Where should piston to cylinder wall clearance be measured?

The correct location to measure piston to cylinder wall clearance is at the ring lands. This area provides the most relevant measurement because it has the greatest impact on the fit and function of the piston within the cylinder. The ring lands are where the piston rings are seated, and clearance here directly influences the performance of the engine, particularly in terms of oil control, ring sealing, and compression.

Measuring clearance at the ring lands ensures that the rings can expand and contract properly during operation, which is critical for maintaining an optimal seal against the cylinder wall and facilitating effective combustion. Additionally, it allows for the assessment of wear patterns and potential issues that could arise during engine operation.

While the other potential locations, such as the top of the piston, the skirt, and the bottom of the cylinder, may provide important information, they do not directly correlate to the critical function of the piston rings in the combustion chamber. Thus, measuring at the ring lands offers the most accurate indication of the piston’s interaction with the cylinder walls under operational conditions.