Best replacement upgrade clutch

[Roadhog]

Hi all. I know this has been discussed many times over the years and reviewing at most of the info , it does not help me too much. So:
I wish to upgrade my A10  1952 plunger six spring clutch to a more modern reliable clutch. So advice please- which is the best replacement clutch to use and what parts are required for a straight change.
Thank you in advance.

[muskrat]

G'day Roadhog.
What is your clutch doing wrong? The semi unit 6 spring clutch is in my opinion the best, certainly much better that the later pre unit 6 spring. In 37 years (of abuse) I've only replaced the plates and springs once!
I doubt you'll find a straight swap (life aint that simple). I believe the spline on the mainshaft is the same as a Notrun clutch, I don't know which model. Then you'd have to adapt the engine sprocket to suit it.
The other alternative is to put a pre unit mainshaft in the gearbox and look at the conversions for them. Still be a bit of work.
Cheers

[Roadhog]

Hi Muskrat. thanks for that, Im confused, I dont think there is anything wrong with my clutch, but reading all the articles that are everywhere, they say the six spring clutch is useless and you have to keep taking off the outer case to adjust it, so to change to a more reliable type is recommended by some. Maybe they are all speaking about the later six spring clutch? I dont know.

[JulianS]

The reviled six spring clutch is the one used on swinging arm models. Nothing like the plunger version.

[berger]

I have not been to the pub, there aint nowt wrong with a 6 spring swing arm clutch if you can be arsed to set it up with a dial gauge and take time setting up  the spring pressures.... but hey ho everything has to be done yesterday with minimum fuss and maximum profit

[Triton Thrasher]

If your clutch works, then in what way is it “useless”?

Just ride the bike.

[Roadhog]

It seems that so many people have written in various articles and forums that the six spring clutch is no use, and best to update it, It seems from what people are saying here that this applies to the later pre unit clutch and not the plunger clutch, i just need to know thats correct, in which case I will stick to what I have, if people do have problems with it, I just want to save myself problems later.

[Swarfcut]

  Stick with what you have.  It is not perfect, but it is pretty good.

  I reckon the plunger semi unit 6 springer  is one of the best clutches BSA ever  made, a soundly engineered  unit, easily capable of handling most abuse.  As Julian says, the poor pressed steel centre S/A version 6 springer is the one  that suffers  the harsh critics.

  The duplex chain means alternative choice is limited. Well set up these clutches work fine, not so well set up they still work OK. You will never completely eliminate the first gear clunk, because there is always a very slight drag in all multiplate designs, even if the plates lift cleanly and completely.

    There is always an element of shake to the plunger clutch chainwheel assembly due to the narrowness of the roller bearing track and clearance between the the back of the clutch centre, the chainwheel centre and the face of the thrust washer on the gearbox input shaft.  I reckon once you are rolling, the gyroscopic effect keeps the clutch rotating in a vertical plane. So accept a bit of rock, they all do that, at least it means nothing is binding.

  Anyone know of a thrust bearing conversion for the push rod/ pressure plate ?  That pressure plate tit has a hard life.

 Swarfy

[duTch]

 I can also verify the 'six-spring clutch' that causes grief is the later one. I also agree with the other comments, mine works quite well but does slip a bit sometimes but I think it's the springs have compressed as any more adjusting and they bind - I did buy new ones, but are wound the wrong way (as are many replacements I've seen)

 As Musko suggests, I had a Noturn diaphragm triple roller chainwheel to use, fitted straight on but diameter is too big....dunno what became of it

 Yep- stick with what you have and stop reading and ride it....

 

.....Anyone know of a bearing conversion for the push rod/ pressure plate ?  That pressure plate tit has a hard life....

 I thought about trying to adapt a Gutzzi one, but the bearings are special and not so cheap ....but there are ways 

[trevinoz]

Swarfy, I made one for my '55 Flash.
I made a mushroom with a thrust washer and radial roller bearing to bear on the end of the pushrod and another with a thread and thrust washer to screw into the pressure plate.
Works just fine but I can't say that it is any better than the original set-up.
This is on a swinging-arm 6 spring clutch.
I can select neutral with the engine running without any bother and selecting first while stopped is also very good.

The action is a bit heavy but the 1-1/16' fulcrum lever causes some of that.
a friend has several 6 spring clutches with the standard pressure plate and his clutches all work as well as mine.
It's all in the setting -up and the increased fulcrum.

[Roadhog]

Great , thank you all. I will stick with the plunger clutch, and put my newly rebuilt motor back in the frame. Thanks again.

[berger]

swarfy are you referring to a poor pressed steel centre made elsewhere out of butter or a properly reinforced and very tough BSA made one, as in the one that doesn't bruise when getting bashed with the plain plates, which end up getting burred themselves instead

[duTch]

 bergs-  The one I had in my RR was troublesome, but yes maybe you're quite well right....if I recall, it was the big special M/S nut that caused me most grief....in the end I adapted a M20 clutch I had, and it worked well- fitted straiht on I think, no actual 'adapting needed.....

 Roady- I'm sure you're aware, but is easy enough to do any clutch work while it's in the frame anyway

[Greybeard]

Plus one for the Plunger clutch.

[Swarfcut]

 Hi berger...I am firmly of the opinion that the plunger clutch is a far more substantial and better engineered clutch than the later S/A type with the pressed steel centre.  I am sure BSA designed the plunger clutch with heavy sidecar use in mind, so it is an altogether more robust unit. The  mainshaft spline fitting is far superior in terms of reliability and ease of maintenance. How many taper shafts end up with butchered keyways? Lots of 'em.

  I would not consider myself a harsh critic of the early S/A clutch, but like beers, some are better than others at doing the job. As you say, set up well it is OK, so maybe it gets the stick because of poor pattern parts.

  I suppose at the end of the day they changed a winning formula when the engineers were over ruled by the cost accountants.

  Trev.. SRM and others offer bearing type pressure plates for S/A clutches but I have never seen one for the plunger plate.  Standard set up works fine, but it is a lot of load on a single point of contact, not good.

  Roady, a well presented motor which has obviously had a lot of time and care put into it. It will be a tight fit getting it into the frame in one piece, so good luck with that. I prefer to load the crankcase and gearbox assembly in first, then add the barrels and head. Positioning the timing side engine plate can be a struggle, also check the mounting bolt threads under the gearbox are good,and nice and easy to slip the bolts in, its no fun under there if the threads are knackered and you have retap a thread in situ or get the whole thing out again.

  From the picture I assume there is no oil in it. No only joking, its a well deserved thumbs up from me.

   Swarfy.