Advance
(of Ignition Timing)
The
term 'advance' describes the setting the ignition timing so that a spark occurs slightly
earlier in the engine's cycle for more efficient operation.
The so-called angle of advance is the angle between the position
of ignition and outer dead-center in a spark-ignition engine.
In modern engines, ignition timing is controlled by a computer,
which uses a lookup table, called a timing map, with spark
advance values for all combinations of engine speed and load.
It is not usually possible to modify such a computer to change
the timing advance curve.
Older engines, however, employ a mechanically timed electrical
ignition system at the heart of which is a distributor. The ignition timing can be advanced in
such a system by rotating the distributor in the appropriate
direction and through an appropriate (small) angle. This results
in the engine producing slightly more power because the air/fuel mixture is given extra time to fully
combust.
How to advance the ignition timing
The tools needed are a timing light and a distributor wrench to loosen
the bolt that holds the distributor in place. The timing light
is connected, in the case of most models, by connecting the
red lead to the positive terminal of the battery, the black
lead to the negative terminal, and the third wire to the reference
spark plug wire. Before adjusting the timing it's important
that the vehicle's engine is running at its normal operating
temperature. The timing light is pointed at the ignition timing
mark on the crankshaft pulley. If the timing light reveals
this mark to be in alignment with a stationary pointer on
the engine block the timing is up to spec. To advance the
timing, the holding bolt of the distributor is loosened just
enough for the distributor to be rotated. The timing gun is
again used to check where the timing has been adjusted to.
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