Automotive Technical Terms: Gaiter to Gyroscopic Effect

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Automotive Technical Terms: Gaiter to Gyroscopic Effect


Throughout this site we use many technical terms, and given the breadth of readership our site enjoys, sometimes we are remiss and incorrectly assume everyone knows what we are referring to. For those that do not, here are some explanations of the technical terms use.
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Gaiter


Gaiter
A covering of cloth, rubber or leather around a flexible item, such as a leaf spring, which permits movement between the two items but effectively sheaths them or seals any gap between them. Thus a gaiter is fitted between a gear lever and the surrounding floor panel, or around drive-shafts connected by universal-joints.
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Gallery


A passage cast in the cylinder block of the engine which forms a reservoir for oil under pressure. The oil is ducted from the gallery to all main bearings and so to the crankshaft.
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Galvanized


Usually taken to refer to a coating of zinc on mild-steel to protect the metal from rusting. Applied either by electro-plating or by dipping in molten zinc. This treatment is sometimes applied to the lower portions of certain vehicle bodies, made up of pressed-steel, in order to prevent corrosion.
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Gap


A set distance or clearance between surfaces of adjacent parts of a mechanism.
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Gap, Contact Breaker


Contact Breaker
The distance between the contact breaker points when in the fully open position, usually in the order of 0.4 mm to 0.5 mm (0.018ins to 0.20ins) but varying from car model to car model.
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Gap, Piston Ring


Piston Ring Gap
The distance between the ends of the piston ring when sited in the cylinder bore. The gap is necessary in order to ensure that the ends do not butt due to expansion at a higher temperature which could cause seizure and breakage of the ring. An excessive gap causes gas leakage.
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Gap, Sparking Plug


Spark Plug Gap
The gap between the central electrode and the earthing electrode of a spark plug. The gap varies from plug type to type and from engine to engine.
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Gas Flow


The path taken by the fuel/air mixture through the carburettor and induction manifold into the combustion chamber. Then the path of the combustion products in to and through the exhaust manifold.
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Gas Thread


A screw thread of fine pitch sometimes employed on pipe fittings.
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Gas Turbine


A type of internal combustion engine into which air is drawn in large volumes and compressed by a centrifugal fan. It is then ducted into specially shaped combustion chambers where fuel is injected and continually burnt. The resulting gases, at high velocity and pressure, are directed by stator vanes on to the blades of a first turbine which drives the compressor fan, and then, via a further set of stator vanes, to a second turbine connected to an output shaft to provide external power. Used in this form in turbo-prop aircraft, in certain stationary engines, and in some experimental vehicles such as the Rover car now in London's Science Museum. Development work on gas turbines for vehicles continues virtually throughout the motor industry.
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Gas Welding


A commonly used modern process of joining together items of steel and certain other metals, by using the high temperature flame of an oxy-acetylene torch to fuse and weld the junction between them. Acetylene mixed with oxygen in the proper portion can produce a flame temperature of nearly 3500CC. Usually, extra metal in the form of wire is added to the molten metal to strengthen the joint. Correctly done, the new joint can be as strong as the original metal.
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Gasket


Head Gasket
A replaceable strip of resilient material clamped between mating surfaces of contiguous parts to effect a seal and so prevent escape of high pressure gases, oil or coolant. It also prevents the ingress of atmosphere. The material must be impermeable to those liquids in contact with it, conformable to surface imperfections and resistant to changes in its environment such as temperature. There is an appropriate material for each application. A sandwich of asbestos fibres between thin sheets of copper or steel is used between cylinder head and cylinder block, as it has to resist flame damage. The gasket between sump and crankcase or rocker cover and cylinder head is often made from cork or, if for use between machined faces, it may be made of waxed cartridge papers. Gaskets should always be renewed when disturbed.
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Gasket Cement


Proprietary solutions, usually with a resinous base, used to coat certain gaskets to perfect a seal and to cement the gaskets to the contacting surface.
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Gasket Fire Ring


Gasket Fire Ring
A U-section steel ring fitted to the cylinder openings in the cylinder head gasket to seal the combustion chambers and which is designed to prevent flame damage to the gasket.
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Gasoline


A hydrocarbon fuel known in Australia as “Petrol”, or in the USA as the shortened “Gas”. It is used in most private motor cars to provide the heat to be converted into mechanical energy for the normal type of internal combustion engine. Produced by the distillation of crude oil, gasoline being some of the lighter fractions, or by cracking of some of the heavier fractions, gasoline is a universal fuel. Additives are used to improve antiknock rating and to prevent icing, gum deposits, rusting and corrosion of containers.
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Gassing


