By: Ron Milam
Last month, as you may
recall, we started a discussion of clutches and transmissions. We talked about
adjustments and eliminating drag by changing transmission oils. There are a few
things more that can be done to further reduce drag. This involves removing the
clutch cover and poking around at the innards. If you have a newer bike with a
separate cover plate for the clutch, this is extremely quick and simple to do.
If you have an older bike, you may have to remove the entire side case. In
either case, you are not getting into the actual transmission. If you are the
least bit mechanically inclined, you should have no problem.
Before you begin, be sure to clean the bike or at least the area
you will be operating on. You can usually complete the job without draining the
oil if you lay the bike on its side. I will dispense with the obvious, but I do
have a small tip that will help prevent damage to the seals on those bikes that
have a one piece side cover. Simply wrap some thin tape around the shaft splines
before removing the cover. This will prevent any sharp edges on the spline from
cutting the seal.
Before you dissasemble your clutch, but after you remove its cover, pull the lever a few times and watch the pressure plate move out and in. The amount of travel may vary between brands, but I think a good number would be about 2mm. If it isn’t moving this much or close to it, you may need to bleed the hydraulic system. The pressure required to disengage the clutch is very low compared to what is required to clamp your front brake. Consequently, you can’t feel it when air is trapped in the syatem. But any trapped air will compress and that will reduce the clutch throw out. If the travel is OK, pull out the plates. I’ll bet you they were stuck together in there. This is because the oil layer between them causes a suction that must be broken before they will separate. If your clutch is dragging, this is where a low cost mod will make a huge improvement. Send your metal plates to somebody that knows how to knurl them. One such person is Bob Ginder, but other folks can do it too. The result of the knurling process is a multitude of small depressions that reduce plate sticking. If you ever saw the dimpled plates in a Japanese clutch you will know what I’m talking about. Along with this and maybe even before you send out your plates for knurling, you should deglaze the friction plates. You can do this easily by placing a piece of 150 grit sand paper on a sheet of glass or other flat surface and lightly rubbing each side of the friction plates in a figure 8 pattern on it. Be sure to clean off excess oil first. You should make a few strokes and then reposition your grip on the plate. This technique will help ensure that the plate surface remains flat and parallel to the one on the other side. You need not worry about prematurely wearing out the plates. You are only removing a tiny amount of material. You should make every effort to do this evenly. Check the plate surface often and change hand position often. You only want to take the shine off. Look to see that the surface is becoming roughened all over the plate. If you have areas that are not cleaning up as soon as adjacent areas, check the plate on your flat surface and look for warpage. If they are warped, they should be replaced. You should also lay the metal plates on the flat surface and check for warping. They should be flat within a few thousands of an inch. If they are warped, they too should be replaced. Do both sides of all friction plates and reassemble, oiling each part as you go. I have the metal plates in my Beta knurled and I am running stock friction plates. I find that every 3 months or so, my clutch will start dragging. When it does, I do the deglazing routine and change oil. The whole thing takes about 30 minutes. I can now find neutral while waiting at a section with the engine running. This may not sound like such a big thing to some of you, but if you have one of those bikes that just jump from first to second and second to first, but refuse to stop at neutral (unless you are in a section ) you know how nice it is.
My son Chris has a ’95 Fantic that has Sureflex brand friction plates in it. The metal plates have not been knurled. That clutch works beautifully. It has a super smooth engagement and no drag. This leads me to believe that if you have good friction plates to begin with, knurling may not be necessary. A set of Sureflex plates cost about $ 80. If playing with oils and deglazing do not solve your problem, I think the Sureflex plates would be a good next step. If you’re still not satisfied, go with the knurling.
In conclusion, I would say that a cluch that does not drag should be your minimum expectation. You should keep working at it until you also have smooth engagement. This will result in lower scores and much less frustration.
Ron