relating to the operation of the clutch on the WD M20 fall into two
categories. The first is clutch drag, caused by the clutch plates not
separating sufficiently when the clutch is ‘lifted’ and still
transmitting the drive from the engine.
second problem is clutch slip. Here the plates are not held together
sufficiently hard to transmit the drive from the engine to the gearbox.
clutch drag is experienced the first thing to check is that the clutch
adjustment is correctly set. The clutch operating arm on the gearbox moves
through an arc on its pivot pin and maximum lift is achieved when the arm
is at 90 degrees to the clutch pushrod. So when the handlebar lever is
pulled in the operating arm should be in a vertical position.. If the arm
requires adjustment use the adjustment screw that is located at the lower
end of the arm. If the arm is moving past the vertical position slacken
the clutch cable adjuster on the gearbox and screw the adjuster in .
Readjust the cable for correct free play and retest. Repeat this procedure
as required until the arm is in the correct position with the clutch lever
pulled in. If the problem is that the arm is not reaching the vertical
position use the same procedure but wind the adjustment screw out instead
of in. Never use the clutch cable to alter the movement of the arm, its
purpose is to connect the arm to the handlebar lever not to adjust its
operation. When the adjustment is completed test the clutch to see if it
is still dragging.
drag is still present the clutch assembly will need to be stripped for
further checks. Remove the entire clutch assembly from the bike and the
clutch sleeve on which the clutch is mounted.
clean all the clutch components. Next fit the clutch rollers into the
clutch sprocket roller track and refit the clutch sleeve. Hold the back of
the clutch sleeve lightly in a vice so that the clutch basket is facing
upwards. Next replace the clutch centre onto its splines and screw on the
clutch spring nut. Do not fit the spring. Screw the nut all the way home
as you would when assembling the clutch ensuring it is completely
first test to do is to lift
the clutch centre to establish whether the clutch nut is hard up against
the centre, there should be no free play between the two. If there is play
present measure the amount of movement. Make a thin washer that is at
least .025” greater in thickness than the amount of free play and fit
this between the nut and the clutch centre. This should lock the centre in
holding the outer edges of the clutch sprocket check for vertical movement
of the sprocket. This should be minimal (no more than
.005”~.010”thou.) Also check for ‘tilt’ of the clutch sprocket. A
large degree of tilt indicates wear in the clutch sprocket roller track,
the clutch rollers and the clutch sleeve roller track.
the amount of vertical lift exceeds the tolerances described
measure the amount of movement. Next remove the clutch centre and
machine the back of the centre, removing the amount measured minus
.005”~.010”. Remove the material from the recess in the back of the
clutch centre (from the end of the splines). Replace the clutch centre,
washer (if required) and the
clutch spring nut. Vertical movement should now be within tolerance and
the sprocket should be free to rotate.
‘tilt’ was found to be excessive first replace the clutch rollers.
These should be .250”x.250” (1/4x1/4). Also examine the roller tracks
on the clutch sleeve and in the clutch sprocket. If either show obvious
signs of wear replacement is the best option, even if this is with better
‘used’ components. The clutch sprocket track is pressed into the
clutch sprocket so just this part can be changed if the sprocket is in
completed this work now take a look at the clutch basket and clutch
centre. The area where the clutch plates operate will wear with use and
become ‘notched’ by the action of the plates. If this notching is not
deep remove it with a smooth file, taking care to remove all burrs on
completion. If the notching is deep the components can be repaired by
welding and filing to restore a good surface. Also check the metal clutch
plates, if these are badly worn on the driving tangs fit replacements.
check the clutch spring. These ‘settle’ with use and it is important
that the ends of the spring are parallel to each other. Place the spring
on a flat surface and place a strait edge across the top to check this. If
the ends are not parallel the spring should be replaced as this will cause
the clutch plates to lift unevenly. Now reassemble the clutch onto the
bike, check the adjustment of the arm and cable are correct and test. If
there is still a problem one final ‘dodge’ is to remove one steel and
one fibre plate from the assembly to create more space in the basket for
the clutch plates to separate. Note however that if this is done the
length of the clutch pushrod may require adjustment to compensate for the
different ‘depth’ of the clutch plate assembly.
slip can occur for a number of reasons. These prevent the clutch from
transmitting power from the engine to the gearbox
clutch slip occurs first check that there is sufficient play between the
clutch operating arm adjuster and the clutch pushrod. (approx. 1/16”)
A lack of clearance will stop the clutch pressure plate seating
fully against the rest of the plates causing slip.
the clutch still slips after setting this adjustment the clutch assembly
will need to be stripped. After stripping clean all the parts thoroughly.
check that the steel clutch plates are flat and have a good surface
finish. After removing any burrs from the plate driving tangs place each
one on a flat surface to check. If the plates are not flat or are badly
worn on the driving tangs or surfaces they should be renewed. Now examine
the fibre plates. If they are badly worn down in thickness they should be
renewed. Standard thickness of new plates is .095”~.100” Also examine
the surface finish of the fibre plates. If they are worn very smooth it is
worth putting some ‘Finish’ back on them using a coarse file or rotary
wire brush. Do not use abrasive cloth as particles will be absorbed into
the fibre of the plates. If the plates have been contaminated with oil
they can be cleaned by boiling in a strong detergent /water
solution. After cleaning leave the plates in a warm environment
until thoroughly dried.
examine the clutch basket and clutch centre for wear on the surfaces where
the clutch plate driving tangs operate. If they are worn here refer to the
information in the section on ‘clutch drag’ for remedial action.
next thing to check is the clutch spring. These will ‘settle’ after
extended use and can be considerably shorter than the original length when
causing a reduction in operating pressure. Replace the spring with
a new one if shortened by more than 3/16”
clutch can now be reassembled. Ensure the gasket face of the clutch cover
is flat. Fit a new gasket and seal with silicone sealant. The M20 clutch
is a dry clutch so it is important that oil does not enter here.
After reassembly is completed adjust the clutch operating arm adjustment screw and cable to give maximum lift and sufficient free play (1/16”) at the clutch pushrod end. Refer to the section on ‘clutch drag’ for the setting procedures. Also ensure the clutch cable is correctly lubricated with a light oil.
|Clutch Spring Specifications|
|Below are the specifications for the clutch spring when new and some information on testing.|
|Outside diameter:||2.317”~ 2.332”|
|Inside diameter:||1.755”~ 1.770”|
|Length:||2.375” (2 3/8”)|
|Replace the spring when the overall length is reduced by 3/16” ~ 1/4”|
|Testing Spring Pressure|
To compress the clutch spring to a length of 1 1/8” long should require a pressure of 240~260lbs.
When the pressure required to achieve this length falls below 215lbs. the spring should be replaced.