In this study the simulation about force and time is built with Lagrange equation which solves the crankshaft dynamics in engine of vehicle. The force will incline as the time inclines with a certain mass of piston of 1.6Kg, 3.2Kg & 4.8Kg in engine on vehicle, meantime as the mass inclines the force will incline too from 16N and 32N to 48N with maximum value at 7E-3s at 700r/m rotation of engine. The bad force will be formed in first and then the good one will be followed at last in terms of former d2F/dt2<0 and d2F/dt2>0 respectively. But the bad force has good stability. If the mass of piston is increased the bigger force may be formed in engine.