Hi everyone I am here in the states and have always had a hard time tracking down a vintage motorcycle mechanic especially one who will work on a bike this old. I have a 1942 BSA M20 and have done a ground up restoration. I have had it running and the gears change when the bike is not running but when I have tried to put it into gear the clutch will not engage. I have the single spring clutch and took it out and rebuilt with all new components and it still does not look like it is separating enough even with the lever all the way engaged. I recently read a post on here where there was a conversion to a triumph clutch. I really love this motorcycle and would love to see it on the road even just to drive it around the block. If it is a strong recommendation to do the swap would someone please tell me all the parts I would need for my motorcycle. I saw in one post that you need the adapter and that Monty sells them but it says BSA 4 spring clutch. It will be an expensive swap but if it gets me on the road I am willing to do it. Thank you for any help. If you know anyone in Arizona that works on these that would be great to.

Monty can sell you the parts ok. https://montysclassicmotorcyclesshop.co.uk/ You would need the Triumph (non rubber cush) clutch and the adapter. BSA actually used that clutch in later years also.

But before that, it's possible that your new after market friction plates are too thick. I've run with the single spring clutches for well over 30 years and find them delightful. But I only ever run with one friction and one steel plate removed. It gives more room in the basket for the plates to separate and with a cable oiled with thin oil is a very light clutch.

It's well worth trying that first and also make your cable adjustments to the book. That is, with some free play at the cable, when the handlebar lever is pulled in, the gearbox lever should be in a perfect upright position.

There might also be some issues with your pushrod length and or your cable free length.

Ron

email (option): ronpier@talk21.com

Do you know the appropriate thickness of the friction plates big chance? So you always remove 1 friction plate and 1 steel plate of what the oem width steel and friction plates were. Also with never being exposed to rain I the clutch and plates get rust on them is there something you can add so it doesn’t get everything oily? Thank you

Yes new the steel plates were .048" (acceptable at .030") The original friction plates were 3/32". There should be a dome (bowler hat) cover to keep the oil off the clutch plates. I have run two M20's with 600cc engines for many years with the top two plates left out of the stack. No slip or drag. Ron

email (option): ronpier@talk21.com

Removing one steel plate and one friction plate is an old 'dodge' to improve plate seperation in the single spring clutch...Original fiber plates were .093" thick when new...However, you should note that if you have the thicker, pattern friction plates the overall plate stack is higher than standard anyway and removing the two plates as described will still leave you with a standard hieght stack and no increase in clearance or any improvement in clutch action...
Purely from the point of view of availability in the states the Triumph clutch would be the way to go..You can probably get most of what you need from American dealers...There are a few things to note when carrying out the Triumph conversion which must be right for it all to work...
If you decide to go down that route I'll post again regarding that subject....Ian

email (option): ian@wright52.plus.com

I did fit a Triumph clutch and adapter from Monty to my BSA/Indian special. For no other reason than the Indian engine has no cushion on the crankshaft, therefore there was a degree of harshness at very low speeds. So I fitted a clutch with a rubber cush centre. It was an absolute pleasure after that.

Otherwise I had no complaints with my Single spring clutch (with two plates removed) even though the 600cc Indian engine has more BHP than the 600cc engine that is in my military M20.:relaxed: Ron

email (option): ronpier@talk21.com

email (option): darrylgubbels@gmail.com

The fiber discs were almost like they were glued to the steel plates. I don’t know how that would have happened. Needless to say I will be ordering all new fiber discs and steel plates. The fiber discs are .125. I ordered them from draganfly. I am going to order all new ones. I had a total of 7 fiber and 7 steel. So now I will be running 6 hopefully that works. Is there an overall dimension of what all the fiber discs plus steel plates should be? Thank you for all your help I’ll let you guys know when I get it back together and if it works.

All I need is that kit nothing else? So I’m guessing you do not need to utilize the single spring? I cannot read some of the stuff in that page. It’s not a bad deal if it works smoothly seeing I need to replace this anyways

Well those new friction plates are each 1/32" too thick. Also you should end up with one less steel plate than fibre plates. (not equal amounts) If you simply add up the original sizes 8 x .093" and 7 x .048 the total is a little over one inch.

It's a sometime occurrence that clutch plates will stick together if left for any length of time. Pulling in the clutch lever and using the kickstart will usually free them.....But not always!! Ron

email (option): ronpier@talk21.com

I was advised that my clapped out gearbox [sidecar use] would work ok if I changed the equally knackered 6 spring clutch on my 1954 M21. I got the clutch kit from Kidderminster Cycles and all I had to do was shorten the pushrod slightly. Clutch is brilliant and the gearbox now acceptable. One has to make sure one gets the correct adaptor as the one for BSA twins is different.

So far I'm very happy with my single spring clutch.

Mark

email (option): pes.sales@btconnect.com

Ian, as I am using the late preunit bsa 4 spring clutch can you advise the " few things to note" when doing this conversion. Thank you Charlie

email (option): millcrocfarm@gmail.com

You will need the correct clutch adapter..The type for swinging arm models is incorrect...In recent years this adapter has had the taper diameter altered to suit the M20 mainshaft AND give the correct alignment with the engine sprocket..You will also need the BSA type mainshaft nut and washer (remember these are basically Triumph clutches)....There are two weights of springs for the 4 spring clutch...A shorter 'heavier' one and a longer less 'heavy' one...You need the longer type for the M20 for a nice light clutch action...You will also have to alter the length of the clutch pushrod slightly...Finally run a 15W-20W oil in the primary chain case to reduce the inclination of the clutch plates to stick together when left standing...Ian

email (option): ian@wright52.plus.com

email (option): darrylgubbels@gmail.com

Darryl, do you have any more information on this clutch conversion or pictures?
Contact details?

Mark

email (option): pes.sales@btconnect.com