A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
S
S Classification (SAE): Engine oil suitable for gasoline engines. The second letter in the classification denotes the quality and minimum conditions that the oil must meet.
S.W.L.: Safe Weight Limit.
SAW: Spark advance word output signal.
Scan Tool: Diagnostic tool that connects to an electronic control module on a vehicle to read fault codes and other data.
Scanner: Diagnostic tool that connects to an electronic control module on a vehicle to read fault codes and other data. Some scanners can also connect to controller area networks (CAN).
Scavenge Pump: The oil pump in the oil pan of a dry sump (oil pan) engine that returns the lubricating oil to a separate reservoir.
Scavenging: The process in the combustion chamber that clears the residual exhaust gases by the incoming air charge. The inlet and exhaust valves are both open for a very brief spell as the engine moves across top dead centre at the end of the exhaust stroke.
Schrader Valve: A spring loaded valve for retaining the pressure in a tyre and to allow for tyre inflation. Fitted into the rim of a wheel either as a separate valve for tubeless tyres or as part of the tube for tubed tyres.
Sciatica: Neuralgia of the hip and thigh.
Scope: Short for oscilloscope - Test equipment with a screen that can display electrical signals.
Scraper Ring: Piston ring that controls amount of oil on cylinder wall.
Screw Thread: A method of increasing force.
Scrub Radius: Effect on the tyre of steering turn.
Scuffing: A rubbing wear due to lack of lubrication or incorrect alignment. Examples are cylinder scoring and tyre tread wear on one side of a tyre only.
Seal: Oil, water or gas tight join.
Seal Land: The area on shafts that an oil seal lip seals against.
Sealant: A liquid material that is used with or, in place of, a gasket to give a gas or liquid seal. Sealants can be either fully setting and go hard after application or non-setting which remain flexible in use. The correct type of sealant should be selected.
Sealing Ring: A rubber (or similar material) ring that fits in or against an item to make an air or liquid tight seal.
Sealing Strip: Gasket to prevent leaks.
Seat: A machined face for making a good seal when matched with a valve.
Secondary Brake: Back up brake system, either mechanical or a split line hydraulic layout.
Secondary Cells: The cells of a rechargeable battery.
Secondary Shoe: Trailing shoe in a drum brake.
Secondary Winding: The high tension (secondary circuit) coil of wire in an ignition coil.
SEFI: Sequential Electronic Fuel Injection.
Seismic Mass: A small mass (weight) that moves to act as a sensing element.
Seizure: Lock up of mechanical parts preventing or restricting proper movement.
Selector Clutch: Part of gear change system that automatically synchronises gear speeds before they are engaged.
Selector Fork: A fork that acts on, and moves a gear selector.
Selector Lever: Any lever to control a system that the driver uses to select a function.
Selector Mechanism: The mechanical connection between the driver and the gearbox shift hubs in a manual transmission.
Selector Shaft: Simple shafts that are attached to and move the selector forks, which in turn move the synchronisers.
Self Adjusting: A mechanism or component that takes up free play automatically by either a mechanism or hydraulic pressure.
Self Test: Start up and monitoring sequences for electronic control systems. Produce fault code data and triggers warning signals.
Self-Servo Action: Description of how the leading shoe on a drum brake system is pulled by the drum such as to increase its braking effect.
Semi Floating Axle: An axle hub arrangement with one bearing mounted inside the axle casing where it supports the axle shaft. The load is carried by the shaft which has shear and bending forces applied to it.
Semi-conductor: A material that can be made to conduct or block electricity. A diode is a good example.
Semi-elliptical Spring: A suspension leaf spring consisting of one or more leaves with mounting eyes or slippers at the ends and having a curved shape.
Semi-trailing Arm: A rear suspension type with a triangular trailing arm that has the chassis mounting points set at an angle to the transverse axis of the vehicle.
Semiconductor: A material that can be made to conduct or block electricity. A diode is a good example.
Sender Unit: Another name for a sensor.
Sensor: Electronic components that send electrical signals to the ECU.
Sensors: Electronic components that send electrical signals to the ECU.
Sequential Fuel Injection: A petrol fuel injection system using ported injection timed in sequence with the engine firing order.
Sequential Injection: See Sequential Fuel Injection
Serial Fault Reader: Equipment that connects, usually to the OBD plug or similar, to read stored faults in an electronic system. See also scanner.
Series Circuit: Electrical circuit that has all components connected one after another. If one component fails the circuit fails.
Series Resistor: A resistor in a circuit that is connected in-line with the supply.
Serpentine Belt: A single flexible drive belt that provides a drive from the engine crankshaft to all ancillary components. Replaces a series of individual belts.
Servo: A servo mechanism (informal)
Servo Cylinder: Ram cylinder that supplements physical forces in operating a control (as for example steering, a brake or clutch), either by direct mechanical amplification or by external power assistance.
