Renovating the 6-spring clutch

[rowan.bradley]

What is the most effective method of renovating the 6-spring clutch? SRM only seem to offer a complete replacement with a 4-spring one that costs £400. I'm not sure I need to spend that much. Is there a method of improving it at a lower cost? Can notches in the slots in the clutch body be ground out? What is the best way to do this? Can new friction elements be fitted to the friction plates?

Thanks - Rowan

[edboy]

if you can replace that ball bearing in the thrust outer plate with some sort of mushroom fixture that keeps the plate square the 6 spring can be as good as any japanese clutch. srm should really come up with the goodies with this one. but plenty of old japanese mushrooms around to rob.

[scotty]

The six spring set up on the swing arm can be ok if you use the best components you can and take the extra fettling to set it up properly.

One improvement you can make is to replace the stock clutch basket bearing with a modified one that gives a bit more surface area of contact. i think Draganfly supply them. see pic

As edboy has stated the outer pressure plate could be modified to accept a radial needle roller lift thingy.
I seem to recall a clever forum member did such a thing with his stock BSA 4 spring clutch and used a top hat lifter bearing of a Suzuki and posted the process...if you search the forum you'll no doubt find it.

[KiwiGF]

What is the most effective method of renovating the 6-spring clutch? SRM only seem to offer a complete replacement with a 4-spring one that costs £400. I'm not sure I need to spend that much. Is there a method of improving it at a lower cost? Can notches in the slots in the clutch body be ground out? What is the best way to do this? Can new friction elements be fitted to the friction plates?

Thanks - Rowan

Yes notches can be filed on inner and outer baskets, new friction plates are not too expensive eg “surflex” brand, these wear so are a consumable item anyway, new cork pieces are available for the outer basket. New plain metal plates are also available but make sure they are made out of thick material, some cheapies on the market are made in thin material and warp and act like additional springs  . I can’t remember the correct thickness, around 1.5mm?

Last outer basket I filed was SO bad I removed the outer oil protection ring first to make the job easier, it’s only tack welded in place, that’s not essential though.

I’ve found the main key to getting the 6 spring to work ok is to use a dial gauge to get the pressure plate to lift evenly, that and use components in as good condition as possible.

Another tip is to cut the push rod in half and put a ball bearing in between the two half’s, this helps reduce drag. The rod may need to be shortened after cutting, by the balls diameter, the cut rod ends should be hardened by heating/quenching after doing this.

It’s also important not to adjust the springs up too tight, as otherwise getting it to not to drag is pretty impossible. Trial and error starting off with springs on the loose side Is best, then tighten them 1/2 a turn until the clutch does not slip. I ran my bike without the primary cover on until I got it right, otherwise you will get sick of taking it on and off 

The 6 spring clutch is pretty well covered in other threads, albeit many say “bin” them!

[JulianS]

The 6 spring with its pressed up centre is very inferior to the 4 spring. Many years ago I ran an  swinging arm A7 with 6 spring and A10 with 4 spring - the former slipped and dragged and was heavy. The latter was light, did not drag and did not slip. Being "new" I asked around to find out how to improve the 6 spring - the unanimous answer even 40 odd years ago was "throw it away and get a 4 spring my boy"

If in doubt find someone with a 4 spring clutch and try it.

[BSA_54A10]

Julian is quite correct.
You can make a 6 spring work a lot better with some mods but it is a lot of work and in some cases you can not because of the grain orientation in the pressure plate.
This by the way is not restricted to the 6 spring & happens with 4 spring plates as well.
If the rolling direction ( thus grain ) passes through 2 opposite holes  ( and thus the center ) the pressure plate will flex around this axis no matter what you do.

This is one of the reasons why all modern clutches use cast alloy pressure plates and many use 5 or 7 springs.

The band around the drum is not there to defect oil, it is there to prevent the drum spreading. Any oil deflection is secondary.
Early clutches did not have the band and the side of the drums do spread eventually going far enough for the tabs to drop out the slots.

You can knock out the cup & ball in the center of a 6 spring and fit the Devimead / SRM top hat radial thrust bearing & lifter.
From memory you need to put a threaded sleeve over the bolt because the hole through the 6 spring plate is bigger.
Not quite as good is to grind the end of the lifting cup off and enlarging the hole to take the SRM mechanism.
The SRM system is designed to allow adjustment which pre unit clutches do not need because we have an adjuster at the other end of the pushrod.
BSA Bill used to make & sell these way back and there might be instructions on his legacy page, I am not sure how much got transferred after he died.   

[Tomcat]

The SRM clutch is the answer to all of your clutch problems. I have one in my Super Rocket and have a perfect clutch.  Well worth the money, and I had to pay postage to AU as well.

[KiwiGF]

Julian is quite correct.
You can make a 6 spring work a lot better with some mods but it is a lot of work and in some cases you can not because of the grain orientation in the pressure plate.
This by the way is not restricted to the 6 spring & happens with 4 spring plates as well.
If the rolling direction ( thus grain ) passes through 2 opposite holes  ( and thus the center ) the pressure plate will flex around this axis no matter what you do.

