The only thing you need to work on a car--besides the car itself--is tools and knowledge. Knowledge can be gotten for free, while tools cost money. In fact, if you don't already have a lot of tools, getting together a decent tool set is the primary impediment to becoming a car mechanic in the first place. While you can get a basic set of cheap starter tools for not much money, a good set of professional-quality tools will cost several thousand dollars. If you're just getting started and don't want to put down that kind of initial investment, you can just buy tools as you need them, but even then, count on needing a lot of tools pretty quickly.
Many of the tools that you'd use to work on a car are similar to the normal, everyday tools that people have around their house for general work: Hammers, saws, screwdrivers, and that sort of thing. On this page, I've specifically tried to focus on tools that are especially useful for working on cars, but you might still notice that many of them are quite "general" and not car-specific in nature.
It used to be that a wrench was pretty much all you needed to take an entire car apart and put it back together again. That's changed, but a wrench set is still the basic tool of most car mechanics.
Although there's nothing wrong with using the classic open-ended wrench ("crescent wrench") that is the image people typically associate with the word "wrench", most mechanics today prefer socket wrenches, which is the kind of wrench that has a little detachable tip so that you can change it to fit any size of bolt. The popularity of socket wrenches is attributable to the fact that the handle can extend away from the bolt you're actually working on, so you don't have to worry about not having enough space to turn the wrench around, which is the classic problem when using crescent wrenches.
While we're on the subject of crescent wrenches, however, it's worth noting that if you're going to get a set of them, you might as well get "combination wrenches", the kind which has an open-ended crescent head on one side, and an enclosed ("box-ended wrench") on the other.
Having said that, socket wrenches have different sizes of connectors, so when you buy sockets, you'll want to make sure you have a socket that fits your wrench. The most common socket connector sizes are 1/4", 3/8", and 1/2". This figure is often called the "drive" of the wrench, so a 3/8"-drive socket wrench is a socket wrench which has a three-eights of an inch connector, and therefore requires sockets with the same size connector. (Although you can get size adapters to match socket wrenches with sockets of different sizes.)
The other important size figure for wrenches, of course, is the size of the actual wrench opening, which needs to match the size of the head on the bolt that you're going to turn. Here's where the long-standing America-versus-the-rest-of-the-world debate pops up: There are two standards for bolt sizes commonly used in North America: SAE (which stands for "Society of Automotive Engineers"), and metric. Predictably, the SAE standard uses sizes rated in inches, while the metric system uses millimetres. Thankfully, most good wrench and socket sets will have wrenches or sockets with all the standard sizes needed for automotive work. Typical standard sizes for each of the two standards are:
SAE: 3/16", 7/32", 1/4", 5/16", 3/8", 7/16", 1/2", 9/16", 5/8", 11/16", 3/4", and 13/16"
Metric: 6mm, 7mm, 8mm, 9mm, 10mm, 11mm, 12mm, 13mm, 14mm, 15mm, 16mm, 17mm, 18mm, 19mm, and 20mm
A torque wrench (sometimes also called a tension wrench) is a wrench designed to only tighten a bolt up to some limit. This is quite important for some types of bolts, which need to be tightened to the manufacturer's specifications instead of just relying on "when it feels right to stop". Over-tightening and under-tightening bolts can both lead to disaster in a car.
Some torque wrenches have a display which shows you how much torque you're applying. Within this category, there are those which are purely mechanical (they have a little lever which bends with the wrench as you twist it, and this lever is a needle on a gauge built into the wrench), while some have an electronic display that shows you digital how much torque you're applying. Besides torque wrenches which show you how much force you're using, there are also some which can be set to a specific torque setting, and then made to "slip" if you try to tighten the bolt further.
Because a torque wrench is really just a socket wrench with an added torque-control aspect, you should look for the same things in a torque wrench that you'd look for in a regular socket wrench. In particular, make sure the drive on the torque wrench will fit your sockets.
