在駐車情況下引擎為機車的振動來源，而引擎振動來源受引擎搖撼力和力矩所影響。先以活塞、連桿、曲軸的慣性力相加得到引擎搖撼力的公式，可由公式改變曲軸重心位置，最佳化引擎搖撼力方向，配合引擎吊架的直交理論，減少搖撼力傳至車架。另外以活塞慣性力和汽缸內的壓力參數推導出搖撼力矩公式，發現搖撼力矩的峰值受汽缸內壓力影響甚大，不因曲軸轉速較小而有明顯變小。

另一方面將引擎利用電腦輔助分析，分別使用為剛體和彈性體模式，我們可以得到各個邊界條件處的作用力和力矩，讓引擎的探討能更加詳細。如將所有的作用力相加整理後，可以得到與公式推導出引擎搖撼力一致的結果。剛體和彈性體分析的力或力矩大小一樣，但在彈性體分析模式時，力和力矩會有小跳動。

Engine is the vibration source of the motorcycle in the state of parking. The vibration sources from the engine are the engine shaking forces and moment. First, we add up the piston, connecting rod, and crankshaft inertia force and thereby obtain the formula of engine shaking forces. We use the formula do the optimum direction of the engine shaking force by changing the center of crankshaft gravity position. The shaking force transmit to frame can be reduced with the orthogonal engine-hanger theory. We derive the formula of the shaking moment from piston inertia force and pressure inside the cylinder. The pressure inside the cylinder has an impact on the peak of shaking moment, and the peak is not significantly reduced when the speed of crankshaft reduced.

On the other hand, we used the computer-aided analysis, using rigid body and elastic body model, to solve the engine vibration problem. The constrained forces and torque at each boundary, show the detail of the reaction. We added up all forces and arrange to obtain the result which is identical to the formula-derived of the engine shaking force. The force or moment is the same order between the rigid and elastic body analysis, except that some fluctuation shown in elastic body analysis.

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