The engine is known as the heart of the vehicle. It converts the chemical energy of fuel into mechanical power. The engine consists of different parts including a piston, carburetor, connecting rod, crankshaft, fuel pump, and combustion chamber. A connecting rod is one of the most important parts of the internal combustion (IC) engine that transforms the reciprocating motion of the piston into rotary motion. This article mainly explains the connecting rod working, parts, types, and applications.
What is a Connecting rod?
The connecting rod is a component of the reciprocating engine that connects the crankshaft to the piston. The connecting rod, together with the crankpins, transforms the reciprocating motion of the piston into the rotatory motion of the crankshaft.
The main function of the connecting rod is to take the reciprocating motion from the piston, convert it into rotary motion and transfer it to the crankshaft. The connecting rods are most commonly used in EC engines and IC engines.
The connecting rod is made of forged steel. It has an I-beam cross-section. Aluminum alloys are also used for the construction of connecting rods. The connecting rods are specifically arranged in sets of the same weight to maintain the balancing of the engine.
In the bike, the aluminum alloy rod is pre-eminent installed for the high speed of the engine. The connecting rod made of aluminum alloy absorbs the high-strength impact and also contains less weight.
If your engine piston and the connecting rod has lightweight, the engine will generate more power and less vibration due to the low weight of the reciprocating parts.
Your engine must have light, stiff, and strong connecting rods because they transmit the thrust from the piston to the crank pin.
Working of Connecting rod
The connecting rod makes a link between the crankshaft and the piston. It must be mechanically strong. The main function of the connecting rod is to transfer the linear motion of the piston into the rotary motion of the crankshaft.
It consists of a small and a large end rod. The smaller end attaches to a wrist pin (also known as a gudgeon pin or piston pin) which can rotate inside the piston. At the other end, the larger end attaches to a crankpin via sleeve bearings to reduce friction. A smaller motor is used for rolling-element bearings that eliminate the use of a pump lubrication system.
The connecting rod has a pinhole on the larger end that penetrates into the bearing and allows oil to be sprayed onto the pressure side of the cylinder wall to lubricate the piston stroke and piston ring.
As the power produced by the fuel combustion process pushes the engine piston, the piston starts reciprocating.
As the piston reciprocates, it transfers this reciprocating motion to the connecting rod. The connecting rod along with the crankpin transforms this motion into rotary motion. After converting motion into rotary motion, the rod transfers the resulted motion to the crankshaft.
Read Also: Crankshaft Types and Working
Parts of Connecting Rod
The connecting rod has the following major parts:
- Bearing cap
- Piston
- Wrist pin
- Shank
- Nut and Bolt
- Small End
- Bearing inserts
- Large End
- Bushing
1) Small End
The end of the connecting rod that connects to the piston pin is called the connecting rod smaller end. This end gets motion by the piston and transmits it to the rod.
2) Large End
The rod end that connects to the crankpin of the crankshaft is called the large end of the connecting rod. The main function of this end is to transfer motion from the connecting rods to the crankshaft via a crank pin.
3) Bush Bearing
The small end and large end connect are secured via bush bearings. The phosphor bronze bushing has a solid eye that connects the small ends of the rod.
The large end connects to the crank pin. The end splits into two sections and is supported by crank-bearing housing.
4) Bearing Insert
The larger end of the rod has a bearing insert attached to the bearing cap. This bearing insert consists of two parts that engage on the crankshaft. This is the area where the rod moves in the opposite direction.
5) Nuts and Bolts
The bolts and nuts use to fix the ends of the rods. As the connecting rod engages to the bottom of the crank, the large end is secured with various nuts and bolts on either side. So, if you combine all these parts, you can use the connecting rod.
6) Shank
The nuts and bolts are used to attach the bearing cap and connecting rod. After nuts and bolts, a section beam called a shank is employed. The rod may have circular, tubular, or rectangular sections.
7) Wrist Pin
A wrist pin uses to connect the connecting rod to the piston. It is a hardened steel hollow tube. The wrist pin is also called a gudgeon pin. The pin passes through the shorter end of the rod and rotates on the connected piston.
8) Piston
The piston is linked to the crankshaft via a connecting rod. The piston works as a moving plug that reciprocates in the compression chamber.
