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Clutch Mod

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 a larger drill bit to remove any remaining rivet above the back plate. It should then be possible to lift off the back plate and disassemble the clutch basket. Make a note of how all the bits go together! Then carefully tap out the old rivets, try not to use excessive force as it is possible to crack the clutch basket. 

The buffer blocks in these pics are  made of Vesconite which is a plastic composite material used to make bearings in high temperature (250C) 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. ) 

You will also need to shorten the bolts supplied as they are too long, this can done after assembly with a small grinder or hacksaw.

If you have any doubts about the nuts coming loose then tack weld them or centre punch the threads on the bolts to deform them so the nuts cannot come loose. I have been using a clutch kit and primary drive gears (pictured above) in my own bike for over a year with no problems. You decide if you want to do it yourself bearing in mind the experimental nature of the conversion.

Disclaimer

These are experimental parts intended for racing and as such no warranty is given or implied and if you decide to buy it is on the understanding that you assume complete responsibility for any possible injury, loss or damage that may occur as a result of using these parts and that you accept these conditions of sale prior to purchase.

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

Sorry but these are now out of stock and I probably won't make any more. 

Mikes XS sells a stock spring replacement kit if you have broken springs

Clutch Hub Cushion Drive Spring Repair Kit

Clutch Hub Cush Spring Repair Kit for 1970-84 650's
Replace broken clutch hub cush springs with this kit.
Includes 6 Cush springs and special bolts that replace hub rivets.

Part #39-6515

or

Ivan Hoey sells stronger Clutch Cush Drive Springs

Clutch primary gear cushion spring kit (6 springs 3 screws & nuts) $45.00 plus post. They go well with a set of high ratio primary gears...... Ivan Hoey ltr.management@bigpond.com

Ivan can do the whole conversion for you as well, talk to him for a price.

Disclaimer

These are experimental parts intended for racing and as such no warranty is given or implied and if you decide to buy it is on the understanding that you assume complete responsibility for any possible injury, loss or damage that may occur as a result of using these parts and that you accept these conditions of sale prior to purchase.

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

Tuesday, 05 May 2015