Bubbles of hydrogen and oxygen which emerge from the plates of a battery through the electrolyte during the charging process. A naked flame can cause an explosion of this mixture of gases.
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Gate Change


Gate Change Gear Lever
A type of gear lever working in a "gate", a grid with slots to accommodate and guide the lever. Used on certain earlier cars especially where the gear lever was sited on the offside of the drivers seat e.g. earlier Bentleys. Still used in some high-performance cars where accuracy of gear changing is vital.
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Gauges


Engineers tools, including Vernier calipers, micrometers, "go-no-go" gauges, slip gauges and feeler gauges, height and depth gauges used for accurate measuring of dimensions of thickness, diameters or clearances between adjacent parts. A term also used for the Instruments which give visual indications to the driver of such important values as rpm, oil pressure and temperature, coolant temperature, fuel contents, charging rate, battery voltage and road speed. Other gauges showing induction "vacuum", compression pressure, exhaust analysis etc., are used by a professional mechanic to diagnose engine condition.
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Gear


A particular train of gear wheels in a gearbox selected to produce a desired overall gear ratio - thus "2nd gear" or "4th gear".
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Gear Wheel (or geared wheel)


Gear Wheel
A metal or fibre wheel having suitably contoured teeth on its periphery to mesh with a similar mating wheel of any diameter. This action provides torque transference from one shaft to another, parallel or angled to the former, reversal of torque, or possibly altering the speed and direction of rotation and the torque.
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Gearbox


A pressed-steel or cast casing usually mounted behind the clutch and on the output end of the engine. It contains an arrangement of shafts and meshing gear wheels which provides a selection of trains giving several velocity ratios between input and output shafts. This provides a means of increasing torque, as necessary, to allow starting from rest, rapid acceleration, the climbing of steep gradients, etc. The gearbox also allows a reversal of the engine torque to drive the vehicle rearwards.
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Gearbox Oil


Lubricating oil specially formulated for use in gearboxes. Mixed with suitable additives to prevent the breaking down of the oil film by the high pressures occuring between the mating teeth of the gears. Formerly, gear oils were of high viscosity causing problems when cold, but modern oils are much lighter now. Whereas certain modern cars use normal engine oils in gearboxes, high-pressure oils are usually necessary for final drive units
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Geared Pump (or Spur-Gear Pump)


A pump for propelling liquid. Frequently used as an oil pump in an engine. It has two mating wheels, rotating in opposite directions, which carry oil between the gear teeth and the almost contacting wall of the chamber from the inlet orifice on one side to the outlet orifice, thus ensuring that sufficient oil pressure is created to properly lubricate the engine.
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Gear Ratio


Used to define the number of times that an input shaft turns in relation to the output shaft.
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Gel Coating


A semi-flexible continuous skin of special polyester resin applied to glass-fibre panels which is used to give a good paint finish, to protect the under surface from corrosion and abrasion damage and to mask the fibre pattern. Such coatings may also be colour impregnated in order to obviate painting.
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General Motors Synchromesh


The General Motors' design was one of the earliest synchromesh mechanisms to incorporate a baulking device and it has been widely used on Vauxhall cars and those produced by other General Motors' subsidiaries, though it has now been largely superseded by the baulk ring design. The design is best understood by reference to the engagement of direct-drive top gear in an orthodox layshaft gearbox.
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Generator


Generator
Generator A device which produces electrical power by converting the mechanical energy which drives the machine into electrical energy. This is done via the agency of a magnetic field in which coils or wire are made to rotate. The term normally refers to a dynamo producing direct current.
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Gland


A seal of rubber, leather, or packed asbestos, around the rod of a piston assembly, as in the case of shock absorbers, or around the spindle of a control valve or pump and which is designed to prevent loss of fluid or steam.
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Glass-Fibre Reinforced Plastic


Polyester resins, thermoplastic or thermosetting, reinforced with fine filament glass-fibres to give great strength and elasticity. Capable of withstanding high temperatures. Used for moulded shaped panels, casings and other moderately stressed structures. Also used in various forms for repair and filling of damaged low-stressed metal panels.
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Glass, Laminated


