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6-spring vs. 4-spring clutches #673528
11/05/16 2:42 pm
11/05/16 2:42 pm
Joined: Nov 2011
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Magnetoman Online content OP

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On the face of it the 6-spring pre-unit clutch should spread clamping pressure more evenly so it should work better than the 4-spring. So, why do people like the 4-spring version better? What is it about the behavior of the 6-spring that makes it worse? I ask the above because I have the primary cover of my Catalina off at the moment so if there are things I can do to improve the 6-spring clutch now is the time to do them.

As a step in this direction I took the springs off a plate I have in my box of spares and measured a few of the important parameters. The springs of that clutch seem to have been made to a nominal 1" length, but compared with the longest one of this batch the shortest is 0.023" shorter. I don't know if this is due to age, or original manufacturing variation, although probably mostly the former. This is a significant difference because they are compressed by only ~0.060" if adjusted according to the manual (i.e. with 1 thread showing above the lock nut). This means if longest spring is compressed by this amount, the shortest will be by only 0.037", i.e. 40% less. Even if they have identical as-yet-to-be-measured spring constants the force exerted by that shortest spring will be 40% less.

Again, assuming identical spring constants, the differences in force due to the lengths could be compensated for by shims or by different preloads. However, just like in forks, they don't have identical effects. I suspect most people adjust their clutch springs according to the manual in order to get close, then tighten or loosen individual nuts to get the plate to spin without significant wobble. That's changing the "shim."

I have yet to measure the spring constants so that's an additional, and significant, source of possible variation. However, if after I measure the spring constants of a batch in order to select a matched set of six, and measure the lengths and make shims to bring them all to the same length, is there some other reason that I'm overlooking for why my 6-spring clutch won't then work at least as well as a 4-spring?

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Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673537
11/05/16 4:57 pm
11/05/16 4:57 pm
Joined: Aug 2015
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Bolton Lancs UK
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Andy Higham Offline
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a lot of the problems with the 6 spring clutch are due to the flimsy pressed tin construction


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673540
11/05/16 5:28 pm
11/05/16 5:28 pm
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Bolton Lancs UK
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Andy Higham Offline
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When I replaced the 6 spring on my A10 the pressure plate had polished marks in line with the springs showing the plate had distorted. The inner hub had run out in every direction.


BSA B31 500cc "Stargazer"
Greeves 200cc "Blue Meanie"
Greeves 350
Greeves 360 Challenger
Suzuki GSX1100 EFE "Sorcerers Apprentice"
GM500cc sprint/LSR bike "Deofol"
Jawa 500cc "Llareggub"
2003 Aprilia RSV Mille "Lo Stregone"
'35 OK Supreme
'36 OK Supreme
Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673574
11/06/16 6:04 am
11/06/16 6:04 am
Joined: Sep 2015
Posts: 315
Kent, England
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Kent, England
I'ts all down to the springs,plain plates and friction you have in your clutch. Many parts now are pattern parts obviously, so you can only adjust within the parameters of parts that you have. A lot is to do with your experience and patience,i.e, making the components you have work. In the Gold Star Book by Mick Walker, he says that the 6 spring clutch woks fine. I bought a set of plain plates for my 6 spring clutch and found that the second locking nut would not fit onto the threads[ not surprisingly pattern parts] so reverted back to the original plain plates, just cleaned and filed them, still working ok, even though they have been in my Goldie since before i bought in 1971. The Goldie has been out of production since 1962 and it's only as good as the parts you can get.
Goldie John.

