I'm just completing a total restoration of a '49 M21 that came with an AA clutch. I've refurbished this and fitted a new set of fibre plates.

When I first reassembled it I couldn't adjust for it to de-clutch at all.
I then removed one flat and one friction and that seemed to help.

However, I've just got the bike running and still can't adjust it so that the clutch works effectively. I have to tighen it so much to reduce the drag when the clutch is in that it starts to slip when I kick it over.

Any ideas much appreciated!

Thanks,
Bernie
Dorset UK

email (option): bernie.a.jones@gmail.com

Maybe there are some dents in your clutch house when you make it flat so those plates can move easley Gr Theo

email (option): oldbikes@kpnmail.nl

Hi Bernie...Firstly is the clutch adjusted correctly with a correct length cable?...At rest the clutch operating arm on the gerarbox should lie at an angle in relation to vertical (with some free play on the cable) and when the handlebar lever is pulled fully in the arm should be vertical...is that the case?...Ian

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

Hi guys and thanks for your replies. I think all the clutch basket parts are good with no distortions or wear.

The clutch operating lever is the horizontal type that connects through a vertical, splined rod to the actuating screw with the ball end that presses onto the end of the rod - hope that makes sense!

With the cable and adjuster tight with no free play then the clutch still drags badly when pulled in so that the engine stalls.

(I also have most of the parts of an old 6 spring clutch but thought that the AA clutch was the better one to use - I'm not so sure now though!)

Thanks,
Bernie

email (option): bernie.a.jones@gmail.com

Hi Bernie..In that case the operating arm should lie parallel to the gearbox cover joint when the handlebar lever is pulled fully in...Is that how it is set up?...Also the part on the bottom of the clutch arm shaft that holds the adjustment screw must be fitted to the splines in the correct position relative to the arm.(the adjustment screw should lie at 90 degrees to the arm) The single spring clutch isn't too difficult to get set up normally, you obviously have a problem somewhere and you have to start by confirming the clutch is adjusted correctly and that the cable is the correct length. Also you must have the cable set up with the right amount of free play..remember that the cable is not there as a means of making clutch adjustments but only to join the operating arm to the handlebar lever after adjustments are made.....Ian

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

And you must have a handlebar clutch lever with correct fulcrum position, or your clutch will never lift high enough to free properly, most repos levers are wrong.

email (option): n.gentner@bigpond.com

Neale,
It's an interesting point you have made in respect to the fulcrum point on replica levers, I need to buy new levers as the original ones I had aren't correct, I would ideally like to get hold of Brass levers but can you recommend anywhere to get quality levers from?
Julian

email (option): 79Aust@sky.com

Julian,

There possibly is a specific source of good levers, but I don't know of it, all I can suggest is scrounge originals, or cut, modify and weld.

Norton, Matchless and Velo also have the fulcrum problem, probably others too.

email (option): n.gentner@bigpond.com

Many thanks for your continuiing help on this! I'm going to check it all over today and see if I can improve it. One other thing I need to check is that I have the clutch rods inserted correctly - I have the short piece with the large head against the actuating lever as this seemed the right way to do it.

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

Hi Bernie...The clutch push rod should be a single piece of 1/4" diameter silver steel, hardenen and tempered on the ends. Reference the amount of lift, the clutch arm moves through an arc and is at the highest point of lift when it is at 90 degrees to the clutch pushrod...that is why the arm should be in that position when the handlebar lever is pulled fully in...Ian

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

The best quality reproduction levers I've seen are here

http://www.vintage-replica.cz/

But the chrome plate is crap!! I expect Jiri will supply them in bare brass and steel for you to get done locally in a dull or cad plate finish. Ron

email (option): ronpier@talk21.com

Hi Ian,
The first rod I received was a single piece but wasn't long enough.
I then checked my parts book and found that 66-3067 seemed to be the rod for the 6-spring clutch and 29-3324 + 65-3943 is listed for the AA so I swapped for these. The overall length seems right so I've stayed with that setup for now but I'll go and measure the combined length to see if that could be the problem.

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

the rod should be straight with no "thick end ".
Sounds like yours has seen better days they do bend easy and oft owners shorten them but forget to harden the last 1/2 " either end.
There is not much clearence between the hole in the main shaft and the push rod so if your has "Upset" then it could be fouling on the main shaft.
Good news is you can cut the bad it out, reharden the end then add some spacers in the middle of the run.
I use old clutch rollers which work a treat.

