Six Spring versus Four Spring Clutch?

[LJ.]

Right lets arouse some sort of discussion here to revive a rather flat forum at the moment...

I now luckily have two A10s both of the same year (1961) and released within two months of each other. They are both identical apart from front/rear mudguard stays, front hub size and Clutch arrangements.

I have on one bike, and I think most owners agree, a four spring clutch which has proved to be a good and easy to set up arrangement over the six spring one.

Well I was discussing this with another A10 owner a week ago and he disagreed, 'Feel my clutch lever' he said, and boy! was it smooth and light! It felt better than my four spring one. There must be some secret in setting up the six spring correctly. I currently have mine all to bits after building up super strength muscles in my left hand. Everything in the housing is near enough brand new. Now I'm wondering how to put it all back together again. I'm not going to use any grease in the primary case anywhere, (I had found grease contaminated plates from 'flung' grease in my M21) I am also going to lightly oil all the plates and then just lightly turn the nuts to just slightly compress the springs ensuring each side of pressure plate is even. Now before I put back the primary cover I shall try to kick start, and if I can turn the engine over without any slip then I may have cracked it. Finally there must be some sort of secret to how the cable is run. I shall certainly use the teflon or nylon inner for smoothness rather than the old metal on metal sort.

Well what do you think? Can I improve any more or do you have any tips to offer?

[a10 gf]

There must be some secret in setting up the six spring correctly.

yes, whatever time it takes doing individual spring adjustments until they lift evenly all around. Even springs, completely straight pushrod and the other parts in good condition, then the 6 spring will be smooth, soft and reliable. And try moving the (well lubed) cable around to see if the clutch gets lighter in a certain position, then try routing it in that direction or get a new cable.

Regards
e

[fido]

I would have thought the M21 should have the earlier clutch like on my A7. This has a domed cover over the plates to keep the chain oil out. This seems to work a lot better than the one on my previous 1959 6 spring A7SS, although the plates do need freeing off before I start the engine. A heavy clutch action is more often the cable than the cllutch springs.

[Beezageezauk]

OK, the argument between the 4 spring and the 6 spring clutch is a valid one if you don't know how to set the 6 spring clutch up properly.  Funnily enough, not many of us do know the secret.  However, a friend of mine has found the problem and has written down his findings.  He sent me a copy which I will copy word for word.  I'm sure he won't mind.  It is a bit long winded but worthwhile digesting if you want a nicely operating 6 spring clutch.  Here goes.

If you're familiar with A10 clutches you'll know that the 6-spring variety gets really bad press and most people say they are pigs to set up and you have to catch neutral when you're rolling etc.  Some people say that theirs are fine.  I might just have found out why!!

The clutch chainwheel runs on a ball bearing with two rows of balls.  The inner part of the chainwheel is therefore the outer bearing surface (sleeve) of the ball bearing.  This sleeve is a press fit in the centre of the chainwheel and the extent to which it is pressed in determines the clearance between the back of the chainwheel corks and the clutch backplate (behind the chainwheel).  On checking my mate's clutch the centre of the chainwheel had not been pressed in far enough ( by just less than 1mm actually).  It turns out that this is critical.  The bearing sleeve was proud on the outer side of the chainwheel.  When we tightened the clutch centre the tightening pressure brought the corks of the chainwheel to press against the backplate behind the chainwheel because the clutch centre was pressing against the chainwheel centre.  (Sorry about the long sentence, but that's the critical bit - it might be worth reading it again!!). 

The solution was to remove the chainwheel and tap the centre sleeve through it until it protrudes enough to come into contact with the backplate just before the corks do.  The idea is to achieve minimum free-running clearance between the backplate and chainwheel corks. 

After making this adjustment the clutch centre tightened up against the inner sleeve of the chainwheel bearing and the tightening pressure transmitted through the inner sleeve of the bearing to the backplate, leaving the chainwheel to spin freely, but also ensuring that when the clutch plates were under pressure the chainwheel corks were pressing against the backplate.  We assembled the clutch in the usual way and it worked perfectly.

So the problem is the corks at the back of the chainwheel, not the clutch plates in front of it.

There you go LJ.  Give this a coat of looking at and you will see that it makes sense.  I'll test your A10 clutch the next time we meet up but before we have a couple of beers.

Beezageezauk.

 

[trevinoz]

I too am running both types of clutches on swinging arm machines. I have modified both to radial needle bearing lift. The 6 spring type I set up the innermost steel plate on it's centre and fitted it on a shaft and machined it true. All steel plates were set up on a jig and machined true. The whole thing was assembled on the bike and adjusted to lift cleanly but there was still some drag which I finally cured by substituting the 7/8 lift clutch lever with a 1 1/16 type. The result is a clutch which releases beautifully every time. No more crunching into first and can find neutral at stop.
My 4 spring is as light as a feather with the cable routed under the tank and through the holes in the ski slope.
I haven't had a go at the plunger 6 spring type yet.

