Auto and Shop Information Study Guide for the ASVAB
The Auto and Shop Information section of the ASVAB test measures your knowledge of vehicles and their parts, as well as the basic tools and practices used in automotive shops. This section is more in depth, as it requires students to know about the different components of vehicle engines and operating systems, as well as the proper tools for different purposes and their protocols as used in shops.
When studying for this section of the test, pay close attention to the different components involved in a functioning vehicle, the common practices followed in automotive shops, and the different types of equipment used.
To answer the auto questions, you will need to know about automobile parts and systems. The parts are the smallest items contained in a car, and the systems use those parts to achieve a general function. We have organized our outline below by systems, but also be alert for the names of parts you’ll need to know.
The shop information here is organized by tool purposes. Tools can be grouped by what general types of tasks they are used for. Be sure to note fine differences in the names of tools.
The paper and pencil form of the ASVAB test combines auto and shop topics into one section, with a total of 25 questions to be completed in a maximum of 11 minutes. If you take the CAT version of the ASVAB, you will see two separate sections: Auto Information, which has 11 questions and seven minutes to answer them, and Shop Information, which gives you six minutes to answer 11 questions.
As with many tests, be sure to focus first on the questions familiar to you. Complete all simple or familiar questions before coming back around to more difficult questions. If you do not know the answer, make an educated guess and move on. Implementing both these tricks and doing adequate studying should result in a desirable score.
Auto: The Engine
In this section, we will examine the basic concepts of the internal combustion engine. You will learn about the various types of engines and their cooling and lubrication systems.
What Does the Engine Do?
The engine is the heart of a car, and its primary function is to convert the chemical energy stored in fuel into mechanical energy that propels the car. In a car, the engine is typically an internal combustion engine, which works by burning fuel inside the engine to produce heat, which is then converted into mechanical energy.
Parts of an Internal Combustion Engine
The camshaft is a mechanical component in an engine that controls the opening and closing of the engine’s valves. It works by converting the rotational motion of the engine’s crankshaft into a reciprocating motion that opens and closes the valves in a precise sequence, which allows air and fuel to enter the engine’s combustion chambers and exhaust gases to exit.
The camshaft is a critical component of the engine’s valve train, and its location and design have a significant impact on the engine’s performance and efficiency. The following terms are related to the camshaft:
timing belt/chain—The timing belt or chain is a component that connects the camshaft to the crankshaft and ensures that the valves open and close at the correct time.
overhead valve (OHV) and overhead cam (OHC)—These terms refer to the location of the camshaft relative to the engine’s cylinder head. In an OHV engine, the camshaft is located in the engine block, and pushrods are used to actuate the valves in the cylinder head. In contrast, an OHC engine has the camshaft located in the cylinder head and operates the valves directly. OHC engines tend to be more efficient and produce more power compared to OHV engines.
single and double arrangements—This refers to the number of camshafts in an engine. A single overhead cam (SOHC) engine has one camshaft that operates all the valves, while a double overhead cam (DOHC) engine has two camshafts, with one dedicated to the intake valves and the other to the exhaust valves. DOHC engines are commonly found in high-performance engines, as they allow for better valve control and higher revving capability.
A combustion chamber in an internal combustion engine is the space where the air-fuel mixture is burned to produce heat energy, which is then converted into mechanical energy. It is typically located in the cylinder head of the engine, and its design plays a crucial role in determining the engine’s performance and efficiency.
A connecting rod in an internal combustion engine is a mechanical component that connects the piston to the crankshaft. It converts the reciprocating motion of the piston into rotary motion of the crankshaft, which is used to drive the vehicle’s wheels. The connecting rod is an important component of the engine’s bottom end and is subjected to significant stresses and forces during operation.
A crankshaft is a mechanical component that converts the reciprocating motion of the pistons into rotary motion, which is used to drive the vehicle’s wheels. It is typically located in the engine block and is connected to the pistons via the connecting rods.
