Author Topic: More Vincent Comet Burman Gearbox Issues....  (Read 8649 times)

Offline VintageBike

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More Vincent Comet Burman Gearbox Issues....
« on: November 03, 2016, 10:07:09 AM »
Folks

A little while ago, I had some clutch related issues on my 1954 Comet.  A new clutch centre, plates, pushrod and operating plunger seemed to remove the horrible noises I was getting.  http://classicmotorcycleforum.com/index.php?topic=5322.0

So far so good.

I have removed and replaced the outer gearbox cover so often during this process, I have gradually come to understand the process for timing the gear selection mechanism....  Or at least, I think I have...  But I still have a feeling this may the cause of the issues I still have.  I have also filled the gearbox with gearbox grease as it seemed very dry.

I currently have 4 good gears and a neutral.  This suggests to me that the selection mechanism is correctly timed?  But when changing from 1st to 2nd, 2nd gear is not there.  However, if I make this change in two discrete steps, i.e. go from 1st into neutral and then from neutral into second, all is OK.  But I can't make the change in one movement. 

All other gears seem to select fine in both directions - although some of the down-changes are crunchy if the engine speed isn't right.  I suspect this is down to the new clutch plates being a little sticky and not freeing up fully.

Any ideas why the change from 1st to 2nd could be so fussy?  I have not removed the inner gearbox casing at all, and the gears worked perfectly before I starting messing with the outer cover and clutch, so I can't help thinking that it is something I have done (my golden rule!). Could the presence of grease in the gearbox be a factor in this?

Thanks in anticipation...

Nigel



Offline Rex

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #1 on: November 03, 2016, 04:12:54 PM »
Is the neutral detent plunger spring too strong, meaning that it engages too easily with the first slot/groove it sees, in this case the neutral, rather than second gear, slot?
Can't be an assembly problem as you're got all five positions in the gearbox.

Offline iansoady

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #2 on: November 03, 2016, 04:20:47 PM »
But the detent is only there to keep the camplate in position once a gear / neutral is selected, not to control its movement. I'd be looking for something limiting the travel of the quadrant / whatever (I'm not familiar with the Burman box).

You could get this sort of effect with the AMC box if the ratchet spring was weak or incorrectly fitted.
Ian
1964 Norton Electra
1969 BSA/Suzuki
1992 Yamaha 250SRV

Offline Rex

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #3 on: November 03, 2016, 07:11:34 PM »
But the detent is only there to keep the camplate in position once a gear / neutral is selected, not to control its movement

Not really. Take the detent plunger out (not possible on all 'boxes admittedly) and it's hard to find neutral as the box goes from 1-2 or 2-1.

Offline chaterlea25

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #4 on: November 03, 2016, 10:02:50 PM »
Hi,
The Burman GB box fitted to your Vincent should only be oil filled,
You need to get the grease out of there !!!!!!
 Theres an oil level plug on the rear of the outer cover near the kickstart shaft
Grease will clog the small oil passages in the gears and shafts
The thickness of the outer cover gasket affects the pressure on the detent plunger
You may also be getting a partial hydraulic lock if grease has filled the spring cavity of the detent
This maybe why the box was whining when you were in the IOM ???

http://www.draganfly.co.uk/images/shop/14/19GB.gif

They are a very simple gearbox, but the gear change must not be hurried
There are some clutch plates on the market that cause all kinds of problems, they are a whitish colour
Throw them away!!!!
I believe that the Honda based clutch conversion is well worthwhile

John

Offline VintageBike

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #5 on: November 04, 2016, 07:25:04 AM »
Hello John

Many thanks for your reply.  I don't have the GB gearbox on my vincent.  I have the older BA(P?) type.

http://www.draganfly.co.uk/index.php/burman-gearboxs/cp-ba

This doesn't have the facility to drain or level oil, and as far as I can gather from all of my manuals and the VOC, it should be grease filled (although some say that adding some oil to the grease can be a good idea).  I shall have to look into this a bit further, but unless I have misunderstood the advice, this should be a grease filled box.

With regard to the clutch plates, I have used Surflex.  Where these the plates that you were talking about?

Cheers

Nigel



Offline iansoady

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #6 on: November 04, 2016, 10:11:47 AM »
But the detent is only there to keep the camplate in position once a gear / neutral is selected, not to control its movement

Not really. Take the detent plunger out (not possible on all 'boxes admittedly) and it's hard to find neutral as the box goes from 1-2 or 2-1.

That is of course true, but what I meant was that there isn't a positive stop there so if the lever moves its full travel, however deep the groove or strong the spring, it should go past neutral into second.

Like when the clutch is dragging and neutral becomes impossible to select as it always overshoots.
Ian
1964 Norton Electra
1969 BSA/Suzuki
1992 Yamaha 250SRV

Offline chaterlea25

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #7 on: November 04, 2016, 07:08:01 PM »
Hi Nigel,
I thought that the BA box was replaced by the GB in about 52 ? but what do I know???
Anyway, here is an example of the crap clutch plates,
http://www.degroot-bsa.nl/index.php?route=product/product&path=75_155&product_id=994

Ordinary grease is not thing to use t ! in old times they added heavy oil to make it pourable
Using just grease the gears will cut a path through the it and can run "dry"
Nowadays you can get semifluid grease  intended for vintage gearboxes, I have also heard of people using a similar produce intended for ride on mower gearboxes

Surflex clutch plates are probably the best available

John

Offline VintageBike

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Re: More Vincent Comet Burman Gearbox Issues....
« Reply #8 on: November 10, 2016, 01:25:58 PM »
Thanks John.

As I haven't removed the inner gearbox cover at any stage, and the timing of the gear selection seems OK as I am getting all 4 gears, I can't help feeling that the grease might be playing a part in this.  It is a "proper" sloppy gearbox grease, but I think I will try adding a bit of oil to it to see if it improves the situation...

N