Trials Australia Forums

It is nice to see you keep your vices handy.... or is it?
I'm a little confused about the method for using the one lying on your fingers. Is it meant to be simply hand held, and I therefore wonder about its actual usefulness, or is it meant to hold the job in its jaws, and then be put into another vice to keep it stable while the job is done?

This is the latest episode of the clutch saga on my model 49 Sherpa T.
I think last episode was about me comparing Barnett drive plates with standard steel drive plates. After the experiment I went back to Barnett friction (drive) plates and Bultaco steel driven plates and still wasn't happy with the amount of drag.
I wasn't happy with the (lack of) flatness of the Bultaco driven plates so decided to try and buy flatter driven plates. My logic was that if the driven plates are not flat there will be more drag than if they are flat.
I couldn't find any laser-cut driven plates but did find that In Motion was selling a clutch kit that included new driven plates as well as friction plates and springs and decided to give it a go.
The brand of the kit is Surflex and compared with the Barnett friction plates, the Surflex friction (drive) plates have a narrower band of friction material, the aluminium part is thicker and there are only four of them. The Barnett kit has five.
The Surflex driven plates are made of steel and despite being cut from sheet steel with a punch and die (not laser cut), are much flatter than any of the driven plates I have and are completely smooth where the friction material makes contact.
The three types of friction (drive) plates are at the bottom and the driven plates are at the top.
Bottom left to right is Bultaco drive plate, Barnett drive plate, Surflex drive plate.
Top left to right is Bultaco driven plate, Bultaco driven plate, Surflex driven plate.

I did about 20 minutes test riding with the Surflex kit and the drag is a lot less now. I suspect the Barnett friction plates would be just as good if I tried them with the nice, flat Surflex driven plates. The Barnett friction plates might even have a lighter lever pull due to having the extra friction plate and having wider friction bands.
Engagement is predictable, instant and happens with only a small amount of lever movement.

You could surface grind all the steels with a magnetic based surface grinder.

I did that on the SWM to fit an extra drive and steel plate but it did have the side benefit of making the plates very flat.

Just make sure you take a lick from both sides so you don’t end up with a Belleville washer when any internal stresses are released.

I do like the idea of being able to reuse the plates but they are so wavy that I'm not sure how much would be left after the surface grinding.
I'll do some measuring of how far they are off being flat

You can usually only fit 4 Barnett driven plates into a Bultaco clutch David. If you put all 5 in there the clutch nuts hit the Primary case. I have the In Motion drive plates in my 199B with Barnett driven plates and as you know that clutch works extremely well. I also found the Barnett plates work much better than the In Motion ones do. I still have a almost new set of them kicking around somewhere.

Bully fanatic wrote:You can usually only fit 4 Barnett driven plates into a Bultaco clutch David. If you put all 5 in there the clutch nuts hit the Primary case. I have the In Motion drive plates in my 199B with Barnett driven plates and as you know that clutch works extremely well. I also found the Barnett plates work much better than the In Motion ones do. I still have a almost new set of them kicking around somewhere. :Bultaco: :Bultaco: :Bultaco:

I suspect that the reason why I can fit five Barnett friction plates in is because I have the curvaceous 1968 design clutch cover on my model 49 which gives more clearance for the nuts than your slinky svelte 1976 clutch cover.
I agree that the Barnett friction plates are a better design than the Surflex friction plates, having much more contact surface area. However, my problem is finding something better (flatter) than the original driven plates. Do you know where I can get Barnett driven plates? My Barnett clutch kit only had the friction plates in it, no driven plates.
Here is what mine looked like: Photo from Hugh's Bultaco web page
https://sep.yimg.com/ay/yhst-1349281678 ... -087-4.gif

Kurt wrote:You could surface grind all the steels with a magnetic based surface grinder.

I did that on the SWM to fit an extra drive and steel plate but it did have the side benefit of making the plates very flat.

Just make sure you take a lick from both sides so you don’t end up with a Belleville washer when any internal stresses are released.