Servomechanism: System or device that supplements physical forces in operating a control (as for example a brake or clutch), either by direct mechanical amplification or by external power assistance.
Servomotor: A motor that supplements physical forces in operating a control.
Shackle: Part of a leaf spring suspension system that allows movement (swinging shackle) or is fixed to the chassis (fixed shackle).
Shackle (Slipper): Allows for changes in length between the ends of a leaf spring as suspension moves.
Sheer Force: A force that tends to sheer or cut something much like the action of scissors.
Shell Bearings: Plain bearing formed from two interlocking and abutting thin walled semi-circular cups.
Shift Fork: A fork that acts on, and moves a gear selector.
Shift Ring: Part of a gear selector mechanism.
Shift Rod: A simple rod that connects the gear change lever to the gearbox.
Shift Shaft: A shaft that is used as part of a gearshift / gear changing mechanism.
Shift Timing: The point at which an automatic gearbox changes gear.
Shim: A thin metal sheet or washer used between two components to adjust free play. Shim material is produced in standard sizes.
Shimmy: Side to side movement of the wheels that causes the tyres to lose some grip on the road.
Shock Absorber: Method of dampening suspension spring shock oscillation. Damper.
Short Circuit: Applied to an electrical circuit when the current flows to earth before completing the circuit. Usually implies that the circuit to earth is overloaded and the wires overheat or a fuse blows.
Short Engine: Engine block containing crankshaft and pistons. Usually referred to when being replaced to overhaul the engine.
Short Motor: The engine block and crankcase together with all internal running components, pistons, crankshaft, etc.
Shrink Fit: An interference fit obtained by heating the outer component or cooling the inner component so that they can be assembled with a push fit. When the temperatures are balanced the parts retain their interference fit.
Shroud: General term used to describe a cover.
Shunt (Electrical): A parallel part of an electrical circuit. An example is the shunt windings of some starter motors.
Side Draft: A carburettor where the choke tube (venturi) is fitted horizontally.
Side Thrust: Forces caused by cornering.
Silencer (Muffler): A component in the exhaust system to absorb the gas shock waves and noise in order to reduce the emitted noise from a vehicle engine. Also known as a muffler.(US term).
Silicon: One of many polymeric organic compounds of silicone with high resistance to cold, heat, water and passage of electricity.
Silicone: One of many polymeric organic compounds of silicon with high resistance to cold, heat, water and passage of electricity.
Simple Gear Train: Two or more gears in direct mesh.
Sine Wave: The wave pattern of an AC current. The positive and negative patterns are an inverse copy of each other.
Single Point Injection: A petrol fuel injection system using a single point injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI).
Single Point Injection.: A petrol fuel injection system using a single point injector in a throttle body in the inlet air supply and positioned on top of the inlet manifold. Also throttle body injection (TBI).
Sintering: A manufacturing process using heat and pressure to form metal and composite components. Examples are brake lining materials and some components traditionally produced by forging or hot stamping.
Sipe: Very narrow groove or cut in the tyre tread that aids the dispersal of surface water between the tyre and road.
Skidpan: Special test track for skidding on!
SLA Suspension: Short and long transverse suspension arms. The upper arm is the shorter of the two. The geometry of this layout keeps the wheel camber reasonably constant during suspension movements. Also known as 'unequal wishbones'.
Slave Cylinder: A hydraulic cylinder receiving a force and operating a mechanism. Examples are the clutch cylinder and the brake or wheel cylinders in brake units.
Sleeve (Cylinder): A steel sleeve used to form a running surface for pistons in an engine. Also known as a cylinder liner.
Sliding Caliper: A brake caliper that has one piston and one sliding section.
Sliding
Sliding Resistance: The frictional value for the surface of a sliding component in contact with the track or road on which it runs. An example is the sliding resistance of a road tyre skidding on a road surface. The sliding resistance is usually less than the rolling resistance.
Slinger: (1) A plate fitted on a rotating shaft in front of an oil seal to reduce the volume and pressure of the oil on the seal. (2) A plate or protuberance on a crankshaft for throwing oil onto the cylinder walls or other components.
Slip: Loss of grip between two frictional faces.
Slip Angle: The difference between the true line and the actual line of a vehicle wheel when cornering.
Slip Ring: Continuous ring of copper used with a brush to transmit electricity through a rotating component.
Sludge (Oil): Lubrication oil deterioration where the oil thickens, mixes with contaminants and forms a thick and glutinous jelly or paste.
Sludging: Description of what happens to oil if it is not changed as recommended - a sludge forms that looks like Mississippi mud!
Smoke Meter: Opacity meter used to measure the amount of smoke in diesel engine exhaust gases.
Snail Cam: A cam that is shaped like a snail shell. In other words it has more effect the further it is turned.
