Quote Originally Posted by aaronng View Post
Since we assume that the engines are identical, then the horizontal axis distance from piston to crankshaft is the same for both engines and the force is the same for both engines, hence the torque must also be the same.
The force on the combustion stroke piston is NOT the same. The example states that one engine has 10% more torque than the other = 10% more force down on the combustion stroke piston.

The remaining 3 pistons (who's motion is determined entirely by the crankshaft, unlike the combustion piston which has an unbalanced [without a load] force) and rods of both engines share the same position function, and thus velocities, accelerations and therefore forces from the crankshaft.