Term |
Meaning |
Air/fuel ratio |
The proportions that air & fuel
are mixed together in the carburettor to form a combustible
gas |
API |
American Petroleum Institute-Body
responsible for testing & classifying oil |
API Grade |
Grade given by the American Petroleum
Institute to determine the type of use an oil is suitable
for |
BDC |
Bottom Dead Center-the lowest point
in a cylinder that the piston goes |
BHP |
Brake Horsepower. The British measurement
for engine power. Also expressed in Kilowatts (KW) |
Big-end |
The larger end of the connecting
rod that attaches the piston to the crankshaft. Usually
located at the bottom of the engine |
Bore |
Diameter of the cylinder |
Bottom-end |
Term used when referring to the
bottom of the engine, usually the crankcase & crank
components |
BTDC |
Before Top Dead Center-The spark
plug usually ignites the fuel/air mix slightly before
the piston reach's its highest point, this position
is known as Before Top Dead Center (BTDC) |
Cam chain |
Chain connected to the end of the
crank shaft at the bottom of the engine & the cam
shafts at the top of the engine |
Camshaft |
Shaft located at the top of the
engine, driven by a chain, belt or gear mechanism. The
camshaft(s) have a series of egg shaped 'lobes' which,
as the shaft rotates, open & close the inlet &
exhaust valves |
Carburettor |
Usually located outside the engine,
close to the top of the engine cylinder head. The carburettor
mixes air & fuel to form a combustible gas which
is then burnt in the engine cylinder |
|
Catalytic converter |
A device used is exhaust systems
to remove or convert some of the more harmful components
& pollutants in the exhaust gases. Often contains
volcanic rock which reacts with exhaust gas components |
CDI |
Capacitor Discharge Ignition-Form
of mechanical electronic breaker used to control the
spark of a/the spark plugs |
Compression |
As the piston travels up to the
top of the cylinder head, it 'compresses' the fuel/air
mixture from the carburettor in the top of the cylinder
head, making the fuel/air mix ready for ignighting by
the spark plug. This is known as 'Compression'. |
Connecting-rod (Con-rod) |
The rod in an engine that connects
the crankshaft to the piston |
Crankcase |
A structurally strong chamber usually
at the bottom of the engine that contains the crankshaft |
Crankshaft |
A shaft, usually made from hardened
steel, which is joined by the con-rod to the pistons,
which is used to drive the motorcycle. Usually runs
across the bottom of the engine & is connected to
the drive chain at one end & the clutch at the other |
Cylinder |
A normally circular cavity used
to house the piston |
Cylinder head |
Component used to block off one
of the open ends (usually the top) of the cylinder |
Detonation or pinking |
Explosion of the fuel/air mix in
the cylinder instead of the usual controlled burning.
Can cause a 'tinkling' noise under an open throttle
& can be highly destructive to an engine |
Displacement |
The amount of volume displaced by
the piston as it moves from the lowest point in the
cylinder to the highest point. |
Double-overhead camshaft (DOHC) |
An engine that uses 2 overhead camshafts,
1 for the inlet valves & 1 for the exhaust valves |
Drivebelt |
A toothed belt used to transmit
movement from the end of the crankshaft to the rear
wheel |
Driveshaft |
Any shaft used to transmit movement
in the engine. Most common application is used to transmit
power from the end of the crankshaft to the rear wheel |
Dry-sump |
A 4 stroke engine lubrication system
where the oil is located in a separate oil tank rather
than the more commonly used oil sump |
ECU |
Electronic Control Unit-A computer
which controls engine electronic operations such as
ignition timing or an anti-lock braking system (ABS) |
EMS |
Engine Management System-A computer
controlled system which manages the fuel injection &
the ignition systems |
EP |
Extreme Pressure-Oil type used |
Expansion chamber |
Section of a 2 stroke motorcycle
or scooters exhaust system designed to improve engine
efficiency & boost power |
|
Final drive |
Component that transfers drive from
the transmission (gearbox) to the rear wheel. Usually
in the form of a chain, drive shaft or belt |
Firing order |
Order in which the cylinders fire
or deliver their power/ignition stroke |
Flywheel |
A rotating disc or mass usually
on the end of the crankshaft used to smooth out power
impulses & to assist clutch engagement |
Friction |
Resistance between two bodies or
objects moving while in contact with each other |
Gasket |
A thin layer installed between 2
metal surfaces to ensure a good seal. Usually made from
cork, cardboard, asbestos or soft metal |
Grease |
A mixture of a metallic soap &
a lubricating oil |
Gudgeon pin |
Pin, usually made from hardened
steel, that connects the small end of the con rod to
the piston. Often referred to as a piston pin |