The cylindrical chamber is where the air-fuel mixture is compressed and burned to produce heat energy, which is then converted into mechanical energy. The cylinder houses the piston, which moves up and down to compress the air-fuel mixture and extract mechanical energy from the combustion process. Engines can have multiple cylinders, and the number and arrangement of cylinders impact the engine’s performance and characteristics.
The cylinder head is a component that sits on top of the cylinder and seals the combustion chamber. It typically contains the intake and exhaust valves, which are operated by the camshaft, and other components, such as the spark plug and fuel injector. The cylinder head plays a critical role in controlling the flow of air and fuel into the engine and exhaust gases out of the engine.
A multi-valve cylinder head is a type of cylinder head that has more than two valves per cylinder. In contrast, a standard cylinder head typically has one intake and one exhaust valve per cylinder. Multi-valve cylinder heads can have three, four, or more valves per cylinder, depending on the engine’s design.
An engine block in an internal combustion engine is the main structural component that houses the cylinders, pistons, and other components. It is typically made of cast iron or aluminum and is responsible for supporting the engine’s weight and providing a rigid mounting point for the various engine components. The engine block contains passages for coolant, oil, and other fluids and is designed to withstand the high pressures and temperatures of the combustion process.
An exhaust valve is a mechanical component that allows the exhaust gases to exit the engine’s combustion chamber. It is located in the cylinder head and is operated by the camshaft, which opens and closes the valve at the appropriate time in the engine’s cycle.
An intake valve is a mechanical component that allows the air-fuel mixture to enter the engine’s combustion chamber. It is located in the cylinder head and is operated by the camshaft, which opens and closes the valve at the appropriate time in the engine’s cycle.
Pistons are cylindrical components that move up and down inside the engine’s cylinders. They are connected to the engine’s crankshaft via the connecting rod and are responsible for compressing the air-fuel mixture and extracting mechanical energy from the combustion process. Piston rings are small metal rings that fit into grooves on the piston’s outer surface. They provide a seal between the piston and the cylinder wall, which prevents the air-fuel mixture and combustion gases from leaking past the piston. Piston rings also help to regulate the amount of oil that enters the combustion chamber to lubricate the cylinder walls, ensuring smooth operation and minimizing wear and tear.
Wrist pins in an internal combustion engine are small, cylindrical components that connect the piston to the connecting rod. They are typically made of steel or other high-strength materials and are responsible for transmitting the reciprocating motion of the piston to the connecting rod, which in turn rotates the crankshaft to generate mechanical energy.
How the Engine Operates
The four-stroke cycle in an internal combustion engine is a process that converts fuel into mechanical energy to power a vehicle. A “stroke” refers to the movement of the engine’s piston inside the cylinder during each phase of the cycle. There are two types of strokes: upward (also called compression stroke) and downward (expansion or power stroke).
Each of the four stages in the cycle—intake, compression, combustion, and exhaust—corresponds to one stroke (either upward or downward) of the piston. Here’s a simple explanation of each stage:
intake—During the intake stroke, the engine’s piston moves down, creating a vacuum that draws in a mixture of fuel and air through the intake valve into the cylinder.
compression—As the piston moves back up, it compresses the fuel-air mixture in the cylinder, making it highly dense and increasing its potential energy.
combustion—When the piston reaches the top, a spark plug ignites the compressed fuel-air mixture, causing it to burn and expand rapidly. This explosion generates a powerful force that pushes the piston back down, creating mechanical energy that moves the engine’s crankshaft. Note: In some sources, this stage is called the power stage.
exhaust—As the piston moves up again, it expels the burnt gases, or exhaust, through the exhaust valve, clearing the cylinder for the next intake stroke.
This four-stroke cycle repeats continuously, turning chemical energy from the fuel into mechanical energy to power the engine and, ultimately, the vehicle.
This diagram depicts the four-stroke cycle:
How Are Cylinders Arranged in the Engine?
Cylinders in an engine can be arranged in various configurations, each with its own advantages and characteristics. The most common cylinder arrangements in internal combustion engines are inline, V, flat, and radial. Here’s a brief overview of each:
inline (straight)—In an inline engine, all cylinders are arranged in a straight line along the same plane, one after the other. This configuration is simple, compact, and well balanced, making it popular for engines with a smaller number of cylinders, typically three, four, or six.
