Remove all carbon from the valves and inspect for warpage, cracks, or excessive burning. Replace valves that cannot be cleaned up and refaced without removal of an excessive amount of metal. Measure the stem diameter at three places using a micrometer, and note the smallest figure. Then, determine the inner diameter of the corresponding valve guide, using a dial indicator at two positions. (First, take one reading at an arbitrary point, then rotate the indicator 90 degrees to obtain the second reading.) Note the larger figure. You can then calculate the stem-to-guide clearance by subtracting the stem diameter from the valve guide's inner diameter.
| Fig. 1: Valve stems may be rolled on a flat surface to
check for bends
|
| Fig. 2: Measuring valve stem diameter with a micrometer
|
| Fig. 3: Measuring valve guide inner diameter with a dial
gauge
|
| Fig. 4: With the valves removed, use a wire wheel to
clean the carbon deposits from combustion chambers
|
It may not be necessary to replace both the valve and valve guide if the stem-to-guide clearance is excessive; replacing either a worn valve guide, or a valve whose stem diameter is below specification, may bring the clearance within specifications. However, it is important to take accurate measurements. Excessive wear in a valve guide or valve stem is often accompanied by a worn mating part, necessitating replacement of both the valve guide and valve stem.
Before installing new or re-usable valves, be sure to remove any carbon deposits from the combustion chambers.
