Most of my riding time is spent on my M199 Sherpa T 350, and like most older bikes it suffered from a heavy clutch action. It was especially annoying at those times when I wanted to use the clutch with one or two fingers and use the remaining fingers to grip the bars. What I did was machine up a stainless steel slave cylinder with a bronze piston and an automotive cup seal and fitted this to a modified side cover.

Stainless slave cylinder and piston

 

 

 

Slave cylinder in engine sidecover

 

 

 

Back side of slave cylinder in (filthy) sidecover

 

 

 

This is an easy mod, and for anyone interested in duplicating it the slave cylinder is 7/8" bore, 25mm OD and 32mm long overall. The open end has a 2mm wide x 28mm shoulder that locates the cylinder against the side cover, while the closed end is drilled and tapped to take the hose fitting. All that's required to fit it is to drill a 25mm hole through the side cover, centred on the original clutch pushrod hole. The back side of the opening may need a little filing to square it up so that the shoulder seats squarely against the case. The slave cylinder can then be Loctited in place. The best master cylinder to use is a Magura  9.5mm (from a KTM for example). The difference this made in clutch feel was remarkable; it's much much lighter. Just keep in mind that the Magura m/c will probably have seals meant to be used with mineral oil, while the standard 7/8" slave seal will be made for conventional fluid. You can get around this by using silicone fluid which is compatible with both.

Clutch/primary drive fluid also plays a part in this - there are fluids that work much better than the usual type F ATF. The best I've found was Castrol Power 1 Racing 4T 5w-40, a non-friction modified motorcycle engine/transmission oil. It allows the use of slightly less spring pressure without slipping than ATF.

 

Edited December 31, 201510 yr by oldjohnno

I can understand this mod as hard as a std Bull clutch can be. Only downside in our vintage club is you would have to ride with a different class of bikes. Not a deal killer. Very nice looking considering it`s using the same case. How long have you used it?

I've been using it for a year or so and try to ride every weekend. As you say, the downside is that in a lot of places it won't be acceptable. But if you can get away with it the action is beautifully smooth.

whatever the "legalities" its certainly a nice piece of engineering and an elegant solution to a problem!

I really like this and had been wondering about trying something similar in a Frontera i am working on as a future potential modification. My concern was wether the bore size within the casting would be sufficent diameter. I was thinking of welding up the side aperture and making a fitting with bleed nipple to mount in the top arm opening. Top marks for trying this and thanks for posting.

Nice mod, vestys has a conversion on his bike, sits where the cable goes

...My concern was wether the bore size within the casting would be sufficent diameter...

 

It's big enough, but only if used with the small KTM 9.5mm master cylinder. And of course anything you can do to reduce the amount of spring pressure required - eg. better plates and clutch fluid - will also help.