Laminated Glass
Used for windscreens and other window panels. Laminated glass is produced as a sandwich of two layers of thin glass firmly bonded to an interlayer of transparent vinyl (originally celluloid). In the event of violent and/or penetrating impact and fracture this type of glass holds together. Thus, it greatly reduces the incidence of skin lacerations in the event of an accident.
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Glass, Toughened


Used for windscreens and other glass panels on certain vehicles. Such panels are produced to a pre-set size and shape by a process of heating the glass and then rapidly cooling it. This technique causes residual internal stresses, greatly increasing its strength and reducing its liability to fracture. In the event of fractures resulting from an accident or a blow to the glass it results in fragmentation of the glass into fairly harmless particles.
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Glaze


A hard, polished film sometimes produced on the friction linings of brakes or clutches which is due to high operating temperatures or pollution by a lubricant which has been carburized.
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Glazing


The filling up of the interstices of the surface of a grinding wheel with minute particles of the abraded material, preventing further efficient grinding.
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Glycol


Abbreviation for ethylene glycol. The most practicable commodity for use as an anti-freeze for the engine coolant. It has a sufficiently high boiling point to prevent evaporation in the event of failure of the radiator pressure cap.
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Governor


A mechanism which limits or regulates the speed of a machine. Such devices prevent over-revving of an engine or are used to maintain a speed set by the control even under varying load. Governors can also control, in part, the changing of ratios in an automatic gear box. There are various forms of governor, but most depend on a degree of centrifugal force to provide the controlling force.
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Graphite


An allotropic form of carbon used for the brushes in generators which collect current from the commutator segments: It is used also for bushes in water pumps and for thrust bearings in some clutches. Used in powder form as an additive to oils and greases, especially to prevent seizure of threads on nuts and studs at high temperatures. Thus advocated for sparking plug threads and exhaust manifold studs.
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Grease


A lubricating compound formed by adding metallic soaps to lubricating oils, with thickening and other additives to make them suitable for individual application. Greases may be general purpose, high melting point, water pump grease and other special greases for particular uses, such as - where in contact with rubber seals.
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Grease Gun


Grease Gun
A special ram designed on hydraulic principles. A grease gun is used to inject grease under pressure into bearing surfaces through suitable application nipples.
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Greenhouse


The upper portion of the automobile comprising the windscreen, side windows, rear window and roof. More applicable to modern cars with large glass areas.
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Grille (or Grill)


A perforated or slotted screen placed before the radiator for protection and decorative effect. Also used over apertures for air entry to heating systems, carburettors, etc.
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Grind


(A) to produce and profile or erode away a surface using a grinding wheel. (B) the process of producing smooth mating over-faces by rubbing them together when coated with suitable abrasives.
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Grommet


Grommet
A guide, usually of rubber, through which a rod or cable protrudes. Grommets also protect pipes, cables, etc. from surrounding sheet metal.
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Gross Horsepower


The horse power derived from the torque registered on a dynamometer by a bare engine i.e. when not driving such ancillaries as water pump, cooling fan, dynamo or alternator, hydraulic pump or air compressor (recorded as SAE). Net horse power is that available at the fly-wheel of the engine as normally installed in a chassis (usually recorded as DIN).
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Grinding Paste


Formed from abrasive particles of selected coarseness in a grease or soap base and used in grinding exercises such as when lapping in poppet valves.
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Ground Clearance


Minimum distance between the lower side of the automobile and the ground.
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Gudgeon Pin


Gudgeon Pin
Also called the “piston pin” or “wrist pin”, it connects the piston to the top of the con-rod by the little end bearing. On car engines this is the hardened alloy steel pin which connects the piston to the small end of the connecting rod. It allows the latter to pivot in the piston while transferring the force of the expanding gases on the piston to the rotating crankshaft. In order to reduce the reciprocating mass gudgeon pins are usually hollow.
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Gumming


The formation of resinous gum on the underside of the piston and in piston ring grooves. This causes the rings to become trapped and unable to effect a gas-tight seal. The gum is produced by high temperature acting on the lubrication oil especially those of cheaper or unsuitable varieties.
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Gusset


Gusset
An angled bracket or a plate used to stiffen an angular portion of a structure e.g. the door pillars where they join the floor pressing.
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Gyroscopic Effect


Gyroscopic Effect
Natural forces of magnitude which are produced when a rotary mass is caused to change its axis of rotation. These forces cause a secondary change of angle at right angles to that intended. Thus a wheel rotating at high speed if swivelled as in steering the vehicle, attempts to incline sideways.
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