Ignition timing |
The moment at which the spark plug
fires. Often controlled by points (in older motorbikes
& scooters), CDI or ECU |
JASO |
Quality standard for 2 stroke oils |
Lambda sensor |
Sensor fitted to exhaust systems
to measure the oxygen content of exhaust gases |
Lubricant |
A substance, usually an oil, that
operates between 2 rubbing surfaces to reduce friction |
Main bearing |
The principle bearing(s) that carry
a component. Usually refers to the crankshaft bearings
in a motorcycle engine |
Mainshaft |
Principle shaft, usually the crankshaft
in a motorcycle engine |
Monograde oil |
An oil that has a very narrow viscosity
or thickness range. e.g. SAE40 |
Multigrade oil |
An oil that has a wide viscosity
or thickness range. e.g. 10w40 |
Oil cooling |
The use of oil to assist in the
cooling of hot parts of a motorcycle engine of other
moving component |
Oil injection |
A system where 2 stroke oil is pump
fed into the engine in accordance with the throttle
position |
Oil pump |
A mechanically-driven device for
distributing or pumping oil around a 4 stroke engine
& into a 2 stroke engine |
Otto cycle |
Another name for the 4 stroke cycle |
Overhead valve (OHV) |
Valves in the top of a 4 stroke
engine that are operated by pushrods |
Overhead cam (OHC) |
A system where a shaft in the top
of the engine, driven by a chain, belt or gear from
the crankshaft, is used to open the valves |
Oversize (OS) |
Term used for a piston fitted to
an engine after a cylinder rebore |
|
Petroil |
Lubrication mixture for 2 stroke
engines. Where the petrol & oil is mixed before
going into the engine |
Piston |
A moving plunger inside a cylinder.
Intended to seal the cylinder & accept or deliver
thrust |
Power band |
The band of RPM in which the engine
produces the most useful amounts of power |
Premix |
2 stroke engine lubrication system,
used especially in older, racing & competition motorcross
motorcycles where the 2 stroke oil & petrol is 'premixed'
in the fuel tank |
Pump |
Component used to propel oil, coolants
or fuel through a circuit, tube or pipe at high pressure |
Rebore |
Removing of the worn or damaged
interior surface of a cylinder to create a new working
surface. As the cylinder becomes bigger or 'oversized',
larger or 'oversized' pistons & piston rings need
to be used |
Reed valves |
A valve that functions similar to
a 'reed in the wind'. Pressure causes the valve to flap
open or closed. Used mainly in 2 stroke engines due
to their ability to work well at high speeds |
Rotary valve |
A type of valve used in 2 &
4 stroke engines which, as it rotates, opens & closes
gas passageways. Usually a disc, conical or cylindrical
in shape & normally found on inlet systems |
|
SAE |
Society of Automotive Engineers-SAE
numbers are used for classifying lubricating oils into
viscosity (thickness) ranges at certain temperatures |
Scavenge |
To clear away, particularly exhaust
gas from a cylinder or oil from a dry sump |
Seizure |
More commonly referred to as 'F**K
IT!! I've seized my bl**dy engine! The binding together
of 2 moving parts, usually through pressure, temperature
or lack of lubrication |
Single overhead camshaft (SOHC) |
An engine that uses a single camshaft
to operate both the inlet & exhaust valves |
Small end |
The smaller end of the connecting
rod to which the piston is usually attached |
Spark plug |
Device used to ignite the fuel/air
mixture in a cylinder. The spark is created by 'arcing'
an electric current between 2 electrodes |
Stroke |
Either the up or down movement of
the piston from the top to the bottom or bottom to top
of the cylinder (So the piston going from the bottom
of the cylinder to the top would be 1 stroke, from the
top back to the bottom would be another) |
Sump |
A well, hollow or reservoir for
excess fluid. A detachable chamber at the bottom of
a 4 stroke engine that contains the oil |
TDC |
Top Dead Center-the highest point
in a cylinder that the piston goes |
Top end |
A general description for an engines
cylinder block, head & valve components |
Total loss |
A system of lubrication in which
the oil is lost or used up after it's been used to lubricate
moving surfaces. E.g. A 2 stroke engine uses a 'total
loss' system as the 2 stroke oil is burnt with the fuel
& air mixture |
Transfer port |
Port (or passageway), in a 2 stroke
engine, which transfers the fuel, air & oil mixture
from the crankcase at the bottom of the engine to the
cylinder at the top of the engine |
Valve |
A device through which the flow
of liquid, gas or vacuum may be stopped, started or
regulated |
Viscosity |
The thickness of a liquid (or it's
resistance to flow). Often indicated by an SAE number,
the higher the number, the thicker (or more viscous)
a liquid is |
Wet Sump |
Commonly used 4 stroke engine lubrication
system in which the oil is carried in a pan at the bottom
of the engine |
