1. truck
   car
2. lawnmower
   boat

All piston engines use connecting rods between their pistons and crankshaft, but it’s the oil dipper on the big end that indicates it’s for a lawnmower motor. As the crankshaft rotates, and the piston nears BDC (bottom dead center), the dipper splashes into the oil in the bottom of the crankcase. This slings oil up onto the piston, the camshaft, and other moving parts, so the engine doesn’t require an oil pump.

1. airplane
   car
2. boat
   truck

Jet airplane engines use nozzles to direct hot turbine gases rearward and provide the aircraft with forward thrust. The nozzle is the rearmost part of a jet engine. Some nozzles can alter their size for efficiency at various airspeeds.

1. boat
   car
2. airplane
   helicopter

A recoil starter is the “pull-rope” kind, used to pull start boat motors, lawnmowers, and so on. This one belongs to an outboard boat engine. A one-way clutch actuates as you pull on the rope handle to turn the crankshaft, then lets go so the shaft can continue to turn freely. A spring-loaded pulley retracts the rope back into the starter housing.

1. RC (remote controlled) car
   Segway
2. weed whacker
   car

Here’s a part that’s common to all piston engines, from a one-cylinder weed whacker motors to exotic 16-cylinder sports car powerplants. This one is from a car engine. The top of the piston squeezes a mixture of fuel and air as it travels up the cylinder, then as the mix explodes, it forces the piston back downward. This turns the crankshaft via a connecting rod, which attaches to the piston’s wrist pin. The grooves around the upper section of the piston are for the compression and oil rings.

1. helicopter
   motorcycle
2. turbofan airplane
   turboprop airplane

A cylinder head is an aluminum or cast iron lid over each piston. In a gasoline engine, it has ports for the spark plug, intake and exhaust valve(s), and possibly a direct fuel injector, along with a camshaft in many cases. This cylinder head is from a motorcycle. Automotive heads may cover two, three, four, or more cylinders, depending on configuration.

1. a tricycle
   an airplane
2. a truck
   a speedboat

Diesel engines operate a little differently than gasoline motors. Instead of spark plugs, diesels use glow plugs, and they only need them to get the engine started and up to operating temperature. After that, the residual heat and high compression in the cylinder head is enough to keep lighting off the diesel fuel/air mixture as the engine runs.

1. car
   turbojet aircraft
2. hot-air balloon
   Segway

Another common part in a 4-stroke piston engine is the tulip-shaped valve. Each cylinder has at least one to let in the unburned fuel/air mixture (intake), and one to let out the burned exhaust gases. The lobes on the camshaft push the valves open, and springs pull them closed during the compression and exhaust phases. Most new car and truck engines these days have two intake and two exhaust valves, along with mechanisms to increase valve flow for more power at higher engine speeds (variable valve lift).

1. truck
   boat
2. plane
   lawnmower

The tappet in a lawnmower engine acts like a solid lifter and pushrod in a car or truck motor. A lobe on the turning camshaft pushes on the tappet which, in turn, pushes open an intake or exhaust valve in the combustion chamber. If the mower engine has overhead valves, the tappet may push against a rocker that actuates the valve.

1. plane
   Tesla
2. boat
   lawnmower

Outboard boat motors don’t have a closed-loop cooling system like a car or truck engine. Instead, they suck in water from a lake, circulate it through passages throughout the engine, and expel it with the exhaust back into the water. The motor turns a water pump impeller to move the water along. Impellers should be replaced every couple of years in outboard motors, unlike those in land vehicle engines.

1. car
   RC car
2. turbofan airplane
   model airplane

The crankshaft is the heart of a piston engine. It has offset journals, or sections of the shaft, parallel to its main axis. The pistons take turns moving these journals via connecting rods (con rods), working together in the same direction. The net effect is a turning crankshaft that can do a lot of work, like turning the wheels of a truck or the propeller of an airplane. This crankshaft is from a car engine.

1. airplane
   boat
2. truck
   lawnmower

A turbine engine operates by spraying fuel into compressed air in a burner, which creates high-temperature gases that produce thrust while escaping out of a nozzle and possibly turning subsequent turbines to spin a fan or propeller. The burner is the section of the engine where combustion occurs to harness the power of the burning fuel and air.

1. car
   boat
2. lawnmower
   Saturn V rocket

A muffler isn’t something you’d typically think of as an engine part in an automotive sense. That being said, on smaller engines, such as for lawnmowers, a small muffler screws right into the cylinder block or head via a threaded exhaust pipe. Inside may be baffles, tubes, holes, and/or heat-resistant packing designed to make the noise of combustion more acceptable.

1. tandem bike
   car
2. turboprop commuter plane
   Stirling engine

Rings fit into grooves around the top of a piston, and act as the main point of contact between the piston and the cylinder wall. Here’s a typical set from a car engine. The solid compression rings help to manage the ever-changing pressures above and below the piston, while the multi-component oil ring helps to keep the cylinder lubricated without allowing oil to escape up into the combustion chamber.

