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If the back clearance of a piston ring is excessive,（）
A . compression pressure in the cylinder will be higher
B . carbon will accumulate behind the ring
C . combustion gases will penetrate beneath the ring land
D . piston side thrust will be increased
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In a diesel engine, when refitting piston rings you should （） Ⅰ.check the ring gap at the smallest diameter of the cylinder Ⅱ. Remove carbon from the ring groove
A . Ⅰ only
B . Ⅱ only
C . both Ⅰ and Ⅱ
D . neither Ⅰ nor Ⅱ
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In the sentence “In some designs the cylinder oil is timed so that the oil injects only on the piston ring belt, the "piston ring belt" means （）.
A . piston crown
B . piston ring groove
C . piston skirt
D . piston ring area
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The piston ring grooves for a standard engine are （）
A . chromium-plate against wear
B . anti-corrosion treated
C . white metal lined against wear
D . flame hardened against wear
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Broken piston rings manifest themselves during the scavenge port inspection by（）
A . Lack of elastic tension, when the rings are pressed into the groove by means of a stick
B . Blackish appearance
C . Fractured rings and missing rings
D . all off the above
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The main purpose of the piston oil scraper rings is to （）.
A . seal the space between the piston and the liner
B . reduce the amount of lube oil burned in the combustion chamber
C . transmit heat from the piston to the cylinder liner
D . damp out fluctuations of the piston side thrust
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These piston rings are so badly worn that they must be （）.
A . renewed
B . welded
C . machined
D . chromium-plated
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A condition contributing to diesel engine piston rings sticking in the ring grooves, is insufficient ring clearance at the ring（） Ⅰ.gap Ⅱ.side
A . Ⅰonly
B . Ⅱ only
C . both Ⅰ and Ⅱ
D . neither Ⅰ nor Ⅱ
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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 edge
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All the rings are slightly rounded on their external top and bottom edges to keep the oil film on the cylinder liner during （） for new piston rings.
A . the running-in period
B . the running process
C . gas exchange process
D . the boiler firing
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Around the combustion chamber, all the main components are bore cooled to give low strains and the smallest, circumferentially symmetric deformations for good sealing between piston rings and liner（）
A . thermal
B . mechanical
C . plastic
D . elastic
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Before replacing a piston you should check the rings to see that all clearances and gaps are （） the permissible tolerances.
A . above
B . at
C . over
D . withi
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The sealing function of the piston ring is brought about by the gas pressure above and behind the piston ring, which forces it （） against the bottom of the ring groove, and （） against the cylinder wall.
A . upwards；inwards
B . upwards；outwards
C . downwards；inwards
D . downwards；outward
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When installing rings on a diesel engine piston, you should check the ring（）
A . diametrical tension
B . gap clearance
C . radial thickness
D . face thickne
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Ring groove inserts are occasionally used on aluminum alloy piston to（）
A . reduce the ring groove wear rate
B . seal against crankcase vapors
C . lessen the wear on aluminum part of the cylinder
D . allow for the greater expansion rate of aluminum
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If the piston ring gap remains insufficient when installing new rings, youshould（）
A . install oversized rings
B . hone the cylinder liner to allow ring installation
C . compress the rings tighter with a compressing tool
D . file the ends of the ring
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Insufficient end clearance on newly fitted piston rings in a diesel enginewill cause the rings to（）
A . jam in the most worn part of the cylinder when the rings expand
B . break in the most worn part of the cylinder when the rings expand
C . wear eccentrically on the side opposite the end gap
D . overheat and jam at the top center on the combustion stroke
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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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When inspecting piston rings through the ports of a two-stroke/cycle diesel engine, black areas on the sealing surfaces are the result of （）
A . insufficient lubrication
B . improper piston cooling
C . blow-by
D . overload operatio
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The main function of piston compression rings is to （）
A . prevent excessive cylinder liner wear
B . reduce friction losses in the engine
C . seal the space between the piston and the liner
D . limit upward flow of lube oil into the combustion space
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Diesel engine piston ring blow-by is usually caused by excessive ring clearance at the ring（）
A . back
B . side
C . gap
D . bottom
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The lowest ring of a piston is （）.
A . a coil spring
B . a sealing ring
C . an oil distributor ring
D . main seal ring
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The sealing rings are in four parts and pressed together around the piston rods by means of （）.
A . nuts
B . bolts
C . coil springs
D . stuffing boxe
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Black areas on the sealing surfaces of piston rings indicate＿.
A.lube oil pumping
B.rotating rings
C.gas pressure behind the ring
D.passage of hot gases
