The Complete Guide to Crankshafts

Table of Contents

I. Introduction

Either by chance or the quest for knowledge, curiosity has led you here and you want to know more about the crankshaft. Turning rotational movement of engine parts known as pistons into the forward movement of the car wheels is the responsibility of the crankshaft – another mechanical component within the engine. But wait a minute, crankshafts take up more responsibilities than just pushing your vehicle forward. Its precision and synchronization with other parts like the timing belt and camshaft ensures your vehicle performs optimally. 

We’ll explore the types of crankshafts, their anatomy, working principle as well as their applications in this write-up. Therefore, fasten your seatbelts and enjoy the intriguing world of crankshafts. Let’s discover why they are such important components in a vehicle. shall we?

II. Anatomy of the Crankshaft

An engine is never complete that is not equipped with a crankshaft. But what exactly does it do? To put it simply, crankshafts translate the vertical movements of the pistons into circular motion needed by the tires to move your car horizontally – either forward or backwards. It also ensures that these vertical movements don’t cause excessive vibration that can cause serious jarring for the engine that can equally disturb your car’s horizontal motions. Ensuring your crankshafts work optimally excuses you from unnecessary car headaches. The crankshaft consists of different complex parts, with each having its singular function. They include:

  1. 1. Crank – This is the link connecting the crankshaft with the piston where the stroke is often determined by the length of the cranks. A longer stroke means more power, but also more stress on the engine.
  2. Main Magazines – the part of the crankshaft that rotates in the main engine blocks and supports the crankshaft by assisting in the distribution of the force produced by the pistons and called the main journal.
  3. Crank Web –  The connection between the cranks and the main journal is made by the crank web which allows the rotation of the main bearing in tandem with the motion of the cranks.
  4. Counterweight – These are ballast-like protrusions on the crankshafts body that help to keep it in equilibrium. These are the counterweights. They are carefully placed to counteract the force created by the pistons.

III. Types of Crankshafts

Crankshaft should be a familiar word for you especially if you’ve been involved with automobiles at some point in the past. But do you know the types of crankshafts there are? Here you go!

  1. Monolith Crankshafts – This is a single-piece forged crankshaft. Hence its name monolith. This is because it was forged from a single material, usually either aluminum or steel and with a method similar to mold manufacturing. This single forging increases their ability to withstand stress and high temperatures. Additionally, because of their single metal forging, they are stronger and are typically common among racers or high-performance building engine mechanics. 
  2. Mounted Crankshafts – Known for their unique assemblage and their two-piece combination, these crankshafts are often mounted – obviously from the name. And the two-piece metals are usually cast iron and steel. They can only resist everyday wear and tear and are majorly used for passenger cars and heavy-duty trucks.
  3. Comparison of Monolith and Mounted Crankshafts – In comparison, the monolith is usually recommended for high-performance engines due to their strength and durability. While the mounted crankshaft is more suitable for passenger cars and trucks as they are not as strong as the monolith crankshafts.

IV. Types of Crankshafts in Marine Engines

Some of the most popular types of crankshafts in marine engines, and their unique properties are mentioned below:

  1. Fully Built Crankshafts – These are several pieces of components fabricated and crafted before assembling to forge a strong crankshaft that works to power the propeller. These types of crankshafts are cost-effective because they are seamless to produce and repair. They likewise can cope with stress. 
  2. Semi-built Shaft Crankshafts – These types of crankshafts are fabricated from steel crankshafts and different steel shafts. They are pieced together to sometime using machining methods like CNC machining to create a strong, durable, and reliable crankshaft by an interference fit method that reduces vibrations. They can be a little bit hard to manufacture in comparison with the fully built crankshaft.
  3. Welded Crankshafts – This requires the joining of two halves together using welding processes to deliver these types of crankshafts. While many automobile professionals attest to its durability this method of crankshaft manufacturing is not popular. In addition, because of its cost, manufacturers have halted the production of crankshafts like this. 
  4. Single Solid Piece Crankshafts – The production of the single-solid piece crankshaft follows from the use of materials like alloys or steel. And while this crankshaft may be unpopular today, it will interest you to note that it is adaptable and fits various engine types. It is formed and joined together using bolts.

V. Crankshaft Operation

We’ve already established the role of crankshafts in translating vertical motion into horizontal movements of vehicles. But how this is done is embedded in its design. While the vertical movement of the piston is ongoing the connecting rod ensures that this vertical motion concurrently translates into the circular motion in the crankshaft. The journals attached to the crankshafts also contribute to the conversion of the linear to rotational motion by the crankshaft. The strength of the crankshaft is a critical factor in resisting the stress generated by the engine and in facilitating this principle. 

