1969 FIAT 500 Spark plug spec

INTAKEEXHAUSTINTAKEEXHAUST
FIG 1 :18 Main specifications of intake and exhaust valves and valves guides (dimensions in mm)
head. Disconnect the t w o side exhaust manifolds.
Note the spark plug HT cables locations and dis-
connect from spark plugs.
2 Remove the rocker shaft pedestal- and lift away the
rocker gear. Extract the pushrods, making a careful
note of their location. Remove the cylinder head hold
down nuts in the order shown in FIG 1 :44 and using a
puller as shown in FIG 1 :9 lift off the head.
Dismantling the cylinder head:
1 Using Fiat valve spring compressor A.60084 or a uni-
versal spring compressor depress the valve spring as
shown in FIG 1 :14 and lift out the cotters. Release t h e
compressor and withdraw the lock cone, oil shield
(inlet valve only) upper spring cup, valve spring and
lower spring cup. Withdraw the valve from the under-
side of the head.
2 Dismantle the remaining three valve assemblies as
detailed above ensuring that all parts are kept in sets
for correct reassembly.
Inspection and servicing of the cylinder head :
1 Remove all carbon deposits from the combustion
chambers and valve ports using a rotary wire brush or a
set of scrapers.
2 Thoroughly clean the cylinder head and to test for dis-
tortion lightly coat the machined faces with 'Engineers
Blue' or lamp
black and place the cylinder head on a
surface plate. Carefully slide to and fro and any streaks
left behind will indicate a distorted surface. A distorted
head will not make a gas-tight seal with the cylinders
and must be entrusted to an expert for correction or,
in severe cases, renewed.
3 Carefully clean the valve guides as shown in FIG 1:16
using Fiat guide brush A.11417 bis. Should the guides
18Reassembly is the reverse procedure to dismantling.
During assembly utmost cleanliness must be observed as
any abrasive material could find its way to the pistons and
cylinder bores causing unnecessary wear. Check that the
cylinder barrel mating face is clean to ensure correct
gasket sealing.Reassembly of t h e cylinder head:
be worn then they should be removed using a press and
a suitable sized drift. The guides are press fitted with a
pinch fit of .00134 to .00244 inch. To install the guides
use Fiat tool A.601 53 as shown in FIG 1 :17. As the
guides have no stop ring during the press fitting, the
depth of insertion is determined by the Fiat tool. If the
tool is not available take the necessary depth measure-
ments before the old guides are removed. The normal
fit clearance between valve stem and guide is .00087 to
.00217 inch with a maximum wear limit of .0059 inch.
To check this see FIG 1:18.
4 The valve seats should always be reconditioned after
decarbonization. It is suggested that this operation be
left to a local service station with valve seat cutting
equipment. The valve seat angle for both inlet and
exhaust valves is 4 5 ° ± 5'.
5 Inspect the valves for soundness or distortion and if the
clearance between guide and stem is within the manu-
facturers wear tolerance of .0049 inch the valve may
be cleaned using a wire brush and the seating face
ground to an angle of 45°30' ± 5'. This again should
be left to the local service station.
Valve springs:
Thoroughly clean the valve springs of oil deposit and
inspect for cracks. It is advisable to check the free spring
height and if this dimension differs from the original
height, details of which are given in Technical Data, the
spring must be renewed. Any decrease in length indicates
that the spring has weakened.

Cylinder head installation:
To refit the cylinder head proceed as follows:
Place a new cylinder head joint on the cleaned faces of
the cylinder barrels. Insert the rocker pushrod and
lubrication pipe sleeves together with the relevant
gaskets and rings.
Fit the washers and nuts to the studs and tighten to
fingertight.
Tighten the nuts in the order shown in FIG 1 :44 and
FIG 1 :46 to a torque wrench setting of 18.1 Ibft. Reset
the torque wrench to a new setting of 23.9 Ibft and
tighten the nuts once more in the recommended order.
Replace the pushrods in the correct order.
Refit the rocker shaft ensuring correct location of the
lubrication tube to the rocker shaft and replace the
plain and lockwashers. Tighten the nuts to a torque
wrench setting of 15.2 Ibft. Reset the tappet to rocker
clearance adjustment.
