Dictionary of Automotive Terms: U-V

- U -

UAW: United Auto Workers. UNDERCOATING: Soft deadening material sprayed on underside of car, under hood, trunk lid, etc.

UNDER-SQUARE ENGINE: Engine in which bore diameter is smaller than length of stroke.

UNDERSTEER: Tendency for car, when negotiating a corner, to turn less sharply than driver intends.

UNIT BODY: Car body in which body itself acts as frame.

UNIVERSAL JOINT: Flexible joint that will permit changes in driving angle between driving and driven shaft.

UNLEADED GASOLINE: Gasoline not containing tetraethyl lead. Must be used with vehicles equipped with a catalytic converter.

UNSPRUNG WEIGHT: All parts of car not supported by suspension system; wheels, tires, etc.

UPDRAFT CARBURETOR: Carburetor in which the air passes upward through the carburetor into the intake manifold.

UPSET: Widening of diameter through pounding.

UPSHIFT: Shifting to a higher gear.

UTQGS: Uniform Tire Quality Grading System.

- V -

VACUUM: Enclosed area in which air pressure is below that of surrounding atmospheric pressure.

VACUUM ADVANCE (Distributor): Unit designed to advance and retard ignition timing through action of engine vacuum working on a diaphragm.

VACUUM BOOSTER: Small diaphragm vacuum pump, generally in combination with fuel pump, that's used to bolster engine vacuum during acceleration so vacuum operated devices will continue to operate.

VACUUM GAUGE: Gauge used to deter mine amount of vacuum existing in a chamber.

VACUUM MODULATOR: Device which uses engine vacuum to control throttle valve in automatic transmission.

VACUUM MOTOR: A device, utilizing a vacuum operated diaphragm, which causes movement of some other unit. VACUUM PUMP: Diaphragm type of pump used to produce vacuum.

VACUUM RUNOUT POINT: Point reached when vacuum brake power piston has built up all the braking force it's capable of with vacuum available.

VACUUM SWITCH (Electric): An electrical switch that's operated by vacuum.

VACUUM TANK: Tank in which vacuum exists. Generally used to provide vacuum to power brake installation in event engine vacuum can't be obtained. Tank will sup ply several brake applications before vacuum is exhausted.

VALVE: Device used to either open or close an opening. There are many different types.

VALVE CLEARANCE (Engine): Space between end of valve stem and actuating mechanism (rocker arm, lifter, etc).

VALVE DURATION: Length of time, measured in degrees of engine crankshaft rotation, that valve remains open.

VALVE FACE: Outer lower edge of valve head. The face contacts the valve seat when the valve is closed.

VALVE FLOAT: Condition where valves in engine are forced back open before they have had a chance to seat. Brought about (usually) by extremely high rpm.

VALVE GRINDING: Renewing valve face area by grinding on special grinding machine.

VALVE GUIDE: Hole through which stem of poppet valve passes. It is designed to keep valve in proper alignment. Some guides are pressed into place and others are merely drilled in block or in head metal.

VALVE HEAD (Engine): Portion of valve above stem.

VALVE-IN-HEAD ENGINE: Engine in which both intake and exhaust valves are mounted in the cylinder head and are driven by push rods or by an overhead camshaft.

VALVE KEEPER or VALVE KEY or VALVE RETAINER: Small unit that snaps into a groove in end of valve stem. It is designed to secure valve spring, valve spring retaining washer, and valve stem together. Some are of a split design, some of a horseshoe shape, etc.

VALVE LASH: Valve tappet clearance or total clearance in the valve operating train with cam follower on camshaft base circle.

VALVE LIFT: Distance a valve moves from full closed to full open position.

VALVE LIFTER or CAM FOLLOWER: Unit that contacts end of valve stem and camshaft. Follower rides on camshaft and when cam lobes move it upward, it opens valve.

VALVE MARGIN: Width of edge of valve head between top of valve and edge of face. Too narrow a margin results in pre-ignition and valve damage through overheating.

VALVE OIL SEAL: Neoprene rubber ring placed in groove in valve stem to prevent excess oil entering area between stem and guide. There are other types of these seals.

VALVE OVERLAP: Certain period in which both intake and exhaust valve are partially open. (Intake is starting to open while exhaust is not yet closed.)

VALVE PORT: Opening, through head or block, from intake or exhaust manifold to valve seat.

VALVE ROTATOR: Unit that's placed on end of valve stem so that when valve is opened and closed, the valve will rotate a small amount with each opening and closing. This gives longer valve life.

