Turning Moment Diagram:

Given figure illustrated a layout of a horizontal engine.

Assume p = effective gas pressure on the piston in N/m²,

A = area of the piston in m²,

m_rec = mass of reciprocating parts, that means mass of the piston gudgeon pin and part of mass of connecting rod 'm₁',

Q = thrust force on the connecting rod in N, and

ω = angular velocity of the crank.     

     (a)

      (b)                                                                         (c)

Q cos φ= p A + m_recx

In case of a vertical engine

Also letting the correction couple, the actual turning moment is

                          M _t = M + M _C