Checking Valve Timing and Clearance

Normally the valve clearance should be checked or adjusted when the engine is cold at an outside air temperature of approx. 20 deg C (68 deg F). The valve clearance is as follows:

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

Valve clearance should be checked a t regular intervals and appropriate care. The following malfunctions can be caused by wrong valve adjustment:

Insufficient clearance:

Burnt or pitted valves and seats.
Warped valves.
Unevenly running engine.
Valve timing off

Excessive clearance:

Valve noise
Increased wear in valve components
Unevenly running engine
Valve timing off

Proper valve adjustment results in a well running engine only when the valves are seating well, the valve guides are not worn, and the valve stem ends are not pounded in or otherwise worn.

Valve timing points:

 Intake opens before TDC  17 deg
 Intake closes after BDC  53 deg
 Exhaust opens before BDC  50 deg
 Exhaust closes after TDC   14 deg

Note :

The above timing points are established with 1.00 mm valve clearance in cold engine. When valve timing has been checked, reset valve clearance to normal specifications.

Lapped or refaced valves and seats seat faster than normal. For this reason, set valves with an additional 0.15 mm (0.006 in) clearance over the specified value for a test run of at least one-half hour.

When the test run has been completed, or before testing engine performance, readjust valve clearance to normal values.
Last modified: Mon, 17 Jan 2005


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