Connecting rod: how does it work and common conrod problems and solutions

Last Updated on July 20, 2022 by sajjad

Though connecting rod is a great parcel to an internal combustion engine, this mechanical device is found in stem engines as well.

The primary purpose of a connecting rod or conrod is to transmit the up and down linear force of the piston to the crankshaft.

A connecting rod converts the linear up and down motion of the piston into the circular motion of the crankshaft.

What is a connecting rod?

A connecting rod is a mechanical device common to most internal combustion engines that connects the piston to the crankshaft.

To keep an engine running, the crankshaft needs to move in a circular motion continuously.

When the fuel and air mixture comes inside the cylinder chamber, continuous combustions inside the chamber move the piston up and down in a linear motion.

The connecting rod attached to both the piston and crankshaft converts that linear motion into circular motion so that the crankshaft keeps moving as long as the engine is running.

How does the connecting rod work?

connecting rod work diagram

Though the connecting rod is a singular metallic rod, it is related to several other parts of the engine that allows the piston to transport its motion to the crankshaft.

  • The constituents parts of a connecting rod are-
  • Smaller end (connects the piston)
  • Bigger end (connects the crankshaft)
  • Rod cap (bottom part)  
  • Bearing inserts (helps to move in the reverse direction)
  • Wrist pin or gudgeon pin (connects the piston to the rod)

The wrist pin or the gudgeon at the smaller end allows the connecting rod to rotate inside the piston.

The bearing inserts at the end of the bigger end allow the connecting rod to move in the reverse direction. 

The energy received from the combustion stroke reciprocates the piston.

Through the connecting rod, this linear motion goes to the crankshaft.

Both bearing inserts through a pinhole lubricates the piston ring and piston stroke to prevent any damage.  That’s how the engine lubrication system keeps running simultaneously.

Which materials are used to build a connecting rod?

As a connecting rod transports the energy of the piston to the crankshaft, it needs to be strong enough to keep the system running.

The four common types of materials that are used to form a connecting rod are-

  • Forged metal
  • Alloyed aluminum
  • Alloyed steels
  • High-performing Titanium

What are the types of connecting rods?

Depending on the material and connection type, a connecting rod can be of more than five different types.

The popular types of connecting rods are-

  • Plain type conrod (in line and opposed engines)
  • Fork and blade (V-twin and V-12engine)
  • Master and slave (Radial engine)
  • Billet (High-speed engines)
  • Cast (high-load/low horsepower)
  • Forged (uses forged metals)
  • Powdered metal (cheaper  alternative)

Most manufacturers use cast and forged type con rods as they are more capable of withstanding higher loads.

Fork and blade con rods are a great part of the V-12 aircraft engines.

Plain type is the typical example of a car engine’s connecting rod.

A connecting rod failure

A connecting rod is an integral part of any internal combustion engine. A faulty connecting rod can be the reason for catastrophic engine failure.

The repetitive movement that a connecting rod performs while transferring the energy to the crankshaft can lead to a fatigue conroad over time.

At that particular moment, wear can be visible which can prompt conroad breakage.

The intervention of water inside the piston chamber can cause a hydrolock. Hydrolock is responsible for irregular sparks inside the cylinder chamber that can eventually damage the connecting rod.

Over-rotation of the pistons inside of a high-performing engine can also prompt connecting rod failure.

Another common scenario that leads to connecting rod failure is when any of the piston pins are damaged.

A bent crankshaft is mostly responsible for such issues.

Identifying connecting rod problems

Noise coming out from the connecting rod is the harbinger of a damaged conrod.

A damaged bearing, worn gudgeon pin, decayed crankpin, and bent connecting rod are some of the probable reasons why noise may come out of the connecting rod chamber.

If you are facing such issues, the following section is for you-

Possible causes and remedies of connecting rod noise

Possible causesRemedies
Worn out bush bearing or gudgeon pinReplacement is necessary
Worn out big-end bearing and crankpinReplacing the split bearing or metalizing the crankpin will solve the problem
Bent connecting rodAfter inspecting the curve, you need to correct it with the help of a professional
Crashed connecting rodShould replace the connecting rod
End-play in the big end bearingYou should use the shim
Due to oil drill blockage, lubricant oil can’t flow properlyOil drill clearance is necessary
Too diluted or thick lube ilNeed to use the correct graded lube oil
MisalignmentNeed to correct the alignment

Maintenance can prevent connecting rod failure 

A malfunctioned connecting rod can prevent the whole engine from functioning. That is why proper maintenance is more than necessary to keep the rod functional for a long time.

Check after a regular interval to ensure that the whole system is okay.