The crankshaft is a perfect component of any engine, responsible for converting the reciprocating motion of the pistons into rotational motion.
And obviously, you need to understand the various parts of the crankshaft and their functions regarding diagnosing and repairing issues, as well as selecting the proper crankshaft for your engine.
In this blog post, we will explore the main parts of the crankshaft and their roles in engine performance.
What are the main parts of a crankshaft?
The crankshaft consists of several distinct parts, each with its unique function. The main parts of a crankshaft include
Main Journals:
These are the large diameter cylindrical sections of the crankshaft supported by the engine block’s main bearing caps.
The main journals are responsible for transmitting the power generated by the engine to the transmission or other drivetrain components.
They are typically ground to a very precise diameter to ensure proper alignment and reduce friction.
Rod Journals:
These are the smaller diameter cylindrical sections of the crankshaft that support the connecting rods and piston pins.
The rod journals are typically offset from the main journals to provide the necessary stroke length for the engine.
They are also ground to a precise diameter to ensure proper alignment and reduce friction.
Crankshaft Throws:
These are the angled sections of the crankshaft that connect the main and rod journals and provide the reciprocating motion required to turn the engine’s flywheel.
The throws are offset from each other to provide the necessary firing order for the engine.
They are also carefully designed to balance the engine and reduce vibrations.
Counterweights:
These are the heavy, often kidney-shaped weights attached to the crankshaft throws that help balance the crankshaft and reduce vibrations.
The counterweights are carefully designed to balance the reciprocating mass of the pistons and rods and prevent the crankshaft from bending or breaking under the operation stresses.
Thrust Flange:
This flat section of the crankshaft provides axial support and prevents it from moving back and forth.
It is typically located at one end of the crankshaft and used to transfer the axial load generated by the engine to the engine block or other components.
Flywheel Flange:
This is a larger diameter section of the crankshaft that connects the engine’s flywheel or flexplate.
The flywheel flange is typically machined to a precise diameter and bolt pattern to ensure proper alignment and engagement with the flywheel or flexplate.
Keyway:
This is a slot cut into the crankshaft that allows it to be properly aligned with other components in the engine.
The keyway is typically used to align the crankshaft with the camshaft or other timing components.
Oil Passages:
These are channels drilled into the crankshaft to flow the oil to various parts of the engine.
The oil passages are carefully designed for proper lubrication of the main and rod bearings, and other engine components like the camshaft and lifters.
What is the purpose of the main journal on a crankshaft?
The main journal on a crankshaft serves several important purposes:
Support:
The main journal provides support for the crankshaft and helps it to maintain its proper alignment within the engine block.
The main bearing caps are bolted to the engine block, helping to secure the crankshaft in place and prevent it from moving around during operation.
Rotation:
The main journal is responsible for transmitting power from the engine to the transmission or other drivetrain components.
As the crankshaft rotates, the main journal turns the flywheel or flexplate, which in turn rotates the transmission input shaft and drives the wheels.
Lubrication:
The main journal is designed with oil grooves and passages that allow oil to flow to the bearings and other parts of the engine.
Proper lubrication is important to prevent wear and tear on the bearings and reduce friction between the crankshaft and the engine block.
Heat dissipation:
The main journal also helps to dissipate heat generated by the engine.
A rotated crankshaft creates friction and heat, which can cause the metal to expand and warp.
The main journal helps to dissipate this heat and keep the crankshaft from overheating and warping.
Balance:
The main journal, along with the counterweights and other components of the crankshaft, helps to balance the engine and reduce vibrations.
Proper balance is essential for smooth engine operation and longevity.
What is the purpose of the rod journal on a crankshaft?
The rod journal on a crankshaft serves an important purpose in the operation of an engine:
Connecting rod attachment:
The rod journal is the point where the connecting rod attaches to the crankshaft.
This connection is essential for transferring power from the piston to the crankshaft and ultimately to the drivetrain.
Rotation:
As the crankshaft rotates, the rod journal turns the connecting rod and the piston, creating the up-and-down motion that powers the engine.
Lubrication:
The rod journal is designed with oil grooves and passages that allow oil to flow to the bearings and other parts of the engine.
Proper lubrication is essential for preventing wear and tear on the bearings and reducing friction between the rod and the journal.
Heat dissipation:
The rod journal also helps to dissipate heat generated by the engine. A rotated crankshaft can cause the metal to expand and warp.
The rod journal helps to dissipate this heat and keeps the connecting rod from overheating and warping.
Balance:
The rod journal, along with the other components of the crankshaft, helps to balance the engine and reduce vibrations.
Proper balance is essential for smooth engine operation and longevity.
What is the function of the crankshaft counterweights?