VALVE SEAT: Area onto which face of pop pet seats when closed. Two common angles for this seat are forty-five and thirty degrees.

VALVE SEAT GRINDING: Renewing valve seat area by grinding with a stone mounted upon a special mandrel.

VALVE SEAT INSERT: Hardened steel valve seat may be removed and replaced.

VALVE SPRING: Coil spring used to keep valves closed.

VALVE STEM (Engine): Portion of valve below head. The stem rides in the guide.

VALVE TAPPET: Adjusting screw to obtain specified clearance at end of valve stem (tap pet clearance). Screw may be in top of lifter, in rocker arm, or in the case of ball joint rocker arm, nut on mounting stud acts in place of a tappet screw.

VALVE TIMING: Adjusting position of camshaft to crankshaft so that valves will open and close at the proper time.

VALVE TRAIN: Various parts making up valve and its operating mechanism.

VALVE UMBRELLA: Washer-like unit that's placed over end of the valve stem to pre vent the entry of excess oil between the stem and the guide. Used in valve-in-head installations.

VANE: Thin plate affixed to rotatable unit to either throw off air or liquid, or to receive thrust imparted by moving air or liquid striking the vane. In the first case it would be acting as a pump and in the second case as a turbine.

VAPOR: Gaseous state of a substance usually a liquid or solid. Example: Steam.

VAPORIZATION: Breaking gasoline into fine particles and mixing it with incoming air.

VAPOR LOCK: Boiling or vaporizing of the fuel in the lines from excess heat. Boiling will interfere with movement of the fuel and will in some cases, completely stop the flow.

VAPOR SEPARATOR: A device used on cars equipped with air conditioning to pre vent vapor lock by feeding vapors back to the gas tank via a separate line.

VARIABLE PITCH STATOR: Stator that has vanes that may be adjusted to various angles depending on load conditions. Vane adjustment will increase, or decrease efficiency of stator.

VARIABLE VENTURI: A carburetor venturi whose opening size can be varied to meet changing engine speed and loading needs.

VARNISH: Deposit on interior of engine caused by engine oil breaking down under prolonged heat and use. Certain portions of oil deposit themselves in hard coatings of varnish.

V-BELT: V shaped belt commonly used to spin alternator, water pump, power steering pump, and air conditioning compressor.

VELOCITY: Time rate of motion. Speed with which an object moves as measured in feet per second, miles per hour, etc.

VENTURI: That part of a tube, channel, pipe, etc., so tapered as to form a smaller or constricted area. Liquid, or a gas, moving through this constricted area will speed up and as it passes narrowest point, a partial vacuum will be formed. Taper facing flow of air is much steeper than taper facing away from flow of air. Venturi principle is used in carburetor.

VIBRATION DAMPER: Round weighted device attached to front of crankshaft to minimize torsional vibration.

VISCOSIMETER: Device used to determine viscosity of a given sample of oil. Oil is heated to specific temperature and then allowed to flow through set orifice. Length of time required for certain amount to flow determines oil’s viscosity.

VISCOSITY: Measure of oil’s ability to pour. (Thick, thin.)

VISCOSITY INDEX: Measure of oil’s ability to resist changes in viscosity when heated.

VOLATILE: A substance that evaporates (turns to vapor) easily. Example: Gasoline.

VOLATILITY: Property of gasoline, alcohol, etc., to evaporate quickly and at relatively low temperatures.

VOLT: Unit of electrical pressure or force that will move a current of one ampere through a resistance of one ohm.

VOLTAGE: Difference in electrical potential between one end of a circuit and the other. Also called EMF (electromotive force). Voltage causes current to flow.

VOLTAGE DROP: Lowering of voltage due to excess length of wire, undersize wire, etc.

VOLTAGE REGULATOR: See Regulator— Voltage.

VOLTMETER: Instrument used to measure voltage in given circuit. (In volts.)

VOLUME: Measurement, in cubic inches, cubic feet, etc., of amount of space within a certain object or area.

VOLUMETRIC EFFICIENCY: Comparison between actual volume of fuel mixture drawn in on intake stroke and what would be drawn in if cylinder were to be completely filled.

VORTEX: Mass of whirling liquid or gas.

VORTEX FLOW (Torque Converter): Whirling motion of oil as it moves around and around from pump, through turbine, through stator and back into pump and so on.

V-TYPE ENGINE: An engine in which cylinders are arranged in two separate banks (rows) and set at an angle (V-shape) to each other.

VULCANIZATION: Process of heating com pounded rubber to alter its characteristics — making it tough, resilient, etc.