Connect the t w o exhaust side manifolds to the cylinder
head. Using new gasket refit the spark plugs and HT
cables. Replace the rocker cover fitted with a new cork
gasket and blower conveyor to the cylinder head
securing screws. Refit the carburetter and reconnect its
fuel line and controls. Refit the air cleaner and elbow
and connect the rocker cover breather pipe (if fitted).
1
2
3
4
5
1 :7 Timing gear overhaul
Camshaft:
The cast iron camshaft is located in the crankcase and is
supported at either end in sets machined directly in the
crankcase. No bushes are used. The camshaft is driven by
a chain from the crankshaft at half engine speed and
operates the overhead valves through tappets, pushrods
and rockers (see
FIG 1 :20).During engine overhaul the camshaft journals and cam
faces should be free of score marks or signs of seizure and
have a bright mirror finish.
The distributor drive gear should be inspected for tooth
wear which if excessive means that the camshaft must be
replaced.
Tappets:
The tappets should be inspected for signs of seizure or
excessive wear. The end surface that is in contact with the
camshaft should be smooth without signs of excessive
wear. Any slight scratches or indentations may be
removed using a very fine oil stone.
Pushrods and sleeves:
The pushrods operate in special axially resilient sleeves
that are compressed on assembly between the cylinder
head and the crankcase. It is through these sleeves that
the engine sump is vented also through which the oil
returning from the cylinder head passes.
Two rubber O-ring seals are fitted to each sleeve to
ensure an oil t i g h t seal between the cylinder head and
crankcase. The sleeves should be checked for distortion
and exact equal length and when refitting new seals must
always be fitted.
The pushrods should be checked for straightness and
the t w o ends that contact the rocker setscrew and the
F50019
The crankcase is an aluminium casting suitably ribbed
to ensure correct air cooling. The main bearing and cam-
shaft bearing bores are machined as also are the tappet 1 :8 Crankcase and cylinders During valve gear overhauls the clearance between the
rocker shaft bore and the rocker must be checked. The
maximum permissable wear between these t w o parts is
.0059 inch. It is recommended that the part which is most
worn be renewed, or in extreme cases both parts. Rocker and rocker shaft: tappet seat must not show any signs of roughness or
excessive wear. 3 Oil shield (for intake valves only) 4 Snap ring
5 Rocker 6 Upper spring cup 7 Valve spring
8 Lower spring cup 9 Pushrod 10 Tappet
11 Oil seal ring 12 Pushrod sleeve 13 Seal ring 1 Intake valve 2 Upper cup lock Key t o Fiq
1 :20 FIG 1:20 Valve, pushrod and tappet assembly FIG 1:19 Camshaft. The arrow points to the lube oil
outlet port

FIG 1 :44 Cylinder head h o ld-down nuts tightening
sequence. 500 Sedan
TIMING CHAIN ENDCYLINDER No. 1 CYLINDER No. 2 FLYWHEEL END
CAMSHAFT
EXPANSION SLOT C/ROD NUMBERROTATION DIRECTION
FIG 1 :45 The correct position of connecting rod-
piston assembly on engine 120.000
30
screws and together with new lockplates tighten to a
torque wrench setting of 23.1 Ib ft. Bend down the
lockplates.
9 Slide the centrifugal oil filter mounting flange, the
oil slinger and the mounting screw together with its
lockplates onto the crankshaft and tighten the screw
to a torque wrench setting of 108.5 Ib ft. Bend down
the lockplate.
10 Assemble the clutch assembly to the flywheel and
using Fiat pilot A.62023 centralize the driven plate
to the pressure plate assembly. Secure the pressure
plate assembly using screws and toothed washers.
11 Fit new oil pan cork gasket, if necessary using a little
grease to hold in position and carefully fit the oil pan
securing with screws, toothed washers and lock-
plates. Bend down the lockplates onto the screw
heads.
12 Fit the oil cooling air conveyor on the oil pan and
secure with screws and toothed washers.
13 Carefully turn the engine over and fit the centrifugal
filter mounting flange rubber seal. Fit the oil filter
cover and secure with screws together with plain and
toothed washers to a torque wrench setting of
5.8
Ib ft.
