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Page 1 - Auto and Shop Information Study Guide for the ASVAB

General Information

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 very 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 being used.

The paper and pencil form of the ASVAB test combines auto and shop 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 to be answered in seven minutes, and Shop Information, which allows six minutes to answer 11 questions.

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.

Study Tips

There is a great deal of information contained in this study guide. Don’t be overwhelmed. As you go through it, keep in mind the following overall understandings you will be expected to have.

What to Know about Engines

Study the basic engine components and how they function—including how different parts of the car interact with the engine, how fuel enters and supports the engine, and how the electrical components of the vehicle impact the overall function of the engine. Also, know how the engine will react to malfunctioning equipment, such as a fuel injector or thermostat, and be familiar with the different engine types and sizes, as well as their maintenance and repair.

What to Know about Operating Systems

The operating system of a vehicle covers all aspects of a vehicle except the engine. This includes the transmission, electrical system, brakes, steering, and ignition. To prepare for this, you should know the basics of these systems. Learn how to identify problems with any given system and its different components and functions. You must know the purpose of a transmission, the importance of accurate steering and brakes in a vehicle, and the potential dangers present in the electrical systems of vehicles.

In addition to the basic functions of different vehicle systems, students must also understand how computers come into play in the overall operation of vehicles. This includes knowing different codes displayed by vehicle computer systems and how to respond to these codes. Though older vehicles may not have computer-based reactions, all new vehicles come equipped with computers able to connect all aspects of a single vehicle.

What to Know about Shop Tools and Procedures

Shops contain numerous tools and types of equipment that must be accurately identified and used by all workers. When studying for this portion of the test, work to identify basic types of tools, as well as more specific or specialized tools. Also, familiarize yourself with the larger tools and equipment used in automotive shops. This may be as common as lifts used to suspend cars during work, or as small as a heavy-duty drill designed to remove high-pressure bolts.

Apart from tools, you must be able to identify the proper procedures used in shops, particularly automobile garages—such as safety tips and tricks or the operation of heavy machinery. Also, study different machines, including how they are used, what purpose they serve, and the proper safety procedures to follow during use.

Basic Test-Taking Hints

As with all 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 studying adequately should result in a desirable score.

Auto: Engine Systems

In this section, we will examine basic concepts of the internal combustion engine. You will learn about the various types of engines and their cooling and lubrication systems.

Engines and Engine Theory

The engine is the power plant of a vehicle, converting the up-and-down motion of a piston to circular motion that can turn wheels on a vehicle and electromagnetic rotors on generators.

The pistons’ up-and-down motion results from fuel burning in a combustion chamber, causing trapped gases to expand. Hence the name internal combustion engine (ICE).

Parts of an Internal Combustion Engine

Engine block—The engine block is the largest single piece of metal on the engine and is the foundation for the engine. The block is where mechanical energy is converted from the combustion of air and fuel. Therefore, it must be strong enough to contain thousands of explosions per minute for many years. It includes passages to circulate oil for lubrication and coolant to control engine temperature. Additionally, it must provide attachments for all the other parts of the engine. To make a single piece to supply all these functions, the block is cast from molten metal. Earlier blocks were made from iron for strength. Today, most blocks are made from an aluminum alloy—being considerably lighter while still durable—for greater fuel efficiency.

Piston—A piston is a cylinder-shaped item with a solid crown (top) that goes up and down in an engine’s cylinders. The piston is pushed by hot gases created by the combustion of the air-fuel mixture to perform the actual work.

Cylinder—The cylinder acts as a guide for the piston, allowing it to travel up and down as the engine finishes its cycle.

Piston rings—Piston rings seal the piston to the cylinder, preventing combustion gases from escaping. Oil rings prevent oil from entering the combustion chamber from the engine crankcase.

Wrist pin—The wrist pin joins the piston to the connecting rod and acts as a pivot point for the connecting rod’s small end to move on.

Connecting rod—The piston/wrist pin system is connected to the crankshaft by a connecting rod. A large end of the connecting rod connects to the crankshaft on the connecting rod journal.

Crankshaft—The piston’s linear (straight line) motion is converted into rotational motion by the crankshaft, which can subsequently be utilized to power a vehicle or drive an accessory.

Combustion chamber—The actual combustion of the air-fuel mixture takes place in the combustion chamber, which is located directly above the piston in the cylinder head.

