connections- as shown in the wiring diagram

Whereas the newer motor as fitted to the bike  has a 4 point multiplug and a separate black wire -not shown in the wiring diagram.

Connections from alternator cover on the newer motor

Currently, I'm not sure why this bike has only 5 wires whereas the older motor had 6, but I'll compare the colours and try and identify the functions of each wire. I'm expecting to simply swap the alternator cover onto the replacement motor but Id like to check function first. Similarly I need to check the connections to the starter motor as described above.

Replacement

I wanted to install the older motor which will necessitate a few wiring adjustments after the motor is physically installed. Install is straight forward but it is a 2- person job- one to raise and position the motor (use wooden blocks to assist raising) and a second to stand by with a podger to ease alignment of the frame  and engine mounting points. Doing it alone is very difficult!

Note there- the mounting bolts M8 (both of them) seemed smaller than the mounting holes in the motor. I will check but the concensus is that these should be M8- mine may be too small or the mounting holes too large.

Having refitted the motor I reattached the ancilliaries. The carb intake tube turned out to have an O ring on the base explaining why there was no gasket. However this O ring was clearly flattened beyond the level of the surfaces and sealing nothing. An air leak here could be one explanation for the lack of power and perhaps the vibration? The O ring is actually a square section but I couldnt find one so fitted a round section of similar size. This did lift the intake tube a little but everything fitted and Im sure its now better sealed.

I needed to sort out the wiring to make the motor connect to the bike. I had intended to simply swap the alternator cover but a comparison showed that these differed internally in their coil arrangement. This meant that the later (more complex) generator coils couldnt fit  onto the older style motor. Accordingly I refitted the older cover and made up adaptor wires to link the spade connectors to the multiplug terminals individually.

Adapter leads made up- spade to pin spade rather than multiplug. Note the earth wire now unused since an additional earth has been run directly to the starter motor. I will probably connect it to earth anyway.

The starter motor leads could simply be swapped once the rubber foot cover was peeled back. This allowed me to fit the newer style 2 pin plug to the older cover. I could then connect the extra earth wire to the rear of the starter motor.

The kickstart shafts also differed between the bikes- the later bike requiring the offset shaft to clear the exhaust hanger bolt so this was also swapped over.

All changed and connected up - and to my surprise the motor started very easily and certainly runs with lower vibration. Im sure the low compression means that there is a lack of power, but there is still more usable power than the previous motor.