Crankcase – Types, Design and Common Failures

In car engines, crankcases are very important parts. They are structural parts like engine blocks. As its name implies, it contains the crankshaft inside it. So, we need to consider the crankcase as a very important structural part. Here you can find detailed information about these systems, types, designs, and common failures.

What is Crankcase?

A crankcase is a structural engine part that contains the crankshaft. You can find the important structural design sections on these parts to house the crankshaft. For example, there are holes where the bearings of the crankshaft are attached.

Crankcases have lots of kinds of designs according to the type of engine. Also, there are different types and shapes of them. They can contain other parts of the engines according to the type.

For example in four-stroke engines, there is an oil sump at the bottom of the crankcase where the engine lubrication oil resides. So, this lubrication oil is pumped to the other moving sections of the engine. You can understand that crankcase has different kinds of applications containing the crankshaft.

Again in the two-stroke engines, there is no oil sump in the structure of this part. And air-fuel mixture comes from the crankcase which is very different if we compare it with the four-stroke engine ones. So, this is a different structure and duty of crankcase.

Types of Crankcases

Crankcases are different in structure in different kinds of engines. You can see the general types of crankcases as you see below. The general types are;

• Combustion gas ventilation
• Oil circulation
• Lubricating crankcase
• Crankcase and compression
• Open crankcases

Combustion Gas Ventilated Systems

In most modern engine systems, some systems have built-in the crankcases of four-stroke engines. They are the ventilation systems to expel the combustion gases that infiltrated into the crankcase.

In the structures of the engine pistons, there are seals at the piston heads. These seals must prevent oil leakage inside the engines. And prevent the exhaust gas leakage into the crankcase. If there are lots of combustion gases inside the crankcase, the pressure inside it will increase and other systems may not work properly.

So, there are combustion gas ventilation systems in the structures of crankcases. These ventilation systems are expelling these gas leaks into the pistons. So, they are very important systems in modern engines with four-stroke cycles.

Oil Circulation Systems

In most internal combustion engines, oil circulation is a very important task. And crankcase has a very important duty in this circulation. There is an oil sump structure at the bottom of the crankcase that contains the engine oil inside it.

The engine oil goes through an oil filter and an oil pump pumps the engine oil to the connecting rods and engine walls. This oil comes into contact with the moving parts of the engine and the cylinders. And the oil drips from the engine parts to the oil sump again.

But the crankshaft does not contact the engine oil. Because the movement of the crankshaft may lead to a problem of frothing the oil become useless in the engine. So, the oil-circulated systems are another important feature of the four-stroke engine crankcases.

Lubricating Crankcase Systems

In most, two-stroke engines, the crankcase structures are very important to take the air-fuel mixture inside the cylinder. And the air-fuel mixture is taken inside the crankcase and directed to the cylinder head.

But in the bigger systems, we do not use air-fuel mixture crankcase relation. In these systems, there is a crankcase that we use only for lubrication purposes. So, their structures are the same as the four-stroke engines.

Crankcase Compression

These systems are the most basic internal combustion engine systems. They include an intake of air-fuel mixture and exhaust of it. And there are no valves for these systems. The downward motion o the cylinder takes the air-fuel mixture inside the crankcase. This downward motion creates a suction effect on the gases.

And the upward motion expels the exhaust gases and between the downward and upward movement, combustion takes place. So, the crankcase is full of the air-fuel mixture.

The lubrication system is also different from the other types. The oil is mixed with the fuel that is injected into the system. So, oil burns with the fuel in these systems.

In general, two-stroke systems are common in smaller applications such as motorcycles, gardening appliances, etc.

Open Crank Engines

In these engine systems, no crankcase contains the crankshaft systems. So, the crankshaft and other engine parts are open to the atmosphere. These systems have many downsides. For example, the lubrication in these systems is not efficient enough.

Big ship engines are open crank engines in general.

Crankcase Materials

In the design of the crankcase, they use different kinds of materials for different applications. The most general materials are;

• Cast iron
• Aluminum alloys

Actually, the materials are same as the engine blocks. And in most internal combustion engine systems, they manufacture the crankcases as unitary parts with the engine blocks.

