CYLINDER LUBRICATION.

Putaruru Press, Volume IV, Issue 164, 23 December 1926, Page 7

CYLINDER LUBRICATION.

SCORING OF PISTONS. The engine must bo started before fuel combustion, lubrication, or any other phase of its operation begins. Recently tests were made with a view to ascertaining just what factors influenced the time required for starting, the problem being to provide the engine cylinders with sufficient fuel vapour to form an explosive mixture and a spark to bring about ignition oi firing. In effect the tests developed that some of the factor which apparently influence engine starting are the fuel-air ratio, the jet size, jet location, spark advance, volatility of the fuel, amount of throttling, amount of chok ing, temperature of entering air, and the jacket water temperature. The all-important point after starting an engine is to obtain the delivery of sufficient lubricating oil to the cylinders to ensure the requisite lubricating film. An alarming discovery was made that this may frequently be impossible of attainment, in the modern engine, for a matter of several minutes after ingDuring this period llic cylinders and pistbns may run dry, giving rise to scuffing or scoring of piston surfaces “Engines which have close big end bearing clearances frequently, run for five or more minutes . .before oil from the pressure feed system reaches the cylinder walls —-under ordinary room temperatures. At lower temperatures the period or dry running is lengthened. This often results in scored or scuffed pistons. Increasing the clearance or providing suitable grooves obviates this difficulty’ ’ —furnishing the apparently necessary oil -to make a film. At higher temperatures but little oil is necessary to maintain this film, especially tiro possibility of ccndersatiou is remote.