By: Ron Milam
For the last 3 months, we have been talking about brakes. I was quite sure that I had completely worn out the subject. But even after all of that, people are still making comments and asking questions. I am now pretty sure that is the most universal problem area on a trials bike. I think the next one might be the clutch. There are great ones and bad ones. I think it would be interesting to first discuss the factors that affect the way a clutch works.
First would be the master cylinder ( for you hydraulically challenged guys with cable actuated clutches this would just be the clutch lever ). These mostly look the same on the outside, but can have varying piston diameters. Second is the slave cylinder. Since these are often made by the bike manufacturer and not purchased, they vary widely in design and piston diameter. Just like on your brakes, the ratio of the 2 piston areas is very important because it affects the sensitivity of the clutch engagement. ’94 Betas had a very quick clutch that was difficult for most riders to use. In ’95 I think it was, they increased the slave cylinder diameter to make the clutch engagement more gradual. The same thing happens on a cable actuated clutch when the actuating arm is lengthened. This is normally done to lighten the lever pull however, not to soften the engagement.
For the average rider there is not much you can do to modify these items. But you can optimize them. If your clutch is too quick, you can position the lever farther from the bar end, so that you are working it near the end. This means your finger has to move farther to engage the clutch, so the movement doesn’t have to be so precise. This has the same effect as what Beta did with their modification in ’95. If you want quicker action, you can just do the opposite. Moving the lever assembly closer to the bar end will place your finger closer to the pivot point and give trigger like engagement. ( It will also cause more bent levers since they will be more vulnerable in a crash. ). Lever free play is also important because your finger has less accuracy when it is stretched out than when it is closer to the grip. Set up your free play so that your finger is in a comfortable position when the clutch is at that critical engagement point. There is a trade off here though. Obviously if you set it with too much play, the clutch may not completely disengage. ( Can you say “5” ? ). I am talking about the adjustment screw where the lever pushes the plunger into the master cylinder. Many levers have another adjustment screw that you can use to tighten up the play that you induced and keep the lever close at hand. If this doesn’t make sense, I’m sorry. I don’t have any pictures, only a thousand words. Look at your lever. You’ll know what I mean.
The third item is the cluch unit itself consisting of friction plates ( faced ), driven plates ( metal ), and springs. This seems simple enough. Let’s quickly mention springs and get them out of the way. If your clutch isn’t slipping, your springs are probably OK. If it is, you should remove them and measure their length. Call your dealer and find out how long they oughta be. If’n they’re too short get some new ones. If’n they’re not, the problem is with the plates. ( Be sure the actuating mechanism is not preventing full engagement ). Hardly anyone complains about slipping. Mostly everybody complains about dragging. Next to engine stalling, hard cranking, brakes failing, fenders breaking, ah heck, forget it. Lets just say most of us experience clutch drag at some time.
The easiest thing to try is to change the oil. Transmission oil is critical to a trials bike clutch. Many people resort to ATF to reduce drag. The result is often reduced drag, but often is also very grabby engagement. When you are trying to finesse your way around a turn by slipping the clutch, and have your front tire lift slightly and wash out, you will know what I mean. Smooth engagement is just as important as full disengagement. ATF helped reduce the clutch drag on my Beta, but after a while I noticed my turning ability was really bad. Not that it has ever been any good anyway, but it was even more badder than usual. I switched my transmission oil to Elf Moto T 10W30 and the result was much smoother engagement. The stuff costs a lot and maybe there is a cheaper substitute, but a transmission doesn’t hold that much and a few dollars worth of something that works is way better than a few cents of something that doesn’t. Along with the oil change, I also had to deglaze my friction plates. Next month I will get into how to do that, and disclose a few other secrets.
Ron