Valve guide clearance is the clearance between the valve stem and the tube or guide into which the valve is inserted. Valve guide clearance is an important aspect of engine rebuilding -- with too much clearance oil can seep down the stem into the cylinder. If this happens the oil will burn in the cylinder and cause the engine to use excessive oil and smoke. Too little valve clearance and the valve will not get enough oil to dissipate the heat and may seize up in the valve guide.
Place the cylinder head on a solid work bench. Remove the valves from the cylinder head by compressing the valve spring and removing the retainer clips.
Insert a dial bore gauge into the valve guide. The valve guide is a tube or cylinder into which the valve stem is inserted and rides up and down as the valve opens and closes. Measure the valve guide diameter using the dial bore gauge.
Measure the valve stems of the valves that will be used in the cylinder head with a micrometer.
Subtract the diameter of the micrometer reading of the valve stem from the dial bore gauge diameter reading of the valve guide. For example, if the dial bore gauge reading of the valve guide is 0.342 inch and the micrometer reading of the valve stem is 0.340-inch, is the valve guide clearance is 0.002 inch.
