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G: Gearbox Burman Box Again


chankly bore

Well Known and Active Website User
Non-VOC Member
Yup. makes sense. Problems often arise when replacement parts are not made to original dimensions. In the case I mentioned above the sleeve was too long and the pawl teeth were also not cut deep enough. The VOC Spares Co. were also getting the kickstart end retaining circlip wrong, but this error has been corrected.Sorry Bruce, your hurtful observation intervened. Cheers mate!
 

John Reynolds

Website User
VOC Member
I will confess to be a slow but persistent learner - I think I have finally understood how to control main shaft end float in a Burman BAP gearbox.

Up front be clear that the ONLY time that I think you can get a true measure of main shaft end float is with the mainshaft with the 3rd gear on it, fitted into the inner cover and the k/s assembly in place and tight on the other side of the inner cover.

On the mainshaft at the k/s end there is a threaded portion that nut 70X fits onto and there is a shoulder there - when tightening 70X it is (should) be tightened up against that shoulder. Starting at the outer k/s end of the mainshaft between the tightened 70X nut face and the outer face of the small bearing firstly there is the Driven Ratchet PR50-41BA and then the Ratchet Pinion Bush PR50-39BA (this bush is installed with its top hat flange against the small bearing inner race). Slip fit over the Pinion Bush is Ratchet Pinion PR50-38BA and the spring PR50-40BA. Essentially this assembly makes a spacer between the nut 70X and the top hat part of the Pinion Bush. Let's call this assembly the Float Control (ok I made that name up!)

Now on the other (inner) side of the small bearing is the 3rd gear that is a slip fit on the mainshaft, with (hopefully) end float between the inner race of the small bearing and the shoulder on the mainshaft. It is the stepped face of the 3rd gear that abuts the small bearing and the mainshaft shoulder on the other side of it that becomes the partner to the Float Control. So we are looking at an assembly that can slide on the mainshaft between the mainshaft shoulder that abuts the 3rd gear and the nut 70X.

I have not been able to locate any reliable documentation that tells what the main shaft end float should be however the suggestions received suggest that around 0.010" end float should be adequate.

So if we are to control the end float of the mainshaft then it can only be done in one of two ways.

If there is excessive end float to reduce it we can fit a shim between the Ratchet Pinion Bush and the Small Bearing. Standard Vincent metric wheel bearing shims available from the Spares Company are ideal for this use - Order H17M/set. Thanks to Greg Brillus for this insight.

If there is insufficient end float then as Mr Bore correctly suggested we can reduce the length of the Ratchet Pinion Bush.

M
Richardson (p.92) states that 'Mainshaft end float should not exceed 1/32 in (0.79 mm).

PS I looked this up after I had read your suggestion that the end float should be adjusted by partially tightening and then punch locking the kickstart rachet retaining nut; you had me questioning myself as to whether I had been correct to fully tighten the nut all these years!!
 

MartynG

Well Known and Active Website User
VOC Member
Richardson (p.92) states that 'Mainshaft end float should not exceed 1/32 in (0.79 mm).

PS I looked this up after I had read your suggestion that the end float should be adjusted by partially tightening and then punch locking the kickstart rachet retaining nut; you had me questioning myself as to whether I had been correct to fully tighten the nut all these years!!
Thanks John - I have updated my earlier post.

Martyn
 

brian gains

Well Known and Active Website User
VOC Member
Still fighting the chattering and lurching I get when I engage 1st gear.
The internal dogs on 1st do look worn on the leading edge suggesting that the sliding clutch on the layshaft is not positively engaging. The changes I've made that may have affected this are to have a new inner bush made up for the gear selector layshaft, also to ensure prescribed end play on this shaft incorporated a 0.030" gasket where previously there was nothing. AND not dismissing that possibly and not certainly that I may not have aligned the '0' synch' marks and this may have had a damaging effect when trying to engage 1st where previously there was no issue.
By extrapolation from my measurements it appears that between the face of the layshaft 3rd gear and the flange of the layshaft inner cover bush there is slightly in excess of 0.080" play. Is there a specified tolerance for this anywhere? I'm inclined to reduce this gap to say 0.030" using a shim and therefore having a knock on effect of the abutting 1st gear pinion engaging more positvely with the sliding layshaft clutch.
Can anyone see an absolute howler in my reasoning?
 

MartynG

Well Known and Active Website User
VOC Member
Brian,
Engagement of first relies in a positive engagement of the sliding gear on the layshaft with the dogs of the first gear. If there is shuddering and or chattering then either that engagement is not good OR there is an issue with the clutch.

I assume you have removed the clutch and washed all in solvent (petrol works) to get rid of the bulk of any ATF that may have been used and replaced it with a proper transmission oil such as MOTUL TransOil 10-30.

When you had the box appart did you examine all of the components of the selector mech? The bit that actually moved those sliding gears. If there is wear there then the engagement will be compromised.

