Funny that you brought up the Barnett spring compression rate. When I put mine in I looked very closely and could see no physical difference. I went as far as compressing the OEM and the Barnett springs alternately with a pair of slip joint pliers. Could not really tell a difference. I figured it was just me. Shrugged my shoulders and put them in.I was watching Sportbike Trackgear's video install of the Ninja 400 Yoyodyne clutch. In the video Brian mentioned his son had previously been running EBC 600RR clutch springs for racing. It had strengthened the clutch, but lost slipper effect. A tradeoff I'll take any day.
Anyone tried the same thing? Or does anyone know of tougher springs from another bike that would fit? Stock Ninja 400 springs are 20mm outer diameter, 14.5mm inner diameter, around 42mm long.
I've looked at using washers to preload the existing springs, but the design makes it awkward. The plate at the engine cover end of the spring has protrusions to capture the spring. The pressure plate end of the spring has elongated holes so the slipper clutch can ramp.
I've got the Barnett springs installed, but honestly I'm suspecting they've worn out or something. They've had 24,500km of use. Clutch is slipping in 4th between 8000-10000rpm. Clutch stack height well within spec. Steels are flat and looking good. I've got the adjusted length pull rod, not that it should affect anything yet. Was running on the same synthetic oil for a few thousand k's before it started slipping, the same stuff I've always used. Swapped to mineral to see if any difference, none.
I removed my clutch cable return spring and was surprised how much of a floppy wet noodle the clutch lever was with just the Barnett springs providing resistance. Out of curiosity I swapped the factory springs back (only had 1000km of use) in and could have sworn the lever was stiffer at full pull.
To test out spring compression between Barnett vs stock, I rigged up a bunch of weights on a big car battery, the battery supported at one end by the spring, and measured the compression. I couldn't measure any difference. I think the Barnett springs are said to be 10-15% tougher than stock.