Key Takeaways
The following are the key takeaways from this article:
- The crankshaft is a major engine component placed below the cylinders, converting the pistons’ reciprocating motion into rotational motion.
- The crankshaft comprises six major parts: main bearing journals, crank web, crankpin, counterweights, oil passages, and thrust washers.
- The common crankshaft issues include fatigue, worn journals, and dirt contamination, impacting the sensor readings of the crankshaft sensor.
- The common symptoms of these issues include difficulty in engine start, misfiring engines, vibration, and reduced gas mileage.
- The cost to resolve crankshaft issues can range from $50-$1000.
Introduction
The role of the piston is to compress the air-fuel mixture within the cylinders resulting in combustion and movement of the car (3).
Another major component that drives the piston is the crankshaft which converts the reciprocating motion of the piston into the rotational motion. In addition, a flywheel is attached at the other end of the crankshaft that smoothens the power delivery to the car.
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So, the piston reciprocates to create mechanical energy converted into rotational mechanical energy by the crankshaft and the flywheel stores, delivering smooth power to the car (1). This article will further shed light on the history, function, parts, and common problems in the crankshaft.
History of the Crankshaft
The crankshaft was designed by an Arabic invertor, “Al-Jazari,” in 1206. He performed an experiment using a cylinder pump. He connected two rods with a crank system and observed the motion of the cylinder and crankshaft. Later the design of the crankshaft was further developed by Konard Keyser, and in 1551, Giorgio experimented with a crankshaft and a six-cylinder pump (2). Later, this crankshaft was incorporated into the engine of the vehicle. A crankshaft is a vital engine part and is present in the combustion chamber.
Function of Crankshaft
The function of the crankshaft is to convert linear to rotational motion. The crankshaft is very hard and can carry high loads. This weight helps in smoothening the revolutions in the engine.
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In the past, the crankshaft was made of iron, but with modernization, in technology, steel and titanium were used to manufacture the crankshaft. This is because it becomes difficult to rotate the rod due to the heavy weight of the iron. The crankshaft is the basic linkage between the vehicle’s input and output system (2). Without the crankshaft system, the car will fail to operate because this part is used in transmitting the generated energy to all parts of the engine. Moreover, it helps in reducing the vibrations in the engine and helps in improving its efficiency of the engine.
Types of Crankshaft
There are two types of crankshafts, i.e., the monolithic and fabricated. The monolithic type is usually used in vehicles having multiple cylinders, i.e., cars. In contrast, the fabricated type of crankshaft is used in engines having a single cylinder, i.e., motorcycles. The early crankshafts were large and usually heavy (1). The design of the crankshaft was different when designed, and the high number of bearings was. As a result, the length of the crankshaft was longer. Hence, the rotational speed and compression in the engine suffer from delays.
Important Parts of a Crankshaft
Following are some important parts of the crankshaft:
Main Journals
Main journal is the part of the crankshaft that rotates inside the bearing. There are two types of journals in a crankshaft.
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The main journal will form the axis of rotation for the crankshaft, while the connecting rod journals are at the end of the connecting rods. The connecting rod journals run up to the pistons. The number of main journals/bearings varies in every engine and depends upon the operation rate of the engine (4). In diesel/petrol engines, the main journals are responsible for transmitting the force of combustion through transmission through the drivelines. In hybrid engines, this part transmits energy to the generator/storage system. In simpler words, the main journals carry the crankshaft bearings and declare the axis of rotation of the crankshaft.
Crank Web
As discussed above, the main bearings are responsible for rotating the shaft and deciding the rotational axis. In addition, however, there must be a part for connecting the crankshaft with the main bearing journal.
This function is performed by crank web. The Crank web is also known as the cranked arms of the shaft that provides the throw of the crankshaft. This part is manufactured carefully as it is subjected to both twisting and bending moments created by the rotation of the crankshaft.
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So, the thickness and width of the crank web are important elements while designing the crankshaft.
Crankpin
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The engine piston is connected to the crankshaft with the help of connecting rod. The crankpin is important, allowing the connecting rod to be firmly connected with the crankshaft.
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Crankpin has a cylindrical surface that allows rotation force to be transmitted to the large end of the connecting rods (1). Some automakers also define crankpins as connecting rod journals.
Counterweights
Maintaining balance and stability in a crankshaft is important. The counterweights used for this purpose are usually mounted on the crank web.
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The rotation can often cause a counter-rotation that can impact the engine speed and performance during driving. Counterweights are installed to tackle this counter-reaction of crankshaft rotation (2). Counterweights also assist in smoothing the power supply to the engine and achieving higher RPMs in the engine.
Oil Passage and Oil Seals
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The oil passages in the crankshaft pass the oil from the main bearing journals to the big end journals. A hole is drilled on the crank web for oil passage. The oil usually passes to the big-end journals when the crankpin is in an upwards position.
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In this position, the combustion forces the connecting rod to move to a downward position. Suppose you have visually analyzed an opened engine. In that case, you might have observed that the crankshaft has some extent beyond the crankcase (4). So, the oil can leak from these ends, and oil sealings are provided to prevent the oil from leaking through these sealings. The oil seals can be connected at the front end/rear end or both ends of the crankcase.
Thrust Washers
Crankshaft can move lengthways, so two or more thrust washers are present in the crankshaft to prevent this movement. These are usually machined inside the crank web.
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Thrust washers can easily maintain the required gap inside the crankshaft, and the lateral movement can be alleviated (1). In modern engines, thrust washers are made part of main bearings. However, in some older engines, the washers must be placed individually.