Intake valve—The intake valve brings the air-fuel mixture into the combustion chamber. In a closed position, it must seal off the combustion chamber from the intake port.

Exhaust valve—Waste gases are evacuated from the combustion chamber using the exhaust valve. In a closed position, it must seal off the combustion chamber from the exhaust port.

  • Cylinder head—The combustion chamber, intake and exhaust valves, and intake and exhaust ports are all housed in the cylinder head, situated above the piston.

  • Multiple-valve cylinder head—Engines can also be categorized based on how many valves are utilized for each cylinder. A two-valve cylinder head, with one intake valve and one exhaust valve per cylinder, is the least expensive and most prevalent configuration. A multiple- (more than two) valve (more than two) cylinder head can be designed to enhance airflow through the engine and, as a result, engine performance.

Camshaft—The intake and exhaust valves of the engine are opened and closed by the camshaft. The camshaft rotates at half the speed of the crankshaft in the engine.

  • Camshaft location—Camshaft location is another classification used to classify automotive engines. The camshaft, which is controlled by the crankshaft via a timing chain or timing belt, is responsible for opening and closing the engine’s valves. The intake and exhaust valves are situated in the cylinder head in some modern engines, while the camshaft is located in the engine block. This type of engine is known as an overhead valve (OHV) engine since the valves are situated above the piston and the combustion chamber. Engine designers frequently place the camshaft above the valves, eliminating the need for pushrods in an OHV configuration. The valve’s operating principle becomes more straightforward and lighter. With less mass in the valve train, higher engine speeds are possible. Such design is defined as an overhead cam (OHC). Going to a double overhead cam (DOHC), the configuration is a final stage that allows for even higher engine speeds. This installs two camshafts in each cylinder head, one for controlling the exhaust valves and the other for controlling the intake valves.

Engine Operation Concepts

The Four-Stroke Cycle

A four-stroke cycle is being used in the majority of internal combustion engines. This indicates that one cycle of events takes four piston strokes to complete. A stroke is a movement of the piston from the top of its travel in the cylinder (known as top dead center or TDC) to the bottom of its travel (known as bottom dead center or BDC) and back to TDC.

1. Intake stroke—The intake stroke is the first stroke of the four-stroke cycle. During this stroke, the piston moves down the cylinder, opens the intake port valves, and pulls in air through the intake ports. At the same time, the fuel injector sprays fuel into the cylinder combustion chamber.

2. Compression stroke—The compression stroke closes the intake port valves, with the piston moving up the cylinder, compressing the air-fuel mixture.

3. Power stroke—The spark plug provides an electric spark during the power stroke in the cycle. The compressed air fuel ignites and burns, forcing the piston down the cylinder.

4. Exhaust stroke—During the exhaust stroke, the piston moves up the cylinder, releasing the burned gases through the exhaust port, emptying the combustion chamber.

This diagram depicts the four-stroke cycle:

1-four-stroke-cycle.png

Cylinder Arrangement

The configuration of an automotive engine can vary considerably, and this can most easily be classified according to the cylinder arrangement, which represents the relative position of the various cylinders. Automotive engines typically have four, six, or eight cylinders, but some models have three, five, 10, 12, and even 16 cylinders. The following are the main cylinder arrangements in modern vehicles:

  • Inline design
  • Horizontally opposed or flat design
  • V-type design
Firing Order

The firing order refers to the sequence in which the cylinders fire. For four-cylinder engines, 1-3-4-2 is a common firing order. This means that when the first cylinder fires, the crankshaft will turn half a turn, and so on. On the first turn of the crankshaft, cylinders 1 and 3 will fire, while cylinders 4 and 2 will fire on the second turn. In a V-8 engine with a firing order of 1-8-4-3-6-5-7-2, the first turn of the crankshaft will fire cylinders 1, 8, 4, and 3, while the second turn will fire cylinders 6, 5, 7, and 2.

For easy reference, the firing order of many engines is cast right into the intake manifold. For those that don’t, you’ll need to consult the engine’s service manual.