This is one of the reasons why all modern clutches use cast alloy pressure plates and many use 5 or 7 springs.

The band around the drum is not there to defect oil, it is there to prevent the drum spreading. Any oil deflection is secondary.
Early clutches did not have the band and the side of the drums do spread eventually going far enough for the tabs to drop out the slots.

You can knock out the cup & ball in the center of a 6 spring and fit the Devimead / SRM top hat radial thrust bearing & lifter.
From memory you need to put a threaded sleeve over the bolt because the hole through the 6 spring plate is bigger.
Not quite as good is to grind the end of the lifting cup off and enlarging the hole to take the SRM mechanism.
The SRM system is designed to allow adjustment which pre unit clutches do not need because we have an adjuster at the other end of the pushrod.
BSA Bill used to make & sell these way back and there might be instructions on his legacy page, I am not sure how much got transferred after he died.

Hi Trevor, sorry to contradict you but the “band” is conical on all the outer 6 spring baskets I’ve seen (and I have a few on the shelf....) and consequently it design cannot stop the basket spreading, pic attached, it does not even touch the basket where it would spread most (on the the pressure plate side/end of the basket) and it is only loosely tack welded to the baskets “tines” on the sprocket side. I removed the band to file out grooves and did not bother to tack weld it back afterwards thinking it did contribute to the baskets strength, but I have to replace it after I got got clutch slip at high revs! I’ve no idea how it stops clutch slip but that is the experience I have had with removing it.

The pressure plate does not have a cup and ball? It has a hardened insert for the push rod to contact with. What you’ve described sounds like a good mod but please could you elaborate?

[BSA_54A10]

I am well aware of the shape.
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.
Boy did that make a difference.
I was supposed to put the strap back on but never did and thus found that the basket does in fact spread without it there
It was not an easy job to get the basket back into shape although I eventually did get the  band back on.
If it has no structural purpose BSA could have made it out of tin plate.

[rowan.bradley]

BSA Bill used to make & sell these way back and there might be instructions on his legacy page, I am not sure how much got transferred after he died.

Where do I find "BSA Bill's legacy page"?

Thanks - Rowan

[scotty]

http://bsa-a10.hailwood.com

[pjm01]

I had similar issues and after much toil/anxiety went for the complete SRM 4 spring clutch and the clutch action was transformed .... finger light AND I could even find neutral when stationary (mostly).
Recent publicity from SRM shows them offering their (pressure plate + needle roller lifter) instead of the complete conversion ... may be worth a glance at their web site.
I have no connection with SRM, other than a very happy (but poorer) customer.
Peter M

[rowan.bradley]

Are the slots in the basket really fileable? I would have expected them to be hardened.

Do they need rehardening after filing?

Can one really remove the thin steel (conical) outer and not refit it, without undue problems? Do we have a consensus on what is the purpose of this shield?

How does one do the slots in the inner hub, that the plain plates drive?

What about wear on the tabs on the plates? I suppose these are less important, because if they are worn, it would not seem to impede the plates slipping up and down in the slots. But can they be cleaned up by filing or grinding or something? I suppose that if one is going to file or grind the slots or the tabs, one has to be careful to take the same amount off each, otherwise one would end up not sharing the force evenly between all the bearing surfaces.

Thanks - Rowan

[edboy]

the 4 spring clutch really needs a modification for the inner friction plate to but up against the chainwheel, otherwise the chainwheel wears and wobbles about. i dont know if srm modify theirs but their sales provide a nice source of 6 spring parts. i ve never had issues with outer plate warping with my little mod but have found well used plain plates to spread and bind in the clutcthwheel and cause drag. either clutch i would first assemble on the bench and check for burhs and free movement. i use a benchgrinder for dressing plates . i actually prefer the 6 spring clutch once modded.

[BSA_54A10]

Are the slots in the basket really fileable? I would have expected them to be hardened.

Do they need rehardening after filing?

Can one really remove the thin steel (conical) outer and not refit it, without undue problems? Do we have a consensus on what is the purpose of this shield?

How does one do the slots in the inner hub, that the plain plates drive?

What about wear on the tabs on the plates? I suppose these are less important, because if they are worn, it would not seem to impede the plates slipping up and down in the slots. But can they be cleaned up by filing or grinding or something? I suppose that if one is going to file or grind the slots or the tabs, one has to be careful to take the same amount off each, otherwise one would end up not sharing the force evenly between all the bearing surfaces.

Thanks - Rowan

Questions, Question questions.

Slots are not hard and file quite well.
Std practice when doing a clutch otherwise the plates sit in the wear grooves and don't move apart without a lot of effort.

Never heard of hardening them. this is why the key steel was soldered to the working face, it is hard.

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. 

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.

And yes all of the slots need to be both true, square & the same size as do the plates but you file the plates with all of them clamped together.
Not an easy job but very rewarding when you get them done right.