V—In a V engine, the cylinders are arranged in two separate banks, forming a “V” shape when viewed from the end. The angle between the banks can vary, depending on the specific engine design. V engines are compact and can accommodate a larger number of cylinders, such as six, eight, 10, or 12, making them popular for high-performance and larger vehicles.
flat (boxer)—In a flat or boxer engine, the cylinders are arranged horizontally in two opposing banks, with the pistons moving toward and away from each other. This layout offers a low center of gravity and smooth operation but can be more complex and take up more space width-wise. Flat engines are commonly used in Porsche and Subaru vehicles, with the most common configurations being flat-4 and flat-6.
radial—In a radial engine, the cylinders are arranged in a circle around a central crankshaft, with each piston connecting directly to the crankshaft. This configuration was widely used in early aircraft engines due to its compact size and high power-to-weight ratio. However, radial engines are less common in modern automotive applications.
What Is the Cylinder Firing Order?
Firing order refers to the sequence in which the cylinders in an internal combustion engine ignite the air-fuel mixture to generate power. The cylinder firing order is a crucial aspect of engine design because it directly impacts engine balance, smoothness, vibration, and overall performance. Proper firing order helps distribute the load evenly across the engine components and ensures efficient power delivery. The firing order is determined by the arrangement of cylinders in the engine and the crankshaft design.
Here are some common firing orders for different engine configurations:
inline-4—A common firing order for inline-4 engines is 1-3-4-2.
inline-6—A typical firing order for an inline-6 engine is 1-5-3-6-2-4. The inline-6 design has an inherent balance that allows for smooth running, and the firing order further reduces vibrations and harmonics.
V6—For V6 engines, a common firing order is 1-2-3-4-5-6 or 1-4-2-5-3-6, depending on the specific engine design. The V6 configuration requires careful consideration of firing order to minimize vibrations and ensure smooth operation.
V8—For V8 engines, popular firing orders include 1-8-4-3-6-5-7-2 and 1-3-7-2-6-5-4-8.
The firing order of an engine is typically stamped or engraved on the engine block, cylinder head, or intake manifold for reference during maintenance or repairs. It’s essential to follow the correct firing order to avoid engine damage, poor performance, or excessive vibrations.
A diesel engine, also known as a compression-ignition (CI) engine, is a type of internal combustion engine that uses diesel fuel for power generation. Unlike gasoline engines that rely on a spark plug to ignite the air-fuel mixture, diesel engines use the heat generated from compressing air in the cylinder to ignite the fuel. This is where the term “heat of compression” comes into play. Heat of compression refers to the heat generated in the cylinder when the air is compressed during the compression stroke. As the piston moves up in the cylinder, the air inside becomes highly compressed, causing its temperature to increase significantly. In a diesel engine, this temperature rise is enough to ignite the diesel fuel when it is injected into the cylinder. The diesel engine operates in a similar four-stroke cycle as a gasoline engine, with slight differences in the combustion process.
What Does an Engine Need to Operate Effectively?
An internal combustion engine needs three main components to operate efficiently: air-fuel mixture, ignition timing, and combustion. These three components are closely related, and any imbalance or inefficiency in one aspect can significantly impact the engine’s overall performance and emissions.
Air-fuel mixture refers to the combination of air and fuel that enters the engine’s cylinders. The air-fuel mixture is essential for the combustion process, as the fuel contains the chemical energy needed to generate power, while the air supplies the oxygen required for the fuel to burn. The engine’s performance, efficiency, and emissions are influenced by the ratio of air to fuel in the mixture, also known as the air-fuel ratio.
The stoichiometric ratio is the ideal air-fuel ratio at which the fuel is completely burned with no excess oxygen or fuel remaining. For gasoline engines, the stoichiometric ratio is approximately 14.7:1, meaning 14.7 parts air to one part fuel. Achieving this ratio ensures complete combustion, maximizing power output and minimizing harmful emissions.
