How are exhaust valves checked for stretch during an overhaul of a reciprocating engine?

The correct method for checking exhaust valves for stretch during an overhaul of a reciprocating engine is by utilizing a contour or radius gauge. This tool measures the actual shape and curvature of the valve's face and the radius of the tip. As valves extend with heat and operational use, it’s critical to ensure that they maintain their proper geometry to function effectively.

The contour gauge allows mechanics to detect any deviations in the valve's design specification caused by wear or stretching. When valves are subjected to repeated cycles of heating and cooling, they can elongate slightly, which can affect sealing and performance. By using a contour gauge, a technician ensures that the exhaust valves meet the required tolerances and can operate effectively within the engine without causing issues such as loss of compression or poor exhaust management.

Other methods, such as using a micrometer, might measure the diameter but wouldn't provide information about the radius or shape changes that may have occurred due to wear. Meanwhile, feeler gauges check for gaps, which isn’t suitable for assessing structural integrity or linear variations due to elongation. Visual inspection can identify obvious damage or deformation but lacks the precision necessary for determining the extent of valve stretch. Thus, the contour or radius gauge is the most appropriate and accurate tool for ensuring