1958 FIAT 500 sport mode

FIG 1:21 Finned cylinder. Letter A stamped on cylinder
indicates the class to which cylinder belongs, as referred
to its inside diameter
CLASS LETTER
FIG 1 :22 Cylinder measurement points
seats, gearbox companion flange and timing gear cover
mounting flange.
The cast iron cylinders are finned radially to increase the
cooling air surface and are located symmetrically on the
crankcase, each being held by four studs. The cylinders are
installed by sliding into the crankcase bores and finally
held in place by the cylinder head (see FIGS 1 :8 and
1 :21).
Inspect the cylinder bores for score marks, wear and
any other defects or damage. The clearance between the
piston maximum diameter and the cylinder bore should be
checked to ensure that it is within the maximum wear limit
of .0059 inch.
20FIG 1 :23 Checking cylinder diameter by dial gauge
C.687 brought to zero w i t h ring gauge C.672 DIAL GAUGE C 687
RING GAUGE C. 672 The cylinder height must be checked between the seat-
ing face on the crankcase and the top surface and this
dimension should be 3.5433 ±0006 inch.
If this dimension is less than specified the cylinder must
be renewed to prevent possible carbon deposits on the
piston crown and underside of combustion chamber
causing the piston to strike the cylinder head (see
FIG 1 :24). Checking cylinder height: This operation should bring the bore size to correspond
to the oversize piston sizes in order to obtain the correct
clearance between the piston and cylinder. These
limits
are given in Technical Data. It will be observed that the
cylinders are divided into three classes depending on the
bore diameter. The classes are identified by the letters 'A',
'B
1 and ' C , one of which will be stamped on the mating
face with the cylinder head as shown in FIG 1 :21. Pistons
are divided into three classes to correspond with the
cylinder bore sizes. Naturally the piston and bore must
belong to the same class. The maximum available piston
oversize is .0236 inch.
Pistons and rings for the Model 500 sports engine are
not available in oversize dimensions so if the cylinder bore
diameter is above the maximum wear limit new parts must
be fitted.Honing or reboring cylinder bores: It is essential that the diameter measurements are taken
at t w o different heights in the cylinder bore along both the
longitudinal and transverse axles as shown in FIG 1 :22.
It is recommended that to zero the internal micrometer
Fiat ring gauge C.672 is used (see FIG 1 :23).
If bore wear or ovality is between .0059 and .0079 inch
the cylinder bore may be honed. Should however the
wear limit of .0079 inch be exceeded then the bores must
be recut.

Insert a .0079 ± .00197 inch thick oil paper gasket
between the crankcase and cylinder bottom face and a
.0236 to .0275 inch thick graphitized asbestos gasket
between the cylinder and cylinder head. The compression
of the gaskets on assembly will eliminate any very small
differences between the t w o mating surfaces.
Inspection of tappet seats:
The tappet seats should be checked for scoring and
correct clearance which must not exceed .00315 inch.
Should the clearance be greater than the maximum
specified the seating may be reamed to oversize dimen-
sions as detailed in Technical Data. Tappets are avail-
able in .00197 and .00394 inch diameter oversize.
1 :9 Piston assembly
Inspection:
Before inspection the pistons must be thoroughly
cleaned and the ring grooves and piston head decarbo-
nized. Check for deep score marks and signs of distortion
or fracture especially around the skirt and piston pin areas.
Using a feeler gauge ensure that the piston clearances in
the bore do not exceed a maximum of .0059 inch for the
Model 500 engine and .0079 inch for the Model 500
sports engine (see FIG 1 :25) . The measurements should
be taken at the bottom of the skirt and square to the piston
pin axis.
Should the clearance be greater than the maximum
permissible, the cylinders may be rebored and oversize
pistons fitted to m
atch them. Pistons are supplied in the
following oversizes, .0079, .0157 and .0236 inch. It
should be noted that oversize pistons and rings are not
available for the Model 500 sports engine so if the piston
to cylinder wall clearance is greater than the permissible
maximum limit the cylinder and piston assembly must be
renewed.
The piston ring to groove clearance must be checked as
shown in FIG 1 :26 and the ring gap when fitted as in
FIG 1 : 2 7. In both cases the readings should be
compared with the piston data. Piston rings are available
in the same oversize classes as the pistons. When
installing piston rings the gap should be placed opposite to
the piston expansion stops. Ensure that the ring gaps are
scattered and not in a line.
FIG 1:24 Checking cylinder head mating face f o r level
Out-of-true should not exceed .00315 i n c h
F50021
The installation of the piston and connecting rod should
be carried out on a clean workbench as shown in Reassembly of piston: Check that the f i t between the piston pin and boss is a
pinch fit. If excessive clearance is found the boss may be
reamed and a .0079 inch diameter oversize piston pin
fitted. The pin to bore pinch fit must be between .0000 to
.0039 inch. At all times the pins should be installed only
after the piston has been heated in hot water to a tempe-
rature of 80°C. Upon reassembly of the piston to the
engine the expansion slot must be placed facing the cam-
shaft.FIG 1 :26 Checking piston ring-to-land clearance FEELER GAUGE C.316
FIG 1:25 Using feeler gauge C.316 to check piston-to-
cylinder wall clearance

