How is the end gap of a compression ring measured?

The end gap of a compression ring is crucial for the proper functioning of an engine, and measuring it accurately is essential for achieving the right fit and performance. The correct method involves squaring the ring inside the cylinder bore, which ensures that the ring is positioned in a way that accurately reflects its fit and gap when the piston is installed.

Using a flat feeler gauge allows for precise measurement of the gap between the ends of the ring when it is squared in the bore. This process helps technicians determine if the gap falls within the manufacturer's specified limits, which is important for maintaining optimal cylinder pressure and preventing blow-by, where combustion gases escape past the piston rings.

Other methods listed, such as using a torque wrench, measuring with a ruler, and using a depth gauge, do not provide the necessary accuracy or proper technique for measuring the end gap. Torque wrenches are used to measure the torque applied to bolts and fasteners, while rulers may not enable an accurate gap measurement due to the difficulty in obtaining a true square alignment. Similarly, depth gauges are typically employed for different measurements, such as depth or height, and are not suited for measuring an end gap directly.