Clutch drags

[slodad]

Junior just purchased a 1998 YZ250. The previous owner said it would be a good idea to change the transmission oil pretty soon, so right after Junior's first outing we did so. Out of the drain plug came metalflake sludge. The manual specifies 10W/30 grade SE oil for the transmission. Having on hand only Castrol 5W/30 grade SJ and not wanting to make a speed run to Wal*Mart, I figured it would probably work just fine.

I got the opportunity to ride the beast the next time he went out and it struck me that the clutch wasn't completely disengaging, and I'm not talking just a little. If the engine wasn't being revved to 5-6,000 rpm it would lurch forward and stall. Neutral was impossible to find with the engine running. Junior said that he didn't recall it behaving so when he first rode it, but it must be noted that Junior tends not to notice those things.

The bike came with a Magura hydraulic clutch kit and my first thought was that it wasn't moving the actuator arm sufficiently. Replacing it with the stock lever and cable system almost doubled the amount of travel of the actuator and helped a slight amount. However, it still drags enough to kill the engine when putting it into gear.

Any thoughts on the matter?

 

[Jaybird]

Motorcycles are heck on motor oil. The clutch puts the oil through tremendous shear forces and chews it up fast.
Always change your oil out after every other ride or so, no matter how hard the ride was.
More than likely, the clutch plates needs to be replaced. I would change out the basket as well while there. More than likely notched.
Once you know the clutch is in good working order, try to use something other than the XXw30 fluid. I would suggest using Type F ATF. You will hear some disagreement on this, but I have alot of faith in type F atf, as it is loaded with barrier additives and is a very thin bodied fluid.
Type F (don't mistake this with other types of ATF) works in a different way than Dexron/Mercon typoe ATF's do...Type F has a dynamic coefficient of friction that is reduced when the revs are high, which is exactly opposite of how Dexron/Mercon type fluids work.
I know that this would seem to be the opposite of what you need from what you have described...but I feel you have a mechanical clutch problem that first needs to be addressed before you will have any idea of what fluid really works best for that bike.

All that said...even if you do use a xxW30 motor oil, the bike should not do what it is doing. Heck even if you are using a 50wt oil in the middle of winter, it shouldn't do that...well maybe a little.

 

[Rcannon]

Look at the clutch arm as it leaves the case. Is it pointing foreward??

Most of the YZ from 97 and 98 do this. In this position it is almost impossible to release the clutch. Aftermarket perches make the problem worse.

I used a shim from the 250f bikes. Put it on the clutch side of the rod that runs through the case. This rod is too short. Something 2.5 to 3mm thick will help a lot.

Your clutch basket and inner hub is probably grooved. Combine all of these issues and the clutches get really bad.

 

[slodad]

I examined the clutch and the clutch basket has slight notches or grooves on what I suppose are the driving edges of the fingers that align the friction plates. They are probably a few thousandths deep. Certainly less than .020". Would that be enough to prevent disengagement?

In looking at the Yamaha parts microfiche, it appears that the basket comes with the primary gear and the kickstarter gear attached. Is that the same for aftermarket parts such as Hinson? Wiseco advertises that theirs comes with the kickstarter gear, but doesn't mention the primary gear.

How long should a stock clutch basket last under trail riding conditions? This bike will seldom see 8,000 RPM and almost no high RPM clutch slipping. The prior owner claims to have raced the bike weekly and I suspect that he was more inclined to use the clutch than the transmission when things fell off the pipe.

 

[Rcannon]

The clutch basket needs to be smooth. Dont forget to check the inner hub as well.

The hinson uses the stock gear. It is not too big of a deal to remove this from stock. The stock pieces are not worth replacing. I bought Hinson. They are expensive, but they last.

The real solution on this clutch is to extend the push rod. Look at the angle of the clutch arm as it enters the case. Notice the radical angle. There is no way enough cable gets moved to disengage the clutch. Aftermarket perches make this worse.

I switched EVERY...Yes, EVERY piece related to my clutch on the 97 yz 250. Nothing worked until I extended the rod by adding a spacer. With a longer rod and hinson parts the clutch is excellent.

 

[chevy383cid]

Ive got a 98yz125 tell me more about your shim,the arm goes to a 90 degree shaft that goes in to the case and it has a gear made on to it that pulls on the rod that pulls the preassure plate from the plates, where is your shim?

 

[Rcannon]

The rod for the clutch goes into a bearing that rides against the pressure plate. This is where I added the shim. I used a 2.75 mm shim from the YZ 250f valves. This basically extended the rod 2.75 mm and improved the angles. The clutch pulls easy and does not drag. There have been no maintenance issues in 16 hours of riding.

I dont know if th emod will work on the 125. It may be worth a shot. In 96 Yamaha added a 2mm washer behind the inner hub of the clutch without making th erod longer. This is where the trouble started.

 

[chevy383cid]

Thanks , I'll give it a try,There is a shim in front and bebind the bearing,I'll just order two more shims to take up the slack.

 

[Rcannon]

This shim goes inside the bearing sleeve (Yamaha calls it the Rod, push 1) http://www.yamaha-motor.com/sport/parts/home.aspx

It will move the pressure plate out. The movement will be equal to the shim thickness. The shim needs to be about 8mm diameter. A 250 valve shim works almost perfectly and is cheap. You will be shocked at the difference.

Again, this is info for the 250. The 125 may be different.