Question

In balancing of 4-stroke in-line engines, firing order helps to control the magnitude of

• A. Primary force only
• B. Primary couples only
• C. Primary forces and Primary couples only
• D. None of these.

Answer 1

The correct option is B Primary couples only

In case of four stroke in line engines whatever may be the firing order the direction of secondary forces will not change


$\beta =\frac{4\pi }{n}=\frac{4\pi }{4}=\pi$

${\text{Secondary force on n}}^{\text{th}}\text{cylinder}$
$\frac{mr{\omega }^2}{n}2(\theta +(n-1\left)\pi \right)$

Secondary couples are always balanced. Primary couple on the cylinder depends on firing order.
For firing order 1-2-3-4


Primary forces are always balanced but couples are not balanced