 The main change was the increase in cylinder bore from 117 mm (4.625 in) to 127 mm (5 in) and an increase in piston stroke from 133.3 mm (5.25 in) to 139.7 mm (5.5 in).This led to a corresponding increase in displacement from 7.2 liters (441 cu in) to 8.8 liters (540 cu in).The R-5 was a rough running but reliable engine.