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.
- Skill level:
- Moderately Challenging
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Things you need
- Safety glasses
- Work bench
- Dial bore gauge
- Shop wipes
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.
Tips and warnings
- Consult your manufacturer for specific valve guide clearance on both the exhaust and intake clearance for your make and model.
- Be sure to measure all the guides and all the valves, and be mindful that the exhaust and intake valves require different clearances.
- Valve guides can be knurled to slightly enlarge a loose or worn valve guide. However, knurling is a temporary solution.
- Always wear safety glasses when working in or on automobiles and automobile components.
- Oil is a known irritant -- avoid skin contact with oil and other auto related solvents.
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