Briggs & Stratton 104M02-0021-F1 725EXi Series Vertical Engine w/ 7/8 in. Tapped 3/8 – 24 2WK & Keyway Crankshaft (CARB)

3 (three) is a number, numeral and digit. It is the natural number following 2 and preceding 4, and is the smallest odd prime number and the only prime preceding a square number. It has religious and cultural significance in many societies.

7 (seven) is the natural number following 6 and preceding 8. It is the only prime number preceding a cube.

As an early prime number in the series of positive integers, the number seven has greatly symbolic associations in religion, mythology, superstition and philosophy. The seven classical planets resulted in seven being the number of days in a week. 7 is often considered lucky in Western culture and is often seen as highly symbolic. Unlike Western culture, in Vietnamese culture, the number seven is sometimes considered unlucky.

A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting rods.

The crankpins are also called rod bearing journals, and they rotate within the "big end" of the connecting rods.

Most modern crankshafts are located in the engine block. They are made from steel or cast iron, using either a forging, casting or machining process.

An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy.

Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power generation), heat energy (e.g. geothermal), chemical energy, electric potential and nuclear energy (from nuclear fission or nuclear fusion). Many of these processes generate heat as an intermediate energy form; thus heat engines have special importance. Some natural processes, such as atmospheric convection cells convert environmental heat into motion (e.g. in the form of rising air currents). Mechanical energy is of particular importance in transportation, but also plays a role in many industrial processes such as cutting, grinding, crushing, and mixing.

Mechanical heat engines convert heat into work via various thermodynamic processes. The internal combustion engine is perhaps the most common example of a mechanical heat engine in which heat from the combustion of a fuel causes rapid pressurisation of the gaseous combustion products in the combustion chamber, causing them to expand and drive a piston, which turns a crankshaft. Unlike internal combustion engines, a reaction engine (such as a jet engine) produces thrust by expelling reaction mass, in accordance with Newton's third law of motion.

Apart from heat engines, electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, and clockwork motors in wind-up toys use elastic energy. In biological systems, molecular motors, like myosins in muscles, use chemical energy to create forces and ultimately motion (a chemical engine, but not a heat engine).

Chemical heat engines which employ air (ambient atmospheric gas) as a part of the fuel reaction are regarded as airbreathing engines. Chemical heat engines designed to operate outside of Earth's atmosphere (e.g. rockets, deeply submerged submarines) need to carry an additional fuel component called the oxidizer (although there exist super-oxidizers suitable for use in rockets, such as fluorine, a more powerful oxidant than oxygen itself); or the application needs to obtain heat by non-chemical means, such as by means of nuclear reactions.

Keyway may refer to:

• A part of a keyed joint used to connect a rotating machine element to a shaft; see key (engineering)
• A keyhole, a hole or aperture (as in a door or lock) for receiving a key; see lock and key

Vertical is a geometric term of location which may refer to:

• Vertical direction, the direction aligned with the direction of the force of gravity, up or down
• Vertical (angles), a pair of angles opposite each other, formed by two intersecting straight lines that form an "X"
• Vertical (music), a musical interval where the two notes sound simultaneously
• "Vertical", a type of wine tasting in which different vintages of the same wine type from the same winery are tasted
• Vertical Aerospace, stylised as "Vertical", British aerospace manufacturer
• Vertical kilometer, a discipline of skyrunning
• Vertical market, a market in which vendors offer goods and services specific to an industry
• Vertical integration, a management term describing a style of ownership and control

W, or w, is the twenty-third letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is double-u, plural double-ues.