[Brian]

I thought that maybe a few lines about the different clutches might help. There are basically four types of clutches in the era we are interested in. The WD M20's had a single row chain, multiple plate, single spring in the centre type with a dome covering the plates to keep the oil out. The post war singles [B33, M21 etc] had the same clutch as the swing arm A10's, single chain, six springs. The plunger A7/A10's had a duplex chain, six spring clutch, similar in design to the later four spring but with a dome covering the plates. There were a couple of variations of this clutch such as the triplex chain versions as fitted to the Super Flash and some American models but most of us are not likely to come across them. Then there is the four spring type. I have all of these types in various bikes and they can all be made to work well. As is always the case everything must to be in good condition, I only use Surflex plates plus good quality cables. Just because a cable is new doesnt mean it is any good, stay away from cheap stuff. Always make sure there are no grooves worn in the clutch basket fingers. Dont know if any of this will help anyone but maybe.

[LJ.]

Excellent posts! and thanks to each and everyone of you. This will most certainly be a valuable thread to many who just don't have a clue in setting up a successful working clutch of any description.

It is so easy to just dump the six spring and go for the four spring effort which would be a shame because we would then be turning our classic bikes into... well, like dumping the magneto for an electronic Boyer system, when a perfectly maintained Magneto works wonderfully.

Thanks again for your advice...
Cheers!

[G/F DAVE]

  I have a four spring clutch fitted in place on my civillian M20 as the old six spring used to slip under load ie; one pillion passenger & two in the box. I think its actually a pre-unit bonneville clutch with a adaptor for taper ,has easy action on clutch lever & still on bike today working well with no problems after 24yrs ownership. My A10 plunger has standard six spring clutch but with no top hat fitted. take your time to set up clearance for plates and make sure they lift equally, I also have fitted a ariel arrow mushroom headed clutch rod end .this is approx 80mm in length and I have shortened original rod to suit ,This gives greater contact area on pressure plate and I have no problems with finding neutral and gear change is crunch free.I also use ATF oil in chaincase to lube primary chain as this is a thin oil I have no problems with clutch slip.I think a lot of problems with heavy clutch levers are down to cables & routing them. A lot of pattern cables are to long & you have to find a route to get rid of the extra length which may not be the best. I always make up my own cables & on my A10 I route it from gearbox onto top of primary cases onto left hand frame tube up to clutch lever no sharp bends .works well for me..all the best Dave..

[trevinoz]

Let's go one better, I have modified a four spring clutch to three spring but have yet to road test it. I got hold of a three spring hub and brazed a stop lip on the end as per four spring type and assembled it into the four spring basket, with three spring pressure plate obviously, and radial bearing lifter. It is easier to adjust the run out.
A friend has gone even better and used the cast duplex basket after machining the teeth off and fitting a single row sprocket. He had to use 44 teeth as he thought 43 would weaken the basket.
   Trev.

[Brian]

Its obvious that various people have come up with different ways to alter/modify their clutches but have we reached a point where clutches are getting modified for no real gain, change just for the sake of change? It is possible to put japanese bike clutches in but why??? All the original BSA clutches can work well and the four spring is a very good clutch, I just cant see the need to alter it. Is it possible people are modifying clutches to overcome problems that dont exist, for instance a heavy clutch may just be a simple cable problem or too much tension on the springs. Just my thoughts, what do others think?

[a10 gf]

Can only speak for myself, the original 6 spring on my plunger has always been working perfectly, no plans or need to alter anything. If parts are in good shape and it's set up properly, I can't understand why there should be any problems.
e.

[fido]

I've always wondered why BSA abandoned the bolt together engine and gearbox in favour of the later movable  gearbox. The early design seems a lot better with it's duplex chain. Perhaps it was a cost cutting exercise so there were more parts in common with the B series singles.

[groily]

Reckon you're right Fido. Also - would there have been too much fresh air in the s/arm frame if the bolt-on box had been retained? Groily

[G/F DAVE]

Has anbody ever fitted a plunger motor into S/A frame ?????, I have seen one and looked like a standard A10 until you looked closely, who ever built it had shortened the frame to suit the engine size.this is the A10  BSA should have developed, instead of the pre-unit, Everything on a bolt up motor expands at the same rate as engine temperature rises, it has a duplex primary drive, in all a compact motor.I have a accident damaged S/A A10 frame & I am tempted to go for the disc cutter to fit a plunger motor into it.I reckon steering could be a bit quick with altered wheelbase,But could be cured with the right rake & lenghtened swing arm,I have two projects on the go at moment this could be the next after they are finished. After all people have shortened norton featherbed frame to suit unit triumph motor without affecting handling, Dave..........

[old PJ]

LJ i use the four spring clutch and its been very good i think the six spring clutch is very easy to get the parts for which clutch plates you using , I use serflex and they seem ok, I had trouble years ago with worn plates and it was the dogs that was the problem they had worn bad with big lumps out of them and that made it hard to change gear, 
OLD PJ