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

Well I've had the cover off and checked the setup, rotated the lever a couple of splines to get it spot on and also adjusted so that it's parallel with the cover when fully pulled in. I also moved my clutch lever (std aftermarket job) out a little on the bars to increase clearance and get a bit more pull.

It's much better - still drags a little but I hope that will reduce as the new friction discs bed in. It looks like I could get more movement if I fitted a lever with a greater 'throw' so thanks for the suggestions and links

I've attached a picture of one of the rod parts - I couldn't persuade the other to come out and didn't fancy pulling the primary cover to poke at it - anyway it's just a plain rod. Sounds as if this is an unusual setup?

Thanks again everyone.

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

That looks like someone has been trying to improve the lift of the clutch, ala Norton and many more modern makes.

It is possible to successfully do this mod to the single spring BSA clutch and several persons have done so.

The intent is to use the "Top-hat shaped pusher" to resist any tendency for the outer pressure-plate to "cock" as it lifts.
Cocking occurs due to understandable imperfections in springs, back when all parts were new and made by BSA, the fix was to replace the spring. With current quality of replacement parts a new spring may not cure cocking.

A Norton "pusher" can be used, as can modified engine valves (some valves from industrial stationary engines even have correct 1/4" stem)
Stem to head radius and thickness of the head are critical (not a lot of space)

But there are caveats:
The ball seat adjuster in pressure plate must be deleted.
The centre area of pressure plate must run true to periphery, pressure plate can be corrected by judicious work followed by a light skim.
The loss of adjuster means the shortened pushrod and "pusher" have to be hand fitted fairly precisely. (not a five minute job)
The "pusher" must have minimal clearance in mainshaft, any slop defeats the entire modification.
Some, but not all mainshafts are bushed for pushrod, if you are lucky enough to have a bushed shaft, the bush can be removed and diameter of pusher stem can be increased accordingly. (more resistance to bending)
If cocking is extreme the pusher may eventually fracture (due to repetitive bending moments inducing metal fatigue)

Mod not recommended for the mechanically inept.

email (option): n.gentner@bigpond.com

Hi Neale,
Many thanks for the further info - I think its interesting that my parts manual shows the AA clutch push rod as originally being in two parts rather than this being an after market modification but I haven't yet found anyone else who has the same parts fitted ( I got mine from Draganfly in UK ). I fitted it with the short piece and larger end against the actuating lever as I thought that it would be designed to fit that way to take account of the slight 'sweep' of the push rod lever screw across the end of the rod as it rotates and swings a little.

However, I have also noticed that as the clutch pressure plate lifts it tends to do so more on one side than the other which I think is what you refer to as 'cocking'? I thought this might be due to the way that the spring is made - being harder to compress on one side due to the way that the coil is cut with both open ends being on the same side of the spring.

So maybe the two-part push rod that I have was actually designed to be used the other way round with the 'top hat' end against the ball in the pressure plate?

Regards,
Bernie

email (option): bernie.a.jones@gmail.com

Bernie,

My 49=58 parts book lists but does not illustrate 2 x AA pushrods (or probably 2 parts of a pushrod) 29-3324 & 65-3943
I once had a 1958 M21 (ex PMG) with single spring clutch, it had one piece pushrod 66-3067.

Yes, the uneven lifting is what I refer to as cocking.

I don't think what you have will be effective as a pusher, for mod to work:
Head/tophat has to push flat against pressure plate (delete adjuster entirely, ie press threaded fitting out of pressure plate)
Head of what you have is too small for pressure plate, needs to be at least 3/4", preferably bigger.

The 49 up adjuster(65-3403)in arm has a captive ball, I suppose its possible BSA intended the ball to wipe across the wider tip of AA pushrod.

In operation with a normal pushrod, the adjuster ball is often found to be recessed into actuating arm.
With AA pushrod this could not be allowed to happen, or the adjuster body would graunch againt pushrod. Also great care would have to be taken that AA head/tophat does not bottom on mainshaft

email (option): n.gentner@bigpond.com

Maybe another thing to consider relating to clutch drag. I was measuring my friction plates for wear after some years of use and found that they were still thicker than the original new plates as quoted in the standards book. It would seem that the modern pattern plates are too thick and will therefore overcrowd the basket. I have always run my WM20 with one friction and one steel plate removed. It gives plenty of room for separation and results in a very light clutch. I never experience any slip even though I am now at 600cc either on the road or if kicking through compression. Ron

email (option): ronpier@talk21.com

Hi Ron,
Yes, total height of plate stack is more important than the "correct" quantity of plates.

