Glossary

These engines have one power stroke for every revolution of the engine versus every other stroke on 4-cycles

All 4-cycle engines require four piston strokes or cycles to complete one power cycle. The flywheel on one end serves several functions, the first of which are engine cooling and inertia. The other functions are holding the external magnets for ignition and internal magnets for charging if equipped.

The rate of increase in velocity with respect to time; equal to net torque divided by inertia.

A device used to eliminate dust and dirt from the air supply. Filtered air is necessary to ensure that abrasive particles are removed before entering the combustion chamber. Dirt allowed into the engine will quickly wear the internal components and shorten the life of the engine.

The temperature of the surroundings.

Rotating member of a brushed DC motor.

To reduce to minute particles or to a fine spray.

A component designed to break the force or flow of air on the engine.

Shrouding covering internal engine components to prevent damage.

Conductor between the commutator and the external circuit of a brushed DC motor.

Government regulated department which determines standards for emissions by-products.

Lobes push the lifters at the proper time to allow air and fuel in and exhaust out of the cylinder. Teeth on the camshaft gear time the camshaft movement to the crankshaft movement.

An engine component that mixes fuel and air for combustion. A precursor to fuel injection, carburetors are found now only on small engines. They are less efficient than fuel injection.

Restricts airflow during cold starting for a richer air-to-fuel ratio.

By combining full choke and a primer, engines will starter more easily, especially in cold conditions.

This system has a manual choke level on the carburetor or the choke is in the control and operated remotely by a speed control cable.

Describes a system where a measured output value is compared to a desired input value and corrected accordingly (e.g., a servomotor system).

Mechanical device in a brushed DC motor that passes current from the brushes to the windings.

Provides the end user with the least possible pulling effort during starting. The system operates by momentarily opening one of the valves just prior to Top Dead Center (TDC) on the compression stroke. The system most commonly used on 4-cycles is mechanical. This type disengages after the engine is started. When disengaged, the engine creates full power.

The link between the piston (piston pin) and the crankshaft.

Device used for connecting cables; usually come in pairs of female and male.

This is a one way check valve that allows air out and prevents air from coming in. It allows the engine to develop a vacuum in the crankcase during operation to reduce oil consumption.

Converts the up and down piston movement to the rotational force (torque) through an offset crankpin or rod journal.

The cylindrical shape of the chambers where air and fuel are mixed and burned inside an internal combustion engine. Each chamber is counted as one cylinder. In general, the greater the number of cylinders an engine has, the greater the power and fuel consumption. To conserve fuel, some modern 8-cylinder engines have been designed to shut down cylinders when they are not needed (highway cruising, for example).

Houses the piston, crankshaft, and along with the cylinder cover, all the internal components. The block is a one piece diecast aluminum alloy cylinder casting which may have a cast iron liner.

Provides the bearing surface for the power take off (PTO) end of the crankshaft and camshaft. This bearing may be a bushing, a ball bearing or the cover material itself.

A one piece aluminum alloy casting that is bolted to the top of the cylinder block. The overhead design contains all of the valve train except for the camshaft, lifters and push rods.

A measure of the size of the engine, usually in cubic inches or cubic centimeters, more specifically is the volume the piston displaces.

Electronic Control Unit.

Electronic Fuel Injection.

Amount of axial displacement resulting from the application of a load equal to the stated maximum axial load.

Environmental Protection Agency, government body that sets federal emissions regulations.

The process through which engine waste is drawn out of the engine.

Allow the burned gases to pass out of the combustion chamber.

A plastic component consisting of a series of vanes radiating from a central hub, which is rotated by the crankshaft and cools the engine.

Provides inertia to keep the engine running smoothly between power strokes. By attaching a fan to the flywheel air flow is created and directed over the cooling fins. Hence the term Air Cooled Engine.

A material (usually rubber) or a part (O-ring) used to seal a joint so it won't leak.

A screen, usually plastic or metal, placed over the fan so large debris is not ingested into the engine.

Engine component that determines engine speed from ignition pulses.

A measurement of power, usually mechanical.

A device that maintains zero valve clearance eliminating the need for valve adjustments.

Electronic CDI (Capacitor Discharge Ignition). This system eliminated ignition points and their need for regular service. The benefit to the operator is low speed firing of the spark plug. This system requires approximately 1/3 the pulling speed of competitive inductive ignition systems. Which translates to 1/3 less effort for the end user.

A measurement of an object's ability to resist a change in velocity, this property is dependent upon the mass and shape of the object.

An opening on the engine through which fluid or air is drawn in.

2-cycle engines are lubricated by a gas oil mix. The correct mix ratio of oil and gas combines with air and the venturi and enters the crankcase. During engine operation, the oil clings to all the internal moving parts for lubrication.

Original Equipment Manufacturer.

Vertical shaft only. Consists of a steel plunger and a nylon or aluminum housing that rides an offset on the camshaft. The rotary pump consists of a lobed gear in a rotating ring that is driven by the camshaft. Both of these systems pump oil under pressure to all critical areas.

Describes a system that operates without feedback.

The valve is located on the cylinder head. This increases combustion efficiency and increases horsepower by 20% over the same displacement L-head engine, and a 20% overall fuel efficiency.

Paper type air filter elements can only be serviced by replacement. Do not attempt to clean a paper filter element.

The maximum torque that can be delivered for even a short period of time.

Transmits the force of the burning and expanding gases through the connecting rod to the crankshaft.

These provide the seal between the cylinder wall and the piston. The rings keep the combustion pressures from entering the crankcase and also wipe the oil off the cylinder wall and return it to the pump.

Openings in the cylinder that allow gases to pass into and out of the combustion chamber. The ports are opened or closed by the upward and downward movement of the piston.

The rate at which work is done; equivalent to torque times rotational speed, voltage times current, etc

Also known as manual fuel injection. A primer button that pushes a metered amount of fuel out of the main nozzle. This requires 3-5 complete pushes of the button, waiting 3 seconds between each prime. After the engine is warmed up, no priming is needed for restart. These carburetors are used on rotary mower engines and some small horsepower engines.

Torque-producing capacity at a specified speed.

A reed valve is activated by crankcase pressure or vacuum. A decrease in crankcase pressure opens the reed, allowing the fuel air and oil mixture to enter the crankcase. Increased crankcase pressure closes the valve, preventing the escape of the fuel-air and oil mixture back through the carburetor.

The stationary member of a motor.

A force that rotates a body.

A volume of space that has little or no pressure due to the absence of air or any other gasses; there are differing degrees of vacuum, which is why Empire Magnetics offers three different grades of vacuum rated motors and related products.

Allow air-fuel mixture to enter the cylinder and exhaust gases to exit. The valves provide a positive seal when closed.

Maintain contact on the camshaft, move the push rods to pivot the rocker arms and move the valves.

Return the valves to the closed position and must be strong enough to maintain valve lifter and cam lobe contact. The valve retainers lock the spring to the valve stem.