Abstract: The need for engine maintenance is determined from valve stem wear by placing a cavity-containing housing of predetermined height on the cylinder head so that an exhaust valve stem on the cylinder head extends through the open bottom end of the housing into its cavity. A height measuring device, such as a depth micrometer, is supported on the top end of the housing and extends into the cavity of the housing until it contacts the top of the exhaust valve stem. At this point, the reading on the height measuring device indicates the distance between the top of the exhaust valve stem and the top of the housing. By subtracting this distance from the known height of the housing, the height of the exhaust valve stem can be calculated. By comparing the height of the exhaust valve stem when the engine is new to its height as periodically measured after the engine has been used, the increased height or "tulip condition" of the valves can be diagnosed, indicating the need for engine maintenance.