1959 FIAT 500 Top

CHAPTER 1
THE ENGINE
1 :1
1 :2
1 :3
1 :4
1 :5
1 :6
1 :7
1 :8
1:9
1 :10
1 :11Description
Engine removal (sedan—all versions)
Engine removal (station wagon)
Engine disassembly (sedan—all versions)
Engine disassembly (station wagon)
Cylinder head removal, servicing and
replacement
Timing gear overhaul
Crankcase and cylinders
Piston assembly
Connecting rods
Crankshaft and main bearings
1 :1 Description
The 'New 500' two-cylinder aircooled engine operates
on the four-stroke 'Otto Cycle' and is fitted directly to
the transmission unit which incorporates the rear drive
assembly as shown in FIG 1 :1 and FIG 1 :2.
With the power unit fitted at the rear several advantages
are obtained including better load distribution to the
wheels when the vehicle is loaded, elimination of propeller
shaft reducing the size of centre tunnel and better use of
available space.
The cylinder block comprises t w o cast iron cylinder
barrels w i t h cooling fins. The bottom of the cylinders fit
into machined seats in the aluminium crankcase.
The aluminium crankcase carries eight studs on which
are located the t w o cylinder barrels w i t h the aluminium
cylinder head on the top.
A two bush crankshaft of special cast iron is fitted into
the lower half of the crankcase. The crankshaft is
F5009 provided with a counterweight and is hollow to allow for
lubrication.
The steel connecting rods have thin wall bearing halves
on the big-end, and bronze bushes in the small-end. The
offset piston pin is of steel and retained in the piston by
two circlips.
Light alloy pistons are used and are of the taper-oval-
shaped type with a maximum diameter at the base of the
skirt, along an axis perpendicular to the piston pin. Pistons
are fitted with four rings as follows, one compression at
the top, two standard oil scraper rings and one side slotted
oil scraper ring.
The one-piece aluminium cylinder head is finned to
provide a larger cooling surface and carries the inlet and
exhaust manifolds.
The inlet passages merge into a single centralized
flange onto which is mounted the carburetter. The exhaust
passages run almost parallel to the axis of the engine. 1 :12
1 :13
1 :14
1 :15
1 :16
1 :17
1 :18
1 :19
1 :20
1 :21
1 :22Flywheel and starter ring gear
The oil pump
Lubrication, oil filter, relief valve
Valve timing
Valve stem to rocker clearance
Engine assembly (sedan—all versions)
Engine assembly (station wagon)
Power plant mounting
Adjustment of generator and fan belt drive
Modifications
Fault diagnosis

FIG 1:1 Left side view of the power plant to suit
500 Sedan
10
FIG 1:2 Right side rear three-quarter view of the power plant for 500 Station Wagon Mounted on the top of the cylinder head is the overhead
valve rocker mechanism that is operated by a chain driven
camshaft through tappets and vertical pushrods.
The carburetter is of the downdraft type fitted with a
starting device that is controlled by a lever on the central
floor tunnel. A pleated paper element air cleaner and
silencer is fitted to the carburetter air intake. A mechanical
diaphragm type fuel pump operated from the camshaft by
a pushrod, supplies petrol to the carburetter from a fuel
tank located at the front of the vehicle.
Engine lubrication is provided by a gear pump driven
from the camshaft and mounted within the timing cover
drawing oil from the engine sump. The oil is cleaned by a
centrifugal filter situated at the rear end of t h e crankshaft
and pressure is controlled by a valve mounted on the
pump body. Crankcase ventilation is provided for through
a rubber hose connected to the top of the rocker cover.
The engine is cooled by air from a centrifugal blower
mounted on the generator shaft and housed in a specially
designed cowling conveying air to and around the engine.
The air temperature is governed by a special thermostat
fitted in the engine cowling.

