Cush centred clutch for B33 tin chaincase?

[mikeb]

Its time to do something about the 6 spring clutch in by b33 – a 1949? xb engine in a plunger frame. It’s a tin chaincase and (I believe) a tapered mainshaft. EDIT: Its a 1947 XB (you'd think i knew that)

I’m thinking about a 3 or 4 spring triumph clutch with a cush centre. I’d prefer a cush centred clutch so that gives me options around the current cush drive space – ideally one day a sprag clutch for an electric start (I know that's optimistic...). From lots of goggling I believe it’s possible tho I’ll need:

• the longer tapered clutch hub adapter, called 42-3107A (eg on feked) that sits the clutch in a bit closer to the gearbox
• I may need to add a spacer inside the current cush drive for chainwheel alignment
• I may need to fettle or reverse the sliding plate behind the clutch so it meets the scroll.

SRM tells me their clutches are too big to fit the tin chaincase. So:

• Will be above plan likely work?
• What cush centre clutches off what bikes are likely to fit the tin chaincase?

Thanks!

[chaterlea25]

Hi Mike,
A chance bought autojumble shaft adaptor
Fitted straight into a ZB chaincase and the 4 spring clutch lined up perfectly with the engine sprocket . If only I knew it's part number?
I have done all or combinations of the mods you listed on other tin cased ZB bikes, I have not had any problems with clearance to the outer cover, except trying an SRM cush drive nut!!.
You can also space out the rear case  a bit if needed..
I have not tried a cush drive clutch centre but it might be ok if you are able to solidly fix the engine sprocket  to the crank?
A guy I know heavily modified a Pearson electric starter on his ZB 34, but I have not seen the insides of the cases
You will just have to "Suck it and see"

John

[mikeb]

Thanks for the comments John. I saw your posts about making this job work, so was a bit surprised SRM said their clutch won’t fit. I wonder if they can’t be bothered with dodgy mods like this (fair enough).

The issue must be about where the clutch sits on the clutch hub’s taper and the chainwheel basket size:

1.  if the basket sits too far out on the taper and hits the tin chaincase, then I assume get the taper turned in further to sit the clutch more inboard….? Rather that than pack out the chaincase somehow.

2. As far as I can tell from the interweb the chainwheels on the 6-spring (42-3223) and the 4-spring (42-3266) are both approx. 154mm ID and depth appears similar-ish 35mm?? And I think the cush centre and ‘normal’ centre 4 spring clutches are physically the same size…? But the plates on the 6-spring (67-3242) are about 10mm less in diameter than the standard 4 spring (42-3262) or cush (57-1362) plates which suggests otherwise.
 
Question - Does anyone know the relative (or absolute) sizes of the early 6-spring assembled clutch vs the 4-spring cush centre clutch?
I could take the chaincases off the A and B and measure, but if someone just knows that would help the planning stage.
 

cheers

[KiwiGF]

Thanks for the comments John. I saw your posts about making this job work, so was a bit surprised SRM said their clutch won’t fit. I wonder if they can’t be bothered with dodgy mods like this (fair enough).

The issue must be about where the clutch sits on the clutch hub’s taper and the chainwheel basket size:

1.  if the basket sits too far out on the taper and hits the tin chaincase, then I assume get the taper turned in further to sit the clutch more inboard….? Rather that than pack out the chaincase somehow.

2. As far as I can tell from the interweb the chainwheels on the 6-spring (42-3223) and the 4-spring (42-3266) are both approx. 154mm ID and depth appears similar-ish 35mm?? And I think the cush centre and ‘normal’ centre 4 spring clutches are physically the same size…? But the plates on the 6-spring (67-3242) are about 10mm less in diameter than the standard 4 spring (42-3262) or cush (57-1362) plates which suggests otherwise.
 
Question - Does anyone know the relative (or absolute) sizes of the early 6-spring assembled clutch vs the 4-spring cush centre clutch?
I could take the chaincases off the A and B and measure, but if someone just knows that would help the planning stage.
 

cheers

Hi Mike, maybe ask Bob Newby (BNR) if their chain drive clutch will fit?

I fitted a BNR belt drive to my ‘49 B31 but it many hours to mod the chaincase and of course it doesnt look OEM (close up)

[JulianS]

The 1958/59 alternator B31 and 33 use a 4 spring cush centre clutch but with one less bonded and inserted plate making it a bit thinner.

The chain wheel is a bit thinner than the A10 4 spring.

The B31/33 assembly (but not the sleeve which sits on the gearbox shaft) is very similar to the Triumph 5T pre unit alternator assembly which also has 4 bonded and 5 plain plates.

