Oil Loss Past Pistons Available to Purchase

The AUTHOR USED A LABORATORY TEST rig rather than an engine in order to eliminate unwanted variables and to bring the remaining ones under the eye of the operator. The test rig is illustrated diagrammatically in Fig. 1, and contains a piston which can be fitted with any desired combination of rings and is reciprocated in a vertical cylinder by an electric motor. The piston is rigidly fixed to a piston rod closely guided above and below the cylinder, but in some tests the upper guide was removed so that the piston then contacted the cylinder as in a normal engine. Cyclic pressure variations were avoided by mounting a reservoir above the cylinder giving a clearance volume of ten times the swept volume and keeping the cylinder pressure within 7 per cent of the mean pressure. Mean pressure could be maintained at any value from a vacuum to 150 lb/sq.in. Commercial nitrogen cylinders were used. The oil jets to the lower side of the piston could supply 1.0 pint/min. An SAE 30 oil was used. Speeds used varied from 750 to 3,000 r.p.m. Differential thermal expansion between piston and cylinder assembly was kept small by operating both cylinder‐jacket water and oil supply at 86°F. (30°C).