by mr_luke » Thu Apr 18, 2013 7:02 pm
As Dave says, I think you have a problem with something worn and/or in need of lubrication, dropping the clutch from engaging, rather than worn out friction plates. To start with I would check the handlebar lever and the cable move freely without catching. Then I'd take the alternator cover off: inside the cover the cable acts on a lever which is "screwed" into splines machined into the cover. Check that this lever is moving freely without catching anywhere. I think there is a grease nipple on the splines. There should be a return spring between the lever and the cover, so make sure that is present and in good condition. The lever acts on a steel rod which runs through a hole in the middle of the gearbox mainshaft. As above, check the rod moves freely without catching. You should be able to pull it out and check it's not bent or otherwise damaged.
If you still have no luck, further investigation will require you to take the clutch cover off the other side of the engine. You'll need to drain the gearbox oil first, and you *might* find you need a new gasket upon reassembly. If you get as far as removing the three shouldered bolts which hold the clutch pressure plate in, be very careful not to overtighten them when you put them back in - they're very easy to snap.
Good luck!