Clutch Problems

Problems 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.  
The 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  


If 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.

If 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.

First 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 tightened.

The 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 place.

Next, 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.

If 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.

If ‘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 good condition.

Having 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.

Finally, 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.

Clutch slip

Clutch slip can occur for a number of reasons. These prevent the clutch from transmitting power from the engine to the gearbox

If 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.

If the clutch still slips after setting this adjustment the clutch assembly will need to be stripped. After stripping clean all the parts thoroughly.

Next 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.

Now 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.

The next thing to check is the clutch spring. These will ‘settle’ after extended use and can be considerably shorter than the original length when new 2 3/8" causing a reduction in operating pressure. Replace the spring with a new one if shortened by more than 3/16”

The 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 
Load parameters
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.