Burman gear box

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william shortall
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Burman gear box

Postby william shortall » Sat Feb 08, 2020 10:58 am

Can any body please help having just had my gearbox stripped the number on the box is
GB then over stamped 39 is 7J then 56
GB7J56 underneath is FC then underneath that is C342

GB7J56
FC
C342
The engine is a 1951 _52 / 4G and the mainshaft is bent , and the inner clutch casing has been repaired and shows signs of scoring.
Dragonfly told me this could be with the shaft being to short . I ordered one ,when it came the diameter is to wide, i have looked on there website and they give a few different diameters could anybody please point me in the right direction.
There are a couple on E bay but i dont know what i am looking for

Pete.Silson
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Re: Burman gear box

Postby Pete.Silson » Sat Feb 08, 2020 12:52 pm

William,

Your original number GB3956 was from a 1956 NH350 - presumably someone overstamped it when they converted it for SQ4 use.

Burman GB mainshaft FWHa.jpg

The different mainshafts can be identified from the length between the 3rd gear splines and the clutch-centre splines. The photo above shows a mainshaft from a later NH gearbox (3630-56) where this length is 3-1/64". The length for a SQ4 mainshaft (3629-52) should be 3-1/2".

I ordered one ,when it came the diameter is to wide...

To which diameter are you referring? As far as I am aware the shaft diameters are all the same.

Pete

william shortall
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Re: Burman gear box

Postby william shortall » Sat Feb 08, 2020 1:52 pm

the shaft diameter in the box is 21.8mm and 270 mm long which is slightly bent
the shaft i have been sent is 23.8mm diameter and 295 mm long
am i better off getting the correct box or sorting this one

Simon.Gardiner
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Re: Burman gear box

Postby Simon.Gardiner » Sat Feb 08, 2020 2:04 pm

Persevere with your box 'cos apart from the mainshaft lengths GB boxes are pretty much identical.

I'm puzzled by your reference to different diameters - I don't have a box apart to do measurements but GB boxes don't have different shaft diameters. If your old mainshaft isn't obviously loose maybe you've been sent a wrong one.
The 'bible' doc for GB mainshaft length dimensions is in this thread:
viewtopic.php?f=4&t=8843&p=61355

You should be able to use the measurements to identify if you've got a correct shaft or exactly where it's wrong - if it's no help maybe photos of your mainshafts or comparative dimensions might help?

HTH

SG
'55 Huntmaster, '56 VH, ' 51 VH, '80 R100RT, '00 Sprint ST (but all those Ariel parts can only make one running bike...)

william shortall
Posts: 25
Joined: Mon Jun 25, 2018 1:51 pm
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Re: Burman gear box

Postby william shortall » Sat Feb 08, 2020 2:10 pm

Many thanks i will send this one back to Dragon next week and see if they have a shaft to fit .

william shortall
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Joined: Mon Jun 25, 2018 1:51 pm
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Re: Burman gear box

Postby william shortall » Sat Feb 08, 2020 2:11 pm

I will try to send photos tomorrow

Pete.Silson
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Re: Burman gear box

Postby Pete.Silson » Sat Feb 08, 2020 5:01 pm

21.8 mm is right for the diameter and 270 mm is about right for a SQ4 mainshaft length so it looks like you have been sent the wrong shaft from Drags.


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