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Author Topic: Clutch mod  (Read 795 times)

Chasfield

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Clutch mod
« on: June 25, 2013, 10:50:08 AM »
I made myself a replacement for the inner dished plate of my 4 speed clutch. I cut the middle out of a plain plate and JB welded the remaining outer portion to another plate. This gives a cross section that nicely clears the big circlip that retains the clutch basket. It also gives dead flat contact with the clutch basket liner and the first lined friction plate. This has transformed the clutch. The distortion/springyness of the original dished plate was wrecking the clutch release action and compromising plate contact area. The modded plate adds 1.5 mm to the stack thickness, so I substituted two friction plates that are thinner than standard (4mm rather than 5mm) to bring the stack back to normal spec. I had to get this right because there is a danger that the outer dished plate would fall off the inner hub at full lift if the clutch basket is over filled.

I will post a picture of the modded plate at some point.

I reckon you could get the same improvement by using some kind of press to true up the dished plates (if they need it). I will have a try with my outer dished plate, for which my modded one is not suitable as a replacement - the outer dished plate has to reach in a good way to engage with the hub adequately.
« Last Edit: June 25, 2013, 05:18:37 PM by Chasfield »
2001 500 Bullet Deluxe

mrunderhill1975a

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Re: Clutch mod
« Reply #1 on: June 25, 2013, 04:12:27 PM »
I knew JB-weld is good stuff, but I am shocked that it would hold parts of a homemade clutch plate.  I would like to see the photos.

Chasfield

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Re: Clutch mod
« Reply #2 on: June 25, 2013, 04:57:49 PM »
Yeah, I thought about soldering the plates together but in the end went for JB Weld because the application would be as an adhesive involving a large surface area. Also, JB Weld is heat stable up to 500F. I roughened the mating surfaces well and scrupulously de-greased them to the point where they would bloom over with oxide in a few seconds.

I think it would take dynamite to get them apart again.

« Last Edit: June 25, 2013, 05:08:57 PM by Chasfield »
2001 500 Bullet Deluxe

Chasfield

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Re: Clutch mod
« Reply #3 on: June 25, 2013, 05:05:32 PM »
This picture shows why I did the mod. The inner edge of the plate misses its neighbour by more than 5 thou. If your dished plates are like this, then I guarantee the clutch won't release cleanly.
« Last Edit: June 25, 2013, 05:20:50 PM by Chasfield »
2001 500 Bullet Deluxe

Chasfield

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Re: Clutch mod
« Reply #4 on: June 29, 2013, 05:06:07 PM »
I had a go at truing up another dished plate. With some deft blows using a soft hammer and a bit of leverage against a gap in the paving stones in my back yard, I was able to un-dish the working surface of the plate so that it makes flat contact with its neighbours. In fact, these plates are pretty pliable and minor warping can be readily overcome with some fairly gentle bending over the edge of a work bench.

With the whole clutch pack optimised, I am now getting by with the six standard clutch springs. This was definitely not possible before and I had to use the 3/3 mix of heavy duty/normal springs, which makes for an unpleasantly heavy clutch.
2001 500 Bullet Deluxe

Chasfield

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Re: Clutch mod
« Reply #5 on: June 30, 2013, 06:19:15 PM »
I went out today with a cold transmission... and the clutch slipped at max torque. The standard springs just can't quite handle the output of a Bullet with the usual free breathing upgrades.

So, I cut one and a quarter(ish) turns off a set of three heavy duty springs and installed them with three regular ones. I ground the modified springs to some degree of flatness but one end is now not finished like a factory spring, with the neat, ground flat, fine pitch turn that promotes even loading. I have installed them so that they are in a kind of circular symmetry to preserve even pressure plate lift. The good end is innermost, against the pressure plate.

Outcome: no slip, no drag, still no gorilla hand strength needed.
« Last Edit: June 30, 2013, 07:32:31 PM by Chasfield »
2001 500 Bullet Deluxe

Kevin Mahoney

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Re: Clutch mod
« Reply #6 on: June 30, 2013, 09:29:55 PM »
An old racing trick taught to me by George Helms (RIP) is to slot the flat discs with a bandsaw. It prevents the plates from warping when they are hot under hard use.

