Where should piston ring end gap be mesured?

Piston ring end gap should be measured in the cylinder bore at a point approximately halfway down the piston stroke, typically around the middle of the cylinder. It's important to insert the piston into the cylinder to the correct depth before measuring the gap with a feeler gauge, ensuring that the rings are square to the cylinder wall for an accurate reading. This method helps to assess whether the end gap is within specified tolerances for optimal engine performance.