In practice, fuel is atomized, or broken into tiny droplets, when it enters the cylinder to facilitate mixing with the air and promote efficient combustion. The air-fuel ratio can deviate from the stoichiometric ratio, resulting in either a lean or rich mixture:
lean mixture—A lean mixture contains more air than the stoichiometric ratio, meaning there is excess oxygen. While lean mixtures can improve fuel efficiency, they can also cause higher combustion temperatures, which may lead to engine knocking, reduced power output, and potential engine damage.
rich mixture—A rich mixture contains less air than the stoichiometric ratio, meaning there is excess fuel. Rich mixtures can provide more power in certain situations, such as during acceleration, but can also lead to increased emissions, reduced fuel efficiency, and fouling of spark plugs or catalytic converters.
Ignition timing refers to the precise moment when the air-fuel mixture in the cylinder is ignited to initiate the combustion process. In gasoline engines, the ignition is typically achieved by a spark from the spark plug. In diesel engines, the ignition occurs due to the heat of compression. Proper ignition timing is crucial for achieving optimal engine performance and efficiency, as it determines when the combustion process starts relative to the piston’s position and movement. If the ignition occurs too early or too late, it can lead to reduced power output, increased fuel consumption, and higher emissions.
Ignition timing is typically measured in degrees of crankshaft rotation relative to the piston’s position in the cylinder. There are two common terms used in ignition timing:
before top dead center (BTDC)—Ignition occurs before the piston reaches the top of its compression stroke.
after top dead center (ATDC)—Ignition occurs after the piston has passed the top of its compression stroke and is on its way down.
Combustion is the chemical reaction between fuel and oxygen that releases energy in the form of heat and pressure. In internal combustion engines, combustion occurs inside the cylinders, transforming the chemical energy stored in the fuel into mechanical energy to power the vehicle.
Pre-ignition and detonation are two abnormal combustion events that can cause engine damage:
pre-ignition—Pre-ignition occurs when the air-fuel mixture ignites prematurely, before the spark plug fires or before the fuel is injected in a diesel engine. This early combustion can cause high cylinder pressures and increased temperatures, leading to engine knocking, reduced performance, and potential engine damage.
detonation—Detonation, also known as engine knocking or pinging, is an uncontrolled and violent combustion event that occurs when the air-fuel mixture ignites spontaneously due to high pressure and temperature conditions in the cylinder. This creates pressure waves that cause a knocking or pinging sound and can result in engine damage, such as cracked or damaged pistons and cylinder heads.
Auto: The Cooling System
There are two types of cooling systems in a car: air-cooled and liquid-cooled. Most modern cars use a liquid-cooled system. The coolant system circulates a mixture of water and antifreeze (coolant) through the engine to absorb and dissipate heat. The coolant absorbs heat as it flows through the engine and is then pumped to the radiator, where it releases the heat to the atmosphere. This process helps to regulate the temperature of the engine and prevent overheating.
Parts of the Cooling System
The components of the cooling system work together to regulate the temperature of the engine and prevent overheating. They include:
water pump—It circulates the coolant through the engine and radiator.
radiator—It cools the coolant by transferring heat from the coolant to the air.
radiator cap—It regulates the pressure in the cooling system.
radiator hoses—They transport coolant between the engine and the radiator.
thermostat—It regulates the temperature of the coolant by opening and closing the flow of coolant to the radiator.
bypass tube—It ensures that coolant continues to flow through the engine when the thermostat is closed.
water jacket—It surrounds the engine cylinders and conducts heat away from them.
coolant recovery bottle—It allows for expansion and contraction of the coolant as it heats and cools.
Care of the Cooling System
To care for the cooling system in a car, it’s important to regularly check the coolant level, inspect the radiator and hoses for leaks or damage, and flush the system periodically to remove debris and contaminants. It’s also essential to use the correct type of coolant for the car and to replace it as recommended by the manufacturer. Neglecting the cooling system can result in engine overheating, which can lead to engine damage and expensive repairs.
