Such a port divider, being exposed on all sides to the outrush of exhaust gas, runs hot. As the piston clatters up and down its bore, its rocking can cause the divider to hammer softened piston material into the piston ring groove, trapping the ring and destroying its seal. To lubricate the divider, small holes were drilled in the exhaust skirt of the piston along the track of the divider. This allowed crankcase compression to push oily air onto it. To reduce pressure on the divider, it was also common for builders to relieve the surface of its hard plating (or liner, if present) a bit. And finally, to keep the ring sealing, the top and bottom edges of the piston ring groove were chamfered at 45 degrees in the region near the divider, so that any hammering that did take place could not trap the ring.