Secondary Balance of Multi-Cylinder In-Line Engine:
Already we have seen the existence of secondary force in one cylinder and we let various cylinders in last instance. The conditions of equilibrium of secondary forces and couples might be written in the similar way as Equation (1) and (2) but along the imaginary secondary crank of length r/ 4n here n = l . In this case the forces connected along all secondary cranks and their moments regarding a reference plane should vanish, that means
----------- (3)
----------- (4)
As an instance let us examine a 2-cylinder engine with cranks in the similar plane and at 180o. Identical cylinders are located on the similar side. The engine is schematically depicted in Figure 4.
In such a configuration the primary forces that are equivalent to reciprocating masses located at crank pin are equivalent for all of angles of crank along the line of stroke. Therefore, they are balanced.
The secondary cranks make two times the angle at which real crank is along the line of stroke. Therefore, the secondary crank for crank along angle θ shall be at 2θ and secondary crank for the other crank shall make 2θ+ 2 × 180 = 2θ along the line of stroke. The secondary force for both of the pistons will be added and a 2Fs unbalanced force shall act on engine frame.
Thus far as moment because of primary forces are concerned they shall not vanish as the equivalent and opposite forces are acting in two parallel planes. Thus moments are not balanced.
The secondary forces acting in the similar direction and being equal shall have their resultant pass through a point which is in the middle of two cranks and hence no moment about that point. However, about any other point moment will be present.