1. kite
   Nissan LEAF
2. turbofan airplane
   motorcycle

A spark plug lights the fuel/air mixture many times per second in a gasoline engine. Electrical energy from the ignition coil creates an arc between the center and ground electrode(s) at the tip of the plug, which extends into the combustion chamber above the piston. This spark plug is from a motorcycle, but it looks and acts much like those found in car and truck engines. Some two-cycle outboard marine engines use spark plugs without a ground electrode arm; the entire rim around the center electrode acts as a ground and the spark can jump whichever direction offers the least resistance.

1. boat
   hovercraft
2. truck
   leaf blower

This is an easy one. The propeller on an outboard motor turns in the water and makes your boat go. Turn it one way, and you go forward; put it in reverse gear, and you can back into that nice, shady cove. Turboprop and piston-engined airplanes have propellers, too, but with blades tailored to air dynamics and sometimes with variable pitch.

1. truck
   turbojet airplane
2. RC model airplane
   hoverboard

An engine’s crankshaft may use one or more timing chains to turn the camshaft(s). The pulleys on a four-stroke motor are different sizes so that the crankshaft will turn twice for each rotation of the cam(s). Many engines use a timing belt instead of a chain. The inner surface of the timing belt is toothed, as are its pulleys, because any slippage might cause the valves to open at the wrong time, collide with the pistons, and ruin your day.

1. piston-engined airplane
   helicopter
2. Segway
   boat

Here’s an igniter plug from the turboshaft engine of a helicopter. It’s used to ignite the fuel-air mixture to start (or restart) the motor. Once the turbine is running, the igniter plug isn’t needed and shuts off.

1. boat
   truck
2. airplane
   car

Adding a fan to a turbojet aircraft engine gives you a turbofan. Part of their thrust comes from a high-pressure turbine, as in a turbojet, but the majority of a turbofan’s impetus is from its fan driven by a second, low-pressure turbine. You can think of the fan as a smaller propeller that fits inside the engine’s cowl. At subsonic speeds, turbofan engines provide a compromise between fuel economy and speed for airliners and many fighter jets.

1. boat
   lawnmower
2. car
   plane

The governor in a lawnmower engine keeps it running at the speed set by the throttle. When the mower blade encounters thick grass or weeds, it’s the governor that makes the motor compensate for the heavier load.

1. truck
   weed whacker
2. turboprop
   solar car

Four-stroke engines don’t have oil mixed into their fuel like a two-stroke, so most use an oil pump to circulate lubrication to the moving parts. This oil pump from a truck siphons oil from the crankcase, moves it through a filter, and then to all the internal parts that need it.

1. flathead lawnmower
   car
2. weed whacker
   turboprop

When the lobe of a camshaft presses on one end of a rocker (either directly or through a pushrod and lifter arrangement), the rocker acts like a seesaw and pushes open a valve (intake or exhaust). This rocker from a car engine has a roller tip to reduce friction as it presses on the valve tip.

1. helicopter
   motorcycle
2. boat
   car

Even with oil to reduce friction, piston engines produce a lot of heat. Things would get out of hand quickly without extra cooling. A water pump sends antifreeze coolant through the engine, and then through a radiator to disperse the heat into the air. This car radiator catches airflow as you drive around, and also gets a boost from a fan when necessary.

1. turboprop
   ramjet
2. turbofan
   motorcycle

A carburetor sprays a mist of fuel into incoming air, creating the optimal mixture to burn in a motor’s cylinder(s). Before fuel injection became the norm in cars and trucks in the mid-1980s, the vast majority had carburetors. This particular kind of carburetor is a side draft model for a motorcycle engine. Most lawnmowers still use carburetors because of their low cost.

1. jet airplane
   truck
2. car
   motorcycle

In the turbine engine of an aircraft, the compressor forces incoming air into a smaller space before it’s mixed with fuel and ignited in the burner. The compression increases the amount of work (thrust) the burning mixture can create as its resulting gases rapidly expand. An axial compressor like the one shown uses several rotor stages to pressurize air straight back through the engine.

1. lawnmower
   hydrofoil
2. truck
   turboprop

Internal combustion engines have closely fitted parts that slide past each other on a thin film of oil, so it’s very important to keep grit and particles out of the lubricant using an oil filter. This truck filter is an example of the breed. Carmakers recommend replacing the oil filter at every oil change or two. It’s cheap insurance to make your engine last longer.

1. weed whacker
   lawnmower
2. rocket
   car

In a fuel injection system, as opposed to a carburetor, an electronic control unit tells one or more injectors when to spray atomized fuel into the incoming air. Injectors are basically solenoids that hold back pressurized liquid fuel until they’re electrically activated. Modern cars’ injectors squirt fuel into the cylinder head’s intake ports or even directly into the cylinder itself.

1. airplane
   boat
2. truck
   car

An outboard boat motor’s skeg plays a couple of important roles. One is to protect the spinning propeller from underwater objects and the lake bed. The skeg also acts as a rudder to help steer the boat in the right direction.

1. lawnmower
   jet airplane
2. truck
   piston-engine airplane

Diesel fuel, like brake fluid, tends to absorb water vapor pretty easily. For this reason, many diesel vehicles feature a water separator to remove it from the fuel. Every so often, when the separator gets full of water, you drain it by twisting a valve. Some water separators are combination units that also act as a fuel filter.

