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Piston Dimensions



Parts and dimensions
1Piston crown
2Piston skirt
3Top land
4Piston-ring zone
5Compression height
6Piston height

Appropriate micrometer accurate to 1/100th of a millimeter

The piston is a relatively complicated component to measure because of it's oval shape and the resulting changes when being heated. It's diameter can be measured using a micrometer with an accuracy of between 0,05 to 0,01 mm. A micrometer for pistons having a diameter of 75 - 100 mm is shown in the above pictures 2 and 3. With each full rotation of the sleeve (50 division lines), the spindle moves 0,5 mm on the scale of 75 - 100 mm.

Clearance between the piston and the cylinder-wall in a cold engine
Heat land in the direction of the piston pin axle0,21 mm
Heat land at 90° to the piston pin axle0,23
Top of the piston skirt in the direction of the piston pin axle0,2 mm
Top of the piston skirt at 90° to the piston pin axle0,1 mm
Bottom of the piston skirt in the direction of the piston pin0,1 mm
Bottom of the piston skirt at 90° to the piston pin axle0,05 mm

Cold-measuring at 90° to the piston pin axle at the bottom of the piston skirt


The compression height is the most important dimension of the piston. It is one of the factors determining the total height of the engine. Because 80% of the pistons mass is found in the area of the compression height, it influences the design and also the weight of the piston. A different value here of course, also changes the compression ratio of the piston engine. 07/11


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