Diesel Engines

The diesel engine is another internal combustion engine variant. Diesel engines, often referred to as compression-ignition engines, are far more straightforward and reliable than gasoline engines, owing to the absence of a spark-ignition system. Diesel engines, rather than utilizing a spark to start combustion, employ a substantially higher compression ratio to produce enough heat of compression to ignite the air-fuel mixture. A diesel engine’s compression ratio can be anywhere from 16:1 to 22:1.

Engine Operation Requirements

The following subsections outline the basic engine operation requirements.

  • Air-fuel mixture—Air and fuel must be mixed in the proper proportions for an engine to work efficiently. Whenever there is too much air or too much fuel, combustion suffers. The stoichiometric ratio is the optimal air-to-fuel ratio, and the engine’s fuel system is responsible for maintaining that balance. The air-fuel ratio is determined by comparing the mass of the air to the mass of the fuel added to it.

A lean mixture is one with too much air and not enough fuel. Because there is more space between the fuel molecules in a lean mixture, it takes longer for a flame to move from one particle to the next. A rich air-fuel mixture, on the other hand, contains too much fuel and not enough air. Because of the short distances between fuel particles, rich mixtures burn significantly faster and much cooler.

  • Ignition timing—Ignition timing is the point in the combustion cycle when a spark is produced at the spark plug. This is defined in relation to the crankshaft position of the engine. For example, an ignition timing of five degrees before the top dead center (BTDC) means that the spark occurred five degrees before the top dead center on the crankshaft.

In order to create the most efficient downward force on the piston at higher engine speeds, the flame must be ignited earlier. This is referred to as advancing the timing.

Retarding the timing means adjusting the spark timing to occur later in the combustion cycle. As part of standard engine functioning, certain engine operating conditions may require retarded timing.

  • Combustion—A spark from the engine’s ignition system initiates the efficient, complete combustion of a compressed air-fuel mixture in a gasoline engine. It’s a flame that initiates at the spark plug and quickly travels across the combustion chamber, heating the gases and producing pressure in a consistent and regulated manner.

  • Pre-ignition—Pre-ignition is an abnormal condition in which combustion is initiated by something other than an electric arc at the spark plug.

When an air-fuel mixture erupts rather than burns, it is referred to as detonation. It frequently occurs when an engine’s air-fuel mixture is lean.

The Cooling System

In modern automobile engines, there are two types of cooling systems. The first is air-cooling, which removes excess heat by circulating air over cooling fins on the outside of the engine. Water-cooling is the second type. A water-cooled engine collects heat with a liquid coolant and then rejects it through a radiator. Cylinder temperatures must promptly achieve operating temperature and remain consistent over a wide range of ambient conditions in order to provide optimal emissions and efficiency.

Coolant

The coolant is the most important component of the cooling system. A 50/50 mixture of antifreeze and water is typically used in engine coolant. Frozen coolant can cause major engine damage (including a broken block and/or cylinder head); thus, it’s essential to use freeze-resistant coolant. Ethylene glycol is by far the most popular antifreeze. A 50/50 mixture of ethylene glycol and water does not freeze until it reaches -34° Fahrenheit. This same 50/50 mixture also enhances the coolant’s boiling point, which is crucial in hot weather because it increases the coolant’s heat transfer efficiency.

Parts of the System

The following are the primary components of a water-cooling system:

Water pump—The water pump is in charge of transferring and controlling heat by circulating coolant via the cooling system.

Water jacket—The water jacket is the hollow portions of the engine block and cylinder head that permit coolant to transfer through them.

Thermostat—The thermostat regulates the engine temperature by allowing coolant to flow into the radiator when the coolant temperature goes beyond a set threshold.

Bypass tube—When the thermostat is closed, coolant from the cylinder head flows back into the water pump through the bypass tube.

Radiator hoses—Radiator hoses permit hot coolant to flow between the engine and the radiator of the vehicle.

Radiator—A radiator transfers heat from the coolant to the outside air.

Radiator cap—A radiator cap ensures system pressure is maintained and allows coolant to flow smoothly between the reservoir and radiator.

Coolant recovery bottle—The coolant recovery bottle acts as a reservoir, allowing coolant to flow in and out of the cooling system as the engine temperature increases or decreases.

How the Cooling System Works

A water pump operated by a belt or timing chain circulates coolant through the engine. The engine crankshaft drives the belt; hence, the water pump is powered by the engine. Coolant is pumped into the engine block via the water pump. The coolant then travels upward into the cylinder head before returning to the water pump’s inlet via the bypass tube. The coolant will circulate in this fashion as long as the thermostat is closed (the engine is below operational temperature).

