Valves and Valve Springs Dimensional Inspection

The locations for checking runout and edge thickness of the valves are shown in Figure 1. Measure the edge thickness of valve heads. If, after re-facing, the edge thickness is less than the limit specified by the manufacturer, the valve must not be re-used. The edge thickness can be measured with sufficient accuracy by a dial indicator and a surface plate. Out-of-roundness is usually caused by a stuck valve. If a valve sticks, the rocker shaft tends to work up and down when the valve offers excessive resistance to opening. Inspect for out-of-roundness and oversize using a telescopic gauge and a micrometer.

Figure 1

Inspect the valve for stretch and wear, using a micrometer or a valve radius’ gauge. [Figure 2] If a micrometer is used, stretch is found as a smaller diameter of the valve stem near the neck of the valve. Measure the diameter of the valve stem, and check the fit of the valve in its guide.

Figure 2

Compression is tested with a valve spring compression tester. [Figure 3] The spring is compressed until its total height is that specified by the manufacturer. The dial on the tester should indicate the pressure, in pounds, required to compress the spring to the specified height. This must be within the pressure limits established by the manufacturer.

Figure 3

Inspect the shaft’s diameter for correct size with a micrometer. Rocker shafts are often found to be scored and burned because of excessive turning in the cylinder head. Also, there may be some pickup on the shaft (bronze from the rocker bushing transferred to the steel shaft). Generally, this is caused by overheating and too little clearance between shaft and bushing. The clearance between the shaft and the bushing is most important.