Timing light

Last updated
Timing light, combination instrument with RPM, volt meter and dwell angle meter. The actual light is on the far end.
The black clamp connects to the battery -, the red clamp to +, the green one to the breaker side of the coil (for RPM), the big black clamp in the foreground is an inductive pick-up that clamps around a spark plug wire. Timinglight.jpg
Timing light, combination instrument with RPM, volt meter and dwell angle meter. The actual light is on the far end.
The black clamp connects to the battery -, the red clamp to +, the green one to the breaker side of the coil (for RPM), the big black clamp in the foreground is an inductive pick-up that clamps around a spark plug wire.

A timing light is a stroboscope used to dynamically set the ignition timing of an Otto cycle or similar internal combustion engine equipped with a distributor. Modern electronically controlled passenger vehicle engines require use of a scan tool to display ignition timing.

Stroboscope instrument used to make a cyclically moving object appear to be slow-moving, or stationary

A stroboscope also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces brief repetitive flashes of light. Usually the rate of the stroboscope is adjustable to different frequencies. When a rotating or vibrating object is observed with the stroboscope at its vibration frequency, it appears stationary. Thus stroboscopes are also used to measure frequency.

Ignition timing

In a spark ignition internal combustion engine, Ignition timing refers to the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke.

Otto cycle otto cycle

An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical spark ignition piston engine. It is the thermodynamic cycle most commonly found in automobile engines.

The timing light is connected to the ignition circuit and used to illuminate the timing marks on the engine's crankshaft pulley or flywheel, with the engine running. The apparent position of the marks, frozen by the stroboscopic effect, indicates the current timing of the spark in relation to piston position. A reference pointer is attached to the flywheel housing or other fixed point, and an engraved scale gives the offset between the spark time and the top dead centre position of the piston in the cylinder. The distributor can be rotated slightly until the reference pointer aligns with the specified point on the timing scale.

Timing mark

A timing mark is an indicator used for setting the timing of the ignition system of an engine, typically found on the crankshaft pulley or the flywheel, being the largest radius rotating at crankshaft speed and therefore the place where marks at one degree intervals will be farthest apart.


A crankshaft—related to crank—is a mechanical part able to perform a conversion between reciprocating motion and rotational motion. In a reciprocating engine, it translates reciprocating motion of the piston into rotational motion; whereas in a reciprocating compressor, it converts the rotational motion into reciprocating motion. In order to do the conversion between two motions, the crankshaft has "crank throws" or "crankpins", additional bearing surfaces whose axis is offset from that of the crank, to which the "big ends" of the connecting rods from each cylinder attach.

Flywheel device

A flywheel is a mechanical device specifically designed to efficiently store rotational energy. Flywheels resist changes in rotational speed by their moment of inertia. The amount of energy stored in a flywheel is proportional to the square of its rotational speed. The way to change a flywheel's stored energy is by increasing or decreasing its rotational speed by applying a torque aligned with its axis of symmetry,

Fuel-injected engines, or engines with microprocessor controls may require special procedures to allow basic spark timing to be observed without control effects from the engine computer. On most automotive engines, the timing is set based on the #1 cylinder. [1] In few cases an engine is timed off another cylinder, such as the International Harvester V8 engines, which use #8, and the Isuzu 4Z series four-cylinder, which is timed off the #4 cylinder, or the 3 cylinder Saab two-stroke engine which is timed on the middle (#2) cylinder.

International Harvester company

The International Harvester Company was a United States manufacturer of agricultural machinery, construction equipment, trucks, automobiles, and household and commercial products. Its reorganized successor, after spin-off of several of those businesses, is Navistar International.

Saab two-stroke

The first Saab two-stroke engine was based on a DKW design. The SAAB engine, a two-cylinder with 764 cc engine displacement and 25 hp was transversally placed in the 1950 - 1956 Saab 92, giving it a top speed of 100 km/h (62 mph). With the 1954 model engine output was raised to 28 hp (21 kW). It had some features only found in modern cars such as one ignition coil per cylinder.

Simple timing lights may just contain a neon lamp operated by the energy provided by the ignition circuit. Timing lights using xenon strobe lamps electronically triggered by the spark provide brighter light, allowing use of the timing lamp under normal shop lighting or daylight conditions.

Neon lamp Light source based on gas discharge

A neon lamp is a miniature gas discharge lamp. The lamp typically consists of a small glass capsule that contains a mixture of neon and other gases at a low pressure and two electrodes. When sufficient voltage is applied and sufficient current is supplied between the electrodes, the lamp produces an orange glow discharge. The glowing portion in the lamp is a thin region near the cathode; the larger and much longer neon signs are also glow discharges, but they use the positive column which is not present in the ordinary neon lamp. Neon glow lamps are widely used as indicator lamps in the displays of electronic instruments and appliances.

A timing light may be a self-contained instrument, but is sometimes combined with a voltmeter, RPM meter, and a dwell angle meter, or may be incorporated into a more comprehensive instrument such as an engine analyser. Self-contained units used to time automotive engines have an inductive pickup that clamps around the proper spark plug wire and serves as the trigger for the strobe. Power for the strobe comes directly from the vehicle's battery. Some older timing lights require the removal of the spark plug boot in order to attach a direct pickup between the wire's terminal and the centre conductor of the spark plug.

Voltmeter instrument used for measuring electrical potential difference

A voltmeter is an instrument used for measuring electrical potential difference between two points in an electric circuit. Analog voltmeters move a pointer across a scale in proportion to the voltage of the circuit; digital voltmeters give a numerical display of voltage by use of an analog to digital converter.

