The largest diameter of a camground piston is, multiple choice question is given below:
Q. The largest diameter of a camground piston is
(a) along piston pin axis
(b) at the piston land
(c) at 45° to the piston pin axis
(d) al 90° to the piston pin axis
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A piston is ground slightly oval or elliptical in shape for the compensation for expansion caused by heat of cumbustion.
All portion of the piston do not expand same; the top of the piston gets the hottest so it expands maximum. The skirt gets the coolest so it expands minimum. For this reason the top diameter of the piston will be smaller, and the bottum diameter of the skirt will be a little larger, than the diameter at the top of the skirt.
Also, the expansion of the piston is not the same all around its circumference. The diameter measured across the piston pin axis will expand more than the diameter measured perpendicular to the piston pin axis. Therefore, the piston is “cam ground”, or made slightly oval in shap, with the smaller diameter measured across the piston pin.
When the piston heated to operating temperature it will then be round in shap similar to cylinder bore. If the piston is not cam grounded, the piston to cylinder wall clearance will be more than operating clearance and piston diameter will not be same bore diameter after expansion. This can cause piston slap.