Internal combustion engines are the power units responsible for spinning the wheels in automobiles, and they do this by converting chemical energy into mechanical energy. To put that more simply—an internal combustion engine makes it possible to burn fuel (chemical) which, in turn, makes the wheels of the car move (mechanical). Combustion in this case is referred to as “internal” because the fuel-burning process occurs inside an engine.
To understand how an engine works, this piece will discuss all its main parts and the role that each part performs in the overall operation of a car engine.
An engine block—also known as “cylinder block” or simply “block”—is a metallic structure that contains the major parts of an internal combustion engine. It is cast with cylindrical hollows (called cylinders), oil ducts, and coolant passages. In most modern cars, engine blocks are made from aluminum alloys, while in trucks and older vehicle models, engine blocks are made from cast iron.
Common Causes of Engine Block Failures
Engine blocks are designed to last, but some causes can shorten their useful life.
1. Leakage – if you notice a puddle of liquid under the engine, that’s a sign that there could be a leakage. Leaks could come from the radiator, heater core, water pump, loose hoses or freeze out plugs, or even a crack in the block itself.
2. Worn cylinder – the walls of a cylinder may wear out and crack. Seriously damaged cylinders or engine blocks will have to be rebuilt.
3. Porous block – poorly-cast materials may cause porosity in the engine block. No amount of repairing can solve porosity in an engine block. If you detect this condition and it is still within the warranty period of the manufacturer, you can have the engine block replaced completely.
The cylinders, cylinder head, and the pistons collectively make up the combustion chamber, which is the engine part where all the explosive action happens. You can think of the cylinders as the sides, the cylinder head as the top, and the pistons as the bottom of the combustion chamber.
Pistons are the small cylindrical moving pieces inside a combustion chamber. These small cylindrical pieces (pistons) slide up and down inside the cylindrical hollows (cylinders) and are tightened by piston rings. When combustion takes place, the explosive force pushes the pistons down. The movement of the pistons works the crankshaft to do its job.
This piston type is one of the oldest designs used for internal engines. It does not only function as a piston but also acts as a cylindrical crosshead. It is longer than it is wide and has a groove for an oil ring below the gudgeon pin. Back in the days, trunk pistons were used mainly for diesel and petrol engines.
Low-speed engines typically use crosshead pistons to reduce the sideways forces acting on the piston.
Common Problems Involving the Pistons
The following are common issues involving the pistons:
1. Overheating – bent or blocked injection oil, improper piston installation, malfunctions in the cooling system, and restrictions in the linear surface area may cause overheating. Overheating may damage the bore on the cylinder head, which will affect the piston’s performance.
2. Breakage of the piston crown – faulty injection nozzles and inefficient cooling systems may cause the piston crown to crack.
3. Impact marks – protrusion of the piston, excessive machining, carbon deposits, insufficient valve clearance, and incorrect valve recess may cause impact marks.
Piston rings help to seal the chamber where the pistons move. There are a number of piston ring types used for various engines, and they are:
1. Compression piston rings – this type was developed to help seal in the combustion gases and transfer heat from the piston to the piston walls.
2. Wiper piston rings – this type is often called backup compression or Napier rings, and was designed to act as backup in preventing leakage and ensuring that the linear surface is kept clean from excess oil. It has an angled surface which cleans or wipes excess oil from the surface to ensure that the engine functions optimally.
3. Scrapper piston rings – also referred to as oil control rings, scrapper rings are responsible for controlling the amount of oil that passes between the cylinder walls. They spread the oil evenly around the circumference of the linear surface. They have holes on their radial center, which allows scrap oil to flow back to the crankshaft and not down to the other parts of the engine.
Underneath the engine block is the crankcase. It houses the crankshaft, which is the part of the engine that transforms the linear motion of the piston into the circular motion that drives the wheels to move. Crankshafts are designed to withstand high degree of wear-and-tear and constant torsional vibrations from abrupt acceleration and deceleration. For this reason, they are forged from nitride steel or alloyed heat-treated steel.