Revolutions per minute is the number of turns in one minute. It is a unit of rotational speed or the frequency of rotation around a fixed axis.

Contact breaker

A contact breaker is a type of electrical switch, and the term typically refers to the switching device found in the distributor of the ignition systems of spark-ignition internal combustion engines.

Related Research Articles

Ignition magneto

An ignition magneto, or high tension magneto, is a magneto that provides current for the ignition system of a spark-ignition engine, such as a petrol engine. It produces pulses of high voltage for the spark plugs. The older term tension means voltage.

A spark plug is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/air mixture by an electric spark, while containing combustion pressure within the engine. A spark plug has a metal threaded shell, electrically isolated from a central electrode by a porcelain insulator. The central electrode, which may contain a resistor, is connected by a heavily insulated wire to the output terminal of an ignition coil or magneto. The spark plug's metal shell is screwed into the engine's cylinder head and thus electrically grounded. The central electrode protrudes through the porcelain insulator into the combustion chamber, forming one or more spark gaps between the inner end of the central electrode and usually one or more protuberances or structures attached to the inner end of the threaded shell and designated the side, earth, or ground electrode(s).

Petrol engine internal combustion engine designed to run on gasoline

A petrol engine is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels.

Strobe light

A strobe light or stroboscopic lamp, commonly called a strobe, is a device used to produce regular flashes of light. It is one of a number of devices that can be used as a stroboscope. The word originated from the Greek strobos, meaning "act of whirling."

An ignition system generates a spark or heats an electrode to a high temperature to ignite a fuel-air mixture in spark ignition internal combustion engines, oil-fired and gas-fired boilers, rocket engines, etc. The widest application for spark ignition internal combustion engines is in petrol (gasoline) road vehicles: cars and motorcycles.

Distributor device in the ignition system of an internal combustion engine

A distributor is an enclosed rotating shaft used in spark-ignition internal combustion engines that have mechanically-timed ignition. The distributor's main function is to route secondary, or high voltage, current from the ignition coil to the spark plugs in the correct firing order, and for the correct amount of time. Except in magneto systems, the distributor also houses a mechanical or inductive breaker switch to open and close the ignition coil's primary circuit.

The wasted spark system is an ignition system used in some four-stroke cycle internal combustion engines. In a wasted spark system, the spark plugs fire in pairs, with one plug in a cylinder on its compression stroke and the other plug in a cylinder on its exhaust stroke. The extra spark during the exhaust stroke has no effect and is thus "wasted". This design halves the number of components necessary in a typical ignition system, while the extra spark, against much reduced dielectric resistance, barely impacts the lifespan of modern ignition components. In a typical engine, it requires only about 2–3 kV to fire the cylinder on its exhaust stroke. The remaining coil energy is available to fire the spark plug in the cylinder on its compression stroke.

High energy ignition, also known as H.E.I., is an electronic ignition system designed by the Delco-Remy Division of General Motors, and introduced on some GM vehicles in 1974, including the Camaro Z28 Special High Performance and 1974 Buick Century Gran Sport Stage 1. It was used on all engines from 1975 through the mid-1980s. There were many design variations over the years, and provisions for computer controls were added for some applications starting in the late 1970s. A predecessor system was optional on Pontiacs as "code 704 UPC K65 unitized ignition system" for the 1972 and 1973 model years.

Ignition coil induction coil in an automobiles ignition system that transforms the batterys low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel

An ignition coil is an induction coil in an automobile's ignition system that transforms the battery's low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel. Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car's 12-volt supply. The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads. Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser). More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil. A modern passenger automobile may use one ignition coil for each engine cylinder, eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses.

The Duraspark II is a Ford electronic ignition system.

Dead centre (engineering)

In a reciprocating engine, the dead centre is the position of a piston in which it is farthest from, or nearest to, the crankshaft. The former is known as top dead centre (TDC) while the latter is known as bottom dead centre (BDC).

Capacitor discharge ignition

Capacitor discharge ignition (CDI) or thyristor ignition is a type of automotive electronic ignition system which is widely used in outboard motors, motorcycles, lawn mowers, chainsaws, small engines, turbine-powered aircraft, and some cars. It was originally developed to overcome the long charging times associated with high inductance coils used in inductive discharge ignition (IDI) systems, making the ignition system more suitable for high engine speeds. The capacitive-discharge ignition uses capacitor discharge current to the coil to fire the spark plugs.

The following outline is provided as an overview of and topical guide to automobiles:

Trionic T5.5 is an engine management system in the Saab Trionic range. It controls ignition, fuel injection and turbo boost pressure. The system was introduced in the 1994 Saab 900 with B204L engine.

Crankshaft position sensor

A crank sensor is an electronic device used in an internal combustion engine, both petrol and diesel, to monitor the position or rotational speed of the crankshaft. This information is used by engine management systems to control the fuel injection or the ignition system timing and other engine parameters. Before electronic crank sensors were available, the distributor would have to be manually adjusted to a timing mark on petrol engines.

Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.

Trembler coil

A trembler coil or vibrator coil is a type of high-voltage ignition coil used in the ignition system of early automobiles, most notably the Benz Patent-Motorwagen and the Ford Model T. Its distinguishing feature is a vibrating magnetically-activated contact called a trembler or interrupter, which breaks the primary current, generating multiple sparks during each cylinder's power stroke. Trembler coils were first used on the 1886 Benz automobile, and were used on the Model T until 1927.


  1. Mark Schnubel Shop manual for advanced engine performance, Cengage Learning, 2005 ISBN   1-4018-7787-7, page 52-53

See also