ASVAB Auto and Shop Information: Engines, Car Systems, and Shop Tools

What the Auto and Shop subtests are

The official ASVAB site describes Auto Information as knowledge of automobile technology and Shop Information as knowledge of tools and shop terminology and practices. On the computer test (CAT-ASVAB) they're two short subtests:

The official site says the two are combined into one score, labeled AS, on both versions of the test. On the paper test, they're a single subtest: Auto and Shop Information, 25 questions in 11 minutes. That works out to about 36 to 42 seconds a question on the computer and about 26 seconds on paper, so this subtest rewards knowing the part or the tool on sight.

AS isn't part of the AFQT, the score that decides basic eligibility. It matters for jobs. The official composite formulas include it in the Air Force Mechanical score (AR + 2VE + MC + AS), the Marine Corps Mechanical score (AR + MC + AS + EI), and three Navy composites: Mechanical 1, Mechanical 2, and Operations 1. The Army's composites other than GT are weighted combinations of all subtests, and GoArmy names Auto and Shop among the subjects for its Combat, General Maintenance, Mechanical Maintenance, Operators & Food, and Surveillance & Communication categories. The line score formulas guide has the full tables.

The testing program's prep page says taking technical courses helps with the Auto, Shop, Electronics, and Mechanical Comprehension subtests. If you haven't had those courses, the sections below are a starting set, not a full course, and each fact names its source. Full ASVAB prep has 101 Auto and Shop Information questions with explanations for practice after the review.

How a four-stroke gasoline engine works

The Department of Energy describes the basics: in an internal combustion engine, the fuel burns inside the engine. The engine has a fixed cylinder and a moving piston. The expanding combustion gases push the piston, which turns the crankshaft, and a system of gears in the powertrain carries that motion to the wheels. Most of these engines are four-stroke engines, meaning it takes four piston strokes to complete one cycle.

NASA Glenn's description of the ideal cycle, stroke by stroke:

In a gasoline engine, a spark from the spark plug ignites the mixture. A diesel works differently. DOE says a diesel draws in and compresses only air, then sprays fuel into the hot compressed air, where it ignites. That's why DOE calls gasoline engines spark ignition and diesels compression ignition.

What the main car systems do

Two owner-level facts from fueleconomy.gov: the right tire pressure is usually on a sticker in the driver's side door jamb or glove box and in the owner's manual, not the maximum printed on the tire's sidewall. And it recommends the manufacturer's grade of motor oil: using 10W-30 in an engine designed for 5W-30, for example, can lower gas mileage by 1% to 2%.

This page doesn't describe the steering, suspension, brake, or charging systems part by part, because the sources used here don't cover them. If your practice misses land there, add them to your review list.

Hydraulics, worked with Passy's numbers

NASA Glenn's page on Pascal's principle and hydraulics states the rule this way: when pressure increases at any point in a confined fluid, it increases by the same amount at every other point in the container. Because pressure is force per unit area, the two pistons of a hydraulic system share one relationship: F1 / A1 = F2 / A2. NASA's example is a hydraulic car lift.

An example with original numbers, for an ideal system with no losses. A 100-pound force pushes on an input piston with an area of 1 square inch. The output piston has an area of 4 square inches.

• Pressure in the fluid: 100 pounds ÷ 1 square inch = 100 pounds per square inch.
• Force on the output piston: 100 pounds per square inch × 4 square inches = 400 pounds.
• Distance: NASA notes that the volume of fluid pushed down on one side equals the volume lifted on the other, so A1 × D1 = A2 × D2. If the input piston moves 4 inches, the output piston rises 1 inch, because 1 × 4 = 4 × 1.

The force is four times larger, and the distance is four times shorter. NASA compares a hydraulic system to a lever, since it multiplies force, and the Mechanical Comprehension guide shows the same kind of trade with levers. OSHA's rules for jacks, hydraulic ones included, are in the power tools section below.