The material of a crankcase must be solid enough to withstand the high external moving actions of the other parts of engines. For example, the material should not be affected by the rotation of the crankshaft. And also, they have enough mechanical strength to carry the other engine parts.

The thermal and vibrational characteristics of the engine crankcases are very important also. They must possess very good thermal conductivities and the characteristics must not change with the increasing temperatures. The vibration absorption capabilities of these materials are also very important.

Cast Iron

If we consider all the parameters above, cast irons are superior materials for crankcase applications. Because they have very good mechanical characteristics and hard materials. And they are tough enough to withstand the external dynamical effects.

And also, cast iron materials are very good in thermal conduction which makes them also very good for this application. The vibrational characteristics of these materials are also very important.

In the common cast iron applications the percentages of the elements;

• 91.2-97.3% of iron,
• 2-4% of carbon
• 0.3-1% of manganese
• 0.1-0.5% of phosphorus
• 0.3-3% of silicon

These are the general percentages of the cast iron materials that we use in the crankcase designs.

Aluminum Alloys

In engine block and crankcase applications, aluminum alloys are also very common materials. Their structural properties are satisfactory for engine applications in middle sizes. Also, they have lower in weight if we compare with cast iron.

The thermal and vibrational characteristics of aluminum alloys are similar to cast iron materials. So, this makes them proper materials for crankcase applications.

Crankcase Manufacturing

Crankcases are very complex systems to manufacture. Because, they have lots of ventilation holes, holes, and sections for the attachment of the other engine parts. So, they are very complex structures that we need to use different manufacturing methods. 

The most general production technique is sand casting for engine crankcases. In sand casting applications, we can obtain very complex shapes with good surface characteristics. But, preparing the models and cores, and the sand are the main important labor things.

Also, we need to design the crankcase system to be appropriate for the sand casting applications. We can produce the shape of these systems in sand casting operations. Furthermore, the placement of cores to obtain the internal structures is also very important.

After the sand casting operations, we need extra machining and finishing operations to obtain the general structures of crankcases.

Additional machining operations may be required to obtain the surface textures and surface characteristics that we need from the crankcases. For example, the attachment holes of the bearings of the crankshaft have a tight tolerance for their assembly of them. So, we can apply extra milling operations to obtain these structures.

And also, as additional surface finish operations that we may use to obtain the surface characteristics.

General Crankcase Failures

Like the other mechanical systems, we deal with the failures of crankcases. These are the general symptoms that we can have from the crankcase systems. But in general, crankcase ventilation system failures are the most common problem.

Oil Leakages

This is the most common problem that people deal with in their crankcase. If there are leakages at the bottom of your engines, you will see oil drips at the bottom of the car that you parked.

The main cause of this problem can be the excessive pressure at the crankcase because of the exhaust and oxygen gas build-up. So, these excessive gases can be a problematic issues like oil leakages. There can be a problem with the PCV valves in your crankcase that expels the excessive exhaust gases and air from the crankcase.

Engine Performace Decrease

An increase in the gas mileage and a decrease in the engine performance can be the symptoms that you to have crankcase problems. The oil inside the crankcase will be contaminated because of the other gases. And the filthy oil will lead to the problem with a decrease in engine performance. Again, it will be a very good start to be suspicious about PCV valves.

Conclusion on Crankcases

As you see above, the crankcases are very important structures in internal combustion engines. They contain the oil that lubricates the engine parts. And also, it is the housing that contains the crankshaft.

There are different structures and types of crankcases in different engines. These structure changes occur because of the working principles of engines. But the main difference arises between the two-stroke and four-stroke engines.

Also, the materials differ according to the size and applications of the crankcases. In general, cast iron and aluminum alloys are the common materials that we use in crankcase applications. This is because they possess very good structural and thermal capabilities.

Around the general crankcase malfunctions, the failure of the PCV valve is the most common one. The outcomes of the failure of these valves can be very problematic for your engine. Because, when this valve does not work properly, the pressure build-up can be a problematic issue.

These are the general points about the engine crankcases.

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FAQs About Crankcases