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Burman Gear box input shaft

derek

Well Known and Active Website User
VOC Member
The input shaft (clutch shaft). How is this firmly held? If the nut on the free end is tightened, it clamps the 3rd gear pinion to the ball race hence making the shaft hard to turn. The drawing showes a distance piece on this input shaft at the clutch end, bearing on the output shaft end. This woud stop the third gear pinion being trapped! But! If the nut is then tightened, the input shaft is locked against the distance piece?
As I see it the only way for the box to work correctly, is for the nut not to be fully tightened, being put on with locktight! but is this good engineering and is it possible that the nut will slacken off???
 

nkt267

Well Known and Active Website User
VOC Member
I think your problem may lie at the kickstart ratchet end.The spacer that the spring goes around and that the ratchet pivots on is the only part that limits the end float in the mainshaft.Check the spline at the ratchet end if it is worn then the fixed part of the ratchet may pull further down the mainshaft when the nut is tightened and lock the shaft.I had a problem with excessive end float and overshimmed the spacer and that locked the mainshaft..If I can find a spare one I'll measure it and post the dimensions on the Forum..You may have to get the spacer shortened..John
 

Len Matthews

Well Known and Active Website User
VOC Member
Good advice John. The nut that secures the K/S ratchet must be tight. I went to the TT once with a Comet owner who had that nut unscrew which meant his clutch was inoperable because the mainshaft complete with clutch slid sideways. In other words, the lateral location of the whole assembly is dependent on that ratchet nut.
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
The top hat shaped steel bush (PR39BA) on which the ratchet (PR38BA and spring) spins measures 0.814 inches on my gearbox. The end float is too much and I'm hoping it will decrease enough when I add the gasket to the inner case joint. Otherwise a shim will be needed.

The main shaft nut tightens aginst the driven ratchet and the spline ends and is a rather hit and miss affair......not too clever in my humble opinion. I think Triumph gearboxes add a lock washer.

Vic Youel

(vicyouel on Skype if anyone wants to video conference)_
 

nkt267

Well Known and Active Website User
VOC Member
Hi Vic.I always thought there should be a lock washer on the nut.I have found a couple of Burman boxes where the shaft has been staked over,not a good idea when it comes to removing it..
I had just over 1/16inch end float in my box which I thought was too much and shimmed accordingly and locked the shaft.I found that about 25-30thou was about right for the shim which I put between the sleeve and the inner cover bearing,all ok so far.
 

derek

Well Known and Active Website User
VOC Member
Gearbox input shaft nut

Thank's everyone for the advice, I have found that the nut was recessed and thus passing over the end of the splines and tightenning up on the kickstart rachet, thus clamping the shaft to third gear and ballrace.
I now realise that the shaft does not tighten to the ballrace, but floats in it. (not good engineerin practice!) Therfore it means that the distance piece at the drive end between the input and output shafts is very important, is this 1/2" thick as the distance between mine measures 0.515".
All of the above seems to indicate that shims to the tophat sleeve
are not required.
When I have aquired the correct size distance peice I will fit the input shaft.using locktight between it and ballrace and tophat sleeve.
 

A_HRD

Well Known and Active Website User
VOC Member
Distance Piece

The dimensions of the distance piece are 1.500 x 1.750 x 15/32 (i.e. just under 1/2 inch). They are available from the usual suppliers. They weren't hardened back in the days when I bought one and they wore out quickly on the seal face helped by road-grime. But given the high price of them now, I would hope that they are hardened....(?).

Peter Barker
Bristol, UK
 

Vic Youel

Well Known and Active Website User
Non-VOC Member
Hello Derek,

You have certainly had me thinking.... I believe that the input shaft end float is ONLY controlled by the top hat piece and shims at the ratchet end.

I have proved it to myself whilst completing the assembly my Burman this afternoon. I needed 15 thou of "hand and chisle cut" shims between top hat and bearing to yield a few thou of float allowing for slight bearing slop. I did find that when assembling it that because the ratchet spring has an I/D approximating to that of the outside of the rim of the top hat piece, it can get trapped behind it. This has the effect of tightening the shaft against the third gear and locking the shaft. Are you sure this is not the problem you are experiencing?

I used plenty of loctite of course after torquing the nut up at the ratchet end.

Cheers

Vic

PS I do agree with you that this shaft can "float" in the ratchet side bearing but it does not seem to have caused any wear in my box.
 
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