Snatching: Term used to describe the action of a clutch when the take up is too sharp/severe.
Sodium Hydroxide: A chemical used as the inflater for some air bags.
Soft Jawed Vice: A vice with soft material fitted to the jaws to prevent damage to any components held in it.
SOHC: Single Overhead Camshaft Engine.
Solder: A mixture of lead and tin used to join wires and terminals.
Soldered
Solenoid: A coil of wire. Usually used to refer to a device containing an electromagnet.
Solenoid Switch: Electro-magnetically activated electrical switch.
Solenoid Valve: A valve operated by a solenoid. Fuel injectors are good examples.
South Pole: The term used to describe one of the poles of a magnet where the magnetic field lines of force end.
Spacer: A metal sheet or washer used between two components to adjust free play.
Spade Terminal: A flat blade terminal used to make an electrical connection.
Spark Ignition (SI): The ignition of petrol by a spark in the combustion chamber of an engine.
Spark Plugs: Used to provide a small gap in the combustion chamber of an engine, for a spark to jump across.
Specific Gravity: The ratio of the density of a substance to that of water.
SPI: Single point injection. Electronic throttle body fuel injection system.
Spider: 1. Arachnid with eight legs...2. Name sometimes used for the shaft on which planet gears rotate in a differential.
Spigot: A bearing between two shafts mounted end to end axially.
Spigot Bearing: Bearing for a spigot shaft. Usually used to refer to the bearing inside the end of the crankshaft, into which the gearbox input shaft fits.
Spindle: A rotating shaft.
Spindle Arm: (1) Lever that imparts the steering action to the steering knuckle or stub axle assembly, as from a tie rod or track rod. Also steering arm, though this term is often used for the lever that imparts steering action from drag link to steering knuckle. (2) An intermediate arm in a steering system.
Spindle Bushes: Simple bearings on which a spindle rotates.
Spirit Level: A device full of liquid with a bubble that moves to the centre when it is level.
Splice: A joint in two or more cables made by crimping or soldering the cables together.
Spline: Axial groove on a shaft and hub.
Splined
Splines: Axial grooves on a shaft and hub.
Split Pin: A soft steel pin that has two sides that are folded out to secure the pin in a hole. Sometimes called a cotter pin.
Split Rings: Two continuous rings of copper used with brushes to transmit electricity through to a rotating component such as an alternator rotor field winding.
Split Slip Ring: Two continuous rings of copper used with brushes to transmit electricity through to a rotating component such as an alternator rotor field winding.
Splitter: Tool used to split ball joints or track rod ends from the steering arms.
Spokes: Thin metal rods that join the wheel hub to the rim and support the weight of a vehicle.
Spongy (Brakes): Usually caused by air in the hydraulic brake lines. A soft and imprecise feel to the brake pedal.
SPOUT: Spark output Signal.
Sprag Clutch: A uni-directional rotary clutch that uses a series of shaped (like a figure 8) rollers and springs to either freewheel or grip the outer tracks to transmit a rotating force.
Spring Clip: Small fixing device that can usually be removed by hand.
Spring Eye: A hole formed at the ends of leaf springs to allow fixing to the chassis.
Spring Ring: Small spring fixing device like a circlip.
Sprockets: Gear wheels usually used to drive or be driven by a chain.
Sprung Mass (Weight): The part of the vehicle supported by the suspension springs.
Spur Gear: A gear wheel with straight cut teeth.
Spurious Data: Data that falls outside what is expected.
Square Wave: The wave pattern formed by a digital signal.
Squeal: High pitched noise (screech) from friction components. Examples are brakes, clutch and drive belts.
Squirm: A twisting or side-to-side movement.
SRI: Service Reminder Indicator.
SRS: Supplementary Restraint System.
Stabiliser Bar: A torsion bar that connects the suspension on each side of a vehicle's axle to transmit movement from one side to the other in order to reduce vehicle roll when cornering.
Stall Speed: The maximum engine speed (rpm) of a vehicle with automatic transmission that can be obtained at full throttle against the brakes without moving the vehicle. A test procedure to check the torque converter.
Stalling: When an engine stops because it is running too slowly or due to some other influence such as a learner driver!
Stamping: A manufacturing process using punches and dies to cut objects out of sheet materials.
Star Wound Stator: An alternator stator winding with the three-phase coils connected at the center in order to give a large voltage output. The normal winding for light vehicle applications. Also 'Y' type stator.
Starter Motor: A powerful electric motor that produces high torque to rotate the engine for starting.
Starter Solenoid Feed: Small wire that causes the solenoid to operate. Feed is from the starter switch and usually a relay.
Starter Switch: The switch that operates the starter motor. Usually part of the ignition switch.
Static: A term that indicates components that are stationary. The opposite of dynamic when the components are in motion.