Camshaft 001.jpg

Check the end float on the camshaft - it should be 0.002" but will increase with wear - you can shim it with a hardened washer as a temp fix, real fix is to replace the bushes it runs in.. also check the selector forks;' that engage the sliding gear, any sign of ridges on them means they are on the way out and need replacing. Also remove the split pins that hold the engaging pins in place and examine the engaging pins - again any sign of wear - replace them.

As you will have already found there can be hydraulic lock as you try to set up the gearbox and for that reason all end float measurements must be done with the box completely free of grease or oil.

Just an after thought - are the primary chain adjuster bolts - 2 of them - under the gearbox firmy secured? If no it may just be that the box itself is moving back n forth as you select first.

Don't feel disheartened - It took me 3 attempts of strip clean measure and reassemble before I sorted my box - and I found working with it in a large baking dish (to contain grease and small parts ) a real boon during the strip down stage.

Martyn
 

brian gains

Well Known and Active Website User
VOC Member
"three attempts", i'm envious.
Cam bush checked and replaced, yes, PO had shimmed. Cam pins replaced as all was apart. Selector forks OK, Checked clutch as running out of ideas, plates flat, deburred all tangs, washed in acetone. Did find a spline on inner drum was missing but believe to be historic damage as no loose bits or collateral damage. Measurements for end play only taken when the shafts come to positive stop and no indication of hydraulic pump action. Adjuster bolts replaced and heli coiled.
I have the indicated wear on 1st gear internal teeth, I shall retrace my steps / assembly from there.
And to think I thought getting a Ducati bevel drive cam shimmed correctly was a faff!
ps main and lay shafts checked and not bent.
 

vin998

Well Known and Active Website User
VOC Member
VOC Forum Moderator
On my series A Comet the Burman box always felt as if it was not working correct with a crunch into first gear, slow gearchange and generally felt like a rough transmission when using the bike. After a lot of checking and re-checking the gearbox and clutch over the last 10 years I finally decided to change the Burman clutch for a Conways Honda conversion and that solved all the gearbox problems. The gearbox now changes a lot quicker and silently and the rough transmission feeling has disapeared.
The conclusion I came to was all my Burman gearbox problems were due to the Burman clutch.
 

brian gains

Well Known and Active Website User
VOC Member
I only hear positive reports regarding the Honda clutch but my gear issue has manifested itself since work due to crankcase damage and repair.
Having cogitated on this a little more; the layshaft 3rd gear and 21T gear at the end bear on their respective bush flanges fully across the face so no wear would be immediately apparent unlike the inner gear cam shaft bush that has a larger dimeter than the bearing end of the shaft so that in the event of wear a stepped flange face becomes apparent.
Is it possible that on the layshaft the inner bush was not fully seated by the PO in order to take up wear and that following the Tig work and normalising in an oven I have ensured that it has now been fully seated allowing for more paly in the lay shaft. Does anyone have a dimension for the thickness of the bush flanges at either end of the layshaft? I'm grabbing at straws here I know.
 

MartynG

Well Known and Active Website User
VOC Member
I only hear positive reports regarding the Honda clutch but my gear issue has manifested itself since work due to crankcase damage and repair.
Having cogitated on this a little more; the layshaft 3rd gear and 21T gear at the end bear on their respective bush flanges fully across the face so no wear would be immediately apparent unlike the inner gear cam shaft bush that has a larger dimeter than the bearing end of the shaft so that in the event of wear a stepped flange face becomes apparent.
Is it possible that on the layshaft the inner bush was not fully seated by the PO in order to take up wear and that following the Tig work and normalising in an oven I have ensured that it has now been fully seated allowing for more paly in the lay shaft. Does anyone have a dimension for the thickness of the bush flanges at either end of the layshaft? I'm grabbing at straws here I know.
Brian,

Are you able to measure the end float in the layshaft? I cannot find anything specific to it but for the mainshaft Richardson suggests max endfloat of 1/32" and its reasonable to apply that to the layshaft as well. If you have more than this hardened shims at the end closest to the kick start may move the whole layshaft assembly a sufficient distance to improve the sliding gear/ first gear engagement. This is just a suggestion, not something I have done.

Another thought is to make up some supports on the bench to hold the inner ends (those at the drive output) of the 3 shafts and mount them all onto the inner cover so you can see whats happening as you move through the gears. Bugger of a job but it may reveal the cause.

