Modifying the clutch basket

As you have probably read in the XS News 51, there is a possible weakness in the clutch shock absorber spring area. Anyone who has looked at the back of their clutch basket will more than likely than not have found one or two broken springs. If by some mischance a piece of one of these broken springs finds its way into the primary drive gears then you will most likely end up with an engine in two pieces!  The kit consists of three new springs to replace the six originals and three blocks of Nylon like material that act as buffer blocks to limit the travel of the springs and new button head bolts and half nuts to hold it all together. The springs are harder than the originals by virtue of their heavier wire gauge and the number of coils. 

To install the kit it is necessary to first disassemble it, This is done by carefully drilling the "peened" end of the rivets on the back side of the clutch basket. Drill as much of the original rivet out as you can using a drill press so you drill straight. I then use an old valve which happens to be the right stem size and press them out using a hollow support so it won't crack the basket. (I stopped using a punch because I did crack a clutch basket). Make a note of how all the bits go together!

The buffer blocks in these pics are  made of Vesconite which is a plastic composite material used to make bearings in high temperature (250°C) dirty environments and lasts up to ten times longer than bronze so it should be perfect for this purpose.

Now that it's apart, look at the back of the basket and you will notice there are long and short slots in the primary gear for the springs.

 In standard trim the springs work in two stages, the three springs in the short slots act as primary springs initially until there is enough rotation to engage the three springs in the longer slots which then come into play as secondary springs. Unfortunately there is enough rotation before the collars in the oval shaped holes stop the travel to almost completely compress the primary springs and this apparently causes them to break eventually. By putting heavier primary springs and buffer blocks in place of these secondary springs the travel is limited and thereby reduces the risk of breakage. This idea was originally thought of for racing. For those who worry about this you might want to try using three standard springs as primaries and putting the heavier springs in as secondaries instead of the buffer blocks. 

The new springs go in the short slots and the buffer blocks go in the long slots. (see picture - above left)

Above:- standard gear fitted to a clutch basket with kit installed.

Below:- modified basket with high ratio primary drive gears with kit installed.

DO NOT INSTALL THIS KIT WITHOUT USING LOCTITE 262 ON THE THREADS!!!!

I have decided to change the kit to include button head bolts and half nuts instead of rivets. This will make it much easier for you to do the conversion at home without the need for special equipment like a hydraulic press. You will have to buy some Loctite 262 and it is essential that you use it to lock the nuts ands bolts on assembly. ( It costs about $12 from Bearing Service. ) 

I haven't tried this yet so it might be prudent to check the clearance between the clutch hub and the bolts used in the basket when assembling, it might be necessary to grind some of the head of the bolt down a bit for clearance.

No guarantees or warranties are given or implied and no responsibility taken for failure or damage, the conversion is done at your own risk.

Remember these clutch baskets were not not meant to pulled apart, Yamaha wants you to go out and buy a new one.
If you are careful and think about what you are doing it can be done successfully for a fraction of the cost of a new clutch basket

I now have some more in stock for AU$60 including postage and packaging for Australian buyers. Overseas buyers will incur the
additional cost of postage.

If you have any queries about this modification contact Terry at toota@internode.on.net or call 0408746881

Thursday, 22 May 2008