14 Ensure t h e faces of the cylinder head and cylinders
are free from dirt and oil and carefully slide the
cylinder head gasket over the studs ensuring that it
is the correct way up. Insert the tappets in the same
order to removal together with the sleeves, pushrods,
oil delivery line to the rocker arm shaft and the casing
with its seal ring.
15 Thoroughly inspect the cylinder head to ensure that
it has been correctly reassembled, carefully slide it
over the studs and secure using the four cap nuts
internally and four standard nuts and plain washers
externally. Tighten the nuts in the order as shown in
FIG 1 :44 or 1 :46 to a torque wrench setting of
23.9 Ib ft.
16 Fit the rocker arm shaft and arm assembly together
with the two supports. Tighten the supports using
screws, plain and toothed washers to a torque
wrench setting of 15.2Ibft. Adjust the tappet-to-
rocker clearance as detailed in Section 1 :16.
17 Temporarily plug the intake duct hole to ensure that
no foreign matter finds its way into the engine.
Install the spark plugs having ensured that they are
clean and correctly adjusted.
18 Reassemble the engine cowling and air
exhaust
throttle valve assembly which should be secured on
the top side using t w o nuts, t w o plain washers and
two toothed washers, on the underside with two
screws and t w o toothed washers, and centrally using
one screw and one spring washer.
19 Fit the toothed washers on the end of the spark plug
electrode and tighten the terminals together with the
special rubber boots.
20 Refit the fan, generator and ground cable assembly
and secure the crankcase, also the warmed air intake
shrouding. Finally tighten the generator to fan nuts.
21 Fit both lower exhaust silencer mounting brackets
onto the crankcase but do not tighten fully. Fit the
air conveyor and secure to the engine cowling using
six screws, six toothed washers and one nut together
with a toothed washer. Join together the t w o

3:1
3:2
3:3
3:4
3:5Description
Operation
Routine maintenance
Ignition faults
Removing and dismantling distributor (sedan
and sports)
CHAPTER 3
THE IGNITION SYSTEM
3:6
3:7
3:8
3:9
3:10
Removing and dismantling
(station wagon)
Timing the ignition
Sparking plugs
The distributor drive spindle
Fault diagnosisdistributor
3 :1 Description
The ignition system fitted to all the models covered by
this manual consists of an ignition coil, ignition distributor
fitted with contact breaker points, a centrifugal automatic
advance system, condenser, low- and high-tension
wiring, spark plugs and a power supply provided by a
generator and battery. The wiring diagram is shown in
FIG 3 : 1
1 The low-tension circuit which is sometimes called the
primary circuit includes the power supply, contact
breaker points, condenser and ignition coil primary
winding.
2 The high-tension circuit which is sometimes called the
secondary circuit includes the ignition coil secondary
winding, distributor rotor, distributor cap with terminals
and the central brush, high-tension cables and the spark
plugs.
3 : 2 Operation
The contact breaker unit in the distributor interrupts
the primary circuit by the points opening. The sudden stop
in the flow of current in the primary winding, does not cause
arcing at the contact breaker points because it discharges
into the condenser connected in parallel w i t h the contact
F50047
breaker points. With the sudden collapse of the primary
circuit, the intensity of the magnetic field drops causing
an induced high-tension current in the ignition coil
secondary winding. The high EMF is distributed to the
sparking plugs by the ignition distributor rotor.
The automatic advance mechanism comprises a plate
carrying t w o weights which are symmetrically pivoted on
the plate at one end. Also attached to the weights at
opposite ends to the pivots is the cam carrier shaft with
special tension return springs. Under the action of centri-
fugal force as the rotational speed increases, the weights
move outwards causing the cam carrier shaft to move
angularly compared to the distributor drive shaft thus
causing advancement of the ignition timing.
The contact breaker assembly comprises the cam on the
drive shaft and t w o contact points, one of which is
stationary while the other is under the influence of the
cam, the action of which is transmitted by a rubbing block.
The cam has t w o lobes to control the opening and closing
of contact points. The stationary contact point is mounted
on an adjustable support to enable the contact breaker
point gap to be adjusted.
