单项选择题

When comparing different fuels for different engines, the ignition quality of diesel fuel oils becomes a less critical consideration as （）

A.the amount of lube oil additives increase
B.piston speeds increase
C.injection pressure decrease
D.engine speeds decrease

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单项选择题

To reduce the weight of the reciprocating parts, pistons of high-speed engines are made considerably shorterThis results in （）

A.less piston slap and quieter running
B.increased crankshaft bearing wear
C.slightly greater piston wear
D.decreased side pressures

单项选择题

Which of the following statements concerning cylinder liner wear is true?（）

A.Liner wear is distributed equally between the upper and lower portions of the cylinder
B.Excessive liner wear causes wear between piston ring and groove
C.Excessive, but uniform liner wear will not cause wear between piston ring and groove
D.Liner wear is normally greatest in the middle of the cylinder

单项选择题

If clearance between a piston and the cylinder wall is excessive, piston slap will occurThe slap itself is caused by （）

A.alternation of side thrust
B.a breakdown of the lube oil film on the cylinder wall
C.worn piston boss piston pin bearings
D.fluctuating gas pressure in the combustion space