FIG 1 :40 Engine detail showing lube oil passages
Key to Fig 1 :40 1 Splines in crankshaft for oil passage
to filter 2 Oil inlet into circuit from filter 3 Hole for
oil passage to main bearing
FIG 1 : 4 1 Timing marks on sprockets. On later cars the
crankshaft key way is on the underside
size that centrifugal force does not sling oil into the area
where the foreign matter is collected. The outer flange
inner face has radial vanes on its face which retain the
foreign matter and the oil is conveyed to the centre of
the filter.
The oil to be filtered issues from the side splines 1
(see FIG 1 :40) of the crankshaft and is forced by the
slinger to the periphery of the filter where it is cleaned and
returns to the centre of the filter and into the crankshaft
drilling 2. The inner flange or hub and the slinger are
secured to the crankshaft by a special hollow screw 6 as
shown in FIG 1 :39, the outer flange is attached to the
hub by six screws.
28
If the camshaft has been disconnected from the crank-
shaft for any service operation the valve gear will have to
be retimed and to do this proceed as follows:
1 Turn the crankshaft until the reference line on its
sprocket is pointing towards the camshaft as shown in
FIG 1 :41.
2 Turn the camshaft until the reference dot on its
sprocket registers w i t h the crankshaft sprocket. Leave
the shafts undisturbed and carefully mount the chain.
Should it be necessary to check the valve timing and
sprocket marks, proceed as follows:
1 Fit Fiat C.673 tool as shown in FIG 1 :42.
2 Temporarily adjust the valve stem-to-rocker arm
clearance of cylinder No. 1 at .01 77 inch for the inlet
valve and .01 50 inch for the exhaust valve (Model 500
engine) or at .01 54 inch for both valves (Model 500
sports).
3 Rotate the crankshaft and set the flywheel timing mark
at 'O' on the graduated sector. Check that the sprocket
marks are correctly lined up in this position.
If the engine is being assembled, to install the driven
gear, proceed as follows:
1 Set the timing mark on the drive sprocket towards the
centre of the camshaft.
2 Position the driven sprocket on the camshaft mounting
flange with four screw holes in line and tighten two
mounting screws only.
3 Rotate the camshaft until the driven sprocket mark
registers w i t h the reference line on the drive sprocket.
4 Remove the driven sprocket without moving the
camshaft. Install the timing chain and replace the
driven sprocket. Tighten the four screws to a torque
wrench setting of 6.5 Ib ft.
1:15 Valve timing
The oil pressure indicator sender unit is located on the
righthand side of the cylinder block and is connected to
an indicator light in the instrument cluster on the dash-
board.
The red indicator lights only when the ignition is
switched on and goes out when o i l pressure has built
up to between 8.5 and 14 Ib/sq in.
Should an accidental shortcircuit occur in the oil
pressure indicator circuit, the sender unit may be damaged
so the cause must be traced and rectified before the unit
is renewed.
Oil pressure indicator sender unit:
To ensure a reliable lubrication system there must be
no oil leaks from the gasket between the outer and inner
flanges. Every t i m e t h e engine is overhauled the filter
must be dismantled, cleaned and new gaskets fitted.
To clean the filter, remove the six screws and washers
and separate the drive pulley and hub. Carefully scrape
the inner surfaces to remove all sludge.
Upon reassembly the filter to crankshaft hollow
mounting screws must be tightened to a torque wrench
setting of 1 08.5 Ib ft. The cover to mounting flange screws
must be tightened to a torque wrench setting of 5.8 Ibft.
Cleaning and inspection:
A groove is machined on the outer flange periphery to
form a pulley for the generator and blower drive belt.

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.

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