After just completing the Essex/Herts Air ambulance run of 132 miles on my 1970 Thunderbolt. In the last 20 miles when I changed from 4th to 3rd the lever didn't spring back into central position. If I touch it with my foot it centralised. It was ok 3rd to 2nd etc and also no problem changing up through the gears, any ideas?
The return spring is probably cracked or broken or may need adjusting. It happens a lot. Take the outer cover off and take a look. If there is evidence of it being mis-shapen or cracked, it will be obvious. If it needs adjusting then one of the legs will be standing off the pressed steel cup. This cup has a bolt hole in the centre which is eccentric to the outer dia. Just slacken off the screw and turn it until both legs touch.
Good luck
Chris
Thanks for the reply and advice. I have ordered a new spring from Draganfly although the old one looks okay. I will fit that first if it remains the same I will try your suggestion.
Many thanks again.
The spring arrived today from Draganfly and is different to the fitted to my bike, any ideas?
Picture attached.
Hi,
The gear change spring changed in 1966 from 68-3084 to 68-3125, both 2 coil.
Later years 1970 on, had the 57-4009, 3 coil.
https://www.draganfly.co.uk/bantam/product/11262-gear-change-return-spring/category_pathway-1423
Draganfly A65 year index doesn't show the correct spring but if you use the above link it states A65 A50 1970 on.
I have the 2 coil fitted to mine without issues. Also your model might be a year before the adjuster was introduced, but if you have one fitted it maybe worth trying to adjust.
A couple of things to check. Primary chain tension, after prolong use the hot engine reduces tolerances and gear change can be a problem, check the chain throughout its rotation for tight spots. The gear change quadrant shaft for wear on the inner bearing surface, wear here effects the selection.
Best wishes...
Many thanks for for your help and information. I will order the right spring now. I have the later clutch system so cannot fit the two coil spring as it fouls it. I will have another look. I was stuck in traffic going into Harwich for probably 30 mins or so after a non stop 60 mile plus run so it was probably running pretty hot.
New 3 coil spring now ordered!
I think I have found the problem. I decided to take the inner case off to expose the gear change mechanism and found the small screw which holds the retaining plate for the plungers to be loose. Allowing the plungers to protrude further than normal. I need a new kick start pinion but everything else looks good.