Valve Tappet Adjustment

Excessive valve clearance will cause tappet noise and negative clearance will cause valve damage, excessive wear of the cam follower, and loss of power.

Therefore, the valve tappet clearance should be maintained properly.

  1. Turn the fuel valve to the "STOP" position, remove the fuel lines from the fuel valve body, raise the seat and remove the fuel tank.
  2. Remove the cylinder head cover A (inlet side) and B (exhaust side).
  3. Remove the point cover and the dynamo cover.
  4. Rotate the generator rotor counterclockwise and align the "LT" mark (1) on the generator rotor with the index mark (2) on the stator. If the index marks of both the inlet and exhaust camshafts are aligned to the index marks on the bearing holders, this position is the top dead center of the intake stroke, therefore, the rotor should be turned one complete revolution to bring it to the top dead center of the compression stroke, in other words, the purpose is to place the left hand piston at the top dead center of the compression stroke.
  5. Check the left hand cylinder tappet clearances in the exhaust and inlet valves. Insert the feeler gauge (3) between the cam and the cam follower. If a slight drag or resistance is felt as the gauge is inserted, the clearance is correct. If the clearance is too close or too loose, adjust the tappet. The standard clearance for both the inlet and exhaust valves is 0.0012 in. (0.03 mm) when the engine is cold. Adjustment by loosening the cam follower shaft lock nut (5) and turning the cam follower shaft (4) with a screw driver as shown in the photo. Specific clearance can be obtained at two positions of the follower shaft, but only one of these is the correct adjustment point.


    The clearance is reduced when the adjustment is made as shown in the table below.

    Right side

    Inlet: Turn counterclockwise
    Exhaust: Turn clockwise

    Left side

    Exhaust: Turn counterclockwise
    Inlet: Turn clockwise

    NOTE: The check or adjustment of the tappet clearance should be performed while the engine is cold. The clearance may tend to increase as the temperature rises. Make sure that the adjustment has not been disturbed while tightening the lock nut, by rechecking the clearance after the lock nut has been tightened.

  6. Next, rotate the generator rotor 180 counterclockwise to bring the right hand piston to the top dead center of the compression stroke and then check both the right inlet and exhaust valve tappet clearances in the same manner as for the left hand side.