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Series A clutch


Andy B

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VOC Member
Can anyone send me some good pictures of a original series A clutch, I have the original gearbox and at least two complete clutchs but the inner clutch that fits the gearbox shaft is not correct for the basket as it is too big, I got the bike as a basket case and believe other parts have been added to the mix making my job more difficult
 

billirwinnz

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VOC Member

Andy B

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VOC Member
That's the clutch in my early 36 TTR. In 1936 Burman introduced larger diameter plates. Mine still has the smaller ones.
Thanks for that Bill, although the clutch bits I have are not the same so I'm probably even more confused. I have a 4 stud inner basket, the inner splines are quite chewed out, I have two outer baskets with duplex cogs and at least two sets of plates, original gearbox as per my build sheet, I think there has been some level of skullduggery taken out on the inner basket???
 
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billirwinnz

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VOC Member
Hi Andy
It sounds like you have the right outers as most other clutches have only single row sprockets. The early clutches had plates of about 145mm across the outer lugs. I see from the Burman drawing that they also had 4 springs. I'm only familiar with my own bike and its possible that road-going A singles had the 4 spring clutch. There must be others out there with much greater knowledge than I have.
Bill
 

A_HRD

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VOC Member
Andy,
All 'A' singles were originally equipped with the 4 spring clutch. But they were prone to slip and when the 5 spring variant arrived (very late 30s or just post-war?), many owners changed to it with good results.

As Bill says, if you have the duplex sprockets attached to the clutch baskets, at least that part is right. There should be 6 x rubber shock-absorbers built-in, right? There were various splined clutch centres with various depths, it is worth getting a deeper one, if you can, so that you can fit an extra friction plate.

The worst problem with these clutches on the As was the short engagement of the mainshaft splines with the clutch centre - not much more than 1/8th inch. So start by checking mainshaft for wear and the corresponding inner-splines in the clutch centres. A clever welder could probably make good if you can do the fettling donkey-work to reclaim the splines from the weld.

I'm not going to be around much for the next couple of weeks so I'm not in a position to assist with photos or measurements; perhaps someone else can chime in please? Alternatively, why not email your questions to Andrew Walker?

Peter B
 

billirwinnz

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VOC Member
I notice in photos of 1934 (JAP), 1935 and 1936 TT bikes that all have 5 spring clutches. Perhaps the early TTRs with the smaller clutch drums also used 5 spring clutches as mine does?
 

A_HRD

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VOC Member
Bill - and Andy B,
It is likely that, with the passing of 80 years already, we'll never know anything for sure. But just to add to the conundrum, I've just been looking at a photo of a TTR with a 4 spring clutch! (It's in a weird format and won't attach here).

Meanwhile, I took this photo of alleged A parts which just goes to show the massive availability of Burman parts over the years - essentially the same but, in many cases, different enough not to fit! Starting at 12 o'clock, is a NOS slotted clutch basket with slots 1/4 wide and 1-5/16 long. But I have another (not shown) with 1" long slots. At 1 o'clock is the metal shroud that goes over the basket. Then there is the (5 spring) clutch centre that stands 1.5" high (this might be a C Comet one?) and below it, the one that stands 1-1/4" high! Next, is how the back of an A clutch should look; and alongside it (at 7 o'clock) is my TTC clutch (4 spring) with one of the original thin tin-plate pressure discs - with adjustment facility. At 9 o'clock is another tin-plate disc - but undrilled and having no adjustment facility! And finally at 11 o-clock is the later Burman pressure-plate (some have adjustment, some not). Always use this one on a Series A 5-spring clutch, or beef-up the tinplate one with more layers of welded-on tinplate (on the inside) for the 4-spring clutch; why? because it warps badly in use and causes all manner of problems!

The first of Bill's links is about 33% not relevant to Series A machines - so expect to get even more confused if you study it closely! The second link (the 1926-35 one) is a good likeness of the early 4-spring Series A clutch; and not far off the later 5-spring variant.

I'm not even going to mention the 7" A Twin clutch....!!!

Peter B

P1080198.jpg
 

billirwinnz

Well Known and Active Website User
VOC Member
Thanks Peter.

The more I learn about As the less I realise I know. There was certainly a great deal of variation over the four years they were produced.
 

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