I measured the flattest OEM driven plates I could find. They were all deformed in a similar way - domed like a belleville washer but on a much smaller scale. The height of the doming ranges from about 0.05mm to 0.15mm. The plates are 1.5mm thick. If I can't buy nice new flat driven plates I will have a go at surface grinding them. Nothing to lose. They aren't going in any of my bikes the way they are

Hi Everyone,

Hopefully Christmas was good to you all?

David Lahey wrote:I agree that the Barnett friction plates are a better design than the Surflex friction plates, having much more contact surface area. However, my problem is finding something better (flatter) than the original driven plates. Do you know where I can get Barnett driven plates?

David, have you tried using the Surflex driven plates with Barnett friction plates? Pretty sure you will know this as you stated they are punched and not laser cut. One side will have a burr and I think it is best to have the burr facing the same way in the stack.

In other news, I thought I would share what I have been up to, I started with a sheet of ply so chosen because the layers make it easy to cut a uniform depth. Bored a hole in the middle and ran several holesaws through two layers to form a locating recess for the spigot that the rear sprocket mounts onto and then ran a smaller holesaw for the axle spacer to fit through.

Then I screwed the hub to the ply and marked the location of hub and valve for reassembly later. One thing that has always bothered me about this wheel is the rim was never installed in the right position making the valve difficult to access because it was one spoke hole out, maybe it was a Friday afternoon and our Italian friend was thinking of something other than valve access?

In this case 45 mm pine matched the offset from sprocket flange to rim so I screwed 3 pieces to the ply to locate the rim in relation to the ply. Using two off cuts, I scribed the outside of the rim and cut to shape in the bandsaw and screwed them to the 45 mm pine to locate the rim on centre:


Now that everything is screwed together and I have a reference of rim to hub location, the spokes can be cut out of the way:

It is after I cut the spokes that I realise why our Italian friend misaligned the valve hole, he must have been mega frustrated trying to get the extra long nipples into their respective holes and his focus and I presume temper were tested! So I then have to cut the spokes flush with the nipples and hammer them out of their respective holes in the reverse order that they were installed.

My jig will get tested when I have to work out spoke lengths and start to make new spokes.............
It did however pass this test:

Greg Harding wrote:Hi Everyone,

My jig will get tested when I have to work out spoke lengths and start to make new spokes.............
It did however pass this test:

1609320218888.jpg

We have had prior experience in the strange ways that gravity behaves at Coffs Harbour - remember the floating KT250????

Greg Harding wrote:David, have you tried using the Surflex driven plates with Barnett friction plates? Pretty sure you will know this as you stated they are punched and not laser cut. One side will have a burr and I think it is best to have the burr facing the same way in the stack.

No not yet Greg and it is something I don't think I need to try. I'm quite sure the Barnett friction plates will work better with the Surflex driven plates than the Surflex friction plates work with the Surflex driven plates so I don't think it needs testing. My problem is that I only have enough Surflex driven plates for one bike and to buy another Surflex kit just to get more Surflex driven plates is an expensive option. If money was not a concern I would simply buy another set of Barnett friction plates and another Surflex kit.
Maybe my story needs a bit more background info.
There are two trials bikes involved in this experiment. One of them will probably end up with Barnett friction plates and the other will probably end up with Surflex friction plates. The model 49 is the test mule at the moment and the current clutch pack is in there to see how much extra lever force was required to prevent slippage with the four Surflex friction plates and Surflex driven plates compared with the (previous best setup) five Barnett friction plates and the driven plates.
The next riding test is planned to be four Surflex friction plates plus one Barnett friction plate and the Surflex driven plates. I already did a test fit with this arrangement and the pressure plate (just) engaged fully.
For info, Surflex friction plates are thicker than Barnett friction plates. The basket isn't quite deep enough for five Surflex friction plates but five Barnett friction plates is a good number for the model 49 basket and clutch cover.
Yes it's a good idea to install any punched plates with the burrs all going the same way. I think in the case of the Surflex driven plates you would be impressed with the quality of the cut and the tiny size of the burr. Probably not as good as laser cut would be though.