Gunson 77008 Handbook

Handbook

Advance Xenon

Timing Light

Part No. 77008

If this product fails through faulty materials or workmanship, contact our
service department direct on: [phone]. Normal wear & tear are
excluded as are consumable items & abuse.

Guarantee

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3

Index

SAFETY PRECAUTIONS ........................... 4

WHAT IS IGNITION TIMING? ..................... 5

WHAT IS ADVANCE TIMING LIGHT? ........ 6

PRODUCT DESCRIPTION .......................... 7

NSTRUCTIONS FOR USE .......................... 8

ADDITIONAL INFORMATION ..................... 9

a. 6/24 VOLT VEHICLES

b. MAGNETO IGNITION SYSTEMS

c. ROTARY ENGINES

d. RETARDED IGNITION

DIAGNOSTIC TESTS ................................ 10

a. Testing Centrifugal Advance Mechanism

b. Testing Vacuum Advance

c. Testing Vacuum Retard

d. Detection of Distributor wear or inaccuracy

e. Effects of incorrect ignition timing

GENERAL WARNINGS .............................11

GUARANTEE ............................................. 12

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What Is ignition
Timing

5

Safety Precaution

4

Using this timing light necessarily involves working under the bonnet while the engine is running.
This is a potentially hazardous situation, and the user should take every precaution to avoid any
possibility of injury. The following guidance should always be followed:

• Never wear loose clothing, particularly ties, long sleeves etc that can catch in moving engine
parts, and always tie-up or cover long hair.

• Ensure that the car is on firm level ground, and is out of gear and the handbrake firmly applied
at all times.

• If for any reason the car is jacked up or the wheels removed, always ensure that the car is
well supported, and never rely on a car jack alone, always use ramps or axle stands. Be wary
of axle stands and jacks sinking into soft ground, and remember that asphalt surfaces may
appear firm, but may give way under the concentrated load of a jack or axle stand.

• Do as much of the work as possible with the engine not running.

• Always route cables well away from hot or moving parts, (particularly the exhaust pipe and
cooling fan) and check that cables are in a safe position before starting the engine.

• Always guard against getting the timing light or fingers too close to moving, hot or electrical
parts. Be especially wary of the fan, fan belt, fan belt pulley, exhaust manifold, exhaust pipe,
and HT parts of the ignition system. Remember that thermostatically controlled fans may
suddenly start with no warning.

• Take care to avoid placing metal tools where they may cause an electrical short, such as near
the car battery.

• Take care not to place tools etc where they may be dislodged by engine vibration.

• Treat High Tension components with respect, remembering that electrical shocks can cause
involuntary movement which may result in secondary injury. Remember that sparks can jump
quite a distance. Also remember that severe unexpected HT shocks can be received from old,
worn, damaged or wet components (e.g. HT leads, coil, and distributor).

• Keep all sensitive electronic equipment away from HT voltages, and do not make any
electrical connection to HT voltages except as expressly advised by the makers of the
electronic equipment.

• Remember that Low Tension Voltage, present on the LT terminal of the ignition coil and at the
contact breakers, can also give quite an electrical shock.

• Never ever attempt to use automotive diagnostic equipment intended for 12v applications on
domestic AC mains 240V supplies.

• Make all electrical connections with power off, so as to avoid the possibility of electrical
sparks, which can ignite fuel vapour or inflammable battery gas emissions.

• Take care not to inhale exhaust gas. Never run the engine inside a garage or in a confined
space. When running the engine, always ensure that there is adequate circulation of fresh air.
Ensure that there are no leaks in the exhaust system near where you are working.

• Keep children and pets away from the car while work is being carried out.

Petrol engines operate on the principle of using a spark plug to ignite a compressed mixture of
petrol and air in the cylinders of the engine. In practice, each spark plug fires slightly before a
piston has reached the top of its compression stroke. This is so that the petrol/air mixture has time
to fully ignite before the commencement of the power stroke. The faster that the engine is rotating,
the greater is the angle before top dead centre (BTDC) that the spark plug has to fire.

Besides engine speed, the optimum timing of the spark depends on other factors, including the
degree of suction in the inlet manifold (manifold vacuum), and whether leaded or unleaded petrol is
being used.

If the ignition timing of the engine is not correct, then either the performance or the economy of the
engine will suffer, or both, and the engine exhaust will be high in hydrocarbons (HC), to a degree
that might cause the vehicle to fail statutory exhaust emissions tests.

Car manufacturers vary in the amount of service data on ignition timing that they make available
information on the user. They also vary on the facilities that they provide on the engine to enable
the timing to be measured, and also on the facilities that they provide on the engine to enable the
timing to be set or adjusted.

In some modern engines, no service data is provided, and no method is provided for measuring or
adjusting the ignition timing.

However, many manufacturers continue to provide data on ignition timing, and provide timing
marks on the engine to enable the timing to be measured using timing light, and provide some
means by which the timing can be adjusted.

Usually, the data is provided at a particular engine idle RPM (the handbook usually also states
whether the vacuum pipe should be connected or disconnected). This is generally referred to as
“STATIC” timing. There are often corresponding timing marks on the fan belt pulley or engine
flywheel (“STATIC timing marks”), and the STATIC timing can be adjusted by rotating the distributor
in its housing.

Such ignition systems are designed so that if the user sets the “static” timing correctly, then the
automatic advance mechanisms will take over and ensure that the ignition timing correctly adjusts
to other driving conditions.

Manufacturers also commonly provide a Top Dead Centre (TDC) mark in addition to a “static”
timing mark. Some manufacturers provide a TDC mark and no “static” timing mark.

Perversely, car manufacturers usually provide no timing marks for engine speeds other than
idle, even though timing data may be given for other speeds the workshop manual. It is in such
situations that this timing light is very useful, since it can be used to measure the degrees of
advance of ignition timing with respect to static timing, or TDC (or with respect to any other
timing marks), and hence can be used to check service data where no suitable timing marks
are provided on the fan belt pulley or flywheel.

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