What is the normal gap for piston ring ends?

[McKarter]

Piston ring end gap is 0.4-0.6mm; side gap is 0.25-0.4mm; back gap is 0.35-0.55mm. Below is an introduction to measuring the three gaps of piston rings: End gap measurement: End gap refers to the gap at the opening when the piston ring is installed in the cylinder, to prevent the piston ring from seizing due to thermal expansion. When checking the piston ring end gap, place the piston ring flat in the cylinder, push it flat with the piston top, and then measure the gap at the opening with a feeler gauge. The first ring has a larger end gap than the other rings because it operates at higher temperatures. Side gap measurement: Side gap refers to the vertical clearance of the piston ring in the ring groove. Excessive side gap affects the sealing function of the piston, while insufficient side gap can cause the piston ring to seize in the groove. To measure, place the piston ring in the groove and use a feeler gauge. Back gap measurement: Back gap refers to the clearance between the back of the piston ring and the bottom of the piston ring groove after the piston is installed in the cylinder. It is generally expressed as the difference between the groove depth and the ring thickness. The back gap of a standard oil ring is relatively large. A common practice is to install the piston ring in the groove; if it sits below the ring land and can rotate freely without any resistance, it is considered suitable.