单项选择题
In order to keep the oil film on the cylinder liner during the running-in period, the piston rings are slightly rounded（）
A.on both the external and internal top edges
B.on both the external top and bottom edges
C.on both the external and internal bottom edges
D.on all the four edges
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相关考题
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单项选择题
In some type of two-stroke engines, besides some small holes for（）, starting valve, safety valve, indicator cock, and central opening in each cylinder cover for mounting the（）
A.fuel valves；exhaust valve
B.exhaust valves；inlet valve
C.fuel valves；inlet valve
D.exhaust valves；fuel valve -
单项选择题
In a two-stroke engine, there are always a series of openings known as （）, and in some circumstances, there are also openings known as （）, in the part of the cylinder liner.
A.scavenging air ports；exhaust ports
B.inlet ports；scavenging air ports
C.scavenging air ports；inlet ports
D.exhaust ports；inlet ports -
单项选择题
If the engine is naturally aspirated, or is a small high-speed type with a centrifugal turbocharger, the period of valve overlap（）,ie when both valves are（）, will be and the exhaust valve will close some 10°top dead canter（）.
A.open；short；after
B.closed；short；after
C.open；long；before
D.closed；long；before
