DICTIONARY OF AUTOMOTIVE TERMS - "Ov"

Oval piston:

A special piston developed by Honda, able to accommodate eight valves and two spark plugs

Oval track:

A race course which is shaped like an oval rather than a circle. Sometimes used to describe any race track, other than a road race.

Ovals:

See wide ovals

Oven:

See:
drying oven
primer oven
top coat oven

Overall gear ratio:

The ratio of engine revolutions to road wheel revolutions, producing road speed as a ratio of engine speed (sometimes expressed as mph per 1000 rpm)

Overall length:

The extreme length of a ship measured from the foremost point of the stem to the aftermost part of the stern

Overall ratio:

See steering overall ratio

Overall repainting:

A type of paint job that involves the entire vehicle

Overall rim diameter:

A measurement from the top of the flange to opposite top of the flange 180° away.

Overaxle pipe:

See kick-up pipe

Overbore:

To drill out the cylinder and put in larger pistons to increase the capacity or clean up damaged cylinder walls

Overcapacity:

The situation where maximum global production of automobiles exceeds the total global demand for automobiles.

Overcharge:

Refers to the condition that occurs when too much refrigerant or oil is in the system

Overcure:

Vulcanizing a tire longer than necessary. It can result in the deterioration of certain physical properties.

Overdrive:

1. A unit with a planetary gearset which turns the driveshaft faster than the transmission output shaft.
2. An additional gearbox which is mounted in the driveline. Normally the final drive ratio is 1:1; but the overdrive makes it less (e.g., 0.87:1). The overdrive can reduce gas consumption at sustained high-speed driving, engine noise, and engine wear. Also called "overdrive transmission." Also see aftermarket overdrive
3. Gearing in which less than one revolution of a transmission's input shaft causes one turn of the output shaft. The purpose of overdrive is to reduce engine rpm in high gear for better fuel economy. Example: A transmission with an overdrive top gear has a ratio of 0.70 to one. Turning the input shaft 0.7 revolutions causes 1.0 revolution of the output shaft.

Overdrive transmission:

A transmission with a high gear which acts as an overdrive.

Overflow:

To spew out tread compound at the mold parting line or at the edge of the matrix skirt. This excess material should be trimmed or buffed off the finished product.

Overflow hose:

A tube located in the radiator fill hole that allows excess liquid to escape from the cooling system under conditions of extreme heat, pressure, or overfilling. Also see coolant recovery system.

Overflow pipe:

A tube located in the radiator fill hole that allows excess liquid to escape from the cooling system under conditions of extreme heat, pressure, or overfilling. Also see coolant recovery system.

Overhang:

The distance between the outermost front or rear point of a vehicle and the wheel centers of the respective axle. Also see load overhang

Overhaul:

See:
rebuild
engine overhaul

Overhead cam (OHC):

See:
overhead camshaft
double overhead cam
dual overhead cam engine
single overhead cam

Overhead cam engine:

See dual overhead cam engine

Overhead camshaft:

(OHC) The camshaft that activates the valves is mounted above the head and driven by a long timing chain or cam chain. In contrast, a pushrod engine has the camshaft below the cylinders so that thin rods (pushrods) are moved by the camshaft and activate the valves. An engine with an overhead cam means that the distance between the cam and the valves is much shorter, so the valves respond quicker and valve adjustment can be more accurate. Also this system allows for higher engine speed because of fewer moving valvetrain parts. A system with only one cam is called "Single Overhead Cam" (SOHC). In some instances there are two camshafts above the heads (one for the intake valves and the other for the exhaust) and called "double overhead cam" (DOHC).
Also See:
single overhead camshaft
twin overhead camshaft

Overhead position:

A weld made on the underside of the joint with the face of the weld in a horizontal plane.

Overhead valves:

(OHV) Valves located in the head. A four-stroke engine with the intake and exhaust poppet valves located in the cylinder head and not at the side of the cylinder as in a side-valve engine. The valve stems are either at an angle or parallel and the valve discs face the piston, valve actuation pushrod and swing arm. Also see I-head engine.

Overheat:

To make or become too hot. Engine overheating could be caused by a fault in the cooling system caused by a leak, blockage, slipping or broken fan belt; lack of engine oil; or an over-lean mixture. Brake overheating can be caused by prolonged use (e.g., when going downhill) leading to brake fade, binding brake shoes, or seized disc pads or pistons

Overinflated tire:

A tire which has too much air in it, causing premature wear in the tread center. The opposite is underinflated tire

Over inflation:

Excessive tire pressure in relation to the tire size and load carried. It will generally result in wear at the center of the tire tread rather than the outer sides.