Saws and cutting

• Rip cut and crosscut. A University of Arkansas woodworking lesson defines a rip cut as one parallel to the grain and a crosscut as one perpendicular to it. A ripsaw cuts with the grain; a crosscut saw cuts across it.
• Table saw setup. The same lesson says to lock the rip fence before making a rip cut and to always use the miter gauge for crosscuts. It calls for a push stick when the stock is less than 6 inches wide, never raising the blade more than 1/4 inch above the material, no gloves while operating the saw, and disconnecting power before changing blades.
• Coarse and fine saws. The UNC safety manual says to use a coarse saw, 4 to 5 points per inch, for crosscutting green wood, and a fine saw for smooth, accurate cuts in dry wood. Keep saws sharp and well set to prevent binding.
• Hacksaws. UNC says to install the blade with the teeth pointing forward and apply pressure on the forward stroke, not the back stroke.
• Portable circular saws. OSHA's rule requires guards above and below the base plate (29 CFR 1926.304(d)).

Wrenches, screwdrivers, hammers, chisels, and files

OSHA's construction rules also require wooden tool handles to be free of splinters and cracks and kept tight in the tool (29 CFR 1926.301(d)).

Power tools, compressed air, and jacks

These come from OSHA's construction rules for hand and power tools (29 CFR 1926, Subpart I) and the UNC manual:

• Electric tools must be double-insulated or grounded, and you don't raise or lower a tool by its cord (1926.302(a)).
• Guards go on any power tool designed to take them, whenever it's in use (1926.300(b)(1)).
• Compressed air may be used for cleaning only when reduced to less than 30 pounds per square inch, with chip guarding and protective equipment, apart from a few construction cleaning jobs the rule names (1926.302(b)(4)).
• Jacks carry a rated capacity that must be marked and not exceeded, and once a load is raised, it's cribbed, blocked, or otherwise secured at once (1926.305).
• Changing blades or bits: UNC says to disconnect the tool first, and also when it's not in use or before servicing.

If you miss one of these in practice, Fix It in full ASVAB prep saves each missed Auto and Shop question so you can try it again later.

Check yourself: five Passy practice questions

These are original Passy questions, not official ASVAB items.

1. In a four-stroke gasoline engine, which stroke comes right after compression? A. Intake B. Power C. Exhaust D. Cooling

Answer: B. Combustion starts at the end of the compression stroke, and the expanding gas drives the piston on the power stroke. Exhaust comes after power, and intake starts the next cycle.

2. How does a diesel engine ignite its fuel? A. With a spark from the spark plug B. From the heat of compressed air C. With heat from the exhaust gases D. With pressure from the fuel pump

Answer: B. DOE says a diesel draws in and compresses only air, then sprays fuel into the hot compressed air, where it ignites.

3. In an ideal hydraulic lift, a 60-pound force pushes on an input piston with an area of 2 square inches. The output piston has an area of 6 square inches. What force acts on the output piston? A. 20 pounds B. 120 pounds C. 180 pounds D. 360 pounds

Answer: C. The pressure is 60 ÷ 2 = 30 pounds per square inch, and 30 × 6 = 180 pounds. Choice A flips the area ratio, B multiplies the force by the small area, and D multiplies it by the large area without finding the pressure first.

4. On a table saw, what should guide the stock when you make a crosscut? A. The rip fence B. The miter gauge C. The blade guard D. The push stick

Answer: B. The University of Arkansas lesson says to always use the miter gauge when crosscutting. The rip fence guides rip cuts, and a push stick feeds narrow stock past the blade.

5. On an adjustable wrench, which part should take the pressure? A. The fixed jaw B. The movable jaw C. Both jaws equally D. The adjusting screw

Answer: A. The UNC manual says pressure is always applied to the fixed jaw.

Fitting Auto and Shop into your ASVAB plan

• Check the composite first. If the jobs you want don't use AS, put your time into the four AFQT subtests. The line scores guide shows how to read a job's requirement.
• Learn systems as a flow. Fuel in, spark, power stroke, exhaust out, heat carried away by the coolant. A part is easier to recall when you know what comes before and after it.
• Learn tools by job and rule. For each tool, know what it's for and the one thing not to do with it.
• Study in short sessions. With well under a minute a question on either version, recall speed matters more than long reading.

For quick recall between practice sets, full ASVAB prep has 25 Auto and Shop flashcards. You can also try the free ASVAB practice questions, which include technical subtests, and the Electronics Information guide if your composite counts EI too.