單項選擇題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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1.單項選擇題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

2.單項選擇題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

3.單項選擇題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

4.單項選擇題The interior of some diesel engine saltwater heat exchangers are protected from corrosion by the use of（）

A.aluminum plates
B.lead cathodes
C.copper baffle plates
D.sacrificial zincs

5.單項選擇題Proper lubrication of the main bearing is more easily obtained in a single acting four-stroke/cycle diesel engine than in a single acting two-stroke/cycle diesel engine because （）

A.bearing pressure in a four-stroke\cycle acting single diesel engine is continually reversed
B.bearing pressure in a two-stroke\cycle single acting diesel engine is continually reversed
C.the maximum bearing pressure is higher in a single acting two-stroke/cycle diesel engine
D.two-stoke/cycle diesel engines require more complicated lubrication piping