The crankshaft counterweights serve an important function in the operation of an engine:
Balance:
As the engine runs, the counterweights offset the weight of the reciprocating and rotating components, such as the pistons, rods, and crankshaft itself, which helps to reduce vibrations and improve overall engine performance.
Durability:
The counterweights also help to improve the durability of the crankshaft by reducing the stresses.
The counterweights act as a damping mechanism, absorbing the energy created by the vibrations and minimizing their impact on the crankshaft.
Rotational stability:
The counterweights also help to maintain the rotational stability of the crankshaft.
The rotating mass of the engine would cause the crankshaft without the counterweights to twist and bend, which could lead to engine failure.
Harmonic control:
The counterweights are designed to counteract the natural frequencies of the engine and reduce harmful vibrations.
By controlling the engine harmonics, the counterweights help to improve engine efficiency and reduce wear on the engine components.
What is the function of the flywheel flange on a crankshaft?
The flywheel flange is an essential component of a crankshaft, which has several functions, including
Connecting the crankshaft to the flywheel:
The flywheel flange serves as the link between the crankshaft and the flywheel, which is at the rear end of the engine.
The flywheel acts as a counterbalance to offset the engine’s power strokes.
The flywheel flange connects the crankshaft and the flywheel, enabling the transfer of power strokes from the engine to the flywheel.
Providing rotational inertia:
Rotational inertia is the resistance to changes in rotational motion, and the flywheel flange contributes to the rotational inertia of the crankshaft.
The rotational inertia of the flywheel flange helps in maintaining the engine’s speed during power strokes.
The flywheel flange’s rotational inertia also contributes to the smooth operation of the engine by reducing fluctuations in engine speed.
Reducing vibrations:
The flywheel flange helps in reducing engine vibrations by acting as a counterbalance to the engine’s rotating components.
During the power strokes of the engine, the flywheel flange rotates in the opposite direction, which helps to reduce the vibrations produced by the power strokes.
The flywheel flange’s counterbalancing effect also helps in reducing the wear and tear on the engine’s components.
Balancing the engine:
The flywheel flange plays a crucial role in balancing the engine. Unbalanced engines can produce excessive vibrations, which can lead to engine damage or failure.
The flywheel flange ensures that the engine remains balanced by offsetting the forces generated during the power strokes.
This balancing effect is particularly important for engines that operate at high speeds or produce a lot of power.
Supporting accessory drive components:
In some engine designs, the flywheel flange also supports accessory drive components, such as the alternator or power steering pump.
The flywheel flange provides a mounting point for these components, ensuring that they are securely attached to the engine.
This support helps to reduce the wear and tear on the engine’s components and ensures that the accessory drive components operate smoothly and efficiently.
How are crankshafts manufactured?
The production of crankshafts involves several steps, starting with the selection of high-strength durable materials.
Below there are the steps involved in manufacturing crankshafts:
Forging:
The first step in manufacturing a crankshaft is forging.
Forging is a manufacturing process that involves heating the metal to a high temperature and then shaping it using a hammer or press.
The forging process creates a solid, dense metal structure with improved strength and fatigue resistance.
Forged crankshafts are typically used in high-performance engines, where strength and durability are critical.
Machining:
After forging, the crankshaft undergoes several machining processes to refine its shape and dimensions.
The first step is rough machining, which involves removing excess material from the forging and shaping it into a rough outline of the finished crankshaft.
Next, the crankshaft undergoes several finishing processes, including grinding, milling, and drilling.
These processes refine the shape of the crankshaft and create precise bearing surfaces for the engine’s connecting rods and main bearings.
Heat treatment:
After machining, the crankshaft undergoes heat treatment to improve its strength and durability.
Heat treatment involves heating the crankshaft to a high temperature and then cooling it rapidly, creating a hard, durable surface layer.
Heat treatment also helps to eliminate internal stresses in the metal, improving the crankshaft’s fatigue resistance.
Surface finishing:
After heat treatment, the crankshaft undergoes several surface finishing processes, including polishing and shot peening.
Polishing helps to create a smooth, low-friction surface, reducing wear and tear on the engine’s bearings.
Shot peening is a process that involves bombarding the surface of the crankshaft with small metal pellets, creating a compressed surface layer that improves its fatigue resistance.
Inspection:
After manufacturing, the crankshaft undergoes several inspection processes to ensure that it meets the required specifications.
The inspection process includes measuring the dimensions of the crankshaft, checking for cracks and defects, and testing its fatigue resistance using a dynamometer.
What are some common problems with crankshafts?
Like all mechanical components, crankshafts can develop problems over time. Here are some common problems that can occur with crankshafts:
Cracks:
Crankshafts can develop cracks due to the high stresses and temperatures involved in their operation.