9) Bearing Cap
The bearing cap has a wear fit that controls the operation, and side clearance adjusts a proper bearing cap seating.
Construction and Functions of Connecting Rod
The connecting rod has two types of ends: a small end and a large end. The large end is at right angles to its length so that it can easily assemble on a crank pin. Two bolts and nuts are used to fix the bearing cap on the connecting rod housing.
The latest engines don’t contain the bearing metal fused into the large end bores but use a discrete mild steel bearing shell.
The cup bearings have wear fits, but they handle side clearance and overrunning to ensure the bearing caps fit properly. Some engines use spur bearings. In such a case, a thin piece of metal is employed. This metal piece is known as shin.
The shins fill thinner to balance the bearing wear and to ensure proper bearing clearance between the crankshaft and connecting rod. The smaller end of the rod is fixed with a phosphor bronze bushing and screw to close the eyelet around the crankpin.
You must keep in mind that all connecting rods in the engine must have the same weight. Otherwise, significant vibrations may appear. When assembling, the connecting rod and bearing cap must match each other. It usually has an identification number, so you don’t get confused when removing the engine for repairs.
Types of Connecting Rods
The connecting rod has the following types:
- Powered metal conrods
- Forged rods
- Cast rods
- Billet conrods
- Master and slave rod
- Fork and blade rod
- Plain type rod
1) Plain Type Rod
These types of connecting rods are used in opposed and in-line engines. The larger end of this rod is connected to a crankpin and fixed with a bearing cap.
A stud or bolt uses to install bearing caps onto the ends of the connecting rods. During the reassembly of the engine, you must replace the rod in the same relative position within the same chamber to ensure proper fit and balance.
2) Fork and Blade Rod
The fork and blade rods are employed in V12 aircraft engines and V-twin motorcycle engines. In each engine cylinder pair, the “fork” rod splits into two sections at the larger end, and the “blade” rod tapers from the opposite cylinder to accommodate this space in the fork.
This assembly removes the stall torque that arises when the cylinder pair balances against the crankshaft.
In large-end bearing arrangements, the fork rod features a wide bearing sleeve that covers the width of the rod and the central gap.
Then the blade rod turns directly out of this sleeve, not on the crank. This moves the two rods backward and forward, decreasing the surface speed and force on the bearings. However, the bearing speed is not continuous rotation but reciprocating motion, which is the main lubrication problem.
3) Master and Slave Rod
The radial engine has master and slave rods. In this engine, one piston contains a master rod. This piston directly connects to the crankshaft. Other pistons link their respective rods to the rings around the edge of the master rod.
The drawback of the master-slave connecting rod is that the slave piston has a large stroke than the master piston stroke. Due to this, the V-engine generates extensive vibration.
4) Billet Rod
This type of connecting rod is made of aluminum or steel. These rods have a lower weight, stronger, and long service life than other types of connecting rods.
The high-speed vehicles use billet rods. In some cases, it uses to decrease the build-up of stress and lighten the natural texture of billet material.
5) Cast Rod
These connecting rods have the capability to handle the load of stock engines. Therefore, these are preferable than other types of connecting rods.
One of the main advantages of the cast connecting rod is that it has a low production cost. You can’t use it for high-performance applications. The cast rod has a transparent seam in the center that makes it different from the forged rod.
6) Forged Connecting rod
Some connecting rods are made by the forging process. These rods manufacture by pressing the material into the shape of the edges. The aluminum or steel alloy uses for the construction of these rods according to the application nature.
Nickel alloys and chromium alloys are the most commonly used steel alloys. Therefore, nickel or chromium alloy increases rod strength.
7) Powered Metal Conrod
The connecting rod is also made of power metal which is the best choice for fabricators. It is made from a mixture of metal powders pressed into a mold and heated to high temperatures. The metal powder mixture makes in solid form.
The product is basically made from the finished form, although slight machining may be required. Powdered metal connecting rods have lower costs than steel ones and are stronger than iron ones.