1. lawnmower
   turbojet
2. turboprop
   turbofan

Answer explanation: Just as an engine requires clean oil and fuel, it also needs clean air. This simple lawnmower air filter uses a paper element to catch dust and grit before it can get into the motor and act as an abrasive. The paper in the filter is folded like an accordion so there’s much more surface area to catch contaminants without restricting airflow. A clogged filter hurts fuel economy, so replace them as often as directed.

1. car
   helicopter
2. diesel truck
   Tesla Model 3

A car’s ignition coil(s) stores up energy and releases it to each spark plug in its turn. It takes a lot of voltage to make a spark plug fire -- more than the 12-volt electrical system of the car provides as is -- and so the coil transforms that 12 volts up to 20,000, 30,000, or even 40,000 volts. Cars and trucks used to have a single coil to run every spark plug in the engine, but more recent models dedicate a coil to every cylinder or pair of cylinders.

1. truck
   piston-engined airplane
2. lawnmower
   jet airplane

The stators in a jet engine are counterparts to the turbine rotors, but instead of spinning on the shaft, they remain still. As the rotor blades whirl, pushing air backward through the engine, the stator vanes guide the air toward the next rotor-stator stage. The stators also turn the energy of the moving air into pressure.

1. Segway
   truck
2. M-1 Abrams tank
   helicopter

Engines fire their pistons one at a time to turn the crankshaft, and a distributor like this truck model sends energy to each spark plug in its turn. Early models have a replaceable rotor that spins past metal contacts, one for each spark plug, but later distributors instead use magnetic pickup technology. Many recent car and truck engines don't even use a distributor at all, instead using a crankshaft position sensor to determine when each spark plug should fire.

1. turboprop
   two-stroke motorcycle
2. turbofan
   car

A camshaft has lobed sections that push open intake and exhaust valves as the shaft turns in a fout-stroke piston engine. As a lobe passes by, spring pressure returns the valve to its closed position. The cam lobes’ lift (how far it opens the valve), duration (how long it holds the valve open), and other characteristics determine how much power the engine makes and where in the rpm range that power peaks. Because of this, a different camshaft can radically change the “personality” of an engine, often requiring intake and exhaust modifications and electronic control chip recalibration.

1. piston-engined airplane
   turbofan airplane
2. turbojet airplane
   ramjet airplane

The propeller on an aircraft engine pulls air from the front and propels it behind, much like a ceiling fan turned up to its high setting. In the process, it propels the plane forward. From the beginning, airplanes used propellers powered by piston engines and later turbines. The latter turboprops are still in use today for low-speed commuter planes. In variable pitch propellers, the angle of the blades can change to provide the best efficiency for given conditions.

1. lawnmower
   boat
2. car
   helicopter

An outboard boat motor’s cavitation plate or antiventilation plate is a horizontal plane mounted just above the propeller. It can help a motorboat rise up under acceleration so its hull has less drag-inducing contact with the water. It may also reduce cavitation, or air pockets forming on the leading edges of the propeller blades, which robs performance.

1. car
   weed whacker
2. turboprop
   boat

Cars use electric fans to pull air through the radiator, which cools the engine by radiating heat away from its circulating liquid coolant. When the engine is cold, a sensor shuts off the fan so the motor can warm up to its optimal operating temperature. In earlier vehicles, fans were powered by a pulley on the front of the engine, sometimes with an electric clutch or flexible fan blades to reduce drag when the fan wasn’t needed.

1. pull-start lawnmower
   motorcycle
2. pull-start boat
   pull-start weed whacker

An engine will run as long as it has fuel, air, and spark -- but first, you have to get that cycle started. The energy to do that comes from the battery. Push the starter or turn the key, and the battery powers an electric starter motor to turn the crankshaft and get things going. After the engine starts, the starter disengages and an alternator recharges the battery. This small battery mounts on a motorcycle.

1. car
   jet airplane
2. truck
   motorcycle

An afterburner sprays extra fuel into the rear section of a jet engine and lights it off for additional thrust. The trick works because there’s still a lot of unburned oxygen in the exhaust stream of the jet. It’s not a very fuel-efficient way to power a plane, so engines with afterburners are largely the province of fighter jets whose pilots use afterburners sparingly.

1. boat
   helicopter
2. airplane
   car

Most older, larger engines have a vibration damper or harmonic balancer fitted to the front of the crankshaft. As the name implies, the damper counters vibrations that would be harmful to the engine and shorten its life. Inside, the weighted damper uses rubber, fluid, or some other material or mechanism to absorb engine-killing harmonics and vibrations.

1. pull-start outboard
   pull-start lawnmower
2. truck
   pull-start weed whacker

Basically an electric motor with a lot of torque, a starter like this truck model turns the crankshaft’s flywheel or flex plate until the engine starts running on its own. At that point, the starter’s toothed gear typically slides back on its motor shaft so it’s out of the way of the spinning flywheel. If you’ve ever accidentally tried to start a motor that’s already running, the grinding sound you probably heard was the starter gear trying to mesh with the flywheel. Oops.