Another tale of Burman gearbox woe

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Roger_Redford
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Another tale of Burman gearbox woe

Postby Roger_Redford » Wed Aug 13, 2014 10:42 am

Good morning all,

Having a bit of my own trouble with the Burman gearbox on my HT engined combo.

Was riding along and heard a "snap" when I changed gear, and lost all tension on clutch lever, so assumed the cable had snapped or nipple broken off at the clutch arm... managed to get home with a bit of crunching...

Anyway, removed the fill cap to take a look and cable and nipple all intact and correctly positioned. Looked like the arm wasn't disengaging and returning, almost as if a return spring was missing or damaged. So took the side case off to have a look, with all its messy oil and Swiss-watchery inside, nearly taking my eye out with the kick start spring in the process :shock: but couldn't find any remnants of a broken spring nor see anything along those lines on a diagram...

Any thoughts? What would cause all tension to be lost at the lever and the arm to not move as a result? As I say, cable seems fine...

Apologies for the vaguery, as this is bike is still a learning curve for me, and this is the first time I have had the gearbox off. In advance, what oil should I realistically put back in when I reassemble... I have read a few exponents of each of grease, oil and grease, and solely oil... new gasket as well of course.

Thanks fellas
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admin
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Postby admin » Wed Aug 13, 2014 1:54 pm

Take a look at the clutch as well..?
It will mean the clutch cover has to come off and likely removing the little springs, which is going to be a fiddle with the sidecar in the way ..(but way easier than removing an entire chaincase as on some other lesser makes ... 8-)) )
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Roger_Redford
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Postby Roger_Redford » Thu Aug 14, 2014 9:04 am

Okay thanks John, will do. Sidecar probably coming off anyway for a spell so will be a bit easier that way.

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Keith.owen
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Re: Another tale of Burman gearbox woe

Postby Keith.owen » Thu Aug 14, 2014 9:15 am

Hi Roger,
This sounds nasty.

The return pressure is provided by the clutch springs; let's hope it's not the pivot into which the operating arm fixes that has broken away from the casting.

There really isn't much else that could 'snap' as you put it.

In the worst case it should be possible to repair it though.

Good luck,

Keith

PS. Have you checked that the clutch basket is still firmly abutted against the drive shaft - it is possible for the securing nut to come undone and for it to move sideways back and forth as you operate the clutch!
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Roger_Redford
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Postby Roger_Redford » Thu Aug 14, 2014 9:55 am

Thanks Keith.... So if it's the springs, an easy-ish fix, if the pivot has sheared, much gnashing of teeth?

Any advice on the lubrication?

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andrew.chapman
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Re: Another tale of Burman gearbox woe

Postby andrew.chapman » Thu Aug 14, 2014 10:37 am

Is the small oval cover plate (the one with two fixing screws) on the outside of the gearbox still in place? If that fell off or loosened, it would have that effect.

Is it a GB gearbox? If so, you fill it with oil. I use Millers SAE90 Green Gear Oil in the Ariel box. I use fully synthetic Red Line 75w90 in the Sunbeam box. Both are good and both are bronze-friendly but the synthetic stuff offers less drag.
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Re: Another tale of Burman gearbox woe

Postby david.anderson » Thu Aug 14, 2014 10:57 am

Roger
You mention that your bike is HT engine but clearly the frame is not HT. What about the gearbox. If you have the HT gearbox then the clutch pushrod adjuster is screwed into the clutch pressure plate. If that is the case then the adjuster screw may just have come unscrewed and the snap that you felt may have been the adjuster screw pushing out of the last thread.
With a standard GB gearbox the pushrod adjuster is located behind the small alloy casting that is fixed with 2 screws to the outside of the outer cover.
If you have the outer cover off the gearbox and if the clutch arm pivot point is broken it should be easy to see.
With regards to lubrication I use a grease oil mix as it tends not to leak out so quickly.
David

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Postby Roger_Redford » Thu Aug 14, 2014 12:36 pm

Hi David.
Yes it is of course an HS scrambles sidecar frame, but with an HT engine and GB gearbox from an HT. I believe they were favoured frames with many trial duos, for their stiffness.
I will check all these things, as will I with your advice Andrew.
Thanks for the input


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