Re: 6-spring vs. 4-spring clutches [Re: John Alexander] #673576
11/06/16 6:49 am
11/06/16 6:49 am
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Posts: 203
UK Tyne & Wear
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photobob Offline
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I have a 1956 A7 swinging arm model with the 6 spring clutch and as it is set up and adjusted correctly I have no complaints. But as the previous member has stated there are a number of pattern parts which are not up to standard. When I first got this bike I did have a problem with the clutch dragging and no matter how I adjusted it I could no get it to work right. The problem turned out to be that a previous owner had fitted the wrong springs fitting the correct springs solved the problem.Draganfly in England now sell a much improved clutch bearing which is easier to fit than the original and works better. However if the clutch was to completely wear out I would look at fitting a 4 spring clutch as this was an improvement on the 6 spring BSA did change from the 6 spring to the 4 spring about 1960 maybe earlier. Also my 1963 A65 has a 4 spring clutch but BSA once again changed that to a 3 spring version towards then end of production.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673586
11/06/16 8:21 am
11/06/16 8:21 am
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Sydney Australia
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Firstly get the new improved ball cage & bearing
Can't remember if it is a SRM or Draganfly job but it is double width cage and a flat race.
It works a lot better than the pressed tin cage & double row race.
Next have a really good hard look at the backing plate and in particular the tiny flange on the center that the holds the backing plate. If it does not sit square to the centre ( and most don't ) the drum can not run true.
Akso check the inserts n the back of the drum, they have to be flat.
Most prople go to great lengths to flatten the plates and then forget about the drum.
All the usual stuff about notches in the plates and drum grooves goes without saying as does the flatness of the plates themselves.
The inner hub comes in either 2 or 3 different lengths for A, B & M series, can't remember right now but the bolts will foul on the outer case if they are wrong.

The standard method of adjustment has the clutch way way way too tight.
If the bike is not going, this will be a bit difficult but the best way is to true the clutch then anchor the front wheel against something really solid.
Put the bike in gear then back off the adjuster nuts till the kick start just starts to slip, then tighten 1/2 turn.
That will have the clutch as light as it can be and lighter will run truer and of course open cleaner.
If the engine is running , you start the bike then put it in gear and slowly let the clutch out.
engine just stalls when the clutch is almost fully off is about correct.

The B40, A65 & B50 were about 2 to 3 full turns lighter than specked by BSA when done this way
And the only way to true the plates properly is with a dial indicator.
If you can get them to run true to .010" you will have a sweet clutch


Bike Beesa
Trevor
Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673597
11/06/16 11:36 am
11/06/16 11:36 am
Joined: Nov 2011
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Northern Ireland
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B31 Ally Offline
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Im running 6 spring clutches on all my BSA's, work excellently after a few tweeks, patience setting it up and experience but it will work well in standard form too. I machine the wear ridges out of the basket where the driving plates touch, the basket ends up with ridges cut into it so when you pull the clutch in the plates wont separate enough and then they drag. I don't tend to worry too much about the spring lengths, I build the clutch and made a metal mount that screws onto the rear chain case backing plate so that I can stick my dial test indicator magnetic base on to. I then adjust the nuts on the six springs until I get the clutch outer plate lifting level when I pull the lever in, I can normally get it to within 2 thou of an inch if no plates have and slight warps in them. It takes experience to know how much to tighten the nuts so that you don't have a heavy clutch lever, BSA WM20 gives good advice about having a light clutch lever that is still able to drive the bike along without slipping.
Lastly and often over looked is the lever that operates the push rod, if someone had it apart and put the small bit with the ball in it back onto the wrong splines then the geometry of the operating lever the cable goes into is all wrong and wont give you the correct amount of lift to make the clutch work properly. That lever needs to be exactly parallel to the gearbox casing with the clutch handlebar lever fully pulled in to give you the maximum amount of lift. As I work at helicopters and they are full of levers and linkages this is second nature to me when working at any lever or operating mechanism but it may not be as obvious to everyone else.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673608
11/06/16 1:13 pm
11/06/16 1:13 pm
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Magnetoman Online content OP

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Thanks very much to everyone who responded with these very helpful suggestions. No one has yet posted anything pointing out a fatal design flaw with the 6-spring clutch, and nothing mentioned can't be dealt with by measurement, selection/matching of parts, and/or a quick spin on the lathe. To summarize all of the suggestions in the form of a checklist, unless I've overlooked something:

-- Beware pattern parts.
-- Use the replacement bearing from Draganfly (or SRM?).
-- Make sure the flange in the center of the pressure plate sits square with the plate.
-- Flatten the pressure plate.
-- Flatten the plates.
-- Flatten the back of the drum.
-- Remove any notches in plates and grooves in drum.
-- Check that operating arm is at 90-deg. when clutch is disengaged.
-- Select a set of 6 springs for length and spring constants.
-- Adjust nuts so drum runs true to better than 0.010" when disengaged.
-- Put in gear and adjust clutch so it just slips with kickstarter, then tighten nuts 1/2 turn.

