1. if anyone is knocking on the hood
2. when the engine knocks into the transmission
3. even slight signs of detonation problems
4. vibrations in the engine mounts

The knock sensor sends voltage signals back to the ECU, which uses those to determine if the timing for the engine needs to be retarded, before damaging pre-detonation occurs.

1. valve adjuster flux
2. flux capacitor
3. valve cover
4. valve access hole

Valve covers are designed to take the hassle out of adjusting valves somewhat regularly. They come off by removing just a few bolts and go back on with similar ease.

1. oil cone
2. oil fill hole
3. oil pump
4. oil drain plug

Sometimes this can be the hardest part of doing an oil change, if you don't have a wrench that's up to the challenge. You can also use penetrating lubricant on the bolt and let it sit for a little while.

1. oil meter
2. oil overflow reservoir
3. oil dipstick
4. oil collection pan

When the engine is turned off, you can use the dipstick to see if the oil is full enough, or if you need to add a quart or two. You'll need a rag or paper towel to clean the dipstick off to get an accurate reading, though.

1. alternator
2. ignition wire
3. electrical magnifier
4. spark plug

It's amazing to think the spark plugs in your engine are constantly producing sparks to trigger mini explosions in the cylinders, which then turn the wheels.

1. escutcheon
2. bolt gasket
3. exhaust valve
4. O2 sensor

Valves open and close passageways. In this case, the valve opens and closes the pathway in the cylinder head that connects to the exhaust manifold.

1. piston gasket
2. piston seal
3. head gasket
4. magic 8 ball

Piston seals are usually made of rubber or a similar substance, so they create an airtight seal that won't let exhaust gases or the air and fuel mix to seep out in the least.

1. air intake system
2. exhaust system
3. combustion chamber
4. cylinder head

The air temperature sensor gives feedback to the ECU, since this information can affect how much fuel should be sprayed by the injectors. The colder the air, the more oxygen-rich it is.

1. lynch pin
2. litch pin
3. gudgeon pin
4. safety pin

With all the force exerted on the piston and connecting rod each time the air and fuel ignite, the gudgeon pin has to be strong and durable, otherwise the engine would fail quickly.

1. luck
2. magic screws
3. fuel rail
4. fuel injector

The fuel injector has an incredibly precise nozzle, so the car's ECU can regulate with precision how much fuel should make its way into the cylinders at any given moment.

1. if the crankshaft slips
2. where in the engine the crankshaft is located
3. if the car is on a slope
4. how fast the crankshaft is spinning at any given time

Sometimes called a crank sensor, this sensor is vital in managing the engine's timing, which is especially important in a variable valve timing setup.

1. the engine
2. spark plug regulators
3. spark plug tube gaskets
4. spark plug auto gappers

Just how hard replacing the spark plug tube gaskets is really depends on the engine, just like so many other components.

1. It blew up.
2. The cap has spun into the stratosphere.
3. The seal has started leaking.
4. You like to burn money.

If you look at the underside of your engine oil cap, there's a rubber or silicone seal that should create a tight seal. If that fails, you could conceivably replace it, but you might find it easier to just buy a new cap.

1. more air
2. extra fuel
3. extra coolant
4. additional oil

To help starting the car up when the engine is cold, some designs use a pipe that's triggered by the temperature of the coolant and/or a timer circuit.

1. electronic and analog
2. reverse and traditional
3. hydraulic and solid
4. split and binary

You might hear valve lifters referred to as a tappet or lash adjuster, but it's the same thing. Just remember that solid valve lifters need to be adjusted periodically.

1. left
2. right
3. open
4. closed

Most people don't think at all about the valve springs in their engine, even though this part is absolutely essential for proper compression.

1. spin the belts
2. oil the timing belt
3. guide the engine drive belts
4. lubricate the camshafts

Idler pulleys keep the belts that drive the alternator, water pump, power steering pump and AC compressor at the proper tension and moving at the right points around the engine compartment.

