There are many types of ring compressors, but the tapered-bore type is the best. These are available in a wide range of bores sizes from ARP. Before installing the piston, set the crank throw at bottom dead center, and lightly oil the bore. The piston should slide smoothly in the bore. Never try to force the piston into the bore if the ring hangs up--start over. Feel the drag on the piston as it slides down the bore, making sure it isn't binding. Once the rod cap is torqued, rotate the crank and check for smooth rotation.