How should the piston ring gap be correctly checked?

To correctly check the piston ring gap, it involves ensuring that the rings are positioned correctly in the cylinder. This method allows for an accurate assessment of the gap that will exist when the engine is assembled and operating under normal conditions. When the rings are pushed squarely into the cylinder, you can measure the gap at the ends of the ring using a feeler gauge, ensuring that it conforms to the manufacturer's specifications.

This approach is critical because it accounts for any wear or variations in the cylinder size that could affect the ring's performance when the engine is running. Checking the gap with the rings installed in the cylinder simulates the environment in which they will function, which is crucial for an accurate measurement.

The other methods, such as checking the gap with a feeler gauge only or using a digital micrometer, lack this practical application context. The use of these tools on their own does not provide insight into how the rings fit within the engine's operating environment. Additionally, checking while the piston is removed doesn’t yield a realistic measurement either, as it doesn't reflect the engagement that occurs when the piston is in place. Therefore, the best practice is to check the piston ring gap with the rings installed in the cylinder to ensure accuracy and functionality.