BREAK IN LINER WEAR AND PISTON-RING ASSEMBLY FRICTION IN A SPARK-IGNITED ENGINE

Cylinder liner wear and surface roughness were measured at the top-rin g reversal point of a single-cylinder, air-cooled, spark-ignition (gas oline) engine during break-in. In addition, the instantaneous friction al torque of the engine was determined and correlated with the wear ra te and surface roughness during this period. The engine friction, line r surface roughness and wear had their highest values at the beginning of the break-in period. The wear rate dropped sharply during the firs t hour, after which it maintained a steady lower rate. The surface rou ghness and friction took longer than the wear rate to stabilize. Frict ion was found to change in three modes. The first mode took one hour a nd was characterized by a sharp drop in wear rate and a small drop in friction. The second mode was a transition to the third mode, and took about 2.5 hours. The third made lasted about 20 hours and was charact erized by a drop in both surface roughness and friction. The wear rate did not change much during this mode. After the third mode, the frict ion and surface roughness changed at a slow steady rate. The total tes t took 28 hours. Correlations developed for wear rate, surface roughne ss and friction indicated that friction was a linear function of the s urface roughness over the whole period. However, friction war not an i ndicator of the wear rate.