The B31/33 alternator parts book lists 5 bonded and 5 plain, putting a bonded plate next to the pressure plate. however the cross section of the clutch in the owners manual shows 4 bonded and 5 plain.

Worth research if a thinner clutch is sought?

[mikeb]

Thanks Kiwi and Julian.
I think I need to pull the chaincases off the A and B and do some measuring/test-fitting. Tho might be a bit before I find the time to do so. I also have an alternator? tin chaincase off what I think it’s a B (has a larger lump where a cush drive would go) so that may give options.

Kiwi can you post pics and words of what you did to your chain case to fit the Newby belt setup? I’ve emailed them to ask as you suggested. Tho at this stage I’m thinking anything should do such as the cheaper 43T 4-spring cush clutches available online, with the deeper tapered hub adaptor.

cheers

[KiwiGF]

I fitted the full width belt kit not the thinner one …which was probably a mistake. Here is a selection of pics (I have more)

You can see a full width chain type clutch would probably fit and the thinner one (if available in chain drive) almost definitely. The clearance issue was with the belt and larger front pulley, rather than clutch.

[mikeb]

thanks for posting and well done Kiwi. that looks like a lot of work.
why the open section (am i seeing that right?). it looks too small to keep your lunch in.

[KiwiGF]

thanks for posting and well done Kiwi. that looks like a lot of work.
why the open section (am i seeing that right?). it looks too small to keep your lunch in.

If I am understanding yr question right, the recessed section (inside the belt run) is to keep the footrest location oem.

Simon

[RDfella]

I fitted the full width belt kit not the thinner one …which was probably a mistake.

Nah, THIS is a full width belt (our favourite Hogan saying, modified)

EDIT - not forgetting that flat belt drive on the cycle pacer that recently appeared on this forum (courtesy of GB I believe).

[mikeb]

lets see you get that into a tin chaincase RD, then you get the hogan award!

and you did understand my question Simon. tho i'm a bit worried the belt might not handle the b31's torque. also BTW Bob Newby replied that his  chain clutch is non-cush, duplex chained and for Enfields. good to check tho

[chaterlea25]

Hi Mike and All,
I have found a few different depth solid clutch centres, but only one thickness cush centre???
In my opinion a cush drive is essential somewhere in the drive line..
I have  BNR clutch that came with a worn solid front pulley from a GS, it had not done many miles, 1/4 of the teeth show wear from the power stroke I assume..
I sent a standard cush drive to SRM and the fitted a pulley to it...
Beware of the cheaper 4 spring clutches on the market!!  They are made of cheese!!!!!

John

[KiwiGF]

lets see you get that into a tin chaincase RD, then you get the hogan award!

and you did understand my question Simon. tho i'm a bit worried the belt might not handle the b31's torque. also BTW Bob Newby replied that his  chain clutch is non-cush, duplex chained and for Enfields. good to check tho

The BNR belt drive kit is used on hotted up goldies so should handle yr B33 😏 though I didnt expect you to fit a belt just to get a decent clutch. I was fed up with leaks from the primary case and having to top up on longer rides, so went for the belt and a “dry” case.

I had a choice of just two ratios offered, and went for the smallest front pulley BNR would recommend.

[mikeb]

So I’ve pulled the clutch out of the B and the chaincase off the A. there is a lot of wear on the B’s 6-spring cutch hub, the tangs on all the various plates and the basket, and the inner bearing race badly pitted. which strengthens my interest in replacing the whole thing.

Measuring and testing fairly carefully, the basket diameters are essentially the same but the 4-spring is about 1/4" deeper and the pressure plate a different shape. Still, it fits into the tin chaincase and can probably protrude an extra 1/4" inwards before contact.

So if the chainwheel aligns with the front cush sprocket then all should fit. Which is what you’ve all been telling me. I assume people get stuck mainly with the different depth of taper in the hub adapter sitting the 4-spring out further. Or maybe some clutches are different physical sizes.
So… ready to put my money down for a new 4-spring cush-centered.  Only problems is finding one.

John – you say some clutches are made of cheese, which, while best avoided, might be something the B would struggle to cut anyway. I can only actually find one in stock (looks 43T, simplex but I’d need to call and check), on dragonfly:
https://draganfly.co.uk/shop/82052/cush-drive-clutch-assembly/#BSACUSH
Should I be afraid? anyone know of other (cush) options?

thanks

[chaterlea25]

Hi Mike,
I would wonder which shaft adapter is included with that clutch?
If the clutch sprocket is not UK made then Avoid, The better clutches are made by Les Harris (Triumph)
The clutches are identical to the pre unit Triumphs except for the shaft adapter so there maybe alternative sources?
My experiences with drag's have not always been positive and the "OK so return it" attitude leaves a lot to be desired

John