單項(xiàng)選擇題Exhaust valve openings in a diesel engine cylinder head are made as large as practical to （）

A.increase back pressure during the exhaust process
B.facilitate periodic replacement of the valves
C.reduce the pumping loss associated with scavenging
D.reduce tension on valve springs


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1.單項(xiàng)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

2.單項(xiàng)選擇題Diesel engine electric starting motors generally require heavier duty motors and motors and operate at higher voltages than comparable starting motors for gasoline engines due to（）

A.higher speed required
B.flywheel-effect
C.lower starting temperatures
D.higher compression pressures

3.單項(xiàng)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

4.單項(xiàng)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

5.單項(xiàng)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