Here you are kankel :-
A BELTING GOOD YARN
When I collected my 5 speeder from the dealer, a 2013 model, 2 years old with 635 miles on the clock, I was dismayed to hear a loud bang and a jerk when I pulled away hard. On returning to the dealer to complain it was explained to me that this was the belt jumping over the teeth and could be fixed right away with a turn or two on the rear wheel spindle adjusters. Sure enough, the problem went away - for a few miles.
Subsequent occurrences were easily fixed at home and the only worry was the frequency of the job. The more annoying symptom was the complete destruction of the aluminium rear sprocket after only 7,000 miles. Since dumping the problematic belt and replacing it with a chain didn't cure the problem, I started to look elsewhere and eventually discovered the cause to be in the flexible nature of the NVH kit. It was sometime later that I twigged that the reason the problem went away on tightening the belt, was that the belt itself is the third supporting member of the bevel box mounting system.
Anyway now to the purpose of this article - some clues on belt tensioning. Firstly, it should be noted that the rear wheel has to be aligned with belt tracking as the primary concern and little regard is to be given to alignment of the wheel with the chassis centre line. If vehicle centre alignment is too far out ( no idea of a limit for this but I feel that it is purely aesthetic ) then the left/right positioning of the swinging arm in the chassis must be addressed. Some help with this may be found here :-
http://www.bleazey.co.uk/M3W.html#swing. It should be understood that a belt will not track exactly the same on drive as it does on overrun so a happy mid position must be sought. In my case I used trial and error listening to the belt rubbing ( and eventually not rubbing ) on the side plates at the rear sprocket. People have used cameras to watch what is going on and I am sure this simplifies the issue greatly. Having got the required alignment and eliminated all,the nasty squealing, one needs a trick to keep it that way with not too much grief every time a tyre is changed or the wheel spindle moved for whatever reason. I have made a little wooden block which fits neatly between the wheel rim and the swinging arm at the front on the right hand side of the vehicle - a sort of feeler gauge. This can be used to ensure accurate alignment of the wheel whenever the spindle is moved.
If you have the NVH kit fitted then tightening the belt needs to be done so as to eliminate the violent up and down banging of the bevel box and no tighter. If your bevel box doesn't bang up and down you are very lucky and you should go to the next paragraph to see how tight the belt should be. If you have the original welded in mountings for the bevel box then the belt can be left much slacker which gives improved life of wheel bearings, belt and sprockets, swinging arm trunnions bearings and the output shaft bearing of the bevel box itself.
If you do not have the NVH kit fitted then proceed as follows :-The belt tension should be checked in the middle of the run ie. half way between the points where the belt leaves the sprockets. A spring balance and a piece of string looped round the belt will enable you to pull up or down on the belt with a load of 5 kg. this should give a deflection of 8mm. You can measure this with the aid of a straight edge with an 8 mm wooden block fixed on at each end. If the belt is too slack or too tight loosen the spindle nut after removing the split pin and then one flat at a time, and working evenly on each side of the machine, use the spindle jacking screws to move the wheel back to tighten - forward to loosen the belt. A final tension check should be carried out after the wheel spindle has been re tightened and the split pin replaced. There is little point in using a torque wrench to tighten the spindle nut because you have to get the castellations lined up with the hole for the split pin. What I do is to tighten the nut as tight as it will go with 500 mm of lever length ( if you think you can get it to the next notch then it wasn't tight enough! ) and then turn it back to the first available position where the pin will go through.
While under the vehicle ( with it safely supported on axle stands ) it is worth checking the belt condition. Turn the wheel while looking at the inner and outer faces of the belt, there should be no cracking or fraying fibres visible. A small chip out of a tooth, sometimes caused by stones getting between belt and sprocket is acceptable, as is a small puncture mark caused the same way. If there are multiple chips or punctures then you might consider a replacement belt but in any case remain vigilant and watch for deterioration. The teeth of the sprockets should be checked as well and you should expect to find well defined, undamaged teeth with no sharp edges or damage from stones etc.
A final tip is, whenever you remove the wheel spindle, clean it and replace it from right to left, leaving the spacer in the original position. The area of the spindle, where it sits in the brake drum, becomes dirty and sometimes a bit rusty, if the spindle is inserted from the left this dirty area has to be driven, forcibly through the wheel bearings to remove it - put it in from the right and only the clean, greased part of the spindle has to come out through the bearings.
Clunk click every trip guys - or is that another sort of belt?
PS. As to the crabbing effect of not aligning the rear wheel with the centre line of the vehicle - think sidecar outfit!