The Main Components of a Crankshaft
1. Journals – these are the parts of the crankshaft that rotate inside a bearing. There are two kinds of journals, namely:
- main bearing journal – a.k.a. main journal; defines the axis of rotation of the crankshaft
- connecting rod journal – a.k.a. rod journal, crank pins, big-end journals; connects to the big end of the connecting rods
2. Crank webs – the parts that connect the bearing journal to the rod journal.
3. Counterweights – these are lobes that balance out the strong forces acting on the crankshaft.
At the bottom of the crankcase is an oil pan where the oil pump is located. An oil pump is often referred to as the heart of a car engine’s lubrication system. It is designed to draw oil and circulate it. It helps to steady the oil pressure and regulate the temperature in the car. An oil pump that stops working almost always leads to the total failure of the engine.
How an Oil Pump Works
Through the pipe referred to as pickup pipe, the oil pump is able to suck up oil. The nozzle of this pipe is located below the level of oil and is fitted with a filter that keeps particles from getting into to the pump. Oil pumps are also referred to as "positive displacement pumps," because the amount of oil that enters is the same amount that leaves. The amount of oil conveyed from one part of the engine to another depends entirely on the speed, size, and design of the pump.
Why Engines Need to be Oiled
An engine should be lubricated for the following reasons:
- To prevent friction or any form of wear on all the sliding components of an engine
- To ensure that the engine components are properly cooled to prevent overheating
- To protect the engine from corrosion
- To reduce vibration and noise
- To seal the contact surface between the cylinder walls and the piston
The camshaft is often referred to as the brain of an engine because it is the part that controls the amount of combustible mixture that the engine takes in and pushes out. It works with the crankshaft and a timing belt to ensure that the valves close and open with precise timing. Camshafts are commonly made from cast iron, heat-treated steel, or nitrided steel.
A connecting rod is a rigid piece that connects a piston to the crankshaft, but aside from this connecting function, it also transmits power from the piston to the crankshaft.
Rods are typically made of micro-alloyed steel to ensure high strength. They can also be made from high-grade aluminum (light and capable of absorbing high impact) or titanium (light and incredibly strong for high-performance engines).
Problems with Connecting Rods
Connecting rods are constantly under stress, which continues to increase as the speed of the engine increases. They are subject to tension and compression. A common rod failure, referred to as "throwing a rod", may even lead to engine failure.
Valves are the parts of the engine that allow the combustible mixture to flow in and out of the system. Inlet valves open to admit the fuel-and-air mixture, while exhaust valves allow the burned gas to escape. The valves have to open and close with precise timing to ensure the engine’s optimum performance.
A cylinder usually has one inlet and one outlet valve, but it’s not uncommon for some cars to have multi-valve cylinders especially for high-performance cars. The use of multi-valve systems allows engines to breathe and perform better.
A cylinder head is a metallic piece located on the upper part of the cylinders with circular hollows cast on it. It’s where the valves, fuel injectors, and spark plugs are mounted. The material commonly used in the production of cylinder heads is cast iron because it is durable and inexpensive. The downside, though, is its low efficiency in dissipating heat. For this reason, most car engine manufacturers prefer to use aluminum cylinder heads, which are lighter and more efficient in dissipating heat especially for high-performance vehicles like race cars and other fast vehicles.
Functions of the Cylinder Head
Some of the main functions of a cylinder head include the following:
- seals the combustion chamber
- acts as conduit to enable the fluid mixture to reach the combustion chamber
- circulates the coolant to help dissipate heat
Problems with Cylinder Heads
When an engine overheats, it causes a host of problems. It may cause the cylinder head to crack or be damaged. A crack may cause oil to seep into the combustion chamber and affect the engine’s performance. When this happens, there would be a need to change or replace the engine, which is going to be expensive.
More Than the Sum of Parts
As you familiarize yourself with each part as discussed in this article and other references, it would be a good idea to remember what Aristotle said. The whole is more than the sum of its parts, so to speak. Take time to know how one component, regardless of how seemingly small or unimportant it is, affects the whole engine.
Thank you for taking the time to read this piece. If you found it useful or have questions, please let me know by emailing me at firstname.lastname@example.org. You may also want to read my other piece on How a Car Works from A to Z!