Burman R type clutch alternatives.

[CPR]

Hello. Does any one have have any suggestions as to an alternative clutch that will fit a Burman R type gearbox.

In my thread on Burman gearbox lubrication the following suggestion from Chris1 was made. This should make a good starting point for a discussion.

'I know its another thread, but your mention of clutch parts reminds me that if you have no clutch, the taper shaft on the Burman gearbox will take a Triumph centre. This means you can fit a complete clutch which should be easier to find. A pre-unit one has single primary chain and looks similar to the Burman one. I have done this, it depends on your take on originality. Chris1'

[CPR]

Hello Chris. I have had a look at your suggestion to use a Triumph clutch. Unfortunately this is not a route I can take, as my clutch is fitted to the mainshaft via ‘castlelated’ splines not a taper. It would appear that M, SM, ME, SO and O gearboxes have a taper. Model R,T and W have ‘castlelated’ splines.

[chris1]

Ok, the box that I managed to find was I think an SO. Originally the bike was fitted with a smaller version of this (can't remember the type). It was a loverly box to use close ratios and stamped TT. However, it was probably for a 250 and the teeth kept breaking. The SO with Triumph clutch looked like the right solution as I was quoted £600 for a Burman clutch! However, the ratios were so wide it was not nice to ride so I went for a completely non-standard option and fitted a complete Norton Laydown box and clutch. The Norton clutch is splined, don't lnow the size, but nice clutch to use. Another non-standard gearbox often used on vintage bikes is the Norton Dolls Head but more difficult to find, much the same internals as the Laydown. The Laydown can be adapted to take all the AMC sprockets too.
Although not for purists the Norton route gives you a strong gearbox and clutch, 4-speeds and positive stop foot change. It takes a bit of fabrication to fit but worth it in my opinion to get back on the road. I did it as a temporary fix but have no plans to change back. If any one buys the bike they can have it like it is with a free broken Burman box.
I'm never bothered by rivet-counters, but my reply would be that I believe the Norton box is based on the Sturmey Archer box fitted to some Cottons and they were made by Burman anyway.

[CPR]

Thanks for the reply Chris. From what you said it looks like my only option is to persevere with the Burman clutch, unless I go for another gearbox, which might be expensive. Where possible, I like to use original design/parts, but if there is a better alternative clutch then I would fit that.
In the absence of an alternative clutch, I have bought friction plates from Dragonfly, and have had some plane clutch plates made. The only major parts still required are a pressure plate and springs. I have been looking for some time now, but with no luck, so I have produced a drawing for my version of a pressure plate, and if an original does not turn up, then I will make one. Before I start making it though, I thought I would check to see if there was an alternative route.

[prox8]

are you able to post a photo including a ruler- I have a box of bits & have no idea what they are.

[CPR]

Hi Prox8.
The pressure plate would be about 4 5/8" outside diameter. The pitch circle diameter of the 4 holes for the springs is about 1 11/16"
I'll dig out the clutch parts I do have and photograph them.
Not sure how to post pictures, but I'm sure it will become apparent when I try!

[1950red]

Oct 9, 2019 8:05:55 GMT chris1 said:

Ok, the box that I managed to find was I think an SO. Originally the bike was fitted with a smaller version of this (can't remember the type). It was a loverly box to use close ratios and stamped TT. However, it was probably for a 250 and the teeth kept breaking. The SO with Triumph clutch looked like the right solution as I was quoted £600 for a Burman clutch! However, the ratios were so wide it was not nice to ride so I went for a completely non-standard option and fitted a complete Norton Laydown box and clutch. The Norton clutch is splined, don't lnow the size, but nice clutch to use. Another non-standard gearbox often used on vintage bikes is the Norton Dolls Head but more difficult to find, much the same internals as the Laydown. The Laydown can be adapted to take all the AMC sprockets too.
Although not for purists the Norton route gives you a strong gearbox and clutch, 4-speeds and positive stop foot change. It takes a bit of fabrication to fit but worth it in my opinion to get back on the road. I did it as a temporary fix but have no plans to change back. If any one buys the bike they can have it like it is with a free broken Burman box.
I'm never bothered by rivet-counters, but my reply would be that I believe the Norton box is based on the Sturmey Archer box fitted to some Cottons and they were made by Burman anyway.

[CPR]

Hello 1950red. The clutch element of the bike rebuild has moved on a bit. Once again Paul Powell has come to the rescue and supplied me with the missing parts I needed. So the clutch has been put aside ready for when I start fitting the clutch/gearbox into the frame. My attentions are now focused on the engine oil pump/circulation, but I'll start another thread on that one!