email (option): n.gentner@bigpond.com

8 plates crunching to get it into first when stationary 7 plate clicks into first gear when stationary like a 1920 rolls royce

email (option): roger.beck@node6.com

Likewise..I always leave out the last two plates...I've never done it myself but it may be worth considering doing the REME mod to the clutch spring nut if the 'tilt' is very pronounced and you don't have another spring to hand...
I find the single spring clutch pretty reliable once you have it working correctly and have found it to have a nice light action without any slipping at engine capacities of 500, 640 and 720 (SV). It is also worth noting that I never use the cork ring in the back of the clutch sleeve or the felt rings on the pushrod and mainshaft but have never suffered from oil contamination in the clutch.....Ian

email (option): Ian Wright

Bernie, I had this problem with the single spring clutch (uneven lift of the pressure plate.)After fitting a new spring the clutch worked fine and has continued to do so,even with all the plates in.I got my spring from Draganfly.I'm sure with a bit of tinkering you will sort it,and as Ian said,once set up they work well.Mick.

Thanks all - a new spring sounds in order, I suspect that I have the original judging by the condition it was in when I got it! Not sure whether spring steel age hardens but it was a total bu88er to get on!

Ian, you have me intrigued by the 'REME mod' to the nut!

Cheers,
Bernie

email (option): bernie.a.jones@gmail.com

Hi Bernie...I'll mail you the info. from the REME standards book tomorrow...Ian

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

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

Could you explain that a bit more Trevor?...The M20 clutch pressure plate is a steel pressing with equally spaced 1/4" holes around the periphery. It is very stiff due to its shape and with equally spaced holes (and being 'lifted' from the center) whichever way the 'grain' was running it wouldn't make any difference as I can see it. I can only see four operations in it as well..1) blanking out the material 2) pressing it into shape 3) Drilling the holes around the periphery 4) blanking out the hole for the pushrod ball fitting....Ian

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

Because I am a terribel artist ( spelling is not much beter ) this will be all text.
The problem is that there are 6 holes.
looking at the plate these holes are at ( clock positions ) 12 , 2, 4, 6, 8 & 10.
If the grain runs from 12 through the center hole down to 6 then you a primary flexiing axis 12 to 6 and 2 secondary flexing axies 2 to 4 and 8 to 10.
These plates will never lift clean unless you increase the lift or reduce the clamping pressure .
The simple solution is to use 5 holes.
This is the prime reason why the later 3 spring clutches generally work better than the almost identical 4 spring clutches that they replaced.
You can not get a primary bending axis with an odd number of bolt holes.

The ultimate solution was cross rolled deep drawing steel which did not come into general usage till the late 60's early 70's. If you think back suddenly car bodies got really square with sharp edges and really thin metal.

The pressure plate has no cupping and minimal thinning ( well the one I cut in 1/2 didn't ) so it could not have been done with a single press unless it was ironed ( dies with no clearences ) however this is unbelievably expensive to do and kills dies in no time flat. It also shows a specific surface flow pattern which was not apparent in the plate.
However the plate did show reversal at the bends which indicates that it was pressed in one direction then pressed in the opposite direction then pressed back ( sort of like popping a top hat ) . Pressing like this reduces the chances of tears around the quite sharp creases and the sharp creases increase the general stiffness of the plate.
The bolt holes were punched not drilled as there was no rotational distortion of the grains around the holes.

I would hazard a guess that they were :-
Blanked
Forward pressed
Reverse pressed
Finish pressed / trimmed ( very low clearences to correct any shpe irregularaties )
Punched ( bolt holes )
Punched ( center hole & locating slot )

While this could all have been done is a single multi stage multi pass press but considering what I have seen of the factory ( videos ) the press shop seemed to use a lot of small presses with parts bins between them.

I will have to check this but from memory one of the reasons for buying Carbodies was to get access to their big press shop and in particular to make pressed framed motorcycles

