 If
an engine is in good condition, ie if the compression
is good, and both the ignition and valve timing are
correct, then all it needs to start promptly is the
correct amount of fuel and a decent spark.
The
spark requirement depends, for the most part, on the
condition of the battery, because the starter takes
such a heavy current that the ignition system often
does not get its fair share of the available electrical
energy. This explains why it often happens that an
engine that has refused to start
suddenly takes as soon as the starter
switch is released, while the engine is still rotating.
An
even more dramatic illustration is when a car refuses
to start on the starter motor, but starts very easily
when pushed. The first items to check, in this case,
are the battery connections, because they often grow
a layer of deposit inside the terminals. This should
be cleaned out with a scraper; the muck that collects
on the outside can be cleaned off with warm water.
Afterwards, the terminals should be covered with a
layer of petroleum jelly. By the way, a quick test
for a dirty terminal is to close the starting switch
for about ten seconds. Even if the starter motor has
refused to turn, a dirty terminal will heat up, whereas
a clean terminal won't. The difference can usually
be felt by hand.
On
an older car, the condition of the starter motor also
plays a role, because a worn-out starter may have
such a high resistance that it absorbs an inordinate
amount of electrical energy to swing the engine.
Jump-starting
a car has become a hazardous procedure. The central
processing units on many new cars don't take kindly
to the power surges that may occur. The cars should
be parked near each other, but not touching. The "hot"
(usually positive) terminal on each battery should first
be connected to each other. One end of the negative
(earth) cable should then be connected to the negative
terminal of the donor battery. The other end should
be connected to a point on the engine of the receiving
car close to the starter motor, NOT onto the receiving
battery. The donor car should now be started and revved
to about 2 000 r/min, before starting the other engine.
Switch off the donor engine but keep the other engine
running and switch on the lights, heater fan and heated
rear window of the
recently-started car before removing the cables in reverse
order. This will avoid any over-voltage. A
dirty battery terminal should be removed, and the inside
scraped clean.
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