Overlap:

1. The part of the spray band that covers the previous application of paint. A 50% overlap on each stroke is generally recommended.
2. Extension of the weld face metal beyond the toe of the weld.
3. The number of degrees of crankshaft rotation where the both the intake and exhaust valves are open at the same time. This situation will occur only at the end of the exhaust stroke and the beginning of the following intake stroke. Also see valve overlap.

Overlay:

The upper layer of a plain bearing insert. If the overlay is worn, the bearing material beneath it will still allow for a certain emergency operation of the component supported in the plain bearing

Overlay sprocket:

A sprocket with a large center hole and is bolted to an existing sprocket to change the gear ratio.

Overlay paint:

A special type of custom paint where a design on the painted surface is embedded below a coat of translucent paint, giving the impression that two paints are applied to the car. Compare candy paint

Overload:

1. Carrying more weight on a tire than its listed maximum carrying capacity or carrying excessive loads on a tire in relation to its inflation (esp. if underinflated).
2. Load greater than that for which system or mechanism was intended.

Overload protector:

Device, either temperature, pressure, or current operated, which will stop operation of unit if dangerous conditions arise.

Overload spring:

A chassis spring which acts only under heavy load and prevents bottoming

Overrev:

To run an engine above the maximum recommended rpm. To exceed the redline on the tachometer

Override button:

See ABS override button.

Overrider:

A short, vertical attachment to the bumper, to prevent interlocking with other bumpers

Overrun:

1. A vehicle travelling with no throttle and the engine acting as a brake is said to be "on the overrun" or "overrunning."
2. The action of a trailer when it travels faster than the towing vehicle

Also See:
coast
deceleration

Overrun control valve:

A valve in a crossover pipe between the compressor suction and discharge sides of some turbocharger systems. When the manifold pressure drops, as during deceleration, the overrun control valve opens and allows compressed air to circulate through the compressor again; this maintains turbo speed on the overrun, minimizing turbo lag when the throttle is re-opened; not to be confused with a safety-relief valve in the compressor discharge line or with a wastegate valve

Overrun cut-off/shut-off:

See deceleration fuel cut-off

Overrunning clutch:

1. A clutch mechanism that will drive in one direction only. If driving torque is removed or reversed, the clutch slips.
2. A part of a starter motor designed to avoid armature damage caused by severe overrevving.
3. A device in an automatic transmission that disengages the engine on overrun

Also See:
freewheeling
one-way clutch

Overrunning clutch starter:

See pre-engaged starter

Overrunning clutch starter drive:

A starter drive that is mechanically engaged. When the engine starts, the overrunning clutch operates until the drive is mechanically disengaged. Also see freewheeling.

Overrunning coupling:

See freewheeling

Oversize:

Installing a tire larger than needed to carry the load. A common (though not always beneficial) practice on passenger vehicles to increase one size when replacing OEM tires.

Oversize brake shoes:

Brake shoes with thicker linings designed for ukse in drums that have been machined oversize.

Oversize piston:

A piston with a diameter slightly larger than that of the standard piston, used in order to allow for a honing of the cylinder walls

Oversize valve guide:

A valve guide with a slightly larger outside diameter than the standard valve guide, used to repair worn valve guides after their bores have been reamed

Overspray:

The fine mist of paint on areas where it is not wanted (glass, moldings, other painted surfaces, etc). The distinguishing mark of a vehicle that has been painted or had body work done. Compare spray mist

Oversquare:

An engine where the cylinder bore diameter is greater than the length of the stroke.

Over square engine:

An engine in which the bore diameter is larger than the length of the stroke.

Oversteer:

The tendency for a vehicle, when negotiating a corner, to turn more sharply than the driver intends. The rear end of the vehicle wants to swing toward the outside of a turn. It is generally a sign that the suspension roll resistance is too hard in the rear or too soft in the front. A rear-engine vehicle has a natural tendency to want to swap ends, or oversteer, unless its suspension is adjusted to counteract it. A handling condition in which the slip angles of the rear tires are greater than the slip angles of the front tires. An oversteering car is sometimes said to be "loose," because its tail tends to swing wide.
Also See:
lift-throttle oversteer
power oversteer
roll oversteer
tire deviation angle

Overtake:

To pass another vehicle going in the same direction

Overtaking:

The action of your passing a vehicle which is going in the same direction you are.

Overthin:

To add too much thinner to paint

Overtime:

Includes pay received for the number of hours worked in excess of the standard workday or workweek.

Over-travel spring:

A special assembly on some cable-actuated starwheel automatic adjusters that prevents over-adjustment or damage.

Over your shoulder:

Trucker slang for Behind you as in "How's it look over your shoulder?"

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