Found in my archives: 6 spring clutch

[Greybeard]

I was going through some email archives and came across this.



6 GOOD SPRING EXCUSES (excuse the pun)

or

REASONS not TO BE CHEERFUL for using a 6 spring clutch

You have no/too much free play in your cable. No free play wears out the
push rod ends and can lead to a slipping clutch, too much free play means it
is difficult to select neutral or first gear. Adjust correctly as per
manual.

You have the wrong hub. Hub fits on the gearbox mainshaft. Pattern parts
are the worst. There are at least 3 different sized hubs available.

Your push rod has insufficiently hardened ends. Ditto pattern parts. Or
you have forgotten to lubricate the ends.

Your pushrod is not completely straight or worn at the side where it emerges
from the mainshaft. The latter caused by incorrect adjustment. Get another
one.

You have the wrong length push rod. Ditto pattern parts. The gearbox lever
must be at right angles to the cable when maximum pressure is applied i.e.
the clutch is slipping. When the clutch is engaged the lever will point out
slightly. If you can't achieve this then you have an incorrectly sized
clutch cable or clutch hub. Ditto pattern parts.

You have the wrong clutch hand lever that cannot apply sufficient leverage
or movement of the cable. Ditto pattern parts. The 6 spring clutch
generates muscles in your hand you never knew existed.
Your gearbox lever is loose on its shaft consequently the clutch will not
disengage. Fix it.

Your clutch plates are curved not flat. Caused by misalignment,
mistreatment or faulty manufacture. Replacements can be too thick - pattern
parts again being the culprit. You know this when you can't fit the small
nuts on the screws. Different clutches have different thickness plates.
The later ones are more substantial. Cork was used first followed by Ferodo
inserts. Then there came Surflex which was stuck on followed by the latest
white rubbery kind. You can fit the latest in all as long as the thickness
is within tolerance of 0.155-0.165". Otherwise if much thicker use one
less plate.

Your chainwheel and/or its inserts is/are not flat. If you have inserts
they should be 0.300-0.310" thick. Some UK dealers can replace the inserts.
The chainwheels do eventually wear out their teeth. Engine sprockets don't.

Your chainwheel is not aligned with the engine sprocket. Cure - shimming or
grinding engine sprocket. Shimming is thought to be an inferior solution by
some because the shims can break up in use as they are constantly pulverised
by the shock adsorber. Triumph engine sprockets are different
thicknesses from BSA sprockets although they look the same until you measure
them. Ditto pattern parts. Align with inner chaincase removed.

Your chainwheel is not parallel with the engine sprocket. Check if
mainshaft is bent due to running with primary chain too tight. Cure - new
mainshaft or get frame straightened or engine plates "adjusted".

You have the wrong clutch centre (thing with 6 captive screws). See hubs
above.

Your clutch centre captive screws are loose and not captive any more causing
movement in the clutch assembly not envisioned by BSA. Buy a new centre as
S/H ones are usually knackered. Original BSA centres are better and
stronger though.

Your clutch centre is loose. Cure make a holding tool with a long bar and
an old clutch plate. Forget the lockwasher (I agree with Gold Star Ron) and
use Locktite as you do up the mainshaft nut to a phenomenal torque.

You have incorrectly assembled the clutch centre bearing. Easily done if
you follow the parts book drawing because it is wrong. The two halves go
front to back, front to back and not as illustrated.

Your centre bearing is knackered because you assembled it wrong. Doesn't
usually wear out. Wear here will cause chainwheel wobble when clutch is
disengaged.

The plates are tight in the slots. File the tabs down. Also file off sharp
edges. Loose is good.

The springs are not correctly adjusted. Just fit a bit of wire to the
chaincase as a guide and kick over the engine with the clutch disengaged.
Adjust for even clearance (only takes about 2 or 3 kicks) and as loose as
possible. The idea is just to avoid clutch slip at full throttle going
uphill or otherwise you will break cables and/or moving parts due to the
excessive spring pressure.

Your sliding chaincase oil seal is not sliding correctly because you did up
the nuts too tightly. Adjusting primary chain tension by moving the gearbox
causes the oil seal screws to bend as well as the rear chaincase front
section. Cure replace parts and ease off on the spanners and rely on
Locktite. Do not overtighten chain it needs ½" of free movement - that is
gently up and down on a finger.

