It’s well known, that clutch baskets of Kawasaki KZ650/KZ750, as well as that of Zephyr 750 are equipped with rubber dampers. These rubbers shrink and even crumble after a long time of exploitation, therefore cease to perform damping functions. There are three sets of dampers in KZ650/KZ750 and Zephyrs 750: rear wheel, clutch basket and secondary shaft housing. Clutch basket joins secondary shaft and gearbox. All these dampers damp jerks that engine parts receive from rear wheel or when you accelerating/decelerating or gear shifting. Dampers in clutch basket also make gear shifting smooth. So it’s essential to keep those rubbers working.
Clutch basket’ outer, where dampers sit is made in “non-separable” style, and Kawasaki does not provide replacement dampers. However, aftermarket dampers made of Viton rubber are available, and methods of clutch basket disassembling are well known. Thus I am not the first person who did such replacement, and not the first person who wrote tutorial for it, but may be you could find something interesting in my approach to the issue, as I am used to make the work as I deemed necessary.
So what do we have at start? As you may see from photos below aluminium clutch basket outer is riveted by six 5mm rivets to steel gear.
Our next task is most important. We have to remove rivets without even slightest damage to aluminium basket, as later we have to cut the thread in holes where rivet sits. Do not try to punch out rivets as they are, and do not try to drill them out with 5mm drill bit. Instead use 3.5-4mm drill bit and drill rivets’ bodies MOSTLY through.
If you made everything correctly, you have six undamaged holes each of them by 5.1mm in diameter. We have to cut M6x1mm thread. According to specs, such thread needs 5mm hole. However I cut the thread and found result being very sufficient: thread looked fine.
But appearance is not only parameter of the thread. The maximum torque for M6 thread made in aluminium is 12-14 Nm (camshaft caps). Thus, I tightened 6mm bolt with 14Nm to check if thread holds firmly. Test went successfully. That’s why undamaged holes were such essential: be they a little bit larger and thread might be loosed.
I bought two sets of Viton dampers from Turbosteve, one for KZ and one for Zephyr. When I installed one of them on KZ650 clutch basket I found that I wasn’t satisfied with backlash between gear and basket. Thus I took second set of rubbers, and combined dampers until backlash became minimally possible. It was alike the scene from movie “The Good, the Bad and the Ugly”, where Tuco assembles a gun in gun shop.
There is a variety of methods how to fix gear cover back. Here is my version. I chose flanged screws with grade 10.9 and 2701 Loctite (which is temperature improved version of 2700). And if you are a control freak, here is my little invention that will allow you to sleep without bad dreams about wrecked crankcase. In fact it not exactly invention. Everyone who have to replace driving chain before next day ride and found out that his chain riveting tool was lent, but not returned, or not functioning properly. could of invented this method. In fact it’s old school chain riveting method that may be called “bearing ball and hummer”.
To check if it works on screws that I’ve bought for clutch basket, I drilled the end of one of them with 3mm drill bit, screwed a standard nut on it, and then with help of suitable bearing ball and hummer widened drilled opening. After this I tried to unscrew nut and here it is, it didn’t come off.
Screw heads were protruding for about 3mm about gear cover, while suitable protruding is not more than 1.5mm. I protected clutch basket from abrasive penetration and then removed the extra heights with file tool. I equalized heights of heads and then made final grinding using as base thick mirror with sheet of sandpaper on it.