Basket Cases

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David Lahey
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another clutch quiz

Postby David Lahey » Wed Jun 03, 2020 6:58 pm

Kurt's SWM/Rotax clutch post motivated me to post up a question about the clutch in my venerable 1968 Bultaco Sherpa T.
Around that time, :Bultaco: s and :montesa s came with all-steel clutches. All-steel means that the friction surfaces of all the plates is steel. More modern motor designs use steel against friction material on the mating surfaces.
In an attempt to improve the action of Bultaco clutches, some aftermarket clutch plate manufacturers like Barnett have made replacement drive plates with friction material bonded to them. In the case of the Barnett plates in the photo, they are made of aluminium sheet with the friction material stuck on both sides and they are very well made.
Barnett claim that their clutch plates working against steel driven plates have a higher coefficient of friction than steel plates against steel, but how much better is it? This is important because the Barnett plates are thicker than the Bultaco plates. The extra thickness means that only five Barnett plates and five driven plates fit in the clutch basket wheras six Bultaco plates and six driven plates can fit in the same basket.
My question is: Will the Barnett setup give me a lighter or a heavier clutch lever action with the pressure plate clamping force set just high enough to avoid slippage?
Barnett = higher friction but smaller total contact area
Bultaco = lower friction but larger total contact area

The photo shows the five Barnett drive plates and six Bultaco drive plates. I haven't shown the steel driven plates
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Bully fanatic
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Re: Basket Cases

Postby Bully fanatic » Wed Jun 03, 2020 8:18 pm

Hi David. I use Barnett clutch plates in all of my 3 Sherpas. All with longer clutch arms on the case. I also only use 4.5 to 5 turns out on the clutch nuts with Venhil cables. The Barnett plates do grip a lot better than the standard plates. They are all a very easy one finger pull. My M199B is still the best one though mainly because it has very old clutch springs in it. I put new ones in it years ago and took them out almost straight away. Way to hard. Are you using a later clutch nut inner basket in yours? Or a standard pin one? :Bultaco: :Bultaco: :Bultaco:



Phil 850
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Re: Basket Cases

Postby Phil 850 » Wed Jun 03, 2020 8:28 pm

Not a motorcycle clutch expert by any means but !
If the installed spring height is the same, then the force to release will be the same.
Spring height longer (less compression in the spring) will give a lighter clutch.
I would expect friction material to have a greater coefficient of friction than polished steel on steel.
As there is ~20% less friction plates they only need to have 20% more friction to equal the original steel plates.

2c



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Re: Basket Cases

Postby David Lahey » Wed Jun 03, 2020 8:49 pm

Bully fanatic wrote:Hi David. I use Barnett clutch plates in all of my 3 Sherpas. All with longer clutch arms on the case. I also only use 4.5 to 5 turns out on the clutch nuts with Venhil cables. The Barnett plates do grip a lot better than the standard plates. They are all a very easy one finger pull. My M199B is still the best one though mainly because it has very old clutch springs in it. I put new ones in it years ago and took them out almost straight away. Way to hard. Are you using a later clutch nut inner basket in yours? Or a standard pin one? :Bultaco: :Bultaco: :Bultaco:

Yes Graham this M49 has been converted to the later clutch hub design with adjustable spring preload. I will be able to adjust the spring preload up just enough force to prevent slippage however I set up the clutch plates. It also has the later design splined gearbox shaft to enable the use of the spline drive clutch hub. Early M49 motors like this usually have a key drive clutch hub and also very different clutch plates to the later 5 speed motors like yours and this one. This M49 was modified like this before I got the bike. It still has the early 5 speed clutch actuation mechanism using a bendix rather than the later camshaft design like yours.
In the photo you can see that there is no adjuster on the pressure plate. Pushrod adjustment is done at the other end using a screw that goes through the centre of the bendix. If I was to change to the later magneto cover like yours with its camshaft type actuator, I would also need to change the primary drive cover to a later type to allow adjustment of pushrod freeplay.
The engine covers on it are very distinctive visually so I don't want to change to the later type covers.
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David Lahey
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Re: Basket Cases

Postby David Lahey » Wed Jun 03, 2020 9:01 pm

Phil 850 wrote:Not a motorcycle clutch expert by any means but !
If the installed spring height is the same, then the force to release will be the same.
Spring height longer (less compression in the spring) will give a lighter clutch.
I would expect friction material to have a greater coefficient of friction than polished steel on steel.
As there is ~20% less friction plates they only need to have 20% more friction to equal the original steel plates.

