ASE A1 Glossary

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  • a

  • Alloy
    The material that results from the fusion of two or more different metals. For example, the fusion of copper and zinc produces brass.
  • Annealing
    A process of heating metal and then allowing it to cool slowly. Annealing reduces a metal's brittleness and increases its durability.
  • API Service Rating
    The American Petroleum Institute's coding system for classifying engine oils. Gasoline engines are identified with an 'S' prefix for 'spark' ignition, and are rated from 'SA' through 'SJ.' Diesel engines are identified with a 'C' prefix for 'compression' ignition, and are rated from 'CA' through 'CF.' The second letter in the code indicates the oil's specific lubricating qualities.
  • ATDC
    After Top Dead Center
  • b

  • Backlash
    Refers to the clearance or play that exists between two meshing gears.
  • Backpressure
    A term used to indicate the resistance to gas flow in a vehicle's exhaust system. Excessive backpressure reduces an engine's breathing ability,which can result in symptoms ranging from a lack of power to a no-start condition.
  • Battery Capacity Test
    A test used to determine a battery's ability to handle a sustained high-current load for a period of 15 seconds. When tested at 80¡F, a good battery will maintain a terminal voltage of at least 9.6V for the duration of the test.
  • BDC
    Bottom Dead Center
  • Bearing Crush
    Refers to the load applied to a bearing insert when a main or rod cap is torqued into position. Crush results from the slight distance the bearing insert rises above the cap's parting line.
  • Blowby
    Combustion gases that leak past the piston rings and flow into the crankcase during the engine's power stroke.
  • Boss
    An extension or reinforced section of certain components, such as the projections on the outside of the block that accept the engine mount bolts.
  • BTDC
    Before Top Dead Center
  • c

  • Catalyst
    An element or compound capable of causing a chemical reaction without being consumed in the process.
  • Chamfer
    A beveled edge.
  • Choke Pull-off
    A vacuum operated diaphragm mounted on the outside of a carburetor. The pull-off is used to open the choke valve a predetermined amount in order to prevent excessively rich fuel mixtures during cold starts.
  • Cold Start Injector
    A non-computer controlled injector that delivers additional fuel during cold engine starts.
  • Compression Ratio
    Indicates the difference in cylinder volume between BDC and TDC.
  • Coolant
    A blend of water and ethylene glycol-based antifreeze. A 50/50 mixture provides freeze protection down to -34¡F (-37¡C), and raises the boiling point to 265¡F (129¡C) when used in a system with a 15-psi pressure cap.
  • Core Plugs
    Steel discs used to fill the core holes in the engine block. The core holes allow residual sand to be removed from the block following the casting process.
  • Crank Pins
    The offset journals on the crankshaft that accept the connecting rods.
  • Crankcase Pressure
    Pressure that builds inside the crankcase during the power stroke as combustion gases leaks past the piston rings. Crankcase pressure is relieved through the PCV system.
  • Crankcase Vacuum
    A negative pressure that develops inside the crankcase as a result of a properly operating PCV system.
  • Cylinder Liner
    An iron sleeve used to line the cylinder bores of aluminum blocks. Liners are also used to restore a badly worn cylinder in a cast iron block.
  • d

  • Data Link Connector (DLC)
    The computer interface connector that accepts a scan tool; typically located below the instrument panel.
  • Detonation
    A metallic rattling sound emanating from the cylinder as a result of two pressure fronts colliding during the combustion process. One pressure front is initiated through the firing of the spark plug. The second pressure front develops through spontaneous combustion, which results as temperature and pressure rise in the cylinder and cause the mixture to ignite in another location.
  • DI
    Distributor Ignition
  • DMM
    Digital Multimeter
  • Dowel
    A pin extending from one component that fits into a corresponding hole in a mating part.
  • Driver
    A solid-state switch used to control the operation of computer output devices such as solenoids and relays.
  • e

  • EI
    Electronic (distributorless) Ignition
  • f

  • Ferrous Metal
    A metal that contains iron or steel and is therefore magnetic.
  • Flange
    The collar or rim found on certain parts for holding them in place. A crankshaft thrust bearing has a flange on either side.
  • g

  • Glaze
    A thin residue that forms on the cylinder wall through the combination of heat, oil, and friction over a long period.
  • h