The HT current reaches the distributor cap central
terminal, from the ignition coil and is distributed to each
of the spark plugs at the correct time by the rotor arm.

a n 0—20 v o ltmeter. If the circuit is in order the meter
should read approximately 12-volts.
3 Battery to fuse box terminal 30. Connect the volt-
meter between the terminal 30 and earth. No reading
indicates a faulty cable or loose connection.
4 Fuse box. Connect the voltmeter between the other
auxiliary terminal 30 and earth. No reading indicates a
broken or loose connection.
5 Fuse box auxiliary terminal 30 to terminal
number 30 on ignition switch. Connect the meter
between terminal number 30 on the ignition switch
and earth. No reading indicates a damaged cable or
loose connection.
6 Ignition switch. Connect the meter between termi-
nal 15/54 and earth. Switch onto the ignition position,
when no reading indicates a fault in the switch.
7 Ignition switch to low-tension cable connection
on the coil (blue cable). Connect the meter
between ignition coil terminal (blue cable) and earth.
No reading indicates a damaged cable or loose con-
nection.
8 Ignition coil. Disconnect the black low-tension cable
connecting the coil to the distributor side terminal at
the coil and connect the meter between this terminal
and earth. No reading indicates a fault in the primary
winding of the coil and a replacement coil must be
fitted. If the reading is correct remake the connections
to the coil.
9 Ignition coil to distributor. Disconnect the thin
black low-tension cable at the side of the distributor
and connect the meter between the end of this cable
and earth. No reading indicates a damaged cable or
loose connections.
10 Contact breaker and capacitor. Connect the
meter across the contact breaker points. No reading
indicates a faulty capacitor.
Capacitor:
The best method of testing a capacitor (condenser) is
by substitution. Disconnect the original capacitor and
connect a new one between the low-tension terminal on
the side of the distributor and earth.
If a new capacitor is needed, fit a new one complete
w i t h bracket, but if necessary unsolder the original bracket
and solder it onto the new capacitor using as little heat as
possible. Capacitor capacity is .15-.20 microfarads.
3 : 5 Removing and dismantling distributor (sedan
and sports)
To remove the distributor proceed as follows:
1 Rotate the engine slowly until the distributor rotor arm
is opposite the brass segment in the distributor cap
connected to No. 1 plug lead. This will provide a datum
for replacement.
2 Disconnect the cable from the low-tension terminal on
the side of the distributor body. Mark position of distri-
butor on support. Release the distributor retaining nut
and washer from the underside of the top flange of the
distributor support and carefully lift away the dis-
tributor.
3 Pull off the rotor arm. Remove the insulated terminal
assembly from the side of distributor body. Release the
contact breaker carrier plate retaining screws and con-
denser flange screw from the outside of the distributor
F50049 body. Carefully lift out the contact breaker plate
assembly.
4 Before further dismantling note the relative positions of
the driving dog and the rotor arm driving slot at the top
of the distributor cam spindle. The driving dog is offset
and can only engage its driving spindle in one position.
Then when the cam assembly is fitted to the centrifugal
weights during reassembly the timing is not 180 deg.
out.
5 Take out the cam lubrication felt pad recessed in the
rotor arm housing on the end of the cam spindle.
Remove the retaining screw, carefully disengage the
springs and lift out the cam spindle. It should be noted
that there is a small retaining ball and spring located in a
drilling nearly at the top of the drive shaft spindle.
Carefully lift away the weights.
6 Thoroughly clean all parts and inspect for excessive
wear. The distributor cap must not be cracked or show
signs of tracking. The cap terminals, rotor and contact
breaker points can be cleaned with a very fine file.
Emerypaper must not be used. If the clearance between
the rotor and distributor cap segments exceeds .0118
inch both the rotor and distributor cap must be replaced.
Inspect the contact breaker arm rubbing block for exces-
sive wear and also the points for wear so that if the gap
exceeds the last setting limit of .0209 inch and adjust-
ment through the stationary contact carrier screw is no
longer possible (see FIG 3 : 2) , the contact breaker set
must be renewed.
