| 摘要 |
PROBLEM TO BE SOLVED: To reduce the cylinder vertical axis directional total length by setting a stroke distance in the same as a total value or smaller than that of respective radiuses of an installing tail end part of a crankpin and a crankshaft journal measured on a surface of a crank arm. SOLUTION: A stroke distance (h) is set in the same as a total value or particularly smaller than the total value of a radius R1 of a crnakpin installing tail end part 30 of a crank arm 9 and a radius R2 of a crankshaft journal installing tail end part 20. In the constituting size of an internal combustion engine for a portable work machine, for example, an allowable difference of almost 1 mm becomes possible between the total value of the radiuses R1 and R2 and the distance (h). In a crankshaft, the. distance (h) is smaller than a total value of r1 of a circumferential circle 36 of a receiving hole 31 and r2 of a circumferential circle 26 of a receiving hole 21 in response to this. These radiuses are measured on a surface of the crank arm 9 or 10, and the radius r1 is smaller than the radius r2. Thus, the whole cylinder height can be reduced.
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