On recommendation from Ian, I bought mine from Monty's in Devon https://montysclassicmotorcyclesshop.co.uk/

It was for my special M20 which has an Indian engine. The Indian engine has no cush and it was a bit harsh so I bought a Bonny clutch with rubber cush. The rubber cush is not necessary for a normal M20 though. It's a very light sweet clutch now. Ron

email (option): ronpier@talk21.com

I don't where it came from, but I have one here that I don't think has done many miles. The basket is quite well hammered. I was thinking of doing the same, but seeing this has put me off.

Mark

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

You need a complete clutch for a 650 pre unit Triumph but you will need the mainshaft adapter specifically made for the M type gearbox mainshaft....Monty has them in stock currently...You also need the clutch center nut and washer used when fitting the Triumph clutch to a BSA (A10/late B33 for example)...There are two lengths of springs for Triumphs, the longer, lighter ones being the ones to go for for the M20...Save yourself some money by getting the 'non shock absorber' clutch center. As Ron notes you don't need the shock absorber type for the BSA as they have the crank mounted absorber...You'll also need a different length clutch pushrod...I usually buy lengths of 1/4" diameter silver steel and make them to suit...A standard length of silver steel is 13" and is long enough to make any of the BSA clutch pushrods...
I favour parts manufactured by L.F. Harris which Monty supplies...However, the clutch drum/sprockets are currently out of stock nationally. I'm waiting for one myself at the moment...I've fitted scores of these clutches over the years and they are standard fitments on later swinging arm pre unit BSAs and many later models in slightly altered forms...
I've known Monty for decades going back to the days when he worked at Terry Hobbs Motorcycles in Plymouth...I have no specific interest in his business and recommend him only as he is a good supplier...Ian

If it's any help, I have fitted a Triumph clutch to my 49 M33. I bought the clutch from Kidderminster Motorcycles.

I also sourced my clutch from Kiddiminster motorcycles (a few years ago now)

Best thing you can do to any BSA B & M series, I have fitted them to all the M20/21s I have owned.I have one fitted to my 48 M21... fit & forget.Never had any Hammering of clutch basket though, if they can take the stick from my tuned pre unit Triumph then a M20 should not pose a problem. Also like the old single spring clutch good design if you can keep the oil out off plates & get it adjusted to disengage evenly.

Hi Ian
You mention a 650 clutch - I have an nos 350 pre unit clutch which I would like to fit to my 41 m20 when it gets its go on the bench

The post war 3T clutch is the same as pre war triumph - any idea if this would work ?

Br
Job

email (option): jonnyob1@googlemail.com

Brilliant, thanks for the advice everyone, looks like I’ll be giving monty’s a bell after payday! 😁

Anyone going to Newark tomorrow ?

Tom

email (option): t-watts1@hotmail.co.uk

John the Triumph 5SW (500cc) was fitted with the same clutch as the 350 models 3SW and 3HW. ie 4 steel and 3 friction plates. But I've never completely cured mine of some slipping. But when I inspected the pre war civy parts list, the 5S was given the same clutch as the Tigers 90/100 and Speedtwin. ie 5 steel and 4 friction plates. (WO economies?)

So if your clutch is that size I see no reason why it couldn't be used on an M20, providing the right main shaft adapter is used. The M20 might be heavy, but it doesn't have anywhere near the power of those Triumph 500 OHV models. Ron

email (option): ronpier@talk21.com