Cracks can occur in the journal fillets, which are the areas where the crankshaft’s journals meet the web.
Cracks can also occur in the keyways or flanges, which can lead to the failure of the flywheel or other accessory drive components.
Bearing wear:
The crankshaft’s journals are supported by bearings, which can wear over time due to friction and heat.
If the bearings wear excessively, they can cause the crankshaft to move out of position, resulting in engine vibrations or other problems.
Bearing wear can be caused by insufficient lubrication or poor oil quality.
Bent or twisted crankshaft:
Crankshafts can become bent or twisted due to impact damage or excessive torque loads.
A bent or twisted crankshaft can cause uneven wear on the bearings, resulting in increased vibration and reduced engine performance.
A bent or twisted crankshaft may need to be replaced.
Fatigue failure:
Crankshafts can experience fatigue failure over time due to the repeated stresses of the engine’s operation.
Fatigue failure can occur in the fillets or other high-stress areas of the crankshaft, resulting in cracks or other damage.
Fatigue failure can be prevented by ensuring proper maintenance and using high-quality materials.
Improper balancing:
Crankshafts must be properly balanced to ensure smooth engine operation and to reduce stress on the bearings.
Improper balancing can lead to excessive vibration, which can cause damage to the engine’s components.
Proper balancing requires careful measurement and adjustment of the crankshaft’s weight distribution.
How can you choose the proper crankshaft for your engine?
Choosing the proper crankshaft for an engine is essential to ensure optimal engine performance and reliability.
Here are some factors to consider when selecting a crankshaft for your engine:
Engine type:
The type of engine you have will influence the type of crankshaft you need.
For example, high-performance engines may require forged steel crankshafts, while stock engines may use cast iron crankshafts.
Stroke length:
The stroke length of the crankshaft will determine the engine’s displacement and affect its power and torque characteristics.
Longer stroke lengths will generally increase torque at lower RPMs, while shorter stroke lengths will increase high-end horsepower.
The stroke length should be chosen based on the desired power and torque characteristics of the engine.
Journal diameter:
The journal diameter of the crankshaft will determine the size of the bearings used in the engine.
The journal diameter should be chosen based on the bearing size and type recommended by the engine manufacturer.
Material:
The material used to make the crankshaft will affect its strength, durability, and weight.
Forged steel crankshafts are commonly used in high-performance engines due to their strength and durability, while cast iron crankshafts are often used in stock engines due to their cost-effectiveness.
Balancing:
Proper balancing of the crankshaft is critical to ensure smooth engine operation and to reduce stress on the bearings.
The balance factor of the crankshaft should be chosen based on the engine’s operating RPM range and the type of engine.
Manufacturer recommendations:
It is important to consult the engine manufacturer’s recommendations when selecting a crankshaft for your engine.
The manufacturer will often provide specific guidelines for selecting the proper crankshaft based on the engine’s specifications and intended use.
FAQs
What Is A Crankshaft Counterweight?
A crankshaft counterweight is a section of the crankshaft that is designed to offset the weight of the piston and connecting rod during the engine’s operation.
The counterweight helps to balance the crankshaft and reduces vibration and stress on the engine’s components.
What Is A Crankshaft Keyway?
A crankshaft keyway is a small slot or groove machined into the end of the crankshaft flange.
The keyway is used to align and secure the flywheel or other drive components to the crankshaft.
A key is inserted into the slot to provide a secure, non-slip connection between the two components.
What Is A Crankshaft Thrust Bearing?
A crankshaft thrust bearing is a specialized bearing that is located at the end of the crankshaft and provides axial support to the crankshaft.
The thrust bearing prevents the crankshaft from moving back and forth during the engine’s operation, which can cause excessive wear and damage to the engine’s components.
What Is A Crankshaft Snout?
A crankshaft snout is the protruding end of the crankshaft that extends out of the engine block.
The snout is typically used to attach the engine’s harmonic balancer, which helps to reduce engine vibration and noise.
What Is A Crankshaft Oil Hole?
A crankshaft oil hole is a small hole drilled into the crankshaft to allow oil to flow through the journal and lubricate the engine’s bearings.
Proper lubrication is critical to the longevity and performance of the engine’s components.
Conclusion
The crankshaft is a crucial component of internal combustion engines that converts the reciprocating motion of the pistons into rotational motion.
It consists of several parts, including the main journal, rod journal, crankpin, flange, and counterweights.
Each part plays a critical role in the crankshaft’s operation and must be carefully designed, manufactured, and balanced to ensure optimal engine performance and reliability.
Proper maintenance and care of the crankshaft can help to prevent common problems such as cracks, bearing wear, and fatigue failure.
