OIL PUMPING

Hawke's Bay Tribune, Volume XXII, Issue 147, 7 June 1932, Page 5

OIL PUMPING

SOME ILLUMINATING FACTS. A paper recently read overseas by an authority on pistons and piston rings, and their effect in engine operation, furnishes some interesting facts. It stated that it is difficult for one who is not constantly working with these problems to appreciate the very minute quantities of oil which are involved in an engine that uses an excessive quantity of oil by “oil pumping.’’ In an eight-cylinder motor travelling at 60 m.p.h. that consumed a gallon of oil per 100 miles at 3,000 revolutions per minute the quantity of oil consumed per cylinder per stroke was approximately 1-10,000 th of a cubic inch. If this quantity of oil was spread evenly over the surface of a cylinder having a 3}in. bore and sin. stroke the thickness of such a film would be about two-millionths of an inch. These figures are apt to change the opinions generally formed of the action of oil in an engine that pumps oil badly. It has not been uncommon for us to think of oil squitring past the pistons almost in fountains in a motor which would consume a gallon of oil in 100 miles.

It is only necessary to transpose the above figures to the same motor with a normal oil consumption of, say, 1,000 miles per gallon to see it is only required for sufficient lubrication to deposit on the cylinder wall during each stroke an oil film having a thickness of only one-tenth of the oil on the cylinder wall in the oil pumping engine.

A very serious offender that tends to oil pumping is the alignment of connecting rods. A connecting rod out of correct alignment will tend to cock the piston in the cylinder and carry the rings in a plane which is not at right angles to the centre line of the cylinder bore. This has a very decided tendency to unseat the piston rings from the cylinder wall, and is always a serious contributor to both blow-by and oil pumping. Loose crankshaft bearings, both main and connecting rods, also serve to discharge more than the normal quantity of oil to the cylinders, and in many cases the quantity of oil so delivered to the cylinders is greater than can be controlled by a normal piston and ring combination. ’All the oil consumed in an oil-pumping motor is not always discharged into the combustion chambers. It is a known fact that in many cases a considerable quantity of oil is lost through either, or both, the front or rear main bearings, and such losses often deceive the most observing mechanics and drivers. Oil lost at these points is usually only discharged when the motor is in operation, and many times only at high driving speed. It is only possible to cheek such losses through observations made when the engine is operating at considerable speed.