The forces working on the crankshaft as it performs its function are the torsional force and reciprocating force. These forces can be mitigated by forming the crankshaft with large diameter thick walls and balancing to avoid wear and tear, and adverse effects on the crankshaft.

VI. Applications of the Crankshaft

The vital position of crankshafts in the overall engine processes cannot be overstated. The reason is that without the crankshaft, the engine cannot work at full capacity, and movement is hindered. Therefore, crankshafts have numerous applications and they are versatile considering that both four-stroke and two-stroke engines utilize this component. And it is not limited to vehicles as engine-carrying devices like boats and bikes employ crankshafts. However, maintenance cultures that must be adopted for optimal efficiency are constant replacement of its oil, as this allows the crankshaft to be well lubricated at all times. Regular checks for wear and tear that may have been caused by stress on the crankshaft. And, balancing the crankshaft. This ensures that there is no increased wear and tear on other engine components as well. Balancing eliminates the problem of vibrations in the engine and ensures it runs smoothly.

VII. Custom Crankshafts

Having considered all the crucial uses of the crankshaft, its functions, applications, and operations. Many manufacturers sometimes still want to design their tools as per a specific application for them. These custom crankshafts sometimes require special mold design or assembling processes. Therefore, certain standards and features are usually what they look out for. However, as a manufacturer in the market looking for the best, you might also factor in options such as looking for the most balanced crankshaft. This will enable the crankshaft to evenly distribute the weight of the rotating component. Moreso, another option to consider would be a longer crankshaft to help with engine displacement and horsepower. You can as well opt for a narrowly knife-edged counterweight for increased engine response and lower windage. With these custom options, you are going to enjoy reduced engine vibration, increased throttle response, lower windage, and optimal performance. Furthermore, your crankshaft is open to having creative and inventive features that make it look sleek and pleasing. Some other benefits of customizing your crankshaft include reduced wear and tear if properly knife-edged, increased engine durability, increased torque, and flexibility in design.

VIII. Conclusion

In conclusion, whether you drive a car or you own a speed boat, as long as it has an engine, you’ll always find a crankshaft in there doing the dirty job. its anatomy and function are key to keeping your engine in top condition. But again, getting the right crankshaft for your engine is key and the information here is detailed to help you choose the most suitable one. Furthermore, its application is wide, and its working principle determines how efficiently your engine works. Customizing your crankshaft also creates a lot of benefits for you to enjoy. And lastly, with constant technological advancement, the range of crankshafts could be limitless.

IX. Frequently Asked Questions

Over the years, specific questions about crankshafts keep popping up and having the right answers handy is key to avoiding awful and costly damage to your crankshaft. You’ll find the most usual questions about crankshafts highlighted below along with answers. 

A. What are the key roles of a crankshaft?

Synchronizing the piston movements along with other components like the camshaft and the timing belt including ensuring the prompt movement and conversion of the piton’s vertical movement into horizontal motion are the essential roles of the crankshaft. These functions ensure that the engine works optimally and efficiently. 

B, What are the essential elements of crankshafts?

The support platform and the connecting arm form the crucial elements of the crankshaft. The reason is because without the main journal that holds the crankshaft in place within the engine, it wouldn’t have been effective. Also, without the connecting rod linking the pistons with the crankshaft, all other adjoining components will be out of sync which will affect the efficiency of the crankshaft negatively. 

C. What are the various options of crankshafts available?

Crankshaft technology and manufacturing have developed over the years to provide several options, including slit-pin, single-plain, flat-plane, and cross-plane crankshafts. Most importantly, there are features for each of the crankshaft options that distinguish them for engine performance purposes. Some of these options are suitable for rapid prototyping unlike custom crankshafts which take a lot of time to make. 

D. How does a crankshaft work in a marine engine?

The basic operation is the same for both marine and automobile engines as crankshafts are designed to translate vertical motion in piston motions to horizontal movements. However, marine engines are typically larger and operate at a lower RPM than automotive engines, requiring a sturdier and more robust crankshaft to withstand the stresses of marine applications.

F. Can custom crankshafts improve engine performance?

To answer this question, we’ll say Yes. Parameters like power output, efficiency, and torque often receive a boost by way of special design and attention to these specific details during design. One upside of custom crankshafts is the ability to reduce the engine’s weight which often compliments the engine’s performance with a consequent power-to-weight ratio advantage and an increased engine performance. However, custom crankshafts can be costly, and proper engineering and manufacturing expertise is necessary to ensure their reliability and durability.


Gary Liao

Gary Liao

Gary Liao is the Engineering Manager of TDL Company and has more than 20 years of mold design experience.

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