Auto: The Engine Lubrication System
The lubrication system in a car is responsible for providing oil to the engine’s moving parts to reduce friction, heat, and wear. There are two main types of lubrication systems: wet sump and dry sump lubrication.
In a wet sump lubrication system, the oil is stored in a reservoir or pan at the bottom of the engine (the sump). A pump draws oil from the sump and sends it through an oil filter to remove contaminants. The oil is then sent through galleries or passages in the engine block to reach the crankshaft, connecting rods, and other moving parts. As the oil circulates, it lubricates the parts and absorbs heat before returning to the sump to repeat the cycle.
In a dry sump lubrication system, the oil is stored in a separate tank outside of the engine. A scavenge pump draws oil from the sump at the bottom of the engine and sends it to the external tank. A pressure pump then draws oil from the external tank and sends it through an oil filter before circulating it through the engine block, as in a wet sump system. The advantage of a dry sump system is that it allows for better oil control and scavenging, especially during high-performance driving, where oil pressure and flow need to be precisely controlled to avoid engine damage.
Components and Functions of the Lubrication System
The key parts of a lubrication system include:
oil pan—This is the reservoir that holds the oil.
oil pump—This is the device that pumps oil from the oil pan to the engine.
oil filter—This is the component that filters contaminants from the oil.
oil galleries or passages—These are the channels in the engine block that direct the oil to various engine components.
pressure relief valve—Also known as a pressure regulating valve, this component of the car’s lubrication system helps to regulate the oil pressure in the engine. The valve is typically located within the oil pump or the oil filter housing and is designed to open when the oil pressure in the engine exceeds a certain level.
The lubrication system works by pumping oil from the oil pan through the oil pump, oil filter, and galleries or passages in the engine block to reach the crankshaft, bearings, and other engine components. The oil lubricates the engine parts, reducing friction and wear and carrying away heat. As the oil circulates, it also picks up contaminants, which are removed by the oil filter. The oil then returns to the oil pan to repeat the cycle. A healthy lubrication system is crucial to the longevity and proper functioning of the engine, and regular oil changes and maintenance are necessary to ensure its effectiveness.
The lubrication system in a car has several essential functions that help to maintain the engine’s health and longevity. One of the most important functions is lubrication, where oil is used to reduce friction between engine components and ensure smooth engine operation. Another function is sealing, where the oil functions as a sealer between the piston, piston rings, and engine cylinder walls, which helps to seal combustion gases within the combustion chamber for efficient engine operation. The system also has a cleaning function, where additives in the oil help to suspend contaminants, allowing them to be removed by the oil filter. Additionally, the use of motor oil helps to reduce engine noise and allows the engine to run more quietly.
The Importance of Engine Oil
Engine oil is a crucial component of the car’s lubrication system, as it helps to reduce friction between engine components, cool the engine, and remove contaminants from the engine. The oil is typically made of a base oil, such as mineral or synthetic oil, and additives that improve its performance, such as detergents, viscosity modifiers, and anti-wear agents.
The importance of using the correct oil for a car cannot be overstated. Using the wrong type of oil or low-quality oil can result in poor engine performance, reduced fuel efficiency, and premature engine wear. On the other hand, using high-quality oil that meets the car manufacturer’s specifications can help to prolong the engine’s life, reduce engine wear, and improve overall performance.
Engine oil is rated by viscosity, which is the oil’s resistance to flow at a certain temperature. The Society of Automotive Engineers (SAE) developed a grading system that uses a number to represent the oil’s viscosity at different temperatures. The lower the number, the thinner the oil, and the higher the number, the thicker the oil. For example, SAE 5W-30 oil is thinner at low temperatures than SAE 10W-30 oil, but it has the same viscosity at high temperatures.
Diesel oil is formulated differently than gasoline engine oil because diesel engines operate at higher temperatures and pressures than gasoline engines. Diesel oil typically has more detergents and additives to protect against soot and other contaminants that diesel engines produce more of than gasoline engines. Diesel oil also has higher levels of zinc and phosphorus to protect against wear and corrosion.
All Study Guides for the ASVAB are now available as downloadable PDFs