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

Thanks Trevor...very interesting. You have obviously looked at this in some detail...Now I have to say I have never had much trouble getting the single spring clutch to function as intended. With a spring that has parallel end faces and good condition or new components they set up pretty easily in my experience.
So, until your post I hadn't really considered the question of any weakness in the pressure plate....I'd like your views on my initial thoughts as detailed below....
Accepting the logic of your observations to be correct then a percentage of the pressure plates would have this weakness as inevitably some plates would have the holes and the grain in alignment.
Equally some plates would not have that particular weakness. In that event would you consider deflection of the plate not to be an issue?
Also, when considering possible weakness in operation the clutch pressure plate cannot be regarded in isolation as it is part of an assembly.. It is bolted to the clutch sliding plate and that would stiffen the pressure plate, potentially cancelling out any weakness. Although the sliding plate may itself suffer from a similar potential weakness the odds of having a weak pressure plate, a weak sliding plate and the 'wrong' alignment of any potential weaknesses in the two plates is now starting to reduce markedly I would have thought. Additionally, rotating one of the plates in relation to the other would counteract the weakness again...
Lastly, is it a correct assumption that the clutch spring exerts enough pressure on the assembled parts to cause a 'deflection' of the two plates, or rather, what evidence is there for that?...Ian

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

Trevor,
The theoretical flexing of some 15-4313 pressure plates due to rolling direction of the steel may well be correct.
However, 15-4313 is bolted securely to 15-4308 sliding plate and the spring and pushrod act on both as a unit.
It is my contention that any theoretical flex would be minimal in practice.

In my experience, clearly visible uneven lifting is attributable to spring 15-4311 and the fact that any uneven spring forces are poorly restrained by the 1/4" plain pushrod which acts as a pivot.
Your recommendation of the SRM top-hat pusher appears to indicate that you agree on this point.

Furthermore, in my opinion, the SRM parallel needle roller trust bearing in the single spring clutch application is a bad idea. It may be ok in A65s etc, and is certainly ok on regularly fettled race bikes, Manx Nortons had multi-ball thrusts in their heyday.
But the plain top-hat of the normal Nortons never gave trouble and was only deleted when AMC changed to adjustable springs and then finally the diaphragm spring

The Torrington type thrust requires lubrication which is not available in the BSA single spring clutch. Its required location in an M20 is also difficult to service.

Any uneven lifting will apply massive point-loading on one or two tiny rollers instead of the entire bearing.

In the 1980's BMW and Harley switched to similar small Torrington type thrust bearings on their clutch pushrods, (both lubricated) both companies suffered significant warranty claims and quickly changed to more robust thrust bearings.

email (option): n.gentner@bigpond.com

I wont argue with most of that.
It was just a note that some ( not all but some ) plates can flex and will never be able to lift squarely.
Most of this came from work with B 40's trying to work out why some plates pulled square regrdless of how badly adjusted they were while others set with dial gauges still dragged.
As i was working in a met lab at the time I was able to etch all of the plates that I had ( over 100 ) and others that came my way.
I had cut a plate in 1/2 to use as a spring compressor ( before I got the correct tool ) so I polished it and mounted it on the microscope.
I eventually used it as the basis of a paper for the Materials Selection section of a post grad diploma ( that I never finished )

The other problem is DPO's that "lap flat" a warped plate rather than "press flat" or beat flat.
Similar problems happen with carb flanges I have seen some ground down through the O ring hole.

As for the radial roller, as it is running between two substantial hardened bearing surfaces you should not get partial loading of the bearing
To be totally honest I have never fitted one to a single spring clutch but while the M20 was running the 6 spring clutch ( borrowed from the A 10 ) and on 3 A 10's I have used a similar set up as the SRM one, done down here by BSA Bill ( now deceased ) . A rod on a ball in a cup is not a recepie for a good square lift.

the single spring I had in mine when i got it would not select 1st while stationary although it made good clean changes through the gears and would select neural while stationary. I got use to it and just lived with it for 8 years till it was time for a rebore when the A 10 unit went on ( and yes it did foul on the chain case even after i shortened the studs ) which got replaced with a new single spring clutch 6 years latter ( last year ) when it was time for new rings again.
The new one also drags , but not as badly but this is due to wear in the box reducing the lift which will be fixed this month with a rebuilt box with a bigger pin through the clutch arm to take up the wear ( I hope ) depending upon how bad the wear in the clutch arm is .
Funny thing aboyt bike, the more you ride them the faster things get worn.

Bike Beesa
Trevor

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

It's been very interesting reading all the experienced and well-informed replies to this topic! I think that the first thing I will try will be a new spring and if that doesn't fix it then using a push rod with increased surface area against the pressure plate to prevent 'cocking' will be the next thing.

Having spent two years turning some old rusty bits into a bike for which I've just managed to persuade DVLA to issue a number plate (despite their best efforts to find fault with the application - Grrr!) I'm now keen to get on the road so hopefully the clutch will be OK for a few initial shake-down runs around the lanes here.

Thanks again,
Bernie

email (option): bernie.a.jones@gmail.com