Static Balance: The balance of a rotating component about the rotational axis. Wheel balance has both static and dynamic quantities.
Stator
: Stationary part of machine. Examples are the magnetic inductance component of an alternator and the reaction member in a torque converter.
Stator Windings: Electrical windings on the stator of an alternator.
STC: Self Test Connector.
Steering: Mechanism or means whereby the direction of a vehicle is controlled.
Steering Arm: (1) Lever that imparts the steering action to the steering knuckle or stub axle assembly, as from a tie rod or track rod. Also spindle arm (US), though this term is often used for the lever that imparts steering action from drag link to steering knuckle. (2) An intermediate arm in a steering system.
Steering Axis: The point about which the steered wheel turns.
Steering Column: The linkage and outer housing between the steering wheel and the steering gearbox/rack.
Steering Gear: Small pinion that operates the steering rack. OR Worm gear that operates a steering arm.
Steering Gearbox: Gearcase in which the rotary movement of the steering column is converted into angular motion of the drop arm or pitman arm.
Steering Geometry: (1) Position of the wheel and steering swivel mountings. (2) Combination of angles in steering swivel.
Steering Nut: Part of a steering gearbox that moves on the worm gear.
Steering Rack: System where a small pinion works on a flat gear (rack) to move the steering arms.
Steering Shaft: The shaft that rotates as the steering wheel rotates.
Steering Swivel: The turning component that carries the steered wheel, king pin, stub axle assembly and McPherson strut.
Stellite: Hard and temperature resistant metal alloy used to coat exhaust valves.
Stepper Motor: An electrically controlled motor that gives precise incremental movements.
Stepper Motors: An electrically controlled motor that gives precise incremental movements.
STI: Self Test Input.
STO: Self Test Output.
: Stoichiometric Ratio: The chemically correct ratio for air and petrol to achieve complete combustion. An air/fuel ratio of 14.7:1.
Strain: Strain is the amount of extension in size divided by the original length.
Strainer: A mesh filter for basic cleaning of oil or fuel. Usually fitted in the oil pan or fuel tank.
Strangler: Alternative term for a choke flap in a cold start device for a carburettor.
Strap Wrench: A tool used to undo filters. A simple strap tightens around the filter to grip it securely.
Strap Wrenches: See Strap Wrench.
Stress: Stress is a measure of a force or load divided by the cross-sectional area of a material to which the force is applied (N/m2).
Striker Pin: Part of the door latch mechanism.
Stroboscopic: A flashing light. A strobe light is used to check and adjust ignition timing.
Stroke (Cylinder): The length of travel of the piston in the cylinder. Twice the throw of the crankshaft.
Strut: Term used to describe a suspension unit that operates telescopically.
Stub Axle: Alternative name for a king pin assembly or steering swivel.
Stub Axle Assembly: Alternative name for a king pin assembly or steering swivel.
Stud: Threaded rod.
Sub-Frame: An extra chassis component used to support a major part such as the engine or transmission.
Sump: Lower part of an engine or gearbox usually containing lubrication oil.
Sun Wheel: Central gear wheel of an epicyclic gear train or differential.
Supercharger: A mechanical air pump driven from the crankshaft and used to boost the intake air charge for an engine.
Suppressor: An electrical device fitted in parallel with a circuit to reduce the emission of electromagnetic waves at radio frequencies.
Suspension: Means whereby vehicle body is supported on its undercarriage, comprising springs, dampers and locating linkages.
Suspension Arms: Linkages used to construct a suspension system.
SVC: Service connector for octane and idle speed adjustment.
Swarf: Small pieces of metal that are produced during machining.
Swash-plate Compressor: See swash-plate pump.
Swash-plate Pump: A type of pump that uses a rotating plate, that is radially off-set from the axis of the shaft, to operate the pump pistons in their cylinders. This design can also be used for compressors.
Swept Volume: The volume inside a cylinder above the piston crown at bottom dead centre minus the volume above the piston at top dead centre which forms the combustion chamber and is given the term 'clearance volume'.
Switch Pack: General term to describe a collection of switches in one unit, window lift switches in the driver's door for example.
Swivel Axis: Line about which the steering turns.
Swivel
Swivel Pins: Pins used as part of a steering linkage. Often called King pins.
Symmetrical: A description of objects that are the same on each side of their centre line.
Synchromesh Gear: Gear change system in which the speed of rotation of a selected gear is automatically synchronized with that of the mainshaft.
Synchromesh Hub: Cone clutches that are part of a gear change system which equalises the speed of a rotating gear.
Synchronise: Two or more occurrences happening or being made to happen at the same time.
Synchroniser: Part of gear change system that automatically synchronises gear speeds before they are engaged.
Synchronizer: Part of gear change system that automatically synchronizes gear speeds before they are engaged.