Automotive Glossary of Terms - R -
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Definitions for automotive terms and illustrations from rack and pinion steering to run-on engine.
RACE: The surface on the inner or outer ring of a bearing on which the balls, needles or rollers move.
RACK AND PINION STEERING: A type of automotive steering system using a pinion gear attached to the end of the steering shaft. The pinion meshes with a long rack attached to the steering linkage.
RADIAL TIRE: Tire design which uses body cords running at right angles to the center line of the tire. Two or more belts are used to give tread strength. Radials can be identified by their characteristic sidewall bulge.
RADIATOR: Part of the cooling system for a water-cooled engine, mounted in the front of the car and connected to the engine with rubber hoses. Through the radiator, excess combustion heat is dissipated into the atmosphere through forced convection using a water and glycol based mixture that circulates through, and cools, the engine.
REAR MAIN OIL SEAL: A synthetic or rope-type seal that prevents oil from leaking out of the engine past the rear main crankshaft bearing.
RECALL: When a manufacturer recalls vehicles it has manufactured back to the dealership for specific repairs related to unplanned mechanical problems and/or safety issues. Recalls are usually voluntary and are made in conjunction with regulatory control of the National Highway Traffic Safety Agency (NHTSA). They can originate with the manufacturer or with the NHTSA. Repairs performed under a recall are usually free to the consumer.
RECIRCULATING BALL: Type of steering system in which recirculating steel balls occupy the area between the nut and worm wheel, causing a reduction in friction.
RECTIFIER: A device (used primarily in alternators) that permits electrical current to flow in one direction only.
REFRIGERANT 12 (R-12) or 134 (R-134): The generic name of the refrigerant used in automotive air conditioning systems.
REGULATOR: A device which maintains the amperage and/or voltage levels of a circuit at predetermined values.
RELAY: A switch which automatically opens and/or closes a circuit.
RELUCTOR: A wheel that rotates inside the distributor and triggers the release of voltage in an electronic ignition.
RESIN: A liquid plastic used in body work.
RESISTANCE: The opposition to the flow of current through a circuit or electrical device, and is measured in ohms. Resistance is equal to the voltage divided by the amperage.
RESISTOR SPARK PLUG: A spark plug using a resistor to shorten the spark duration. This suppresses radio interference and lengthens plug life.
RESISTOR: A device, usually made of wire, which offers a preset amount of resistance in an electrical circuit.
RETARD: Setting the ignition timing so that spark occurs later (fewer degrees before TDC).
RING GEAR: The name given to a ring-shaped gear attached to a differential case, or affixed to a flywheel or as part of a planetary gear set.
ROCKER ARM: A lever which rotates around a shaft pushing down (opening) the valve with an end when the other end is pushed up by the pushrod. Spring pressure will later close the valve.
ROCKER PANEL: The body panel below the doors between the wheel openings.
ROLLER BEARING: A bearing made up of hardened inner and outer races between which hardened steel rollers move.
ROTOR: (1.) The disc-shaped part of a disc brake assembly, upon which the brake pads bear; also called brake disc. (2.) The device mounted atop the distributor shaft, which passes current to the distributor cap tower contacts.
ROTARY ENGINE: See Wankel engine.
RPM: Revolutions per minute (usually indicates engine speed).
RUN-ON ENGINE: Condition when the engine continues to run, even when the key is turned off. See dieseling.