What method is employed to measure the piston ring end gap?

The feeler gauge is the appropriate tool for measuring the piston ring end gap because it is specifically designed for this purpose. The end gap is the space between the ends of the piston rings when they are installed in the cylinder.

When measuring this gap, a feeler gauge allows the user to insert a thin strip of metal into the gap to determine its size. The gauge typically has various thicknesses, so the user can find the correct one that fits snugly into the gap but does not exceed it. This precise measurement is crucial in ensuring the correct clearance for proper engine function, allowing for thermal expansion and preventing issues such as ring flutter or blow-by.

Other tools mentioned, such as calipers and vernier scales, are more suited for measuring external dimensions rather than the specific gap between the ends of the piston rings when installed. A tape measure is not suitable due to its bulky nature and inability to measure small, precise gaps accurately. Thus, the feeler gauge remains the standard tool for accurately measuring piston ring end gaps in small engine applications.