Although I didn't spot it in their catalog, I've already emailed Draganfly to say I want to order two of their replacement bearings (to replace 65-3910 and 65-3912) to deal with the Catalina's and BB's clutches. If they respond they don't know what I'm talking about, I'll contact SRM.

Rather than swap gauges in my current 300 lb. valve spring tester I've ordered a second unit that I'll "permanently" modify with a 60 lb gauge. That will give me a tester whose range is appropriate for use with the various aspects of clutches.

Although Andy found evidence of distortion of his pressure plate, no one else mentioned this issue. I didn't find any such distortion in the two pressure plates that were within easy reach on the shelf, but if it's there when I disassemble the Catalina's clutch it certainly looks like it would be easy enough to strengthen this component by adding a suitable ring of steel. Has anyone done this?

I'm now waiting for new gaskets, new bearings, and a new force gauge to arrive before I can adjust the Catalina's clutch and put the primary cover back on. Not yet having been able to ride this bike more than ~1 mile since getting it in June has been frustrating, but I know I would later regret it if I didn't take the time to do this right. Luckily, I have other bikes to ride in the meantime, including the BB Gold Star (although with its to-be-cured Crocodile Dundee clutch pressure).

p.s. once everything is in hand and I've made the measurements and adjusted the clutch I'll post an update to the above checklist with all the information I've found. Meanwhile, if I've missed anything with the above list, or there are additional details to consider, please add to this thread.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673617
11/06/16 1:58 pm
11/06/16 1:58 pm
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Posts: 4,461
New Jersey USA
Tridentman Offline

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New Jersey USA
I used the replacement bearing from Draganfly in the 6 spring clutch on my 1960 A7 Shooting Star.
Much superior IMHO to the original pretty flimsy bearing.
People say that BSA changed to the 4 spring Triumph clutch because it was a better clutch.
However I bought an ex City of Birmingham (UK) police A10 in the mid 60s.
This was fitted with both a dynamo (for normal bike electrics) and an alternator on the crankshaft (for police radio). Because of the alternator the normal crankshaft shock absorber was not fitted. I was told that BSA fitted the Triumph clutch because of the shock absorber built into the Triumph clutch.
All hearsay of course but feasible.
I think the 6 spring clutch if set up properly is fine on a solo--after all Goldies were fitted with these and did their stuff pretty well in the Isle of Man.
However having ridden A10s with sidecars with both 6 spring and 4 spring clutches IMHO the 4 spring clutch is more durable in this much more demanding duty.
HTH

Re: 6-spring vs. 4-spring clutches [Re: Tridentman] #673631
11/06/16 4:56 pm
11/06/16 4:56 pm
Joined: Jun 2002
Posts: 934
Jaffrey, NH, USA
Peter Quick Offline

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Originally Posted By Tridentman
Because of the alternator the normal crankshaft shock absorber was not fitted. I was told that BSA fitted the Triumph clutch because of the shock absorber built into the Triumph clutch. All hearsay of course but feasible.


This makes sense to me as I have two B33 alternator type models, 1959 & 1960 and both came with 4 spring clutches.

Peter


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Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673648
11/06/16 9:34 pm
11/06/16 9:34 pm
Joined: Nov 2011
Posts: 126
Northern Ireland
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B31 Ally Offline
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Northern Ireland
Magnetoman, I think you have it all covered in your summary,as I see it to there is no fatal flaw in the six spring clutch, just takes time and patience setting it up. Forgot to say im using the Draganfly replacement centre bearing as well in both my bikes, it is a beefier job than the standard bsa item.

Re: 6-spring vs. 4-spring clutches [Re: B31 Ally] #673651
11/06/16 10:57 pm
11/06/16 10:57 pm
Joined: Nov 2011
Posts: 4,649
U.S.
Magnetoman Online content OP