If the distributor drive shaft side or vertical movement is
excessive the distributor must be renewed.
Weak centri-
fugal weight springs or damaged weights must be
renewed using original Fiat spares otherwise the auto-
matic ignition advance characteristics could be altered.
FIG 3 : 3 Ignition distributor in place on engine SPARK PLUG CABLES
IGNITION COIL CABLE!
DISTRIBUTOR CAP
DISTRIBUTOR BODY
GROUND CABLE
CONDENSER
DISTRIBUTOR SHAFT
LUBRICATION FITTING
DISTRIBUTORSUPPORT-TO--CRANKCASE NUT
[MOUNTING SCREWDISTRIBUTOR
DISTRIBUTOR SUPPORT

FIG 3 : 4 Use of fixture Ap.5030/1 to check ignition
timing
Reassembly is the reverse procedure to dismantling but
the following points should be noted:
1 Lubricate the parts of the centrifugal advance mecha-
nism, the drive spindle and the part of the shaft which
accepts the cam w i t h Fiat VS oil.
2 Ensure that upon reassembly the slot in the rotor arm
housing matches the distributor driving dog. Lubricate
the felt pad in the rotor arm housing.
3 Fit the distributor back onto its support gently rotating
the rotor arm so that the drive dog engages w i t h the
drive shaft mating flange. Provided the crankshaft has
not been turned the rotor arm should finish up pointing
to No. 1 cylinder segment in the distributor cap. Tighten
the distributor retaining nut, refit the distributor cap and
leads to the spark plugs and the LT lead to distributor
body terminal.
4 Add a few drops of oil to the distributor shaft lubrication
fitting (see FIG 3:3).
3 : 6 Removing and dismantling distributor
(station wagon)
The distributor is located towards the top rear of t h e
engine and is bolted direct onto the crankcase rear cover as
shown in FIG 1 : 2 . It is driven direct by a gear in mesh w i t h
a corresponding gear on the camshaft. The basic design of
the distributor is the same as that for the sedan and sports
engine, except that the distributor cap has been redesigned,
there is a gear instead of the dog
drive and no distributor
support. To remove and dismantle the distributor proceed
as previously described taking great care about marking
the location of the distributor to rear cover and rotating
the engine until No. 1 cylinder is on compression. This will
ensure that reassembly is straightforward without loss of
ignition timing.
503:7 Timing the ignition
It is necessary to retime the ignition should the distribu-
tor shaft or camshaft have been removed. To retime the
ignition proceed as follows:
1 On the timing sprocket cover fit Fiat tool AP.5030/1 as
shown in FIG 3 : 4. Ensure No. 1 cylinder is on the
compression stroke with both valves closed. Rotate the
crankshaft until the mark on the centrifugal filter cover
lines up w i t h the 10° mark on the fixture. This setting
corresponds to a 10° static advance BTDC.
2 Check t h a t the points gap is correctly set between
.018 and .020 inch. Turn the distributor shaft until the
rotor points in the direction of No. 1 segment in the
cap and the points are just opening.
3 Without disturbing the distributor shaft, insert the lower
coupling on its toothed end, install the support and
tighten the locknut. Secure the distributor to the sup-
port using the mounting screw.
To check that the distributor is properly timed to the
engine and the centrifugal automatic advance is operating
correctly giving a
total advance of 18° to 28° respectively
proceed as follows:
1 Connect Fiat timing tester AP.5030 with a 220-volt-
single-phase power outlet fitted with a good earth
connection. It is important that the tester is earthed
before it is allowed to operate. Also ensure that the
tester earth terminal is connected to a bare metal part
of the vehicle.
2 Remove No. 1 spark plug lead, insert the strobe light
adapter and reconnect the spark plug lead. Using a
piece of white chalk mark the TDC position on the
centrifugal filter cover.
3 Start the engine and aim the strobe light beam towards
the chalk mark drawn on the centrifugal filter cover.
With the engine running slowly the mark on the centri-
fugal cover must correspond wi th the first white line
on the fixture (10°). Slowly increase the speed of the
engine so operating the automatic advance and the
chalk mark should move counterclockwise until at
maximum speed it reaches the second white mark on
the fixture.
