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With environmental issues at the forefront of the automotive industries, there is a clear need to improve the fuel economy and longer drain performance of four-cycle motorcycle engine oils. Evaluation of oil consumption in actual engines was used to clarify an optimal volatility for engine oils, and the feasibility of using zinc dialkyl phosphate, a sulfur-free additive, as an alternative to ZDTP for improved of fuel economy performance was studied. Engine oils with optimized additives demonstrated excellent friction characteristics and wet clutch performance.

A four-cycle engine oil formulation with outstanding fuel economy and clutch-slippage prevention has been developed for motorcycles. Fuel economy performance was evaluated by testing low-friction formulations with a motor-driven torque measurement tester and an SRV reciprocating friction tester. An optimized formulation containing both a molybdenum compound and a phosphorus extreme-pressure agent was found to give the best low-friction performance. The further addition of a boron-type dispersant maintained the low-friction performance while preventing clutch slippage. When test-produced oils were used for 1800 km in a commuter motorcycle, the fuel economy improved by 6 to 7% compared with an existing commercial oil.

With increasing interest in environmental protection, it has become important to develop biodegradable oils for two-cycle engine that provide low smoke emissions, good biodegradability and good exhaust system blocking performance in land applications. For studying the effects of oil included in exhaust gas for environment, the biodegradability of unburned oil in exhaust gas from two-cycle engine was investigated. The unburned oils when used the oils blended with mineral oil and/or polybutene showed better biodegradability than the new oils. The unburned ester-based synthetic oils showed about the same biodegradability as new oils probably due to their thermo-oxidative stability. But the ester-based synthetic oils showed better biodegradability after exhausting. The developments of new oil to improve the performance of low smoke emissions, good biodegradability and less exhaust system blocking were tried.

Polybutene is generally formulated in two-cycle engine oil in order to prevent smoke and carbon accumulation on exhaust system in motorcycles. The higher content of polybutene in oil is said to be essential to maintain the initial performance of two-cycle engines. However, it is not so known that this polybutene deteriorates the lubricity of bearing. Therefore, we developed a method for evaluating the lubricity of bearing to verify the influence caused by two-cycle engine oils. The test was conducted to measure the temperature of the big end of connecting rod directly while running the engine. The bearing lubricity was evaluated by comparing the temperature of the big end of connecting rod of candidate oils with that of standard oil. A better two-cycle engine oil formulation was able to be led by adding this bearing lubricity test to the JASO(or ISO) standard tests.

The deterioration of the friction reducing properties of engine oils containing molybdenum dithiocarbamates (MoDTCs) in service was studied. A quantitative analysis of MoDTCs and zinc dithiophosphates (ZDTPs) remaining in aged oils revealed that ZDTPs were consumed faster than MoDTCs. The consumption rate of ZDTPs was slow in the presence of MoDTCs and peroxide-decomposing antioxidants. The frictional properties of aged oils were evaluated with a reciprocating friction tester (SRV tester). The friction coefficient measured with the SRV tester was correlated to the properties of the aged oils, such as the TAN increase, TBN, and concentration of remaining ZDTPs.

This paper describes a study of the effects of two cycle engine oil composition on biodegradability and engine performance. With increasing interest in environmental protection, it becomes important to develop an oil that would not harm the environment. Desirable requirement was the development of a biodegradable oil with performance suitable for outboard engines, motorcycles, chain saws, and all other types of two-cycle engines. In addition to biodegradability, two key points for the development of this oil were the selection of a base oil that provided outstanding thermal stability and the blending of ashless dispersants that offered excellent high-temperature cleanliness. The developed oil which is formulated with properly selected esters and dispersants showed better performance than current biodegradable oils in every practical use.

This paper describes a study of the effects of oil composition on visible smoke, engine cleanliness, and piston anti-seizure performance. Two laboratory tests, termed the DSC (Differential Scanning Calorimeter) method, and the HTT (Hot Tube Test) are investigated as screening tests for two-cycle engine oils. Two types of oil were developed to comply with stringent Japanese oil requirements. Firstly, smokeless type oils formulated, with high concentrations of polybutenes were introduced to greatly reduce visible smoke from two-cycle engines of high specific output. Secondly, low-friction oils containing ester type synthetic base stocks were developed to achieve higher engine output in racing applications.