After about 10 hours in the man cave over the last 2 days with little success I m in need of some help. The plan was to fit a Sigma Slipper Clutch and Brembo RCS 16 Clutch M/C to my 2004 Honda SP2. With hindsight perhaps I should have fitted these separately and got each system working individually but being short of time I didn’t and decided to fit both at the same time. Fitting of the slipper clutch went well. All friction plates were like new and within the tolerance of new plates so no point in replacing. I checked the metal clutch plates for warping and they were all perfectly flat. The only things I did decide to replace were the clutch springs as these were worn (but still within limits) so a set of 6 OEM Honda springs were sourced and fitted as a precaution. The fitting of the slipper clutch went well with no problems and all settings were within tolerance recommended and I even phoned Neil Spalding of Motogp fame to check my settings (He owns Sigma Performance) who confirmed all was good. Next task was to fit the Brembo 16 RCS Clutch Master Cylinder and all went well with this or so I thought until I tested the completed set up and found the clutch is not disengaging correctly. Basically with the bike up on the Abba stand and rear wheel in the air I put the bike in gear (engine off) pulled the clutch in and tried to turn the back wheel by hand. It was possible to turn the back wheel but only by exerting a reasonable amount of force so I think the clutch is not disengaging the plates enough and therefore dragging. For info I tried the same test on my Fireblade and the back wheel turns easily when in gear with the clutch pulled in. I put a DTI on the end of the clutch rod to see how much the pressure plate moves when the clutch lever is fully pulled in and found I have 0.7mm of travel which although I have no specific value I m trying to attain (figure unknown) this seems too small. (Note: I found some info on the internet that suggests the travel should be equal to one clutch plate’s thickness so in this case that would equal 2mm but I don’t know how good this info is) I stripped the Sigma slipper clutch to check everything was put back together as per the manual and confirmed this was correct. Next I thought I'll take the slave cylinder off and see how much the slave cylinder moves when the clutch lever is fully pulled in and I got the same value of 0.7mm. This proved to me that the problem is not with the Sigma slipper clutch as it is free to move and the amount of travel at the slave clyinder is equal to amount at the pressure plate so no travel is lost within the actual clutch unit if that makes sense. In my opinion its just that the slave cylinder is not moving enough (0.7 mm) to open up the clutch plates in the stack to disengage fully. As the Brembo 16 RCS has a 16 mm piston and the OEM Honda master cylinder piston is 12.7 mm diameter I thought to myself is the Brembo RCS master cylinder not moving enough fluid to move the slave cylinder and subsequent clutch pressure plate by the correct amount. I don't think this is the case as A, Brembo recommend the 16mm RCS for my specific bike and B the Brembo RCS Master cylinder piston is larger than stock therefore if anything it will move more fluid so in theory the slave cylinder should move more or the same amount for less travel at the lever. Therefore after trying all the above I m assuming the problem is air in the clutch line which means I m not displacing enough fluid out of the Clutch master cylinder to move the slave cylinder by the correct amount. I have checked for leaks and cannot find any. I have tried bleeding at the slave cylinder bleed nipple and the nipple on the Bremo RCS. I have tried injecting DOT 4 clutch fluid at the slave cylinder to reverse fill the system as well as the traditional method of filling at the reservoir by the clutch lever and bleeding the system down at the slave cylinder bleed nipple. I have removed the slave cylinder and tried pumping this by hand to displace the air to the high point at the Fluid reservoir. Trying all the above I have managed to move some air but as the travel is to little at 0.7 mm I think I still have some air in the system but bugger me if I can’t get it out. Note for info although the clutch lever is not spongy it does seem a little lighter than I would expect so this also helps confirm my theory of air in the system being the cause of the problem. In short I have tried everything I can possibly think of with no success and therefore I m looking for some help from someone with more experience on the subject. Do people agree its most likely air trapped in the system or could it be something I have over looked ? Any comments or suggestions are most welcome. Thanks and hope some one can help.
This guy is an absolute star. Had about a dozen PM's on the subject very late last night. Genuine top guy and a credit to this forum. Cheers Colin really appreciate your help mate.
Okay made some progress tonight in the fact the bike now goes in gear but not 100% sure everything is perfect so want to do some more tests tomorrow. After discussing things with Neil Spalding the suggestion was its air in the system so I have bled the entire system again but cannot get any more travel at the clutch plate still only 0.7 mm possibly 0.8 mm being optimistic. Neil Spalding couldn't tell me how much travel I should expect to see either unfortunately. As I'm 99.9% confident all the air is removed and when the clutch lever is pulled in I can rotate the clutch centre by hand I thought maybe that's all the travel that should exist so I thought lets give it a go, I started the bike and thought just go for it and try and get her in 1 st gear. The good result is the bike now goes into first gear and if I'm totally honest perhaps always did its just when I heard the clunking noise I originally backed off. However I'm still not convinced everything is 100% correct as A, the bike makes a loud clunking noise when entering 1st gear which I cannot remember it doing previously and B, the clutch bite point is very immediate now as in just out from the lever fully pulled in. Any suggestions or theorys are welcome or I will just carry on tomorrow and hopefully road test.
Just an update. I purchased a new DTI and mag base that was more suitable for the measurement I needed to do and have now managed to measure the travel more accurately and I'm getting 1.0 mm of travel now. I changed the preload on the springs by backing them out 4 turns, not very scientific I know but I just wanted to see if spring preload had an effect on pressure plate travel after reading the comment on the Sigma Performance website that it possibly could. The outcome is it does but only a very small amount as I got the travel to increase from 1.0 mm to 1.05 mm which is not the 0.5 mm I m think I have lost by changing the master cylinder and clutch pack. I m confident all air is out of the hydraulic system so the only thing I can see it being now is the new Brembo 16 RCS master cylinder not moving enough fluid. I have took some crude measurements for both master cylinders stroke and it looks like the stroke on the OEM Honda master cylinder is much longer so although a reduced diameter bore in comparison to the Brembo item it actually displaces more fluid as the volume is greater. Stock M/C is 12.7 mm Dia Bore with a Stroke of 17.0 mm this would have a displacement of 2153 mm3 Brembo M/C is 16.0 mm Bore with a Stroke of 9.0 mm so this would have a displacement of 1809 mm3 I have contacted Brembo twice to get clarification on the stroke of their Brembo 16 RCS but they are not forth coming with information even though their selector tool on the website says the 16 RCS is the correct M/C of my bike. Without changing back to OEM m/c which is notoriously hard to bleed and therefore has its own potential for error in getting an accurate measurement I think I may have to just accept the reduced travel and take it for a few test rides and see if the clutch operation is OK.
Did you remove the slave from the gbox housing to see how much does the slave piston travel when the lever is pulled in? Is the clutch connection rod ok and free from corrosion as gunk which may be causing it to stick and jam?
Yes I got roughly the same travel at the slave cylinder. Harder to measure as the spring continues to push the piston out but I m confident the travel at the slave cylinder is the same as at the pressure plate (maybe a little more but this is because there will be losses due to the slave cylinder having to over come the spring preload on the clutch plates). I have also had the connection rod out and it is free to travel and free from corrosion also. Good suggestion though and thank you for the input and comment which is genuinely appreciated.