Common Crankshaft Issues
Worn Journals
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The major problem in the engine’s crankshaft is the worn journals. This problem usually arises when the oil pressure in the engine is less.
The crankshaft converts the rotatory motion to the linear motion, and due to the limited pressure of oil, contact is generated with the engine bearings. As a result, the crankshaft is damaged (2). In addition, contact is generated between the oil layer between the journal and the bearing while converting the rotatory motion to linear motion. Still, due to less pressure, direct contact is generated with the bearings.
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As a result, the engine’s noise will be created, and the engine’s performance will become poor. Moreover, the metal of the bearings and the crankshaft will also get damaged, leading to engine failure.
This is because the metal will directly rub each other, and the friction will increase. This will become the reason for excessive heat production, ultimately affecting the engine. Besides, a copper sheen will be observed in the oil due to the worn journals. The bearing has three layers; the second layer is made of copper to provide extra efficiency. Still, due to the constant rubbing of the metals, this layer is mixed with oil and reduces the engine’s health (5).
Fatigue
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The second common issue in the crankshafts is fatigue. This issue usually takes place when different forces are applied to the crankshaft.
These forces are applied to the fillet. The fillet is the crankshaft part where the journal and web parts are connected. The fatigue on the crankshaft usually occurs due to cyclic transformations, heavy loads, or bending (3). Sometimes, the high temperature may also become the major reason for fatigue in the crankshaft. Thus, due to this issue, the vibrations are observed while driving, and there is a strong chance that a car may experience an accident. Therefore, an engine check light is indicated to warn regarding the issue to avoid this situation. Other than it, the major issue that occurs due to fatigue is that the engine takes time to get started, i.e., the spark produced in the combustion chamber is delayed. Also, the vehicle fails to accelerate at high speed.
Dirt Contamination
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Dirt particles are another reason for the faulty crankshaft. This is because the dirt particles will lead to the early failure of the bearing. This situation happens when due to the unfiltered oil, the dirt particles are gathered between the journal and the bearings.
These dirt particles then enter the bearings, rupturing the bearing lining due to constant contact. As a result, the performance of the bearings is impacted (5). In addition, the dirt between the bearings also causes an interruption in the oil circulation. Thus, the bearings and other parts of the crankshaft is not well lubricated and produce heat. This issue will lead to the engine failure of the vehicle.
Common Symptoms of a Bad Crankshaft
Following are a few common symptoms of a bad crankshaft:
Difficulty in Engine Start and Stalling
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The most common symptom of a bad crankshaft is difficulty starting the vehicle. If there is difficulty in rotating the crankshaft, or it is broken, then the crankshaft position sensor will analyze the error.
This will cause difficulty in starting the engine. So, you should check both the crankshaft and the crankshaft sensor to check the reason for the difficulty in starting the engine. Another symptom associated with a bad crankshaft is a stalling engine (3). Suppose the crankshaft has gone bad, or there is an issue in the wiring of the crankshaft position sensor. In that case, the sensor will send a signal to ECU, causing a stall in the started engine. Although a simple wiring problem can also cause difficulty in engine starting and engine stalls, it can be caused by a more severe issue such as a bad crankshaft.
Misfiring Engine and Vibration
Misfiring cylinders and vibration in the engine is other symptoms illustrating that the crankshaft has gone bad. A bad crankshaft will result in the sensor reporting wrong information to the piston impacting its positioning during the combustion process.
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Hence, the respective engine cylinder will misfire. A bad crankshaft can be due to dirt contamination that can impact the sensor readings resulting in misfiring engines. Similarly, a bad crankshaft will also cause the engine to vibrate (5). So, suppose you are feeling uneven acceleration or vibration in the engine. In that case, checking the crankshaft or its sensor is recommended.
Reduced Gas Mileage
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Due to improper conversion of the reciprocating motion into rotational motion, your car might face gas mileage issues.
In this case, the fuel injector sensors will need to receive the right information to inject the right fuel stream into the cylinders. Thus, your engine will use more fuel on short or long drivers impacting the fuel mileage (3). So, you listen to the knocking engine sounds and reduced fuel mileage. In that case, there is a possibility that the crankshaft has gone bad and needs replacement/repair.
Conclusion
To conclude, the crankshaft is an essential engine component that helps convert the piston’s reciprocal motion into the flywheel’s rotational motion. So, the power is uniformly supplied to the vehicle. However, with the passage of time, and bad service maintenance, the crankshaft can face the issues of fatigue, worn-out journals, and dirt contamination. In this case, the drivers will face difficulty starting the vehicle, vibrations, and reduced gas mileage issues. Therefore, getting the crankshaft issue resolved soon to avoid further engine damage is recommended if you face such issues.
FAQs
If the crankshaft is damaged, you might hear a knocking engine sound or notice a significant decrease in the fuel average of your vehicle. In addition, if the sensor/crankshaft is severely damaged, the engine might not start or shut off after starting. Therefore, you should resolve the damaged crankshaft issue soon to avoid engine damage/seizing.
Suppose the engine is starting and the car is driving. In that case, you can drive the car with a damaged crankshaft for intermediate distances. But if the crankshaft is broken, it is recommended to replace the shaft, as the engine will not function with a broken shaft.
Yes, you can repair the crankshaft, given the type of damage. For example, suppose the leading journal, counterweight, or crankpin is damaged. In that case, replacing these components is better than replacing the crankshaft. But if the shaft is broken, then it is better to replace the crankshaft for a seamless driving experience.
