Six spring clutch centre

[Slymo]

Joining the motorway yesterday I had a fierce noise from the primary cover. Had to pull over and walk the bike off the motorway at peak hour which was fun. Turns out one of the posts had pull out of the clutch centre. Never having examined it that closely in the past I see that the posts have been welded in from the back but quite a lot of the weld had either been ground or worn off. My plan is to make new posts and rivet and silver solder them in but I'm a bit worried about clearance with the basket. Anyone have any advice other than replacement with an alternative clutch?

[KiwiGF]

Joining the motorway yesterday I had a fierce noise from the primary cover. Had to pull over and walk the bike off the motorway at peak hour which was fun. Turns out one of the posts had pull out of the clutch centre. Never having examined it that closely in the past I see that the posts have been welded in from the back but quite a lot of the weld had either been ground or worn off. My plan is to make new posts and rivet and silver solder them in but I'm a bit worried about clearance with the basket. Anyone have any advice other than replacement with an alternative clutch?

You can buy new aftermarket inner baskets but I’ve no experience of using them.

The repair you can see is a common one, I think the posts were riveted originally but they do work loose and spin when you put the spring nuts on. If too much weld is put on to stop them spinning then the basket rubs on the outer basket, hence the grinding off of excess weld you can see.

Personally I would try to repair the original by cleaning off the old weld and rewelding it (using mig or tig or gas). If just one post is broken I would just repair that one.

You need to make a good attempt to get the posts lined up centrally in the pressure plate, to prevent one post taking all the force that can result from a worn pressure plate that can rotate a bit relative to the posts.

Edit: you may want to check the outer basket has the clutch bearing outer race correctly located, incorrect “adjustment” can cause the inner basket to rub on it, as can worn outer basket friction pads (from memory!).

[Slymo]

There appears to be a groove on the clutch basket designed to take the riveted heads so I have gone that way. Heating up the tops and beating them should result in a strong attachment. Just as well this one went within a mile or so of home as one or two blows with a punch took the rest of them out no problems. Ill finish the riveting and check the clearance. Might meeting to face it off in the lathe to finish. Obviously there is a bit more machining to do on the balance of the studs before I fit them. :)

[WozzA]

Those 6 spring clutch centers have to be the worst designed bit of kit on our BSA's..
after ripping the guts out of one of mine I found another in my spares box of bits & pieces that had one pin replaced at some stage.. I replaced all of the friction plates & bearing races etc & it still wasn't working correctly..   best idea is to bin the lot..    or buy my old clutch   

[Slymo]

They aren’t that flash but up until the horrible graunching noise it was working pretty well. I rang a chap that has supplied me some bits in the past and he had one also missing one post so it’s clearly a weakness.

[KiwiGF]

Those 6 spring clutch centers have to be the worst designed bit of kit on our BSA's..
after ripping the guts out of one of mine I found another in my spares box of bits & pieces that had one pin replaced at some stage.. I replaced all of the friction plates & bearing races etc & it still wasn't working correctly..   best idea is to bin the lot..    or buy my old clutch   

Just an observation, the inner basket on your clutch is protruding past the pressure a lot more than I’ve seen before. On both my 6 spring clutches the pressure plate is more or less level with the inner basket splines when fully disengaged. Possibly you have a mix of parts? Nice red paint job!

My A10 has a 6 spring with all new parts and works ok, my B31 did not work ok until I installed custom 2mm thick flat steel plates, but then the inner and outer baskets are pretty worn.

I use a dial guage to make sure the pressure plates lift evenly, tedious but it makes a difference, as does having the minimum spring tension that does not allow clutch slip.

Having said that, I’m about to install a newby belt drive on my b31 to solve the primary case leak issue for good 

If I like the belt drive I will get one for the A10 as well, soon the market will be flooded with used 6 spring clutches eh

[Slymo]

Yes nice red pressure plate but I wonder if you have a B31 basket there or similar. My pressure plate sits quite well inside the basket.

[KiwiGF]

Yes nice red pressure plate but I wonder if you have a B31 basket there or similar. My pressure plate sits quite well inside the basket.

A possibly little known factoid, yr inner basket is of the late “reinforced” type, it has strengthened “splines”.....you can see the tips if the strengthening piece, inside the basket, in your pics, not all baskets have that inner strengthening. Due to that strengthening your plates have “stepped” slots to cater for the extra thickness of the spline.