Martyn
 

vibrac

Well Known and Active Website User
VOC Member
I think Ron Kemp had a ported gearbox shell so he could see what was going on inside as gears were selected I guess there is a write up in the archives as he improved the box and made it oil tight for racing ( a difficult goal for anyone to attempt) he was a prolific writer
 

brian gains

Well Known and Active Website User
VOC Member
Martyn; the emphasis of how I arrived at my figure for play on the layshaft was very much by 'extrapolation' and by no means direct empirical evidence. By mounting in 'V' blocks I don't think I would glean any more than is in the youtube vid's you already highlighted.
Vibrac; I'll try and seek out the Ron Kemp article in the archives before I try my own multiple porting exercise with a lump hammer %@#!
seriously, thanks for the suggestions, as I've said previously this is what makes the VOC forum an invaluable asset in disseminating knowledge and experience. In addition. thanks to a couple of generous offers from other Vincent yeoman I hopefully will be able to move this saga forward. Anon.
 
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Marcus Bowden

Well Known and Active Website User
VOC Member
The VOCSC I believe has an open framework for mounting twin g/box internals into to check operations, also the South London boys have a similar rig, we just need to find uncle Ron's Comet G/box rig.
 
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brian gains

Well Known and Active Website User
VOC Member
has this been flagged up previously;
from Stevens - 'Know Thy Beast' pg100.
" layshaft pinions....The longer bush takes the 34T (1st gear) pinion and should be at the clutch end of the box".

while Richardson - 'Vincent Motorcycles' 3rd edition pg 100. " the layshaft is sub-assembled with the longer splines away from the operator (therefore with shorter bush and nearer to the clutch basket) and order of pinions right to left 3rd gear 24T, 1st gear 34...."

i'm taking that the perspective in both these descriptions is as being astride the machine facing forward. Did Stevens mean by "clutch end " the operating lever end, if there were further editions was this corrected or is it Richardson's description of the orientation of the longer splined end that is in error.
I'm inclined to believe Richardson gives the correct description.
 

chankly bore

Well Known and Active Website User
Non-VOC Member
As I've said previously , all pairs of gears, i.e. layshaft plus mainshaft add up to 54, so as our Colonial cousins say: DO THE MATH
 

brian gains

Well Known and Active Website User
VOC Member
Two points; the layshaft can be loaded with gears either way, long splined end or short splined end towards clutch, the 'math' does not help you.
The other point is these are considered the two definitive publications as reference for finding your way around a Vincent, it would therefore be helpful if errors were flagged up for general awareness.
 

MartynG

Well Known and Active Website User
VOC Member
has this been flagged up previously;
from Stevens - 'Know Thy Beast' pg100.
" layshaft pinions....The longer bush takes the 34T (1st gear) pinion and should be at the clutch end of the box".

while Richardson - 'Vincent Motorcycles' 3rd edition pg 100. " the layshaft is sub-assembled with the longer splines away from the operator (therefore with shorter bush and nearer to the clutch basket) and order of pinions right to left 3rd gear 24T, 1st gear 34...."

i'm taking that the perspective in both these descriptions is as being astride the machine facing forward. Did Stevens mean by "clutch end " the operating lever end, if there were further editions was this corrected or is it Richardson's description of the orientation of the longer splined end that is in error.
I'm inclined to believe Richardson gives the correct description.
The long side(7/8") goes into the drive side of the gearbox.
 

chankly bore

Well Known and Active Website User
Non-VOC Member
Well the math. may not help, but one gear on the layshaft is wider than the other. Sorry, I thought this was obvious, my mistake. I agree about the errors in publications. I try to help when I can. I'm up to 68 pages of "Conversation" helping a mate put a Comet together. Anything you want to ask, go ahead, usual disclaimers about human frailty apply. Cheers.
 

chankly bore

Well Known and Active Website User
Non-VOC Member
Orright, now you've wound the clockwork up I'll continue in a series of short jerky movements. I pulled out a new layshaft and gears. I am unwilling, even in the pursuit of absolute accuracy, to pull it apart, but I took the following rough measurements using a vernier caliper. FROM CLUTCH END: bearing register on shaft (length), .760". Width of 21 tooth layshaft gear approximately .926", and the spline length corresponds. From the kickstart end, width of bearing register on shaft .949", width of layshaft 3rd. gear .700" and the spline length corresponds, (well it sticks out about.005"). While you've got it apart, Brian, check the cross-drilled lubrication holes on the two central free running gears. These are often blocked with grease from the 50's! Most post war boxes have these two gears running on bronze sleeves. Oilite or similar is used for the output gear bushes and the two top-hat bushes that the layshaft runs on. DO NOT use bronze for these, it could be fatal. I now have a modern (1985) Japanese bike and am amazed at the detail contained therein; wiring routes, exhaustive torque specifications, using choke only below 20° C and so on. saying that I've only noted one glaring error in "Richardson" which is the wrong placement of ET98 on the cam followers. The illustration in "Richardson" for the gear placement is correct, however he is in error with his description as the second gear layshaft is "free" and the small gear, 21 teeth is fixed on the shaft and is in constant mesh with the 33 tooth main driving gear. I hope this helps someone out there.
 

Albervin

Well Known and Active Website User
VOC Member
In Australia and the UK we say Maths not Math. Grammar and spelling policeman at your service.:rolleyes:
 

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