Author Topic: Single Spring Clutch on an A10?  (Read 1346 times)

Offline LJ.

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Single Spring Clutch on an A10?
« on: 03.05. 2009 22:48 »
Much has been said about clutches on the A7s and A10s and usually they concern either the commonly used six spring early or late (dry or wet) or the four spring jobbies. I've complained about my six spring later wet type and still cant get it right, okay I know the answer is to fit a four spring like what I already have on my second A10, and indeed it is a very good clutch to fit. But it's down to money! This afternoon I took a look over a complete clutch arrangement in a big box of M20 stuff that I got recently thinking that I had an earlier six spring dry clutch, I found it to be a single spring type.

The question then is can I fit a single spring clutch into a late 1960 A10? The clutch centre fits to a spare late mainshaft I have but I'm not sure about any other clearances etc. I've heard the single springs are good on M20s and it would be interesting and unusual if one could be successfully fitted and used on an A10!  *lol*

What do you reckon?
Ride Safely Lads! LJ.
1940 BSA M20 500cc Girder/Rigid- (SOLD)
1947 BSA M21 600cc Girder/Rigid-Green
1949 BSA A7   500cc Girder/Plunger Star Twin-(SOLD)
1953 BSA B33  500cc Teles/Plunger-Maroon
1961 BSA A10  650cc Golden Flash-Blue
1961 BSA A10  650cc Golden Flash-Red

Offline A10Boy

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Re: Single Spring Clutch on an A10?
« Reply #1 on: 03.05. 2009 23:39 »
My guess is that its highly unlikely that this has been done before, so the only way to find out is to do a "trial fit". Sorry if thats not much help.

There is [most of] a four springer on ebay at the moment although i dont know if its condition.


1958 Super Rocket
1974 Kawasaki Z1a
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Online Brian

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Re: Single Spring Clutch on an A10?
« Reply #2 on: 03.05. 2009 23:58 »
I dont know anyone who has put a M20 clutch in a A10 but maybe it can be done. A couple of things to check would be that it has the correct number of teeth on the chainwheel, the centre fits on the mainshaft and the sprockets line up when its fitted. Another possible issue is that a M20 has a lot less power than a A10 so the M20 clutch may not handle it.

The M20 clutch does have a few drawbacks, it can be difficult to assemble due to the large centre nut that has a very fine thread and once fitted there is no way of adjusting the squarness of the lift.

I really dont think it would be any better than the six spring you have, I would go for a four spring even if means saving up for awhile. A good clutch makes a world of difference to a bike.


Offline BSA_54A10

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Re: Single Spring Clutch on an A10?
« Reply #3 on: 04.05. 2009 08:21 »
The taper on the mainshaft is the same for just about all BSA boxes so you can put a single spring clutch on a A 10.
The position of the clutch on the shaft is determined by how big the hole in the center is as the main shaft is a taper, the bigger the hole the closer it goes to the gearbox.
I have gone the other way & fitted an A 10 clutch to my wm20 so if I can go this way then you can go that way.

As per the previous poster I doubt that the clutch will handle the extra power of the A 10 as it is flat out with the M20 even M21's give it all sorts of grief.

The big problem with a 6 springer is usually the backing plate not being flat or the flange that the backing flange sits against is not square so the plate can not sit flat.
I seem to remember that you can also use the twin sprocket from the plunger set up with the duplex chainwheel form the latter unit engines although I could not find the necessary bits to get it to work ( but I am working on it).

What is worthwhile is knocking out the center housing and fitting a top hat and radial roller bearing to the pressure plate so that it lifts square. This usually means that you can back off the springs a turn or two which results is a much lighter & sweeter clutch   
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