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Piston Dimensions
| Parts and dimensions |
| 1 | Piston crown |
| 2 | Piston skirt |
| 3 | Top land |
| 4 | Piston-ring zone |
| 5 | Compression height |
| 6 | Piston 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 axle | 0,21 mm |
| Heat land at 90° to the piston pin axle | 0,23 |
| Top of the piston skirt in the direction of the piston pin axle | 0,2 mm |
| Top of the piston skirt at 90° to the piston pin axle | 0,1 mm |
| Bottom of the piston skirt in the direction of the piston pin | 0,1 mm |
| Bottom of the piston skirt at 90° to the piston pin axle | 0,05 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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