XS650: 8 plate clutch   Leave a comment

Here is a clutch modification done by fellow xsler Peter von Sphinx feat. Herbert Claeren – Peter runs a long-stroke 880ccm motor –  designed to deal with the xstra loads of high performance motors and sidecars.

My winter get away ’09 was to create one similar with a billet basket-strong, doesnt get the chattering wear. The process will be the same, the xsact ammount removed will depend on the dimensions of the parts used. I also fixed a high ratio primary drive gear -68 teeth- to the basket and the opposing gear -32 teeth- to the crank -Ivan Hoey  ltr.management@bigpond.com, he writes

On the XS650 the primary gears are 27 teeth on the crank gear and 72 teeth on the clutch basket. These are 20% higher than the original ratio, exactly the same as those now unavailable, produced by Halco Tuning in England.

So, why do we need to use the higher ratio primary gears?

The available options for secondary gearing on the XS650 are limited, the largest front sprocket that will fit the XS is 18 teeth and the smallest rear sprocket that will fit is about 30 teeth so if you want to go faster you would have to rev the engine higher and getting more horsepower to the top end might not be best option, you’d like to keep those rev’s down a bit and make the engine live a bit longer.

By using the high ratio primary gears you speed up the gearbox allowing more scope for final drive sprocket selection with the added bonus that you also effectively reduce the load on the gearbox and transfer that load onto the engine.

To my knowledge this 8 plate mod has been done with the ’78 and later sprung 6 plate clutch and the earlier, TX-A on 7 plate clutch. I dont know if the TX and earlier 6 plate clutch has been modified.

Original clutch pack internal measurment is 29.4mm for 7 friction plates @3.5mm ea and 6 pressure plates @1.4mm ea.

There are 2 ways to accomplish this.

  • use original 3.0mm friction plates … requires clutch modification
  • use 2.5mm plates from someone like Alto usa (see p 71) … an 8 plate mod is only 0.4mm larger than the stock 7f/6p configuration



Pressure Plates

Total mm

Total mm



























Using 8 x 2.5mm friction plates and 7 x 1.4mm pressure plates gives a total of 29.8mm, 0.4mm more than stock 7f/6p. Easy fix.

9 and 10 plate mods will be doable with the thinner friction plates when the clutch is modified like below.

Careful measurement first is cheap insurance.

I combined this with an hydraulic clutch operator.

  • 8 friction plates @ 3.0mm…24.0mm *XS1-TX were 3.5mm
  • 7 steel pressure plates @ 1.4mm…9.8mm *XS1-TX were 1.6mm
  • Total: 33.8mm,  original 7 plate: 29.4mm, 4.4mm difference

4.4mm is the xstra ammount of space required inside the mechanism.

  • Measure the overall height of the existing 7 plate clutch.

This is your maximum allowable height. Your completed, modified clutch should not exceed this measurement or it may rub the inside of the rhs case on disengagement.

  • Dont forget to allow about 2.5mm for separation

The 4.4mm for the extra plates can be gained by:

  • Turning approx 2.0mm from the inside surface of the boss and
  • Removing approx 2.5mm from the inside surface of the pressure plate

The 2.5mm for separation can be gained by:

  • Removing 1.5mm from the bottom of the boss and
  • 1.0mm from the outside of the pressure plate

After removing 3.5mm from the boss surfaces you must file the friction plate dog spaces in the basket so the plates can sit deeper

Use the later pressure plate with the teeth and make sure that the teeth locate into the boss splines at all times, especially when disengaged. If changing to the later toothed pressure plate changes the overall height before modification dont forget to change the ammount removed correspondingly.

And thats about it. Pretty simple really. Measure, remeasure and then check again before doing anything.


1 .. 8 plate clutch mod from Peter von Sphinx

8 plate clutch mod from Peter von Sphinx


2 .. remove from beneath the boss

remove from beneath the boss


3 .. and from the carrying surface of the boss

and from the carrying surface of the boss


4 .. to look like this

to look like this


5 .. file the friction plate dog receivers down to fit

file the friction plate dog receivers down to fit


6 .. and load up the plates

and load up the plates


8 .. and a little from outside the pressure plate to allow for separation

and a little from outside the pressure plate to allow for separation


9 .. XJ 900 springs, spaced

XJ 900 springs, spaced


10 .. and fitted

and fitted


Hartmut has a 975cc XS650 motor fitted in a sidecross frame. An 8 plate mod lasted to 3rd gear. A 10 plate mod with thinner friction plates and ground pressure plates held out til 4th. So he fitted a dry clutch. No problem now!


Posted January 9, 2011 by xscafe in Motor - Clutch

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