單項選擇題If the compression rings on a diesel engine piston become stuck in the ring groove, the cause may be due to（）

A.excessive ring action
B.excessive ring temperature
C.improper ring rotation
D.excessive ring face wear


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2.單項選擇題The size of the exhaust valve opening is （）

A.most critical in a four-stroke cycle diesel engine
B.most critical in a two-stroke/cycle diesel engine
C.most critical in a four-stroke/cycle diesel engine if it is turbocharged
D.of equal importance in a two-stroke/cycle diesel engine as in a four-stroke/cycle diesel engine

3.單項選擇題If the piston groove drain holes for the oil control rings become clogged, which of the following is likely to occur?（）

A.The oil control rings will seal improperly and wear rapidly
B.The piston will overheat due to insufficient lubrication
C.Excessive oil will remain on the cylinder wall
D.Light brown smoke will emanate from the engine exhaust

4.單項選擇題Many cast iron pistons are designed with heat dams, which serve to （）

A.keep piston crown temperatures elevated for smoother combustion
B.reduce the possibility of overheating the top compression ring
C.help retain the heat of compression to prevent ignition delay
D.help retain the heat of compression to prevent combustion knock

5.單項選擇題The adverse effects of burning high sulfur fuel can be compensated for by using a cylinder oil having sufficient（）

A.dispersant additives
B.floc point
C.alkalinity additives
D.ignition quality