Renovating the 6-spring clutch

[KiwiGF]

Do we have a consensus on what is the purpose of this shield?

I would say there is no consensus on the purpose of the shield, but don’t let that worry you! It’s not uncommon for members to have different experiences etc.

On the subject of filing plates, just my opinion, but I just make sure there are no sharp edges that can dig into the baskets, I file a small 45 degree bevel on tabs etc wh3n necessary to ensure this, I think if a plates tab has “flattened” a bit to give an increased bearing area on the basket, I think that’s a good thing.

On my b31 I’ve fitted a mixture of A10 6 spring clutch and b31 parts, I have used custom made flat (not domed like std plates) plain plates of 2mm thickness, laser cut, then ground to 2mm from thicker material so they are flat to a close tolerance. The thicker plates give a slightly increased bearing surface against the basket. The plates did not cost me much more than std plates.

The only down side of using flat plates (not foreseen) was that I had to use 2 plates tack welded together next to the chain wheel, to make sure the plates engaged properly with the inner basket, this ultimately meant I could only fit 3 friction plates in, with mixture of parts I used, 3 friction plates is actually the norm for a b31, but I hoped to get more plates in due to use of the wider a10 chain wheel, and cos the engine is hotted up a bit, however it does not slip now, whereas it did with standard thickness plates.

I can’t explain why the clutch grips better but I’m happy it does 

[rowan.bradley]

Trevor,

Thanks for your reply.

A mentor took one off one time  in order to file the slots square then silver some key steel to the thrust face on my clutch.

You mean the key steel is silver soldered down the edges of the slots in the basket? Presumably the steel just needs to be as wide as the basket metal is thick, and pretty thin (else it will not leave room for the tabs to slide up and down)? What dimensions did you use? And where did you get it from? How difficult is this to do? Does it need any special techniques or tools?

Most of the baskets I have come across the band was spot welded to the basket sections & is easily drilled out.
Modification or racing, drills the band exteansivle but does not remove it. 

So you think it's OK to remove the band altogether for filing and not replace it afterwards? In your previous message you seemed to be saying that it was necessary to weld it back on.

While the inner does indent, because of the shorter lever effect it does not tend to indent anywhere near the amount that the outer does.
You file them with a 6" smooth file with the end cut off.

Surely the shorter radius would increase the pressure on the tabs to get the same torque, and therefore increase the wear?

Why does cutting the end off the file help?

Thanks - Rowan

[BSA_54A10]

Trevor,

Thanks for your reply.

A mentor took one off one time  in order to file the slots square then silver some key steel to the thrust face on my clutch.

You mean the key steel is silver soldered down the edges of the slots in the basket? Presumably the steel just needs to be as wide as the basket metal is thick, and pretty thin (else it will not leave room for the tabs to slide up and down)? What dimensions did you use? And where did you get it from? How difficult is this to do? Does it need any special techniques or tools?

Most of the baskets I have come across the band was spot welded to the basket sections & is easily drilled out.
Modification or racing, drills the band exteansivle but does not remove it. 

So you think it's OK to remove the band altogether for filing and not replace it afterwards? In your previous message you seemed to be saying that it was necessary to weld it back on.

While the inner does indent, because of the shorter lever effect it does not tend to indent anywhere near the amount that the outer does.
You file them with a 6" smooth file with the end cut off.

Surely the shorter radius would increase the pressure on the tabs to get the same torque, and therefore increase the wear?

Why does cutting the end off the file help?

Thanks - Rowan

The key stock was a bit wider than the thickness of the drum steel it would have been around 1/8" square.
He filed the slots till they were clean , strait & true
Then solldered the key steel so the basket steel was in the middle thus it overhung a bit both inside & outside the drum.
The plates were all then center punched on one tang, clamped together & filed to suit the slots as the slots were all slightly different widths.

The reason to cut the end off the file was to ensure it cuts for it's full length.
The very end of a file has no teeth as you are supposed to hold the end to guide it.

Before he did the clutch job you could hear it rattleing from 200 yards.
Once done it was very quiet and the wider sliding face stopped the tangs making groves in the drum slots so it was smooth and worked as good as any clutch I have ever owned.
And I used to think nothing of tossing wheelies and monos, the bike was good for a real 120 mph ( the government gave me a very expensive piece of paper to prove it ) and pulled very low standing 1/4's.
11:1 pistons, cam the made bricks look round & running on a high doped engine/
Not a job for the mechanically challenged.
He also made a gunmetal bush to eplace the double row ball which cured 2 problems
Clutch basket wobble
Lazy rider riding the clutch at the lights as you had about 15 sec before the bush overheated and grabbed.

[duTch]

Once done it was very quiet and the wider sliding face stopped the tangs making groves in the drum slots so it was smooth and worked as good as any clutch I have ever owned.

 Kinda the same kiwigf had in mind here ? ;
 

, I file a small 45 degree bevel on tabs etc wh3n necessary to ensure this, I think if a plates tab has “flattened” a bit to give an increased bearing area on the basket, I think that’s a good thing.

[Topdad]

Rowan, I fear you are likely to be disappointed . Going to all that trouble and hard work on  ,In my opinion, an inferior item that will almost certainly cause you more problems in the future seems like a recipe for putting you of A10's ! From personal experience after my Plunger A10 ( excellent clutch )  going to a more modern 54 swingarm machine with this type of clutch ,very nearly did it for me . fortunately a friend machined a clutch sleeve to take a triumph clutch and I became a very contented bunny .Sorry to sooooo negative , not my usual stance as anyone who knows me will confirm but having stripped that blasted 6 spring clutch down so many times after so many breakdowns was soul destroying ,I was very pleased to give it to someone some yrs ago and don't know why I kept the piece of crap in my shed for so many yrs , best of luck,either way

[Greybeard]

Plunger A10 ( excellent clutch )

Agreed!