Read Also: Different Types of Engines
Causes of Connecting Rod Failure
Your connecting may go bad due to one or more of the below-given causes:
- Pin failure
- Over revving
- Hydro-lock
- Fatigue
1) Fatigue
The high tension and compression act on the connecting rod during its operation, which leads to frequent fatigue. Eventually, this wears out the rod until it damages or breaks. The shortage of lubrication oil and the existence of dust in the engine can aggravate this issue.
The fatigue problems most commonly occur in older engines. Rebuilding an engine can also lead to fatigue when inserting a new engine. This problem may also occur when you use the wrong or cheap parts.
2) Over Revving
Overlapping or over-revving is another failure reason for connecting rod. This most commonly occurs in the new high-performance engines.
If the tachometer shows a red signal, it means that your car rod is in a risky position. Because at high speeds, the force acting on the connecting rod increases sharply.
3) Hydrolock
A Hydrolock problem appears when water goes into the piston cavity and deforms the rod. This can happen when you drive your car over a flooded road.
4) Pin Failure
Damage to the piston pins can lead to disastrous engine failure. This happens when the connecting rod travels toward the engine block or when the crankshaft bends.
Some engines can cause severe power loss. If the pin breaks due to this problem, the motor will stop immediately. The engine may have survived, or a complete breakdown can also happen.
Applications of Connecting Rod
- IC Engines: Connecting rods are most commonly used in IC engines, including diesel engines or petrol engines. It connects your vehicle’s crankshaft to the piston, converting the linear motion of the piston into the rotatory motion needed to run the vehicle.
- Stirling Engines: They are used in the Stirling engine to connect the displacers or pistons to the crank or flywheel, assisting in transforming the heat energy into mechanical energy.
- Compressors: Connecting rods are used in the reciprocating compressor to link the piston to the crankshaft. They help to compress gases for different applications.
- Steam Engines: They are used in steam engines to connect the crosshead or piston to the crank or crankshaft, transforming the reciprocating movement of the piston into rotary motion, which further drives steamboats, locomotives, or stationary machinery.
- Pumps: These are employed in the reciprocating pumps to transfer the linear motion of the plunger or piston into the rotatory movement required to drive the pump mechanism.
- Textile Machinery: They are employed in textile machinery to transfer motion from the main drive shaft to different machine components.
- Locomotive Suspension Systems: In the suspension system, connecting rod is employed in some locomotives to connect the driving wheels to the equalizing beams.
FAQ Section
What is the function of connecting rod?
The main function of the connecting rod is to transfer the linear motion of the piston into the rotary motion of the crankshaft.
What causes connecting rod failure?
- Engine overheating
- Hydrolock problems. This problem occurs while you drive the vehicle over a flooded road.
- Age of the rod
- Excessive load on the rod
- Failure of the connecting rod bolts
- Damage to the piston pins can lead to disastrous engine failure.
- Poor quality material used for the construction of connecting rods
- Misalignment of the rod
- Exposure to corrosive environments or fluids
What are the parts of Connecting rod?
- Bearing cap
- Piston
- Wrist pin
- Shank
- Nut and Bolt
- Small End
- Bearing inserts
- Large End
- Bushing
What are the types of connecting rod?
- Powered metal conrods
- Plain type rod
- Forged rods
- Fork and blade rod
- Cast rods
- Billet conrods
- Master and slave rod
How do I select the appropriate connecting rod bearings for my application?
- Check the specifications of your engine and select rod accordingly.
- Consider the connecting rod bearing material.
- Consider the bearing clearance. The appropriate bearing clearance is important for preventing excessive wear and ensuring appropriate oil film thickness.
- Consider the rod bearing side. You need to measure the diameter of the crankshaft journal and connecting rod housing bore to find the correct bearing size
- Conisder the bearing coating.
- Select bearings from reputable manufacturers with a good track record of performance, reliability, and quality.
What materials are commonly used for manufacturing connecting rods?
Titanium, aluminum, and steel are the most commonly used for manufacturing connecting rods. Aluminum is famous because of its lightweight features, making it ideal for high-performance applications. Steel, precisely forged or powdered metallurgy steel, is famous for its high durability and strength.
Read Also
- Different types of Engines
- Different types of Pumps
- Working and types of Crankshaft
- Working of Carburetor
- Types of IC Engines