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Originally Posted By B31 Ally
there is no fatal flaw in the six spring clutch, just takes time and patience setting it up.
The ET ignition system, of which I am fond, is another example of something that works quite well, but only if it is set up and maintained with time and patience. We'll see how well my 6-spring clutch works when I'm done with it but I'm optimistic it will be just fine.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673663
11/07/16 7:13 am
11/07/16 7:13 am
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Sydney Australia
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Arh yes the pressure plate.
Now that is a different problem.
The plates were cut from the sheet then placed into stillages before and between the 3 or 4 pressings.
This means that the grain orientation with respect to the position of the holes is quite random.
So if you are one of the "lucky" owners with the grain axis passing through holes 1 & 4 ( also 2 & 3 plus 5 & 6 ) the pressure plate will always flex about that axis.
Not as big a problem as it is with the 4 spring and the only cure is a new or at least different pressure plate.
I had a B40 that would never lift true and could not work out why till I took it into the lab and gave it an etch to find a plain of symmetry from bolt 1 through the center to bolt 3 ( four spring clutch ).
I picked this one out of a box of them because it had the least wear, obviously for a good reason.


Bike Beesa
Trevor
Re: 6-spring vs. 4-spring clutches [Re: BSA_WM20] #673692
11/07/16 12:03 pm
11/07/16 12:03 pm
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Magnetoman Online content OP

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Originally Posted By BSA_WM20
Arh yes the pressure plate.
Now that is a different problem.
In re-reading your original post last night I realized you were referring to a different component but I'll wait until I've gone through checks of the entire clutch mechanism before posting an updated checklist.

Originally Posted By BSA_WM20
stillages
Ah, a new 'English' word to add to my vocabulary. It must be English because it's not in the American dictionary above my desk. Thankfully, Google transcends national boundaries so I didn't have to walk to the other end of the house to consult the massive Oxford Unabridged.

Early in my career I co-authored a manuscript with a very senior colleague who tried to slip in the word 'ullage', which I didn't know, in a way that was sort of appropriate but didn't strictly apply to the situation. Unfortunately, the referee either knew the word, or was intrigued enough to look it up, because he told us in his report to remove it.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673693
11/07/16 12:37 pm
11/07/16 12:37 pm
Joined: Feb 2011
Posts: 3,503
Orygone
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Orygone
Winemakers know "ullage" as the air space crated in a wine barrel with the evaporation of moisture through the oak staves of the barrel.

Also referred to as "angels share"

Bill B...

Last edited by Boomer; 11/07/16 12:40 pm.

Boomer
Re: 6-spring vs. 4-spring clutches [Re: Boomer] #673696
11/07/16 1:02 pm
11/07/16 1:02 pm
Joined: Nov 2011
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U.S.
Magnetoman Online content OP

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Originally Posted By Boomer
Winemakers know "ullage" as the air space crated in a wine barrel with the evaporation of moisture through the oak staves of the barrel.
Unfortunately for us, the referee for our manuscript decided we couldn't apply the term to the decreased concentration of the isotope 3He created in the mixing chamber of a 3He-4He dilution refrigerator...

I lost that one, but now I'll be looking for a way to (mis)apply the word 'stillage'.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673698
11/07/16 1:35 pm
11/07/16 1:35 pm
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Posts: 4,081
argyll. scotland, uk
gavin eisler Offline
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i knew about Ullage, now I have to look up stillage.
My own experience of the 6 spring clutch was on an A10, it takes time to set up properly but works fine , a bit more fiddly than the 3 spring I am used to. A big box of springs for selective assembly would be a boon, i recall staggering the springs so they went weak, strong, weak, strong, weak, strong round the circle, this prevented one side being stronger than the other. I only had 6 to play with.Part of the fiddlines comes from the adjustability, I once had an HD XL which had a similar set up , but, the spring tension was set by a tube spacer, if all the spacers are equal, and the springs are also equal then its a lot easier to set up.

If as Trevor points out , the pressure plates are prone to bending around certain axes, then perhaps two could be sandwiched together to stiffen and cancel out the flexing?

Last edited by gavin eisler; 11/07/16 1:41 pm.

71 Devimead A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
The poster formerly known as Pod
Re: 6-spring vs. 4-spring clutches [Re: gavin eisler] #673710
11/07/16 3:28 pm
11/07/16 3:28 pm
Joined: Nov 2011
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U.S.
Magnetoman Online content OP

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Originally Posted By gavin eisler
If as Trevor points out , the pressure plates are prone to bending around certain axes, then perhaps two could be sandwiched together to stiffen and cancel out the flexing?
The photograph is a mock up of a measurement I'll make on my Catalina's pressure plate after disassembling the clutch and making a jig to hold it on the surface plate.