Your innovation is the sign of a good Bulleteer!

High On Octane

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Re: Clutch mod
« Reply #7 on: July 01, 2013, 01:07:16 AM »
Sounds like you got everything squared away, good for you!  I can appreciate one's ingenuity to fabricate custom parts, especially on a clutch assembly.  I'm glad you were persistent and dedicated yourself to making it right.   Congrats!    :D

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Chasfield

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Re: Clutch mod
« Reply #8 on: July 17, 2013, 11:53:21 AM »
Did some more on my clutch. I had noted that the basket friction lining was quite loose on its rivets but I wasn't too worried because they are held captive and the lining can't really go anywhere. However the consensus seems to be that this is not a good thing. Then I realised that this state of affairs could contribute to clutch drag, if the lining can lift a few thou and chase down some of that precious clutch lift. The final factor that swung it for me is that I worked out that there is a second identical friction lining attached to the back of the basket/sprocket assembly and this too was free to flap around.

So I ordered up new linings and rivets, plus a new primary chain for good measure, and set to work. The old, loose brass rivets are easy to get out if you are patient. I punched them enough from the backside of the basket so that they jammed in their holes then I skimmed off the peened over flair with a drill. Then I could push the rivets out. Some required two punch and drill cycles before they would let go.

Not wanting to suffer loose rivets again (which I think would be inevitable) I decided to JB Weld the linings to the basket and set new rivets. The only disadvantage I can see is that I can't replace the linings again if they wear out. However, the old ones had no discernible wear at 15,000 kms, so the rest of the the clutch would be almost certainly shot by the time I would need to do that.

Right now, the JB Weld joints are curing under load from my valve spring compressor, which makes a handy G-clamp, so I can't yet speak of a successful outcome.

This clutch design has a built in contradiction. It turns out that the basket/sprocket assembly is effectively your fifth lined plate and the extended rim of the main-shaft hub works as your last plain plate. However, the rear lining of the basket also functions as a thrust bearing - so do we want it to slip or do we want it to grip? The problem is that it will always be in contact with the hub when the clutch lifts because the basket sags on its ball race. I think that RE would have been better to confine its function to that of a thrust bearing and make it of smaller diameter and in bronze. The small contribution it makes to clutch grip would be lost but I would trade that for cleaner clutch lift.
2001 500 Bullet Deluxe

Chasfield

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Re: Clutch mod
« Reply #9 on: July 18, 2013, 03:55:50 PM »
Got the clutch back together today. Will test ride tomorrow.

I made a decent job of riveting my basket linings and got the rivet tails peened over neater than the originals. I was helped by the fact that Hitchcocks shipped out copper ones which are more malleable than the brass ones I drilled out.

I worked out a few riveting tips along the way.

1) Buy ten instead of seven rivets, so you have some to practice on.
2) Make yourself some kind of anvil. I set the extension bar from my quarter inch drive socket set in a baulk of timber. This fitted the rivet head perfectly. I rested the opposite side of the clutch basket on a house brick so that the whole set-up was free-standing, leaving two hands to turn the rivet tails over.
3) A ball end punch does most of the work on the rivet. A flat punch (I used the blunt end of a twist drill) works nicely to tidy up the edges.
4) I would suggest feeding four rivets through from front to back and three from back to front (all seven go front to back on a factory clutch). The properly formed heads of the rivets are a nice fit in the counter sinking of the linings and better resist torque loads. The tail side of the rivet can never be as good a fit and the unsupported rivet shafts just eat through the thin counter sunk area of the lining, without the support of a properly formed head. As far as I can see, the inner lining has to work just as hard as the outer one and on my clutch it had definitely worn the worst.

I didn't use this last tip because I have JB Weld under the linings. They won't be turning and fretting out the holes any time soon.
« Last Edit: July 18, 2013, 03:59:31 PM by Chasfield »
2001 500 Bullet Deluxe