ET: Engine (Twin) Kick Start Indexing Problem

G.L. Winter

Forum User
VOC Member
My series B Rapide tends to jam from time to time at the initiation of the kick start down stroke. I fit a new kick start quadrant and ratchet pinion (G82 and G46AS) supplied by The Vincent Spares Company, but the problem persists. Does anyone have a suggestion? Thank you in advance for your kind help.
 

Martyn Goodwin

Well Known and Active Forum User
Non-VOC Member
From OVR 33:
Often one reads about the need to “file” the lead tooth on a Kick Starter quadrant to avoid the dreaded “locking” of the kick starter. Attempting to force the kick starter once locked may result in damage to the kick start shaft, the kick start quadrant, the driven pinion, the rider’s foot or the rider’s leg – and any one or any combination of damaged items is possible.

Once the kick starter becomes locked the accepted release technique is to engage a gear then rock the bike back n forth till the kick starter becomes free, then gearbox back into neutral and try the kick starter again.

The attached picture is a close up of the lead in tooth on one quadrant superimposed over another quadrant clearly showing how it needs to be shaped. Note that its top surface slopes slightly towards the valley of the first “full” tooth.

In order to provide the best opportunity for smooth engagement between the kick start quadrant and the kick start driven pinion it is advisable to polish the lead in tooth, especially its upper surface.

There is also real benefit to be gained if the tip of each tooth on the engaged pinion is also polished.
25795
 

G.L. Winter

Forum User
VOC Member
Thank you, sir, for your prompt and informative reply. It seems that my problem is not altogether unheard of. The picture, as always, is worth a thousand words. Quite a bit of metal removed from that lead tooth! I'll put the quadrant on the milling machine and have a go. One wonders why they aren't supplied with that profile in the first place?
 

fogrider

Well Known and Active Forum User
VOC Member
I made a test jig to see what was going on. If you file the first tooth, what will stop it jamming on the second tooth? It appeared to me from the jig that, if there is 10 thou wear on each of the two shafts and bushes involved, the teeth can jam. The cure, add 25 thou to the tip of the first tooth, that leads the engagement .
No, I haven't tried it on the bike yet, but it works in the jig based on accurately machined shaft centres.
 

oexing

Well Known and Active Forum User
VOC Member
A Vincent is not anything special in this matter, you find same kickstart gear on any other bike. Trick is to grind the first tooth to half its height so it will just wipe over the first tooth on the small gear to engage in the second and move that so much so the second full tooth will do as it is meant to. No polish or funny shape is required, just half size.

Vic
 

fogrider

Well Known and Active Forum User
VOC Member
That seems to be the normal theory, but if you cut half the first tooth away, it misses, you might as well cut the whole tooth off !
I will do my 'add 25 thou ' mod this year, I'm sure the total wear on the small gear, the quadrant , the two shafts and the bushes, is what's behind the problem. If all dimensions were perfect, 'jamming' should not happen, the first tooth just touches and makes the second one fully engage.
Terry
 

oexing

Well Known and Active Forum User
VOC Member
I cannot provide a good photo of kickstart gears for the moment, but half size first teeth are the norm for a reason. Anyway, don´t you see a situation when first tooth exactly meets its top with top of one tooth of the gear ? In just that position the mechanism jams no matter what you try. So to fight this effect you grind the first tooth down to half size.
Will try to do a picture.

Vic
 

fogrider

Well Known and Active Forum User
VOC Member
I understand what you're saying Vic , the teeth do sometimes happen to meet point to point exactly, jamming up. What I'm suggesting is that if the first tooth was 25thou taller, it could not jam in the first place, would start normal engagement which then takes up fully from the second tooth onwards.
I will do that mod , something to gain (maybe), nothing to lose !
Regards, Terry.
 

oexing

Well Known and Active Forum User
VOC Member
Terry,
you cannot have one tooth higher, it will jam in the gear afterwards in the bottom . I did some tests tonight but the battery is low in the camera. Wait a little, I´ll post more photos.

Vic
 

oexing

Well Known and Active Forum User
VOC Member
So I had a close look at what a different first tooth height will do to the jamming problem. I reduced the tooth in a few steps but this did not totally prevent the jamming. Seems the top on top tooth situation can happen at all sizes. I came to my conclusion that the best and safest way to get only very rarely any jamming condition is to modify all teeth on the small gear for very pointy tops and same goes for the first one or two teeth on the quadrant. As you can see in my Youtube clip below you have to very carefully set the pair of gears so they do meet head on head but this should be a rare case. I searched my stock of kickstart sets from various other types and most of them do have the pointy teeth that prevent blocked gears when working with same pointy first tooth on the quadrant. In the photo you see a new gear from the Spares Co. next to my reworked "pointy" gear, a carbide burr in the Dremel and diamond file did it last night. My old quadrant will get some welding at the first tooth for the pointy shape so this should do like in the video hopefully.
Great to have this forum as I did not think about this matter before but when checking my Argentinian box of parts I could see that there is a job waiting before problems only show after bringing the bikes on the road.

Vic

Youtube clip kickstart gear test:

BMW gear box:
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26237


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Vincent gear modified rear :
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