Piston rings are open-ended rings that sit at the top of the piston, the mechanism that lifts up and down creating explosions that power the engine and cause the car wheels to turn. The piston ring provides a seal at the top of the piston and assists in heat management. Piston rings are fickle and require patience to properly place them.
Clean the piston head and the ring grooves if you are replacing an old ring. Do not scrape the carbon out of the grooves. This will only make the area more likely to have excessive leaking. Chemically clean the piston head with an immersion style carburetor cleaner
You must keep ring end gaps within specifications, and these vary based on your engine size. Fast cars, such as race cars, will have looser gaps, to allow for more cooling. Conventional cars should have a tighter ring gap. Consult the car manual for your car, which will provide more detailed measurements for your ring gap. The ring gap should be at least .025 inches. You will have four rings, a top compression ring, a second compression ring,and two oil rings. Each of these rings will be open-ended and the open ends are the "gaps."
The order of ring placement is important. Place the fourth oil ring in place first. It sits at the bottom of the piston head. It should have a minimum gap of .001 inches and a maximum gap of .0030. The third oil ring goes in next with the same gap measurements. The second compression ring follows with a minimum gap of .0015 and maximum gap of .0035. The top compression ring is last with a minimum gap of .0020 and a maximum gap of .0040. These gaps measurements are considered "normal," or standard, for most commercial cars.
As a general procedure for each ring, place the ring into the piston head groove, and use the piston to push it square to the bore. Be careful to not distort the ring as you slide it into position over the piston head. New rings tend to be too tight, so you will file or grind these to size. Make sure to measure and remeasure frequently because you cannot make the ring smaller once you have ground it down. You can use a "feeler gauge" to measure the gap. Make sure to stagger your ring gaps about 120 degrees from one another.