Something I’ve wondered is whether the cups under the springs all have the right diameter hole for the posts to have a bit of movement to help de-stress the posts when the pressure plate moves under load/braking.

Another “gotcha” is the depth of the cups, some are deeper than others which can lead to insufficient thread for lock nuts and other problems with getting the right spring pressure etc.

[RDfella]

Oldish post I know, but have often had these posts come loose (though not adrift) on my B31 race bike. Just clean up the joint and braze. Mucking about with the locknuts and generally forcing things about is the usual cause of failure.

[berger]

my understanding of six spring inners is BSA made a good job of them with the as mentioned triangular reinforced bit inside. I lost my original years ago and was only sold patterns that the bike ripped to bits in no time. all this has been mentioned before. the pattern ones are as soft as butter and the originals have been heat treated and a file glides over them. I put an original in my 6 spring when I found one and it was a different clutch, no flexing of the butter made inner anymore and very good clutch. shame your so far away I have a spare original

[WozzA]

I think I must have had only about 1/2 of the plates in it when that pic was taken?
on the bike it looked good... RED paint made it go faster..   

[Slymo]

Yes there is quite a lot of reinforcement in both the basket and the inner compared to others I've seen. Probably because 1. It's off a Super Rocket which is clearly a monster power wise and 2. (More likely) the gearing when I got the machine was super low and clearly set up for sidecar work. The clutch pulled that pillar because I tightened it a bit more than usual because when really provoked it will slip a bit.  Clearly I pushed it too far but I'm glad I did because the rest were not far from failure.

[Jules]

ref. Kiwi's comment "I use a dial guage to make sure the pressure plates lift evenly, tedious but it makes a difference, as does having the minimum spring tension that does not allow clutch slip." - when I assemble my 6 spring, I wont have the bike anywhere near complete but I'd like to set it up this way. …
So whats the rule of thumb for the initial setting of the nuts preferencing light operation and then how do you disengage it (and hold it there) while spinning it against a dial gauge and trimming the tensions, without a clutch cable???
cheers,

[KiwiGF]

ref. Kiwi's comment "I use a dial guage to make sure the pressure plates lift evenly, tedious but it makes a difference, as does having the minimum spring tension that does not allow clutch slip." - when I assemble my 6 spring, I wont have the bike anywhere near complete but I'd like to set it up this way. …
So whats the rule of thumb for the initial setting of the nuts preferencing light operation and then how do you disengage it (and hold it there) while spinning it against a dial gauge and trimming the tensions, without a clutch cable???
cheers,

I do the job using the clutch lever, just pull it fully back to the handlebar and measure the plate movement at 4 points at 90deg.

To start, measure the plate movement (near its edge) then Turn the pressure plate 180 degrees a (Note pull the clutch lever in and turn the clutch/plate by hand so you dont turn the gearbox mainshaft, as that could be bent) and measure again. Tighten the applicable nuts on the side moving more, repeat until the movement at 180 deg is equal.

Then turn the pressure plate 90deg and Repeat.

I position the dial guage mid way between two springs, then rotate it 180 deg to be between the opposite two springs, which means you adjust 2 springs to make it lift evenly.

When you turn the pressure plate 90 deg to adjust the other plane the dial guage will be directly opposite one spring, so you only need to adjust one spring to get it to lift equally.

The correct starting spring tension is a judgement thing, if you can fairly easily pull the clutch lever in you are in the ball park. I can just about tighten the adjustment nut Using fingers not a spanner when its right. If all your springs are equal length you can tighten one and then make the others match eg same number of threads showing.

Note I measure the pressure plate movement (in region of 2 to 3 mm) which is different to getting the plate to rotate flat when the clutch is disengaged, the pressure plates tend to “wobble” when the clutch is engaged so adjusting it so it lifts into a “flat” position does not definitely result in an equal plate movement at the 4 measurement points.

All This will become clearer when you do the job .....maybe.

[Slymo]

All sorted and back together again. The riveted posts are strong and true and whilst there is the faintest jingle of the domed ends touching the basket when de clutched and without the primary cover the noise is gone with the cover in place. Thanks for all the advice S:)