Always prominent in the thoughts of automotive engineers, the lubrication of an internal-combustion engine presents continuous interest in that characteristic and elusive lubrication difficulties exist which largely baffle correction. Many of these difficulties are still existent because, according to the authors, more energy has been expended in correcting diseases of the lubricating system than has been spent in preventing the diseases by original design. When analysis is made of what has been done in the last few years of study on lubrication, it is irksome to realize that we still have to contend with all the former troubles such as oil-pumping or over-lubrication, fuel dilution of the oil supply, lubrication failures under certain conditions of engine operation, excessive wear on engine parts, and high maintenance-costs. All these defects do not exist in all engines; but one or more of them are present in most engines, and all of them, as well as some others, exist in some engines that are produced in large quantity.
Certain facts relating to the behavior of lubricating systems are presented, and also the conclusions that have been drawn from observation of systems which vary in their mechanical elements. The conclusions have been checked carefully by tests on many different types of engine, and the test results have been strengthened by close observation of the field operation of automotive engines.
All variations and combinations of the splash and of the force-feed lubricating-systems are classified under the term “crankcase systems.” The fresh-oil system differs fundamentally in that it feeds no appreciable surplus to the bearing surfaces, and the slight surplus that may be provided as a safety factor need not be recirculated. The tests involve two types of fresh-oil system; that is, the “full fresh-oil,” providing for the lubrication of all bearing surfaces by small quantities of unused lubricant applied directly to the engine parts, and the “combination fresh-oil and crankcase system,” the latter method furnishing fresh oil in minute quantities for cylinder lubrication and recirculated oil for the lubrication of bearings and other surfaces.
Following a statement of the desirability of research in regard to lubrication systems, the hidden relationships existent between lubricating systems and engine operation are discussed, those elements of engine performance that are influenced by lubricating systems being grouped to include maximum power; fuel-consumption; oil-consumption; detonation; and dependability, maintenance and long life. The results of comparative tests made on a six-cylinder 75-hp. engine are presented and explained, together with accompanying illustrations.