2c

Unlike most other bikes, the spring preload on these clutches is adjustable so you can set it to provide just enough drive, no matter what the stack height is.
Yes, you won the quiz with your last line.


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Re: Basket Cases

Postby brownie » Thu Jun 04, 2020 2:56 pm

Didn’t the early m49’s originally have friction bonded drive plates and adjustable springs with self locking nuts also a ball race thrust instead of the needle roller.
I find the all steel clutch pretty good not that I use it very much Only to put it into gear usually



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Re: Basket Cases

Postby David Lahey » Thu Jun 04, 2020 3:51 pm

brownie wrote:Didn’t the early m49’s originally have friction bonded drive plates and adjustable springs with self locking nuts also a ball race thrust instead of the needle roller.
I find the all steel clutch pretty good not that I use it very much Only to put it into gear usually

Yes Brownie I think that's what's on another M49 engine I've got here. I might drag it out and take a photo. I'm thinking that early M49 clutch design might be the same as what's on a 4 speed motor.
I haven't worked out how the thrust bearing in the pressure plate in my photo works yet.The pushrod end at the pressure plate end is hardened and flat and there is a little hardened steel button that spins easily inside the part you can see in my photo, but the button doesn't come out. The pushrod is a single piece all the way from the adjuster in the bendix to the button in the pressure plate.
As for the action, I have actually ridden it both ways and reckon there is no difference. The clutch was fine with the six pairs of steel plates but I thought I'll give the Barnett plates I bought for another Bultaco a go in the M49 to see if I can get the lever pull even lighter, but I couldn't actually tell any difference. Both times I set up the spring preload so there was just enough drive to kickstart it.
Also both setups are nice and smooth to use.


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Re: Basket Cases

Postby David Lahey » Sat Jun 06, 2020 12:32 pm

I got back to working on the M49 this morning and reckon I found why the clutch pushrod was being spun strongly enough to cause the damage shown in the earlier posting.
Today I pulled apart the thrust button thing in the pressure plate. This is what transfers the axial force from the pushrod to the pressure plate. On later model Bultacos, there is a radial needle roller bearing there. On this early 5 speed motor, there is a tiny ball race with loose balls, like a miniature version of steering head bearings.
When I looked with a magnifying glass I could see that the inner race had been rubbing against the outer race, due to wear of the races and the balls. The places where they were rubbing together are shown in the photos. This rubbing would be why the pushrod was being spun around so strongly.
Luckily I had a few other old style pressure plates and found one that had a thrust bearing that was not worn much, cleaned it out and reassembled the clutch.
While the clutch was apart I went through my spare driven plates and found enough to make a set that are a bit flatter than the ones that came out.
I haven't finished working on the release mechanism on the other side of the motor yet. I'm pretty keen to finish the clutch work off and try out the clutch.
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David Lahey
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Re: Basket Cases

Postby David Lahey » Sun Jun 07, 2020 4:35 pm

brownie wrote:Didn’t the early m49’s originally have friction bonded drive plates and adjustable springs with self locking nuts also a ball race thrust instead of the needle roller.
I find the all steel clutch pretty good not that I use it very much Only to put it into gear usually

I haven't got that M49 motor out yet for a photo of the clutch but I did get out some old style friction bonded Bultaco clutch plates to illustrate what you were talking about.
Here are examples of different Bultaco drive plates. The late style (post 1970) are the plates with the JTJTJT slots in them
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And here are the various types of Bultaco driven plates
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NOT BLOODY Bultaco !!!!

Postby Greg Harding » Sun Jun 07, 2020 9:33 pm

Hi Everyone,

GOLDMEMBER Mmmmm, I am still trying to get my head around that one! Forever the optimist, I can see GOLDMEMBER has good taste.....................
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In colour I mean, even when there is impending DOOM:
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eagle wrote:Do we have after shots of theses Honda ?

Eagle, by now you have probably realized that you have already seen after photos of the BLOODY :Honda: , David probably summed it up the best:

David Lahey wrote:Greg's BLOODY :Honda: from Coffs Harbour was very well presented with "before" photos on a silver platter and it even leaked blood!
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The "How I got the TLR 250 photos"
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were added into the mix because I used the handlebars on my latest creation, perhaps as David put it..............: Franken :Honda: :Honda: :Honda: :Honda:

On a side note, now with Aluminium Sprocket cover:
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