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C: Clutch C45 Clutch Nut Lock Spring

Peter Holmes

Well Known and Active Website User
VOC Member
For not the first time in my years of Vincent ownership I have suffered failure of the C45 locking tang, self evident when the C20 clutch retaining nut unscrews itself and the handlebar clutch lever gradually ceases to disengage the clutch, this normally happens at the most inconvenient time and place, the time before yesterday in the middle of Dartmoor, thankfully yesterday it occurred very close to home, it is in reality a fairly easy fix, even at the side of the road, if you have the required tools and a spare spring, even if you don't have a spring you can simply bend another tang onto the old spring to get you out of trouble. (thanks for the tip Marcus)

But why does this happen repeatedly, am I the only person this happens to, I try to always use a new replacement Club Spares spring, I always do the C20 nut up FT, always to next available slot, no matter how hard it is to get it there, I never back off to the previous slot, the spring always breaks at the weakest point, on the 90 degree bend, my question is, is there a better engineering solution than the one currently used, other than resorting to one of the Loctite products, has anyone managed to make a flat plate key to lock the two slots rather than the rather flimsy spring, and if so how have they retained the key to keep it in place.

I now carry a spare spring and tools to carry out a roadside repair, but I don't really think it should ever be necessary if there was a decent engineering solution to locking the C20 nut in position.
 
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b'knighted

Well Known and Active Website User
VOC Member
You must be the only rider with a problem. Everyone else either doesn’t use their bikes as much as you or uses the modern solution to everything - Loctite, before parking their ornamental bikes indoors.
 

b'knighted

Well Known and Active Website User
VOC Member
On a more serious level, do you find that new springs last longer than rebent roadside repair springs. If so the difference may be relating to heat treatment during manufacture. Another possible difference between your bike and others may be point loading on the spring bend by sharp corners of the slots. Would breaking the slot edges increase spring life?
 

Peter Holmes

Well Known and Active Website User
VOC Member
I always use a new spring as a permanent fix as opposed to a re-bent spring, the re-bent spring is for emergency use only, but my experience is that a new spring is no guarantee of longevity, your suggestion about breaking sharp corners might be a good one to try, but I don't think that is the problem, although the C20 that I am currently using is a Maughan product, very precision machined, a thing of beauty, sharp corners everywhere, but I don't think any C20s that I have seen in the past have had the slot corners broken.
I would have expected the spring to be guillotined on the shear line between the gearbox shaft and the C20 nut, but that is not the case, the little bent tang just breaks off the spring, and then it is just a matter of time before you say to yourself "Hmm that don't feel right" when pulling in the clutch lever.
 
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Trickymicky

Active Website User
VOC Member
I'd have thought that the only thing that could un do the C20 is the chainwheel bushes picking up on it. It there enough clearance? It's a substantial item, but i read somewhere that if the C20 is tightened to excess, it can become barrel shaped, or swell. This would reduce the clearance.
 

timetraveller

Well Known and Active Website User
VOC Member
When it has happened to me I have re-bent a tang with a larger radius to the bend to reduce the stresses on that bend. It is tricky to get the bend sharp enough to fit and not so sharp that it fails but that has worked for me. Buy a new spring :eek: I was born in Yorkshire.
 

greg brillus

Well Known and Active Website User
VOC Member
I've found it happens if there is any backlash play from the C3 shoe carrier and the input shaft, just like an output sprocket nut will come loose if the sprocket is not a size for size fit on the output shaft..........only one cure for that really............
 

Peter Holmes

Well Known and Active Website User
VOC Member
I've found it happens if there is any backlash play from the C3 shoe carrier and the input shaft, just like an output sprocket nut will come loose if the sprocket is not a size for size fit on the output shaft..........only one cure for that really............
I tend to agree with you Greg, although I have not investigated your theory yet, my bike runs so well, and has done so since Tony Maughan rebuilt the engine many years ago, I am very reluctant to disturb things.
What I am tempted to try is to make a Woodruff type key out of the correct thickness stainless steel that will sit in the appropriate slot locking the C20 nut to the shaft, but have the key standing proud of the C20 hexagon flat, use the standard spring with a shortened tang to locate in one of the other C20 slots, then cut a slot in newly made key for the spring wire to locate into, thereby holding the key in place fore and aft, the bottom of the key could rest on the clutch pushrod for stabilisation, it should not matter whether the pushrod is stationary or rotating. It is one last thing to try, I am not really changing anything mechanically, although I might lengthen the appropriate C20 slot a little deeper into the threaded portion for better location.
Does anyone know the precise width of the slot machined into the gearbox shaft, the springs I have to hand micrometer up at .047 thou = 3/64" I would imagine the machined slots are a little wider, perhaps when the pilot clutch is stripped out I will have to feeler gauge it.
I am not an engineer, and don't purport to be one, but do any of you guys out there that know far more than I have a view on this experiment, will it work, could it work, is it flirting with danger, what would the best material to fabricate my key from, I have suggested stainless steel for no real reason, it just seems to be tougher material than mild steel, I have a friend that could probably knock me one up in titanium, but is that a more suitable material.
Any suggestions that save me changing gearbox shaft and clutch shoe carrier would be greatly appreciated.
 
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Bill Thomas

Well Known and Active Website User
VOC Member
I would be more worried about a worn out washer E76,
If the Nut has been loose the washer spins and wears out,
Letting 4 th gear not to be in full mesh with the double gear,
We did Terry Wordinghams and found just a tiny ring , In stead of a washer,
The ring was so hard to see, Somebody fitted a new E76,
But the Bike was not run till we got hold of it !,
Which took all the free play out of the main shaft,
Lucky I always give the shaft a push pull , And found NO play !, So we stripped it out.

Love posting Trev's gearbox photo !.
 

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Peter Holmes

Well Known and Active Website User
VOC Member
I always run with a magnetic drain plug fitted, it is great for checking for ferrous metal debris, I am sure that if a washer had eaten itself away I would know, and my gears selection and continuous engagement is also very good, the only real problem I have is engaging first gear on an uphill incline, but that problem is a well known by product of the Grossett electric start sprag clutch.
 
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