If after comparing measurements with the springs loose and tight I find "significant" distortion (where what constitutes "significant" is to be decided after making the measurements), it would be very easy to attach strengthening rings of steel in one or both of the locations I've marked with red paint. By tacking the rings on with silicon bronze the distortion would be minimal and, in any case, eliminated afterwards on the lathe. However, is there a good reason not to do this?

I suspect the real issue will turn out to be whether or not the top of the "hat" bows outward under the force of the clutch rod acting against the springs. If this happens the amount of lift will be reduced. However, measurements may show that distortion causes the outer edge to lift less than it should, resulting in drag on the clutch plates. Both of these possible effects would be greatly reduced by the addition of strengthening rings.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673712
11/07/16 3:48 pm
11/07/16 3:48 pm
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scotland
triton thrasher Online content
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Is the outermost plate, that the pressure plate presses on, a plain steel driven plate?

If so, can you weld or braze the outer edge of the pressure plate to it? That would stiffen it up.

I've seen it done on a three-spring clutch.


Amateur Loctite enthusiast.
Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673718
11/07/16 5:13 pm
11/07/16 5:13 pm
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argyll. scotland, uk
gavin eisler Offline
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the only reason for not doing i can think of is you are adding mass to gain stiffness, the trade off is probably worth it , you can machine away the centres of the driving tangs to compensate if thats an issue.It would need to be balanced if you were being picky. Shouldered spring tensioning studs that the nuts locked against would make set up easy if the springs were well matched, once you know what the optimum spring tension is , probably not worth the bother. With some artistry the add on stiffeners could reinforce the 50 s UFO vibe


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56 Norbsa 68 Longstroke A65
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MZ TS 250
The poster formerly known as Pod
Re: 6-spring vs. 4-spring clutches [Re: gavin eisler] #673720
11/07/16 5:28 pm
11/07/16 5:28 pm
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Magnetoman Online content OP

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Originally Posted By triton thrasher
Is the outermost plate, that the pressure plate presses on, a plain steel driven plate?
The top clutch plate is a friction one so not ideal for welding to the pressure plate.

Originally Posted By gavin eisler
you are adding mass to gain stiffness,
The additional weight would be small with respect to the rest of the clutch mechanism, as well as at a smaller radius so a much smaller additional inertia.

Originally Posted By gavin eisler
With some artistry the add on stiffeners could reinforce the 50 s UFO vibe
Now that you mention it, although the following UFO clearly has a stiffening ring that allowed it to make the interplanetary trip, it might not be necessary on a Gold Star clutch since the engine lacks warp drive:

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673721
11/07/16 6:17 pm
11/07/16 6:17 pm
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scotland
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Yes MM.

The most inspired clutch design I ever saw it is not.



Amateur Loctite enthusiast.
Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673725
11/07/16 7:17 pm
11/07/16 7:17 pm
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Sydney, Oz
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Shane in Oz Online content
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The SRM alloy pressure plate, which uses a radial roller bearing in place of the top hat would be a very useful addition, along with the other SRM bearings mentioned earlier.

Re: 6-spring vs. 4-spring clutches [Re: Shane in Oz] #673729
11/07/16 7:46 pm
11/07/16 7:46 pm
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Magnetoman Online content OP

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U.S.
Originally Posted By Shane in Oz
The SRM alloy pressure plate, which uses a radial roller bearing in place of the top hat would be a very useful addition, ...
Admit it, you're only suggesting this to try to save future Australian visitors from the pain.

I can't find any items for 6-spring clutches on the SRM 'Clutch Upgrades' pages. If I'm overlooking it, please point me to the correct page.

Re: 6-spring vs. 4-spring clutches [Re: Magnetoman] #673735
11/07/16 9:08 pm
11/07/16 9:08 pm
Joined: Oct 2001
Posts: 1,162
Sydney, Oz
S
Shane in Oz Online content
BritBike Forum member
Shane in Oz  Online Content
BritBike Forum member
S

Joined: Oct 2001
Posts: 1,162
Sydney, Oz
You have to know where they hide it.

It's currently page 7 of the general clutch section.

I have an SRM pressure plate on the Firebird, which seems to work quite nicely.

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