Adjusting Valve Clearance

Valve clearance (cold) is:

Intake   0.10 mm (0.004 in)
Exhaust  0.15 mm (0.006 in)


Excessive clearance causes valve noise and decreased power.

Insufficient clearance results in decreased power, valve overheating or burning, and carburetor flashback which may cause a carburetor fire.

We therefore recommend that the valves be adjusted in a reputable shop.

The valves should be adjusted when the egine is cold.

The best sequence to follow is Cyl. 1, 2, 3, and 4 while rotating the crankshaft counterclockwise.

Prior to adjusting, position the piston on top dead center (TDC) on compression stroke since both valves are closed at that point. If adjustment begins with Cyl. 1, turn crankshaft counterclockwise until both valves are closed and the "OT" (TDC) mark on the crankshaft pulley is lined up with the mark on the crankcase.


  • 1. Remove both rocker box covers (engine cold).
  • 2. Remove distributor cap.
  • 3. Turn crankshaft counterclockwise- -using a box wrench on the crankshaft pulley, if necessary-- until the "OT"-mark on the pulley has lined up with the mark on the crankcase. At this point, the distributor rotor will be pointing towards a notch machined into the distributor housing.
  • 4. Check valve clearance at Cyl. 1.
  • 5. Loosen lock nut on adjusting screw.
  • 6. Adjusting clearance by turning the screw while simultaneously checking the clearance with a feeler gauge.
  • 7. Hold adjusting screw in position when tigtening the lock nut.
  • 8. Recheck clearance.
Last modified: Mon, 17 Jan 2005


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