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Pre unit swing arm gearbox types
#797476 02/03/20 11:33 pm
Joined: May 2012
Posts: 68
jimq Offline OP
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Hi all.

I have a question today which i have tried answering for myself on google and have been surprised i was able to not easily able find a direct answer.

In Basic terms; what is the difference between a standard gearbox, a box marked T and a box marked T2.

Thanks in advance.
Jim.

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Re: Pre unit swing arm gearbox types
jimq #797477 02/03/20 11:57 pm
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Jim: the standard box has bushing on the ends of the layshaft and where the mainshaft goes through the A gear (gear that the sprocket goes on). The T box has needle bearings on the layshaft and the T2 box has needle bearings on the layshaft and where the mainshaft goes starts to go through the A gear. I think there is still a bush for the outside of where the needles end on the mainshaft.

I assumed by standard you are not asking about the various ratios of the gears like STD.

Gordo

click to enlarge

Here is a shot of the parts page that shows both the bushings and needles for the layshaft

[Linked Image from i.postimg.cc]

This parts book page shows both types of A gears

[Linked Image from i.postimg.cc]

Last edited by Gordo in Comox; 02/04/20 12:21 am. Reason: photos added

The roadside repairs make for the best post ride stories.
Re: Pre unit swing arm gearbox types
jimq #797478 02/04/20 12:40 am
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jimq Offline OP
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Hi thanks for your reply Gordo.

Would that mean that a T box could effectively be made a T2 box by replacing the A gear.

Cheers.
Jim.

Re: Pre unit swing arm gearbox types
jimq #797480 02/04/20 12:49 am
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Jim: I have no first hand knowledge but the mainshaft appears to be a bit different in the roller area looking at the diagrams I posted. I do know that the two layshafts are not the same size in area where the needles go..

Someone will know.

Gordo


The roadside repairs make for the best post ride stories.
Re: Pre unit swing arm gearbox types
jimq #797485 02/04/20 1:34 am
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Originally Posted by jimq
Would that mean that a T box could effectively be made a T2 box by replacing the A gear.
No. The A gears for the T2 gearboxes have a needle bearing in one half and a bush in the other half, and to accommodate this the mainshaft for the SCT2/RRT2 has a step in it to provide the somewhat different clearances required.

See also the following for a fairly detailed description of the internals:

http://www.britbike.com/forums/ubbt...e-1957-bsa-spitfire-scrambler#Post757258

Last edited by Magnetoman; 02/04/20 1:48 am. Reason: clarified text
Re: Pre unit swing arm gearbox types
Magnetoman #797491 02/04/20 3:09 am
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jimq Offline OP
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Alright cheers Magnetoman.

that could be my evenings reading.


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