Friction plates and springs hardly ever wear out so save your money. Also I
have found that filing down the wear marks on the clutch centre has very
little if any effect.

Design faults:

The plain rear plate behind the chainwheel tends to wobble about and this
can cause problems. You can weld this plate to the hub in order to reduce
movement - if you do make sure it is square.

Oil doesn't agree with friction. Latest friction material is better at
working in an oily environment. Don't follow Classic Bike advice and dip
new plates in oil. The only oil is needed at the clutch bearing and
possibly at the push rod ends. Also the primary chain needs lubrication.

The only complaint I have is that the screwthreads in the clutch centre
sometimes strip if you use the 2 locking nuts requiring new clutch centres
which are inferior to the original BSA type. It should be possible for
someone to replace the screws but I know of no one who can do this. I use
the Triumph type 4 spring nyloc nuts to prevent this damage. Another reason
why I will never win a Concurs!

Final thought - most of the 6 springers still in use are 40-50 years old.
Most of the parts are damaged and worn out. The clutch never gets the care
lavished on engine parts for instance. If you are careful and thorough with
reassembly, making sure everything is perfectly correct you will find your 6
spring clutch is a very long lasting and reliable piece of equipment equal
to a Triumph 4 spring type. In My Humble Opinion. And if you still don't
like it you can always fit a Pearson clutch as long as you have plenty of
ackers.

[muskrat]

I think I know which forum member would have written that.
Cheers

[Minto]

Sorry to dig this up, but what an excellent write up it is. Just found it in a frantic search for info on clutch push rods, almost all the info I wanted was in there too so big thanks to whoever put it together.

[Swarfcut]

 Good job the 6 spring clutch used on the Plunger bikes was not mentioned......this earlier type is far superior to the later cost cut effort condemned above.

    The poor pressed steel centre version also suffers wear to the ends of the clutch adaptor splines as well as the clutch centre splines. The depth of metal here for transferring the power is miniscule compared to the full depth of the Plunger Centre. Another reason that centre nut needs to be tight.

  The tab washer hangs on by its fingernails and is better omitted, as outlined.

  The poor attachment of the captive threaded spring carriers on the pressed steel centre mean that with a loose one  you can't tighten or undo the nut, a hacksaw blade between the plates solves that one, and a new homepun threaded rod brazed or welded to the centre gives an otherwise scrap part a new lease of life. While you're there, put a dab on the others, and make sure they are all standing to attention, not leaning from a previous owner's effort.

 As a further observation on the bearing races, I put them with the two open sides facing  each other, in a vain attempt to keep the grease in and stop it working its way onto the plate behind the chainwheel.  Anyway, that's how cutaway diagram in service Sheet 308 looks to me. With  assembly  as suggested above there is little to retain the grease on the back race, and once it reaches the plate it will migrate  outwards to the chainwheel linings. The location position of the balls on the inner track is fixed by the paired grooves, but the chainwheel has an element of axial movement with the clutch disengaged. This disappears with the clutch engaged, and its true rotation depends very much on the trueness of the  backplate on the clutch adaptor sleeve and consistent thickness of the chainwheel inserts.

 Swarfy.

[bikerbob]

That is an excellent article, my A7 S/A model has the 6 spring clutch and set up correctly the only problem I have with it is freeing the clutch before starting it usually takes about 3 kicks to get it to free off. I have learn't from experience not to turn the petrol on and flood the carb before trying to free the clutch as at my age I always start the bike on the center stand and it would not be the first time that the bike started  up before the clutch freed off.

[RDfella]

Now I have an elect starter fitted to my GF, I find a different issue. The starter mechanism requires oil in the primary case (something I've avoided for 50 + yrs after the grief I used to have with slipping clutches on several bikes) and guess what? Can't get over 50mph due to clutch slip in 4th gear. Thank goodness the starter works on the crank, otherwise starting would be a problem too. There was a reason BSA fitted their plunger clutches with a cover - sadly, the cheap n nasty swing arm clutch is not so blessed.
Now I suppose I could convert to a superior plunger clutch - but I don't have one plus it would mean changing the sprocket and stripping the gearbox to fit a different mainshaft. Frankly, I can't be bothered. Unless someone supplies cork clutch plates (coefficient of friction of cork is not overly affected by oil) I'll just ride more sedately. Other than the clutch slip, it's a pleasure to ride. Really smooth motor (up to 50) and the best handling of any bike of the 50's / 60's.