I have a 2003 Rc51 that I wrecked in 2009. I've got it all back togeather but I'm having clutch issues. The right clutch cover had taken a hit and cracked so I replaced it and the threaded sleeve that the shifter-return-spring-bolt threads into had half broke off so i had that welded and its all good. With that being said my problem is that the clutch isnt disengaging. In order for me to get that sleeve welded I had to remove the water pump, then the case, the clutch basket, oil pump drive sprocket and chain. I saw no damage to anything else clutch related or otherwise, I had the service manual and put everything back correctly and to torque specs. I also have a 2001 rc51, I thought the problem could be in the hydralic system because I couldnt get pressure so I swapped the entire system from my good one to my wrecked one. Once installed I had pressure, and with the clucth cover off I could see that the push-rod was pushing against the pressure plate and everything appeared to be working good. But when I put the bike in gear with the lever pulled in the clutch would not disengage at all. I made sure the clutch discs were installed correctly, they are the origional and are probably due for replacement but since it was working fine before the wreck I don't know if the discs are my problem. I bought a complete hydralic system off ebay since it was cheaper then buying a new master cyclinder and/or slave cylinder since I couldnt find the reason I couldnt get pressure in the old.
So the new hydralic system came in today and I installed it but I'm still in the same boat. I have pressure, the push-rod is pressing against the pressure plate, but its just not disengaging. I removed the clutch cover on both bikes and put them both in gear. On the 2001(non-wrecked) with the clutch lever pulled in and in gear, the pressure plate would spin backwards while pushing the bike forward then would grab as soon as I let off the lever (normal opperation). On the 2003 with the lever pulled in and in gear, the push-rod would press against the pressure plate but it wouldn't disengage. I removed the pressure plate on the wrecked bike and with the bike in gear while pushing it forward the inner basket would spin backwards, so that makes me think that maybe it is a problem with the clutch discs and also assures me theres nothing internal binding it up. I'm tempted to swap out the entire clutch basket assembly from the good bike and install it on the wrecked one but I havnt yet since I'm dealing with an SP1 and an SP2 and I know for the SP2 they added a judder spring and spacer to the clutch, so I dont know if the clutches swap out.

The SP1 clutch basket and hub are the same for SP2.
The SP2 has the judder spring and seat, plus the larger I.D. friction plate for clearance around the judder spring.
Did you make sure that special inner friction plate with larger I.D. was used with the judder spring assembly?
If not, that could be a problem.
Does the clutch not slip at all, or does it have a lot of drag?

I took the pressure plate off and made sure the discs were where they needed to be. This time when I was tightening down the pressure plate I zip-tied the clutch lever in and had the bike in gear. I would tighten the pressure plate alittle then spin the rear wheel to make sure it was still clutching. At about 1/4in from being completly tight it was dragging hard. Then at completly tight it was grabbing and wouldnt spin at all....