Care of the Cooling System

Cooling systems require maintenance to operate at peak efficiency. The coolant itself is crucial, so having it replaced every two to three years is a good maintenance practice. The coolant’s strength should be maintained at a 50/50 mixture of antifreeze and water. This will guarantee that the coolant has adequate anti-freeze and anti-corrosion properties.

It’s also crucial to make sure the water pump’s belt is in good working order and that the system is free of leaks. Also, inspect for visible evidence of damage or wear on the hoses and radiator.

The Lubrication System

The lubrication system is another important component of engine operation. Without lubrication, the internal parts of the engine would quickly produce enough friction to totally stop (seize) the engine. The following functions are performed by the lubrication system:

The Functions of the Lubrication System

  • Lubrication—Putting an oil film on moving parts reduces friction and allows for smooth engine operation.

  • Sealing—Motor oil functions as a sealer between the piston, piston rings, and engine cylinder walls. This helps to seal combustion gases within the combustion chamber, allowing the engine to operate more efficiently.

  • Cleaning—By adding additives to the engine oil, contaminants are suspended in the oil so that they can be removed by the engine’s oil filter.

  • Noise reduction—The use of motor oil reduces engine noise and allows the engine to run more quietly.

Oil

The lubrication system is largely made up of engine oil. The engine’s moving parts are lubricated using engine oil. Engine oil is composed of two parts: base oil and an additive package.

Viscosity is one of the most important properties of engine oil. Viscosity is the resistance to the flow of oil, and it is measured as a number that is proportional to its thickness.

The American Petroleum Institute (API) is in charge of developing engine oil quality standards. For a gasoline engine, this rating begins with an “S”, and the subsequent letter describes the particular quality standard that the engine oil satisfies.

Engine oil with a “C” prefix for its quality rating is appropriate for use in diesel engines (for instance, a CJ-4, CI-4 Plus, CI-4, or CH-4 rating). The oil that has both an “S” and a “C” rating are appropriate for either gasoline or diesel engines. Engine oil with the SJ/CD rating is a good example.

Parts of the Lubrication System

The following are the main components of the lubrication system:

Oil pan—At the bottom of the engine, the oil pan serves as a reservoir for the engine oil.

Oil pickup tube and screen—The oil pickup tube and screen are immersed in engine oil and filter large solids before directing oil to the oil pump.

Oil pump—The oil pump is in charge of moving oil through the engine’s oil galleries. It is generally driven by the crankshaft of the engine.

Pressure relief valve—The pressure relief valve protects the lubrication system from becoming excessively pressurized.

Oil filter—An oil filter, as the name suggests, filters oil from the oil pump before it is supplied to the various sections of the engine.

Oil galleries—Oil galleries in the engine assembly are passages or drillings that transfer oil to essential components.

How the Lubrication System Works

Lubrication systems are divided into two categories: dry-sump and wet-sump. The dry-sump lubrication system is quite complicated and is normally only found in racing automobiles; therefore, it is rarely seen. Wet-sump lubrication systems are used in nearly all mass-produced commercial and automotive engines. The engine’s oil reservoir is positioned at the bottom of the engine in the oil pan in a wet-sump system. The oil pump uses the pickup tube and screen to draw oil from the oil pan into its inlet. The engine oil passes through the oil pump and then is transferred to the oil filter under pressure. The oil filter eliminates any particles from the oil before sending it to the main oil galleries.

The engine’s reciprocating assembly is the most crucial area in terms of lubrication requirements. Oil is required to reduce friction and remove heat from the pistons, connecting rods, and crankshaft. Oil is transported to these regions through the engine’s largest oil galleries.

Other oil galleries transport oil from the main oil gallery to the engine’s valve train. The camshaft, lifters, push rods, rocker arms, and valve stems are all lubricated in this compartment. The camshaft drive, or timing chain, as well as accompanying gear drives for the oil pump, ignition distributor, and other elements, may be lubricated by this oil.

Care of the Lubrication System

Regularly changing the engine oil and filter, as well as using high-quality engine oil and filters, are essential for lubrication system maintenance. This is the simplest and most cost-effective maintenance procedure for reducing engine wear.

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