单项选择题
For any piston ring to operate smoothly without scuffing ,the ring must be （）.
A.of a material harder than the cylinder liner
B.properly lubricated
C.prevented from compressing
D.prevented from rotating during engine operation
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相关考题
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单项选择题
Shaker, circulation and spray are the three general methods used in（）
A.pre-injection fuel oil treatment
B.lube oil filtration
C.lube oil purification
D.piston cooling -
单项选择题
Wristpin bearings are difficult to lubricate because of their oscillating motion and（）
A.their free-floating design
B.their relatively small size
C.the reciprocating motion of the piston
D.their position in the lubrication system -
单项选择题
Internal combustion engine crankcase vent outlets must be equipped with （）
A.hinged rain guards
B.corrosion resistant flame screens
C.dipsticks for measuring oil levels
D.crankcase ventilation fans
