Connecting Rod Essay

Submitted By alsanad
Words: 2096
Pages: 9

University of Puerto Rico
Mayaguez Campus
Mechanical Engeneering Department


Machine component design
“Piston Rod”

Reinaldo Santiago Bermudez
Josue Cortes Irizarry
Carmen Sanchez
Title: Connecting Rod


• Propose a new mechanic component to analyze the efforts and load that acts on the connecting rod.

• Analyze how the effort and loads acts to propose a better design of the piece.

• Learn new study concepts and improve mechanical parts.

• Analyze the heat effect in this component.


Our group chose the piston connecting rod because it’s exposed to a series of loads that can be studied under the concepts of this course. Also because it is a very important component in the operation of automobile engine and it can establish better designs for its construction. The piston connecting rod is connected to the crank shaft, this mean that we denominate connecting rod to a piece that is holds by one of its ends to a piston that makes a straight movement in line, and by the other end to the crank shaft or a wheel, by this manner being capable to transform a alternative movement in a rotational movement.

The upper end of the connecting rod articulates whit the bolt of the piston, and it’s built-in to an antifriction socket to avoid the wearing down caused by the alternative and oscillating movements of the piston. The fabrication of the connecting rods has different materials like steel, aluminum and others. Knowing it operation and of what material we can analyze it to make de tension calculus and the deflection below the static loads. Also realize calculations of the material index, critical sections, life utility and safety factor, etc. It is possible to indicate that it’s exposed to heat and we will try to see the effect that this cause to our component. By last, our purpose is to analyze the component to propose a better design of this one.

First we begin to find normal stress acting on rings of piston:

Stresses in Piston:

Assuming Cast Iron material: E = 100 GPa
Ring width = 0.00115m
Ring depth = 0.0031m
Free ring radius approx. = 45mm
Free ring gap approx. = 10mm
Angle subtended at center of ring by gap = 10/45 = 0.222radians
Starting with the bending equation: [pic]
Then integrating: [pic]
Length of Beam = 0.09π m
Substituting this length for x
0.22 EI = 0.09 M [pic]
Then the maximum stress in the ring is 120 MPa. How the ring encloses the cylinder area we can conclude that the maximum strength executed by the piston is equal to 120 MPa. .

Having stress over rings in piston we assumed that the stress acting in rings equals same at surface area on piston because of very low tolerance between cylinder and piston rings, and therefore the pressure done by gas and air during combustion at certain static time is the force acting on piston rod. The relation between the strength and the compressive force acting in the rod is given by:

Dpiston= 75 mm (standard bore of 1.6 honda civic sohc motor)

R = (75/2 mm)*(1m/1000mm) = 0.0375 m


This force is concentrate on piston by pressure of explosion by gas and air. We assume that this force is equal in every point of piston surface area, therefore, this force will act directly up on piston rod.


a) rectangular neck of piston rod b) angle of 20º after certain time of expansion stroke c) Force acting over piston rod head and compression force of crankshaft under piston rod are equal Free body diagram:


Bending moment produce by force P represented in the following picture:


The neutral axis and the critical zone we assume at center of rod where probably will be the major deflection: Length of rod is 6 in, critical zone at 3in:


Then the torsion due by torque of