Thin, circular, steel bands fit into grooves around the piston to seal the bottom of the combustion chamber.

把薄的，圆形的，钢圈放进活塞周围的凹槽以密封燃烧室的底部。

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This small end fits inside the bottom of the piston.

小头装在活塞的底部。

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The Bore is the diameter of the cylinder. The stroke is the distance the piston travels from BDC (Bottom dead center) to TDC (top dead center). The Bore is always mentioned first.

内径指的是气缸的直径；行程是活塞从下止点运行到上止点的距离。表述时，内径总是写在前面。

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Mr. McPheeters's weekend ended early, when he busted a piston on Saturday, sending his snowmobile to the bottom of the lake.

WSJ: Snowmobile Riders Race Over Water on Minnesota Lakes