It should be noted that the ignition timing for the model
500 sports engine the static advance is 10°, an automatic
advance of 12° giving a total advance at maximum engine
speed of 2 2 ° .
Should Fiat fixture AP.5030/1 not be available the
advance position may be set as follows:
1 Turn over the
engine until No. 1 piston is on the com-
pression stroke w i t h both valves closed.
2 Rotate the crankshaft clockwise until the reference
mark cast on the centrifugal filter cover is set .5118 to
.5512 inch ahead of the arrow cast on the timing
sprocket cover. This will give a static advance setting
of 10° BTDC.
3 Proceed as directed for ignition distributor timing and
mounting described earlier in this section.
3 : 8 Sparking plugs
The sparking plugs must be regularly inspected, cleaned
and the electrode gap adjusted to a gap of .019 to .023
inch.
The inspection of the deposits on the electrodes is par-
ticularly useful because the colour and type of deposit

indicates the condition inside the combustion chamber
and may be used as a guide to engine tuning.
Before the spark plugs are removed b l o w away any
loose dirt from the plug recesses using a compressed air
jet or tyre pump. Store the plugs in the order of removal
ready for inspection.
Examine the gaskets and if they are about half their
thickness they may be used again otherwise they must be
replaced.
Inspect the electrode end of the plugs and note the
type and colour of the deposit. Normally it should be
powdery and range from b r o w n to a greyish tan in colour.
There will also be slight wear of the electrodes and the
general effect described is one which comes from mixed
periods of high-speed and low-speed driving. Cleaning
and resetting the gap is all that will be necessary.
If the deposits are white or yellowish they indicate long
periods of constant-speed driving or much low-speed
city driving. Again, the treatment is straightforward.
Dry, black, fluffy deposits are usually the result of
running with too rich a mixture. Incomplete combustion
of the petrol air charge may also be a cause and this might
be traced to a defect in the ignition system or excessive
idling.
Overheated sparking plugs have a white blistered look
about the centre electrode and the side electrode may be
badly eroded. This may be caused by poor cooling, wrong
ignition timing or sustained high speeds under heavy load.
To clean the sparking plugs effectively they should be
cleaned using an abrasive blasting machine and tested
under pressure once the electrodes have been reset. File
these until they are clean, bright and the faces parallel and
set the gap to .019 to .023 inch. Do not try to bend the
centre electrode.
Before replacing the plugs use a wire brush to clean the
threads taking care that the electrodes are not touched.
Thoroughly clean the spark plug in petrol, and dry using a
compressed air jet or a tyre pump. If difficulty is found in
screwing the plugs into the cylinder head by hand run a
tap d o w n the threads to clear away any carbon. If a tap is
not available use an old sparking plug with crosscuts d o w nthe threads. Finally tighten the plugs to a torque wrench
setting of 18 to 21 Ib ft.
Sparking plug leads:
The spark plug leads and the lead from the coil to the
distributor cap must be regularly checked for cracking of
the insulation and also correct seating in the distributor
cap and coil top. It is recommended that silicone grease is
smeared around the sockets before the leads are replaced
to ensure no moisture may enter causing difficult starting.
3 : 9 The distributor driving spindle (sedan and
sports engine)
If for any reason, the driving spindle has been removed
from its housing in the crankcase, it must be correctly
meshed w i t h the camshaft gear otherwise it
will be impos-
sible to set the ignition timing.
3:10 Fault diagnosis
(a) Engine w i l l not fire
1 Battery discharged
2 Distributor contact points dirty, pitted or maladjusted
3 Distributor cap dirty, cracked or tracking
4 Carbon brush inside distributor cap not touching rotor
5 Faulty cable or loose connection in low-tension circuit
6 Distributor rotor arm cracked
7 Faulty coil
8 Broken contact breaker spring
9 Contact points stuck open
(b) Engine misfires
1 Check 2, 3, 4, and 7 in (a)
2 Weak contact breaker spring
3 High-tension plug and coil leads cracked or perished
4 Sparking plug(s) loose
5 Sparking plug insulation cracked
6 Sparking plug gap incorrectly set
7 Ignition timing too far advanced