3.2 4t Clutch Problem....any Ideas?

[lineaway]

Thanks for that, I had to think about it a moment. It makes sense. The Beta that I had was a bike I had owned previously with no issues. I always wondered what had caused that!!!

[copemech]

Sounds like a case of primary input shaft end float, caused by spiral cut primary drive and driven gears when under load , (eg hill climb )

suspect imput shaft bearing in right hand case is moving under load, by the time you want the clutch it is having to move back before clutch will work.

The gears are not cut that way in a Sherco. Yet movement under load is still possible I suppose.

I had a 2T that would do this on occasion, thus the case venting thing to watch for. Never had it in later bikes.

Wonder if it is readily duplicatable on certain hills? Can one maintain light pressure on the lever to prevent it?

[canadaler]

Wonder if it is readily duplicatable on certain hills? Can one maintain light pressure on the lever to prevent it?

Yes, it seems to be. I went up the same hill a couple of times, once in second and once in third and had the same issue.

The only way to counter the effect is to pump the clutch lever (about) 4 or 5 times before you crest the hill. You can actually feel the lever has no pressure against it.

I hadn't thought of the possibility of the shaft actually moving under load...have to pull out the parts diagram and consider that one further. I was told by the previous owner...and understood from early posts on this thread as well...that the problem was there from day 1. So it doesn't seem like it is a worn out bearing/shaft issue.

My next test is to remove the oil filler plug in the top of the left case, just behind the cylinder and fairly close to the clutch slave cylinder, then rig up a tube from there up to the frame to vent the crankcase more than its ever been before. Unfortunately, we're buried under about a foot of snow right now so its not possible for me to recreate the climb(s) that bring this on.

Thanks to everybody for the theories and suggestions. Much appreciated.

I'll certainly let you know what I find out.

Oh...one last thought...if there was some sort of torque reaction between the pinion and clutch gear which was forcing the entire shaft and/or clutch assembly to move horizontally (to the right) under load...then it should disengage the clutch under the same load conditions on level ground. I haven't noticed that yet even after having launched it a few times in 3rd from a standing start. Seems to be no issue until you go uphill. In any case, I'll try some more starts on level pavement and try to confirm or refute this theory.

Edited December 18, 2013 by canadaler

[canadaler]

Seems to be no issue until you go uphill. In any case, I'll try some more starts on level pavement and try to confirm or refute this theory.

OK...so I found out I can create the same problem on level ground now. Start off in 3rd gear and keep the load on the gear box by continuing to accelerate for about 10 seconds or more and voila...no clutch again.

I'll pull the clutch cover case to check if there is any end play on the clutch assembly. If there is it likely means that there is a torque reaction under load which is pushing the shaft and clutch assembly to the right. Looking at the parts diagram the cause for that would be a clutch shaft thrust washer that is a little thinner than it really needs to be.

Edited December 21, 2013 by canadaler

[bwmwaima]

Canadale, if checking end play it may pay to take clutch slave cylinder off other end of shaft to get a true indication,

as you say may have been incorrectly shimed from new as there is more than one bike with this problem.

[copemech]

Random thoughts here on the issue.

First, have you contacted Ryan or anyone higher up that may have more info?

My thoughts are this is still a pressure issue. The clutch slave moves about 1.5mm per stroke as I recall. I doubt your internals are shifting 8mm that you must pump that much. It is just getting pushed back by pressure.

There is an o-ring on the slave as I recall. You might try removing it for extra venting as a test. I do not think it will leak much oil, but I am still not sure how much more venting this will provide.

What about the normal vent? Any idea what sort of pressure pulses are there when revving?

And last, what if you hold slight pressure on the lever to prevent pushback. It is a closed system once the return port in the master cyl is closed off, so you may either not experience the problem, or actually get return pressure increase?