Needed to drive air-powered tools. Compressors are rated in terms of how many psi they can supply.
An impact wrench is an air-powered tool similar to a power drill. The simple fact is that a human hand can't always provide the force needed to tighten or un-tighten a large bolt on a car, and even if it can, it takes a long time to turn those big bolts by hand. The impact wrench is fast and exerts much more force than a person could.
Impact wrenches are rated in terms of how much force they can apply, but generally speaking, 300-400 ft. lbs. of torque should be more than enough to work on cars. Also make sure that you have an impact wrench which doesn't require more air pressure than your compressor can provide.
A pretty standard tool for almost any kind of mechanical work. Get a full set of screwdrivers, including slot-head, Philips, and Robertson heads.
There's an additional type of screwdriver that's not as well-known, but which you definitely want for car work: The Torx screwdriver. This is just another screwdriver shape which isn't seen as frequently as the other types; it has a six-pointed shape kind of like a star. You can get Torx screwdrivers from speciality hardware stores without too much trouble. Be aware that the reason Torx screws are used is *because* they're less common; an item held together with Torx screws is a subtle message saying "Casual tinkerers aren't supposed to get inside here". Make sure you know what you're doing before you open any enclosure that's secured with Torx screws.
For draining oil and other liquids into.
For mopping up spills and such.
A small, circular wire brush which you can scratch over a car battery's terminals a few times to clean them off and make them nice and shiny and conductive.
When working on cars, welding is sometimes required.
For dispensing grease.
For doing compression tests on the engine cylinders.
You need some way of lifting up a car so that you can work underneath it. You can certainly use small jacks for this purpose and then get a "creeper", one of those big skateboard-like things which people lie on so they can easily slide under the car; indeed, many mechanics do this, but if you're going to be a serious, honest-to-goodness professional, you need one of those jacks which lifts the entire car up into the air.
There are many car-mechanic operations which require lifting the engine out of the engine compartment. As you can probably imagine, engines are very heavy; too heavy to lift by hand. Mechanics chain the engine to a crane made for this purpose, and use it to hoist the engine up.
For protecting your hands from mechanical scrapes and scratches, and also for protection against hot, corrosive, or poisonous liquids that come out of cars.
When working with cars, these aren't as vital as in some other industries where small pieces of material have a tendency to fly into your eyes, but it's still a good idea to have a pair of safety glasses on hand.
Auto shops can sometimes be noisy. Although most mechanics work without hearing protection, it's usually a good idea to wear some when working with loud machinery.
A feeler gauge is a probe that's machined to a very specific width. The purpose of it is to see how wide a gap is. For example, if you have a gap in an engine that's specced by the manufacturer to be less than 0.01 inches, you can take a 0.01" feeler gauge and see if it fits in the gap; if it fits, the gap is out of tolerance and needs to be re-worked.
Using feeler gauges seems like a pretty simple idea, but there's a bit of an art to them. Since the clearances they measure are so small, it's actually fairly easy for a human hand to force the gauge into a gap. At best, this can lead to the user thinking the gap is unacceptable; at worst, this can scrape material out of the gap, causing the gap (which might have previously been within tolerance) to widen out and, indeed, become unacceptable. Feeler gauges require a subtle touch; if you push them against the gap they're supposed to measure, you'll probably force it in. Learn how to measure a gap with a feeler carefully.
You sometimes need to measure how thick something is to see whether it's worn down to the point where it needs to be replaced. For this, you use a micrometer which takes the form of a pair of calipers.
Steering wheels typically require a specially-made tool to pull off.
A specialized tool which allows you to install and remove piston rings from the engine pistons.
If you are rebuilding a car engine, you want to hone down the interior walls of the engine cylinders so that they are smooth. The hone is used for this purpose. In addition, because of the constant back-and-forth motion of the pistons, a tiny ridge often forms on the cylinder wall at the limit of each piston's movement range. You use a ridge reamer to scrape off this ridge so that cylinder walls are smooth.
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