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The high speed Diesel engine fuel specification has been built around a straight-run petroleum distillate from certain paraffinic crudes in order to have definite physical and chemical characteristics which especially reflect in certain minimum ignition quality, generally expressed in Cetane Number or Diesel Index. Addition of chemical agents have brought about new concepts and make the specification requirements built around straight-run petroleum distillate fuels obsolete for their classification. Large scale usage of Amyl Nitrate Diesel additive fuels in several makes of Railroad Locomotive Diesel engines over extended periods have proven their effectiveness; the freedom from harmful deposits or corrosion in the engine and fuel injection system; also that exhaust smoke conditions were negligible.

Engine performance (availability and operating costs), maintenance (parts affected) and life (general overhaul period) are today a problem of severe duty engine conditions. Severe conditions, generally, are measured in terms of high power output (horsepower per cubic inch of piston displacement or BMEP). Such operations have brought about high piston ring groove and valve guide temperatures, which greatly increase ring and valve sticking tendencies. In the case of some passenger car engines at high speed and some truck and bus engines overloaded, ring sticking is not a problem but high crankcase oil temperatures cause excessive oxidation resulting in varnish on piston skirts and overhead valve mechanism. Time between crankcase drains, alloy type bearings and blowby contamination all relate to the severity of engine conditions.

With 1,250,000 tractors in use today, the question of tractor engine wear in relation to lubrication becomes a very important study. Yet the problem is a very complex one, as the types of fuels vary greatly, the load conditions and time of continuous operation are seldom the same, dust fall is between two and ten tons per square mile per day, and the operation-service, care and engine rebuilding may be doubtful. Besides this, engine design, combustion rates and bearing materials all add to the variables in selecting the adopted lubricant. Clean air, efficient fuels, adopted lubricant and proper care of operation and service are factors affecting wear of a given tractor engine.

The engine deposits withwhich operators are concerned have their source in what is commonly called sludge. Sludge is composed of carbonaceous matter (either from blow-by or from high-temperature cracking); asphaltenes (oxidized oil products); ash (mostly lead oxide and iron bromide where gasoline is used, metals from wear and corrosion and dust from the air); and moisture from condensation. All these component parts of sludge vary greatly depending on engine design, operating conditions, fuel and lubricant used. The whole engine ina sense is a centrifuge and throws this variable called sludge to various parts of the engine. The dead spots collect most with the hottest portions covered with a brittle flint-like carbon or lacquer. In high output engines run for extended periods of time, ring sticking limits the time of complete overhaul. It causes increased cylinder and ring wear. Contrasted to this are sludges formed under cold weather conditions.

Since the publication of the original Classification of Transmission and Rear Axle Lubricants back in 1931, evolution has seen the development of a most complicated and varied number of gear lubricant recommendations for the millions of cars now on our highways. Each year as new features are introduced, changes are made which affect gear lubricant requirements of the past. Yet nothing is done to revise car manufacturers' lubrication charts made up previously each year. A composite grouping of gear lubricants would simplify the servicing of cars on the road. At the present time, the service station attendant is required to follow with exactness lubrication charts for each and every make and model of car if he would keep the car owner out of trouble. On the other hand, the service station needs are best filled by the smallest number of grades required for proper servicing since large inventories and especially gear lubricant dispensing equipment (metered) are costly.

With the increase in horsepower output per cubic inch displacement, gasoline and Diesel engines are more susceptible to ring sticking and piston ring or cylinder liner wear. Formerly crank case oil stability (how the used oil looked when drained after 50 hours or more operation in an engine) was considered of prime importance. It was thought that the tendency of mineral oils to cause ring sticking depended largely on the degree of refinement of the lubricating oil, but this has not proven to be the case with Diesel engines or with high output gasoline engines. Highly solvent treated oils have been shown to be deficient in lubricating value and ring sticking caused by excessive blowby has resulted. Such high output gasoline and Diesel engines will operate on straight mineral oils at reduced loads; but reduced cylinder wear, freedom from ring sticking and sludge reduction can be had only with proven addition agents.

WITH the advent of light motor-oils, S.A.E. 10-W and S.A.E. 20-W and the introduction of copper-lead bearings in passenger-car and motor-truck engines, new lubrication-factors have arisen with respect to motor-oil stability as well as with respect to the nature of compounds used for the breaking-in period. This paper describes a series of tests which were run using S.A.E. No. 11 babbitt bearings and lead-copper and leaded bronze bearings. The relative extreme-pressure characteristics of the various motor-oils, both mineral and compounded, were recorded. In addition, the coefficients of friction were plotted as ordinates (ƒ) and the viscosity, angular speed and pressure (ZN/P) as abscissas were correlated. For this phase of the work, test apparatus had to be developed. The effect of the mineral and compounded motor-oils on the bearing metals and the causes of deterioration, and vice versa, and the effect of the bearing metals on the stability of the motor oils were checked.