Burman 4th Gear Selector Meltdown

tatty500

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Surely someone from near Vic (or Aldershot section) is going to the AGM.
This would easily get the bits to me via Coventry section, and then I'd send them down to Matty (if no-one out-bids him).
Tatty
 

Matty

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Thanks all - if I do get the bits I still think it would be best to get them to "tatty500 " first.
Bury st Edmands is about 50 miles away from me , but Len Matthews is a bit nearer if they can be got to him somehow.

Unfortunately the cost of sending such heavy parts may be quite high - but I have a Vincent Rapide owning friend who sends lots of heavy/large items around by couriers and he may know a reasonably cheap way to do it.

Will see him tomorrow to give him some ignition coils for a Triumph Twin he is restoring, so will find out then.

Matty
 

Matty

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Hi All
As you know I am looking for a gearbox shell for my Comet.
There are two on bay which are BAP. The Swedish one looks OK for a Comet, but the other one which has BAP on it and says it is for Vincent, Ariel AJS etc does not as far as I can see look correct.
I thought the Comet one was BAP but are there other BAP gearboxes which do not fit the Comet or are there other numbers after the "BAP" which define the Comet one.
How do I know which box to buy so that I can ask the seller to make sure it is the correct one for my Comet please?

Matty
 

tatty500

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Matty,
The shell in Sweden is a post-war BAP.
The shell and gear clusters in St Ives are prewar .....adjuster at the top, bulge for k/s shaft bearing, filler cap on shell, worm gear for speedo drive on end of layshaft.....so at the moment there's only one choice.
Tatty
 

tatty500

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At last, here’s what I have discovered.
Since I think the lightweight CP box was the design that was beefed up to create the BAP, this was my starting point. In a CP the design rule seems to be that any moving parts that could touch are kept 1mm apart. Seems reasonable for a metric design.
Moving to the BAP box this same rule holds true everywhere except 4th gear. Here there are two discrepancies, both of which reduce the engagement to its pitiful amount.
1. The inboard face of the output gear is 2mm away from the shoulder on the camshaft. This gear could therefore be 1mm longer with the simple flat face, or maybe even 2mm if the conical face was used here as it is in the CP.
OR
2. The sliding gear is 3mm away from the face of the output gear. This gear could be 2mm longer from the selector groove to the 28 tooth end.
Sadly my particular shell is deeper than two others by 13 and 19 thou, and my output gear is shorter by 2 and 10 thou. Thus 4th gear engagement is reduced by 15 thou and 29 thou in total. These figures are small but the 29 thou = 0.73mm would have increase engagement from 1.3mm to 2mm, or a 50% improvement.
In all of the four output gears I have examined the worn surface of the internal dogs is at best half the 4.5mm dog length. At worst it is less that 1.5mm. (see earlier pictures)
And now I’m stuck, for, even if I buy new gears and selector, I will still be assembling a box with pathetic engagement. Is there any way I could get the sliding gear made 2mm longer?
If I make a 1mm spacer to fit between the output gear and bearing, it will need a wall thickness of 3mm so will it break up?
Recommendations.
1. It is the wear of outer bush in the driving gear and the surface of the mainshaft that creates the rubbing action on the 4th gear dogs. So lubricate the point where the shaft emerges and check for play whenever possible. If the mainshaft is ever removed pack the space between the bushes with fresh grease.
2. If any wear of the 4th gear selector face is noticed this should be the early warning. Investigate further.
3. It was evident that the wear products do not escape from the groove behind the dogs. This must mean the there is no movement of lubricant in this area. So, keep the box as full as you can without too much leakage. Try to use the left hand prop stand after a run.
4. Keep the camshaft as far to the drive side as possible by eliminating the wear at the steel bush at the k/s end.
5. If the revs rise in 4th and you trust your clutch not to slip, then maybe the selector is on the way out.
Stop using 4th and get home in 3rd.
Finally many thanks to Chris, Vic and Matty for the loan of parts
Tatty500
 

Matty

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Thanks tatty500 for the information.

Believe I have found another old Burman casing with a good bearing housing to replace mine, which when I get it and the damaged gears etc. I will use to see if I can in any way improve the depth of entry of the sliding dog into the output gear.

I understand the problem with the small size of the 1mm spacer but think 3mm wall size should be strong enough, provided the sprocket securing nut is really tight.

Presumably this 3mm wall size is determined by the distance from the mainshaft to the flange on the aluminium casting. However, if necessary is there any reason why the flange internal diameter could not be increased (filed out) to accomodate a larger outside diameter spacer?

Without having the bits available yet to look at - is there any reason why a thicker spacer could not be used (say 2mm) with perhaps a taper ground onto the teeth of the output gear or a bit ground off the shoulder of the camshaft to give more clearance?

Am I perhaps thinking too laterally?

Matty
 

Matty

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Hi Jim - thanks I've had a look but they all seem to be for Ariel/Matchless and practically none of the parts fit the Vincent Comet/Panther 600 box.

I believe I have found a good casing however from another Club member but have not got it yet.

Matty
 

tatty500

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Matty,
At 2mm, the sprocket nut is at the end of the thread on the o\p gear, I'm thinking of pimching 0.5 or 1mm on the chain line.
By the way, I find I don't have the phone number you need, I'll get it on Monday.
Contact you soon,
Tatty
 

Robert Watson

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Just getting in on this thread

BAP (and I think all) Burman boxes have a Mark number on them, usually cast in roman numerals, and each then is unique to to the bike (or bikes) to which it was originaly was fitted. I think (from a poor memory) that the pre war A vincents used BAP Mk X111 (13). Boxes can be the same but mounting lugs and offsets here and there can be different but all the internals generally fit. Different mainshaft extension lengths are really common as well
Look at the mark number on your box and then look for one the same.
 
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