1. spread butter on the threads
2. keep them loose enough to jiggle the engine cover
3. torque them to spec
4. turn them counterclockwise

Not only do you need a torque wrench to tighten the bolts enough, you should always follow the manufacturer's recommendation for the tightening pattern.

1. flow regulator
2. flux capacitor
3. exhaust valve
4. intake valve

While the camshaft triggers the motions of the valves, it's the actual valves that either let the gases flow in the engine or sit.

1. guard against oil leakage
2. to maintain an airtight seal with the cylinder walls
3. stop backfiring
4. maintain proper engine temperatures

The piston ring is usually made of rubber or a similar substance and it sits in a groove that runs around the sides of the piston, forming an airtight seal that the air/fuel mix and exhaust gases shouldn't flow past.

1. a bowl
2. a spoon
3. a pipe
4. a banana

It might sound simple, but the water outlet on your car's engine is essentially a pipe that connects to the water jacket, letting hot coolant flow out of the engine and toward the rest of the cooling system, namely the radiator.

1. the cylinder
2. lots of packing grease
3. oil
4. connecting rod bushing

The purpose of the connecting rod bushing is to reduce vibrations in the engine, but they're made of a durable metal, so they don't dampen as much as rubber bushings would.

1. It holds the camshaft sprocket in the right position.
2. It allows you to write with the camshaft.
3. It records camshaft movements.
4. It contains a lethal injection.

The camshaft knock pin fits on the end of the camshaft. Not only does it hold the camshaft sprocket where it should go, the pin lines up the two parts correctly.

1. gudgeon pin
2. cylinder seals
3. valve seals
4. exhaust vortex

Replacing valve seals is actually a pretty easy job, but it is a little on the tedious side. If you must pass emissions in your area, doing this will be essential.

1. loss of compression
2. The check engine light comes on.
3. The engine will leak oil.
4. Your mom calls you to dinner.

At the end of the camshafts in a car's cylinder head is a rubber seal, designed to keep the oil inside the engine. Normally these last a long time, but in older engines the seal may fail.

1. camshaft
2. crankshaft
3. piston
4. valve

Even though they're small, the main bearings have a difficult and critical job, considering the crankshaft is converting the up-and-down forces of the pistons into a rotational force.

1. They cost less.
2. They increase compression ratios.
3. Clamping loads are more consistent.
4. They look better.

Not every engine has torque-to-yield head bolts, but just about every automaker uses them when the cylinder head is made of aluminum.

1. valve cover gasket
2. ignition wires
3. engine mount
4. engine hanger

The valve cover is located at the top of the cylinder head, making it a likely source of the leak. Of course, the oil cap is another potential origin.

1. modulator
2. retainer
3. capacitor
4. lid

The valve spring, keeper and retainer work together to create a constant amount of pressure, which snaps the valve closed tightly.

1. spark plug
2. ignition key
3. pushrod
4. valve spring

Essentially, a rocker arm is an oscillating lever that's actuated by a pushrod, which is actuated by the lobes on the camshaft.

1. to look cool
2. to guard against detonation
3. it adds strength to the valve
4. reduce engine vibrations

Engines have plenty of moving parts, and that means vibrations are inevitable. The valve guide is the cylinder that the valve moves back and forth in. This bushing just tries to reduce vibrations created by that movement.

1. camshaft
2. valves
3. head gasket
4. spark plugs

The valves in a non-interference engine never occupy any space the pistons do, even at different times. That means they're never at risk of colliding, which can damage the pistons as well as the valves.

1. hub
2. crankshaft pulley
3. differential
4. flywheel

Sometimes called the harmonic balance wheel or crankshaft sheave, is an essential part of the engine's timing system.

1. spoons
2. lobes
3. peninsulas
4. gnomes

Camshafts aren't perfectly straight shafts, otherwise the engine wouldn't run properly. They contain uneven lobes that determine when, how much and for how long the valves open.

1. O2 sensor
2. knock sensor
3. air temperature sensor
4. throttle

The air temperature sensor sits in the air intake, gathering data that helps the ECU measure how much gas should be injected into the cylinders. The colder the air, the more oxygen atoms in each cubic inch of it.