Has any-one fitted a modern deep groove bearing to replace the rollers in a single spring M20 clutch, or the Triumph type as fitted to A10's.
A 6007 bearing is very close, without too much machining.
Just wondering what the bearing size would be??
Thanks keith

email (option): keithatkinson@hotmail.com

Its only for when the clutch is pulled in when the engine is running. its overkill to change it & the design suits the purpose.

Hi Kieth...I fitted one to my WB30 and my mates WB29 as the original clutch centers were unavailable and not common to any other model. Personally, I also particularly dislike the BSA 6 spring clutch as well and wanted to replace it with a Triumph clutch if possible....I used a modified M20 clutch sleeve with a ball bearing mounted into a modified Triumph clutch basket...
The whole thing took about a week to workout and make but it worked very well...One advantage of the bearing is that it completely eliminated the 'rock' of the sprocket inherent in the loose roller design and produced a very clean 'lift' of the plates...
I have thought of modifying my M20 in a similar manner the next time the clutch requires attention, as the roller track in the clutch sprocket is no longer available and wear in this part (and the sleeve) makes the clutch run out of true when the plates are seperated..I agree with Fred that the original set up does work, but this particular modification produces a more accurate operation of the clutch, which has to be a good thing...Ian

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

Ian, fair points, I think I'm the only person in the world who gets on OK with that 6 spring clutch : D

Hi Fred..There are others who argue for the 6 spring clutch...some because they have one that works, others on the basis of originality...
My view is that the clutch is poorly designed and cheaply made compared to either the M20 single spring clutch or the Triumph one...
History tells the story...The AA never had the 6 spring clutch, sticking to the single spring one until 1960 when the alternator was fitted to the M21, and then they had a Triumph clutch until the end. (1963)..BSA wasted no time and immediately took the Triumph clutch and adapted it to the BSA range as soon as they bought the company...Now I wonder why they did that?.. ....Ian

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

Not doubting for a minute they are a bizarre creation, but the M24 runs one nicely & with 6 springs its going to be 6 times better than a single spring : )
I do run a single spring clutch happily on my V Twin.

FWIW the old time speed way racer who tought me to ride fitted a solid bronze ( think it was actually leaded gunmetal ) bush to my A 10's 6 spring clutch.
It made a masssive difference to the clutch and also made the primary much quieter.
It also taught me to select neutral & not ride the clutch at the traffic lights as it would heat up & lock solid if held in for longer than a couple of minutes.

email (option): wariron@tpg.com.au

Solid bush sounds fun : D
particularly as the design needs the drum to move forward slightly when you pull the clutch in giving built-in misalignment (OK not enough to matter) but a binding bush wouldn't help.

Good advise there as always. You don't happen to know the bearing size do you?
On my triumph clutch adaptor, a 6007 is about 0.25mm to big, with an ID of 35mm. Also the OD is 62mm, which is a suitable size for the clutch sprocket.
Thanks Keith

email (option): keithatkinson@hotmail.com

Hi Kieth...I can't recall the bearing number..but I do have a spare one somewhere in the workshop so I'll look it out tomorrow and confirm the size.
Starting wih the clutch sprocket (a Triumph one) I pressed out the hardened roller track and bored the sprocket out to give a press fit on the bearing. However, the bearing was slightly wider than the back wall of the clutch sprocket, so I machined a 'top hat' holder from aluminium, also a press fit onto the bearing, which accommodated that extra width.
Next I pressed the bearing into the holder and then pressed the bearing through the clutch sprocket. That way when the flange of the holder came up against the back of the sprocket I knew everything was square.
I then drilled and tapped three holes through the holder and sprocket and screwed it to the back of the sprocket.
What you have to ensure when working this out is that the bearing, once positioned in the sprocket protrudes the right amount to position the clutch center correctly when it is fitted to the mainshaft adaptor..This is important as the spring screws in a Triumph clutch are prevented from turning by a shoulder on the rear face of the center. They are kept in position by the proximity of the screw heads to the inner face of the clutch sprocket when the center is fitted..
As I say I used a modified M20 clutch sleeve so there were differences...
With the BSA/Triumph clutch adapter you may be able to do what I did with the M20 sleeve. There is also a difference between the bearings inner diameter and the outer diameter of the M20 sleeves bearing track...However, in that case the difference is greater so was actually easier to adapt...
I got over the problem by making a 'split collar' which I machined to the same inside diameter as the clutch sleeve bearing tracks outer diameter. The outside diameter I machined to be a sliding fit in the bearing...
I then just put the split collar over the adaptor and slid the sprocket over it. Once fitted the clutch center prevented the split collar coming out...
So, a possible solution might be to have the clutch adaptor ground down on the bearing track diameter to give yourself more to play with dimensionally and then make a split collar in the same way.
The other thing you need to be mindful of as well and you will have to work out is where the clutch sprocket will then end up in relation to the engine sprocket...You may find you have to look at slimming down the back 'shoulder' of the clutch adaptor to make some more room for the bearing (and you might have to reduce its diameter as well so that it fits inside the back of the 'top hat' and against the bearing....As I said initially...it took me a while to work everything out.... ....Ian

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

Thanks for the advise Ian; I will paste your information into a folder, for reference later as I go along. I will work away at this little project over time.
I have the triumph clutch, and I'm working on fitting it to my 1948 - 1951 BSA bitza. I have married the narrow front frame to the wider rear section successfully, and it is coming along nicely.
Now I don't want to aggravate the purists, but I am going to fit a sealed ball bearing, because I want to fit a toothed belt primary drive, and do away with the chain, and chaincases altogether.
I have a belt on my WLA, and it works a treat.
I will have to fit the clutch pulley centrally with regards to the bearing to prevent excessive side load.
I will have to machine the adaptor with the top hat further in, to allow fitment of a wider bearing. The oil scroll area of the adaptor, is now free space. The inner and outer bearing tracks will have to be ground, rather than machined in a lathe, due to the hardness, I would imagine.
With your detailed explanation I should be able to eventually manufacture a set-up that works properly.
I'll report how I get on.
Thanks Keith

email (option): keithatkinson@hotmail.com