Burman Gearbox Query

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Burman Gearbox Query

Postby Transfergear » Sat Apr 21, 2018 3:28 pm

Hi Everyone, this is my first posting so hope it's ok. I have a 1952 Model 18 with a Burman GB gearbox. It was leaking oil from the drive side so I had to strip it down to replace seals etc. On inspection there was wear on most of the bushes (which look original with cut oilways etc.) so I decided to source new bushes and bearings from various suppliers. On trial fitting, the bushes on main and layshafts are a good fit apart from the 1st gear layshaft bush which is 3 thou larger than the shaft.

Thinking the shaft may be worn (although it didn't look like it was) I sourced another NOS layshaft from Draganfly and another 1st gear bush only to find the layshaft diameters were the same (albeit the replacement shaft has the worm drive on the end of the shaft). The bush was again 3 thou bigger. See picture.

Has anyone experienced this and have a solution to fix it because 3 thou play seems excessive....I may as well just leave the old bush in place!

AMC,Vincent GB box bush part number:19-8-14 - I bought Ariel part no: 3653-52 which should be the same?

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Re: Burman Gearbox Query

Postby dave16mct » Sun Apr 22, 2018 11:03 am

It sounds like the wrong bush or incorrect size. It's listed as 19-8-13 in the spares list and the club stock this for £10.80, although they're low on stock. Was there play on the mainshaft before you stripped it? If not I'd re-use the old bush.
Cheers Dave.

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Re: Burman Gearbox Query

Postby Dixter » Sun Apr 22, 2018 1:31 pm

Hi Transfergear: among the many free resources of our club is this little jewel, the British Army’s standards for assembling G3L Motorcycles including Burman gearboxes. This reference is hidden in Christian’s Archives at:

http://archives.jampot.dk/book/Workshop ... ndards.pdf

While this manual discusses the Burman CP gearbox and you have a GB, I think we can safely assume that Burman engineers and designers would have used similar design principles in both boxes. Lacking any other specific information, I have long relied on the information within this reference manual. For every component inside your bike, the Army has provided the Nominal dimension, the normal clearance, acceptable clearance upon rebuild, and condemnation limits.

For the layshaft journal to bushing clearance on a brand new Burman CP box, Burman allowed 0.0035”, and acceptable clearance is 0.006”. Condemnation limit is 10 thou.

I’d encourage you to download the manual, and look up the values. I think you will find great comfort in knowing your gearbox is full of loose assemblies. These are rugged ole Brit designs, not Swiss watches.

Ciao,
Dick Casey
Dick Casey

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Re: Burman Gearbox Query

Postby robcurrie » Sun Apr 22, 2018 4:46 pm

Transfergear, when you say trial fitting, do you mean that you pressed the bushings in, if not bear in mind that the inside diameter will decrease once pressed in. I'm not familiar with the Burmans, so if I'm mistaken, please ignore this.

Rob C

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Re: Burman Gearbox Query

Postby Transfergear » Mon Apr 23, 2018 7:57 pm

Dixter wrote:Hi Transfergear: among the many free resources of our club is this little jewel, the British Army’s standards for assembling G3L Motorcycles including Burman gearboxes. This reference is hidden in Christian’s Archives at:

http://archives.jampot.dk/book/Workshop ... ndards.pdf

While this manual discusses the Burman CP gearbox and you have a GB, I think we can safely assume that Burman engineers and designers would have used similar design principles in both boxes. Lacking any other specific information, I have long relied on the information within this reference manual. For every component inside your bike, the Army has provided the Nominal dimension, the normal clearance, acceptable clearance upon rebuild, and condemnation limits.

For the layshaft journal to bushing clearance on a brand new Burman CP box, Burman allowed 0.0035”, and acceptable clearance is 0.006”. Condemnation limit is 10 thou.

I’d encourage you to download the manual, and look up the values. I think you will find great comfort in knowing your gearbox is full of loose assemblies. These are rugged ole Brit designs, not Swiss watches.

Ciao,
Dick Casey


Thanks Dick as you say this is a great comfort and it solves my problem. I've measured clearances of the existing bushes and shafts and they are nowhere near the rebuild limits so I should have done this before looking at replacing bushes to make as you say a 'Swiss watch' :lol: Just need to replace the mainshaft bearings and oil seal (origional problem) and hit the road now summer has arrived Thanks Phil

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Re: Burman Gearbox Query

Postby Transfergear » Mon Apr 23, 2018 8:02 pm

[quote="dave16mct"]It sounds like the wrong bush or incorrect size. It's listed as 19-8-13 in the spares list and the club stock this for £10.80, although they're low on stock. Was there play on the mainshaft before you stripped it? If not I'd re-use the old bush.
Cheers Dave.[/quote

Thanks Dave Problem now resolved see my response to Dixter's post. I was looking for a problem that didn't exist - all limits of current box are well within limits - Doh! Thanks Phil

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Re: Burman Gearbox Query

Postby Transfergear » Mon Apr 23, 2018 8:05 pm

robcurrie wrote:Transfergear, when you say trial fitting, do you mean that you pressed the bushings in, if not bear in mind that the inside diameter will decrease once pressed in. I'm not familiar with the Burmans, so if I'm mistaken, please ignore this.

Rob C


Thanks for this Rob - I'll bear this in mind should I need to re-bush in the future - as you csn see from responses to the other posts - the current bushes are fine...experience is a great thing, thanks Phil

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Re: Burman Gearbox Query

Postby JDFS79 » Tue Apr 24, 2018 6:30 am

Which you luck with the rebuild , i have spent a lot of time trying to figure how to resolve several problems with a similar gear box ( same year and model) , if it wasn't for the club forum I think I will never done it right. Just beware of the gap between the main bearing and main drive gear I had to make a spacer to fit between them in order to prevent 4th gear to jump out , this after several attempts of trial and error ( 4 times total) :headbang: .
Cheers and have fun.

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Re: Burman Gearbox Query

Postby Transfergear » Tue Apr 24, 2018 7:18 am

JDFS79 wrote:Which you luck with the rebuild , i have spent a lot of time trying to figure how to resolve several problems with a similar gear box ( same year and model) , if it wasn't for the club forum I think I will never done it right. Just beware of the gap between the main bearing and main drive gear I had to make a spacer to fit between them in order to prevent 4th gear to jump out , this after several attempts of trial and error ( 4 times total) :headbang: .
Cheers and have fun.

Thanks I'll make sure I check that before final assembly as taking the box out (more than once) doesn't sound like so much fun! regards Phil

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