[rowan.bradley]

The plates were all then center punched on one tang, clamped together & filed to suit the slots as the slots were all slightly different widths.

Does it matter if the tabs are narrower than the slots, or that the slots are different widths? I would have thought that it really did not. The only time that the plates might move to the other side of the slots would be when engine braking. My basket shows no wear at all on the opposite side of the slots from the normal drive side, which supports this theory. What really does matter, it seems to me, is that the pressure faces of all the tabs are in contact with the edges of the slots, otherwise the force will not be shared equally between the tabs. After all the filing and soldering keysteel, the pressure faces of the slots may not be exactly equally spaced, and (it seems to me) this must be replicated in the filing of the tabs. Also of course, the plates must always be put into the basket with the same tab in the same slot. Seems like this filing will need to be a pretty careful fitting job.

Thanks - Rowan

[JulianS]

I dont think you need to over think the filing of the slots and plate tabs - certainly on the 4 spring it does not seem to matter if the tabs are a bit irregular, just remove the burred edges and remove the notches  from the chainwheel so the plates dont snag.

Ultimately what matters is that when you ride the bike it does not slip and does not drag and that you can select gears and neutral without the box grinding and jerking.

With the swinging arm 6 spring you may find it takes a number of attempts before it works reliably and to your satisfaction.

[KiwiGF]

I agree with Julian, just get filing! For the inner basket you can run the file through both sides of the basket therefore using the opposite side as a guide.

You can do the same for the outer basket if you remove the conical band, but that’s often not necessary in order to clean the basket up, it depends on how bad the notches are.

I have not bothered to try to match plates with slots etc. I agree theory says you would benefit from that but in practice I think the contact is pretty hit and miss anyway, and the plates will hopefully “adapt” to uneven pressure on tabs rather than the baskets. I certainly would not file all basket tines to match one particularly worn one.

I have thought at times that by replacing friction plates periodically that slight notches are not so much of a problem as the extra thickness from new plates changes the contact point position on the basket anyway.

I still think the most important part of setting the clutch up is getting the pressure plate to lift evenly (use a cheap dial gauge and get each plate to move (say) 080’ at 4 positions when 5he clutch lever is pulled in,  the 2nd most important is not to over tighten the springs. There is a bit of an art to this, I measure the pressure movement in 4 positions rather than try to get an even “run out” of the plate as it is turned, as the clutch may have an inherent 020’ “wobble” that could mean the plate movement would be 060 one side and 080 if the wobble was not taken into account. I generally can get the 4 movements to within 008 of each other pretty easily.

PS it does not matter if tabs are narrower than slots, but I’d replace plates which have very worn tabs. It’s usually the plain plates tabs that seem to suffer more wear.

[BSA_54A10]

keeping the plate tangs as close to the slot width reduces the amount of hammer you get every time you let the clutch out.
Just like running into a brick wall from 1 pace away and 10 paces away.

Now to keep things in perspective, I would not bother doing it now days.
Too much effort for too little result when you can just toss in a 4 spring with a cast pressure plate.
But back in the 60's things were different

[Topdad]

spot on !!

[KiwiGF]

The plates were all then center punched on one tang, clamped together & filed to suit the slots as the slots were all slightly different widths.

Does it matter if the tabs are narrower than the slots, or that the slots are different widths? I would have thought that it really did not. The only time that the plates might move to the other side of the slots would be when engine braking. My basket shows no wear at all on the opposite side of the slots from the normal drive side, which supports this theory. What really does matter, it seems to me, is that the pressure faces of all the tabs are in contact with the edges of the slots, otherwise the force will not be shared equally between the tabs. After all the filing and soldering keysteel, the pressure faces of the slots may not be exactly equally spaced, and (it seems to me) this must be replicated in the filing of the tabs. Also of course, the plates must always be put into the basket with the same tab in the same slot. Seems like this filing will need to be a pretty careful fitting job.

Thanks - Rowan

I needed to use a different pressure plate on the 6 spring clutch on my B31 (I noticed a spare one I had was less deeply domed than the current one, which meant i could fit an extra friction plate, odd that there are so many small variances unbetween the 6 spring parts!).

Anyway, the reason I discarded it originally was it had worn slots  . This (to me) is a bad fault as the result of this sort of wear is that sideways stress is then applied to the 6 studs on the inner basket, as the pressure plate can rotate relative to the inner basket. You often find inner baskets with loose studs, probably as a result of this stress.

I decided to fix the plate I had rather than try to buy an identical one (with the desirable to me, shallower doming).

I welded the slots and spent a few hours filing them to fit the basket 

In addition I drilled out the spring cups to 7.5mm (they were originally just over 1/4”) to increase the clearance over the studs.  Hopefully this will also reduce the stress on the studs, should the pressure plate rotate relative to the studs.

I also had to bend the studs around a bit to get them central to holes in the pressure plate.

I mention these various tips, as if the inner basket is filed to get rid of notches, this may have the knock on effect of having to reduce the slot width in the pressure plate 

The pic attached shows the welded up pressure plate, the small file needed to file the slots to size, and the method of attaching a dial gauge to get even pressure plate lift.