Engine Friction–Effect of Oil Viscosity and Break-in on Cranking Resistance

A simple technique of tracing the deccelaration of an engine upon shut off is used to determine the cranking resistance of small single cylinder utility engines under different ambient conditions.

The technique is also used to differentiate the frictional losses from the mechanical losses during cranking, without the aid of a dynamometer, Viscosity of the crankcase oil is found to be the single most important property of the oil which correlates with cranking resistance. Considerable improvement in crankability can be attained by polishing of the engine bore, but only at the risk of increased wear under normal operating conditions.