Engine Maintenance and Modification Bradley Artigue

FIAT 124 Spider
Engine Maintenance + Modification
when the spark is delivered and the fuel/air mixture and cylinder pressures are optimal.
If the spark occurs at top dead center then the piston is already moving down when
these optimal conditions are possible. Therefore the spark is forced to occur just prior to
top dead center; the fuel/air ignition begins and reaches its maximum at the appropriate
time.
A variation in ignition advance is required to maintain optimal efficiency. Beyond the
“hard” setting of 0 or 10 degrees BTDC the ignition distributor has a metal plate that
moves according to engine speed. This movement, governed by either centrifugal or a
combination of centrifugal and pneumatic force, varies the advance so that the spark is
delivered at the optimal point, up to 32 degrees BTDC (depending on series, some were
limited to 28 degrees).
Spiders manufactured prior to 1978 have centrifugal advance plates, the movement of
which is driven by the spinning of the distributor shaft. As the shaft increases in speed
the centrifugal force moves the advance plates outward, increasing the advance.
On Spiders manufactured after 1978 (the CS2, CS0, and all Pininfarina Spiders) the
vehicles were fitted with a Marelli electronic ignition with a pneumatically-operated
advance mechanism. It has often been misidentified as a pollution control – it certainly is
not. The diaphragm in the distributor varies the amount of advance when it is pulled by
the drop in air pressure that occurs when the throttle opens. As the throttle opens and
more air enters the engine the amount of advance increases. This design makes the
ignition advance dependent on the actual load of the engine rather than the speed of the
engine; arguably a more efficient design.
9.4 Firing Order and Initial Timing
All FIAT Spiders fire in the order 1-3-4-2. The initial timing is set so that the camshafts
and crankshaft are in the initial position, with camshafts aligned with pointer holes and
crankshaft aligned to the block mounted pointer. When this initial position is met the
engine is set to fire on the #4 cylinder (figure 43).
Crankshaft Camshaft Distributor Rotor Position
PULLEY TIMING MARK IS
AT 0° BTDC
Figure 42: Initial Ignition Setting
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