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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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A means of locking a wheel, hub or pulley to a shaft to prevent relative rotation. The key consists of a short length of hardened steel of rectangular section which fits into keyways or grooves machined longitudinally into the surface of the shaft and into the core of the hub, this being simpler to produce than mating splines. A variant is the Woodruff key which is sector-milled into the shaft. In many cases the shaft and hub are a taper fit. |
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The facility on automatic transmissions for immediately obtaining a lower gear for rapid acceleration by sudden and full depression of the accelerator pedal. A similar feature is incorporated on some overdrives. |
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A thousand basic units. Thus a kilogram is 1000 grammes and a kilometre is 1000 metres. |
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The process of balancing a road wheel while it is rotating at high speeds, when even if in static balance the wheel may vibrate and tend to shimmy due to unbalanced couples set up by centrifugal force on components of mass in different rotational planes, these reversing every half turn. See also Dynamic balance. |
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The capacity of a body in motion to do work solely due to its mass and velocity. |
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The principle of utilizing the kinetic energy of high outflowing exhaust to aid the final extraction of residual gases when the piston has reached top dead centre (TDC). |
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The resistance to movement between two surfaces, already in relative motion, which is less than the static friction that exists between the surfaces when they are stationary. |
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Found more often on older cars, the alloy steel pin on which the steering knuckle, which locates the hub assembly, pivots while steering the vehicle.
The inclined steel pivot is in a steel housing that allows front wheels to turn side to side as well as move up and down. Generally replaced by a pair of ball joints on most modern cars. |
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The angle between the king pin (or swivel axis) and the vertical fore and aft plane that assists in obtaining centre-point steering without undue camber angle (inclination of the wheel). The king pin axis is inclined inwards to the top. |
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The hammering effect of a bearing having excess radial clearance on its journal due to incorrect selection, wear or damage. Big-end bearing knock is indicated by a heavy note, whereas small-end knock is of higher pitch. |
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Detonation on petrol engines, caused by rapid combustion of the end gases in the combustion chamber accompanied by high frequency pressure waves impinging on the cylinder walls to produce a knocking sound. It usually occurs during heavy loading�for example, when the throttle is fully opened. |
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A feature of compression-ignition (diesel) engines due to the delay between the point of initial injection of fuel and the onset of combustion, the delay depending on the cetane number and quality of the fuel. During the delay unburnt fuel accumulates and then tends to burn uncontrollably with rapid release of energy and shock waves giving rise to a knocking sound. |
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A front suspension component that acts as a hinge to support a front road wheel and to allow it to be turned in order to steer the car. The pivot points were originally king pins but later cars use ball joints. |
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A hinged joint between two rods, with a pin connecting the eye in the end of one rod to the forked end of the other. |
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A roughened surface, particularly on the circumference of a control wheel or knob, which affords the operator a grip. |
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A body-frame repair and alignment system in which a damaged vehicle is attached to a rigid, flat, steel base with multiple anchorages. Air or hydraulic rams are then used, via chains at appropriate angles, for pulling at clamps attached to the damaged vehicle structure. Optical devices resembling gun sights are then used to establish correct alignment. |
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