  • Hypereutectic Piston
    An aluminum alloy piston with a silicon content greater than 12 percent. The addition of silicon increases the piston's strength, wear resistance, and thermal stability.
  • k

  • Knurling
    A procedure used to restore the inside diameter of a worn valve guide.
  • KOEO
    Key on, engine off
  • kPa (kilopascals)
    6.895 kPa = 1 psi
  • l

  • Land
    The area of metal on a piston that separates the rings from one another.
  • Lapping
    An alternative to machining the valves and seats. Lapping involves applying an abrasive compound between the valve face and seat, and then spinning the valve by hand to conform the two surfaces.
  • m

  • Magnetic Sensor
    A device commonly used for monitoring crankshaft position. The sensor contains a permanent magnet and produces an AC voltage when triggered.
  • Manifold Absolute Pressure (MAP) Sensor
    An electronic device that converts intake manifold pressure into an electrical signal. In some electronic transmission/transaxles, the computer uses the signal from the MAP sensor to adjust line pressure according to changes in altitude.
  • Manifold Vacuum
    The vacuum signal originating from below the closed throttle plate. Manifold vacuum is highest during deceleration and lowest at wide-open throttle.
  • Margin
    The area between the valve face and the head of the valve.
  • o

  • OHC
    Overhead Cam
  • OHV
    Overhead Valve
  • Oil Pump Screen Bypass Valve
    A valve in the pickup screen that opens under low-temperature conditions when the oil is too cold to flow freely. The valve also opens in the event the pickup screen becomes clogged.
  • p

  • Piston Slap
    The noise caused by excessive piston-to-cylinder wall clearance. Piston slap is loudest when the engine is cold, since the clearance is greatest under this condition.
  • Positive Crankcase Ventilation (PCV)
    A system used to remove blowby gases from the crankcase. Most PCV systems use a spring-loaded valve to regulate the volume of crankcase vapors entering the engine, while some use a fixed orifice.
  • Powertrain Control Module (PCM)
    An on-board computer that manages fuel delivery, spark timing, idle speed, emission control sub-systems, and other powertrain functions such as the torque converter clutch and transmission shift solenoids.
  • Primary Voltage
    The voltage produced in the primary winding of the ignition coil when primary current is interrupted and the magnetic field collapses. Primary voltage is typically 200-300 volts.
  • Prussian Blue
    A material applied to the valve face for checking the seat contact area.
  • r

  • Reluctor
    A metal wheel with specifically spaced notches or teeth used to trigger a magnetic sensor. On some engines, the crank sensor reluctor is an integral part of the crankshaft.
  • Reverse Flow Cooling System
    A system that allows coolant to flow through the cylinder heads prior to flowing through the engine block. Reverse flow cooling provides more stable combustion chamber temperatures than conventional cooling systems.
  • Rotator
    A type of spring retainer that allows the valve to turn as it opens and closes.
  • s

  • Secondary Voltage
    The voltage produced in the secondary winding of the ignition coil when the magnetic field collapses. Secondary voltage is used to fire the spark plugs.
  • t

  • Thermal Time Switch
    A temperature-sensitive device used to control a cold start injector.
  • Throw
    Refers to the distance between the centerline of a crankshaft's main bearing journals and the centerline of the crank pins (rod journals).
  • Torque-to-Yield (T-T-Y) Head Bolt
    A fastener designed to be torqued just short of its yield point so that maximum clamping force will be applied to the cylinder head gasket. T-T-Y bolts should not be re-used.
  • v

  • Vacuum Relief Valve
    Part of a radiator pressure cap. The vacuum valve opens to allow atmospheric pressure to enter the system as the coolant contracts following engine shutdown. This action prevents the radiator and/or hoses from collapsing.
  • Valve Overlap
    The period between the exhaust and intake strokes when both valves (intake and exhaust) are opened at the same time.
  • Valve Spring Installed Height
    The distance between the spring pad in the cylinder head and the bottom of the spring retainer. This dimension is typically checked with the valve seated in the head, the spring retainer and keepers installed, and the valve spring removed.
  • Viscosity
    An oil's resistance to flow.
  • z

  • Zero Lash
    Refers to the absence of clearance between valve train components. Properly functioning hydraulic lifters maintain the valve gear in a zero-lash condition.