Forces Acting On The Crank Mechanism

Gas force act on the piston;

Side thrust or normal force act on the piston pin direction;

Vertical reaction force;

Tangential force;

Connecting rod force;

Inertial force.

In an internal-combustion engine, the connecting rod handles all of the forces between the wrist pin of the piston, and the crankshaft. With pinned (freely rotating) connections at both ends, these forces are nearly pure compression and tension.

Let’s look at the four strokes (of a four-stroke ICE), and the connecting-rod forces in each:

Intake stroke: Tension, working to increase the size of the cylinder chamber, to reduce the pressure and draw fresh air and fuel in through the intake valve.

Compression stroke: Compression, working to decrease the size of the now-sealed cylinder chamber and compress the air/fuel mixture contained within.

Power stroke: Compression, after the combustion of the fuel dramatically increases the pressure in the closed cylinder chamber; the power is transmitted down to the crankshaft.

Exhaust stroke: Compression, working to increase the pressure and push the hot combustion byproducts out of the now-opened exhaust valve.

As most of these forces are compressive, the key parameter in the design of a connecting rod is prevention of buckling.

The connecting rods also experience thermal and vibrational stresses; these are quite significant compared with what other mechanisms may experience, but not nearly as large as the primary forces listed above.

Thank you Mr. Sathish and Mr. Tamilselvan. 

For IC engines, if we have a value of piston effort, we can calculate connecting rod force. But for compressor, it is little bit difficult. So, to calculate connecting rod force (weight of connecting rod should be taken) for a compressor, what's the formula I've to use? 

https://pdfs.semanticscholar.org/bcb8/f5b79f338b3e1f8eb72a064b6be2979d546f.pdf

click on above link and read that paper you will be clarified