The interior of the car can be heated by the engine
warmed air being ducted into the front compartment and
controlled by a lever on the heating system tunnel.
Engine ignition is by a battery, ignition coil and distribu-
tor which is driven by a gear on the camshaft. The engine
is started by an electric starter motor which is mounted on
the gearbox casing and is controlled by a lever located
behind the gearchange lever.
The complete power unit is mounted by a spring support
at the centre of the rear b o d y crossmember and by t w o
rubber pads mounted laterally to the gearbox.
1 :2 Engine removal (sedan—all versions)
To remove the engine from the car proceed as follows:
Raise t h e rear of t h e car and place on firmly based
stands placed under suitable brackets on the underside
of the body.
Disconnect the battery positive terminal clamp from the
battery terminal post. Release the clip securing the main
petrol pipe to the tank sender unit and ease t h e pipe
from the unit. Drain the oil from the engine sump into
a suitably sized container.
D i s c o n n e c t t h e rear number plate light wire (see
FIG 1 : 6) . Release t h e engine compartment lid check
strap from its slot and separate the lid from the body by
sliding the hinge apart.
Remove the cables attached to the ignition coil, also
to the generator and the starter motor. Remove the
starter motor control tie rod.
Release the oil pressure
indicator cable, the main petrol pipeline at the pump,
the accelerator and starting device controls.
Remove the t w o hoses of the heating and cooling
system which are the input hose to the blower and the
hose for the car heating system. Release and lift out the
engine apron. Remove the starter motor mounting bolts
and carefully lift away the motor.
Using a garage hydraulic jack with suitable cradle (see
FIG 1 : 7) or a rope sling relieve the engine weight
from its mountings. Remove the nuts securing the
gearbox to the engine and the flywheel protection
apron.
Remove the bolts fixing the elastic support to the cross-
member. Remove the rear crossmember mounting nuts
noting that the engine earth cable is held by one
mounting nut and lift away the crossmember.
Carefully ease t h e engine away from the gearbox
ensuring that there is no strain placed on the clutch
shaft. Lower the engine to the floor taking care that no
weight is allowed on any of the attachments. 1
2
3
4
5
6
7
8
1 :3 Engine removal (station wagon)
To remove the engine from the station wagon proceed
as follows:
1 Raise t h e rear of the vehicle and place on firmly based
stands placed under suitable brackets on the underside
of the body.
2 Disconnect the battery positive terminal clamp from
the battery terminal post. Release the clip securing the
main petrol pipe to the tank sender unit and ease the
pipe from the unit. Drain the oil from the engine sump
into a clean dry container of suitable size.
3 H o l d t h e rear door open and secure using string to stop
it swinging to the closed position. Secure the luggage
compartment floor panel in its upright position.
F50013 4 Remove the cables attached to the ignition coil, also
to the generator and starter motor. Remove the starter
motor control tie rod. Release the o i l pressure indicator
cable, the main petrol pipeline at the pump, the accele-
rator and starting device controls. Disconnect the air
filter housing.
5 Remove the hose connecting the car heating system
to the engine cowling. Disconnect the clip holding the
air pipe to the blower and carefully disconnect the pipe
from the blower cowling. Remove the starter motor
mounting bolts and carefully lift away the motor. FIG 1:5 120.000 engine assembly: cross-section view
through a cylinder

LID CHECK A R M
FIG 1:6 Engine compartment lid open LID LOCKING
HOOK
NUMBER PLATE
LAMP CABLE NUMBER PLATE LAMP
CABLE JUNCTION
CROSS MEMBER ARR.2O74.
FIG 1 :7 Engine removal using the jack with cross-
member Arr.2074
6 Using a garage hydraulic jack with a suitable cradle
relieve the engine weight from its mountings. Remove
the nuts securing the gearbox to the engine.
7 Remove the nuts securing the rear bumper blade and
panel to the body. Note that the engine earth cable is
held by one mounting nut. Carefully dismantle the
engine elastic mounting or release the bracket from the
engine rear cover by removing the two nuts and washers.
Lift away t h e rear panel assembly carefully making sure
14
FIG 1 : 8 Engine components: crankcase, cylinder head,
timing sprockets cover To dismantle the engine proceed as follows:
1 Remove the exhaust silencer by releasing the two
collars for attachment to the engine and the two con-
nections for the exhaust pipe. It will be noted that
there is one exhaust pipe connection on either side
of the cylinder head.
2 Place the engine on a firm wooden top bench. Remove
the two tappet cover retaining nuts and washers and
lift away the cover. Remove the connection for cooling
air delivery to the sump cooling ducts at the side of
the sump.
3 Remove the air cleaner after first releasing the two
bolts on the air cowling and the two nuts for the air
elbow connection to the carburetter.
4 Remove the generator drive belt by releasing the
three nuts so splitting the semi-pulley. Lift away the
drive belt.
5 Remove all the bolts securing the air conveyor
ducting to the cylinder head, to the crankcase and
also to the engine cowling assembly opposite to the
air conveyor. Release the accelerator control tie rod
and carefully lift away the air conveyor assembly
complete with the generator after first removing the
clamp fixing the generator to the crankcase. 1 :4 Engine disassembly (sedan—all versions) t h a t rear air ducting panels are not strained or the
mating faces damaged.
8 Carefully ease the engine away from the gearbox ensur-
ing that there is no strain placed on the clutch shaft.
Lower the engine to the floor taking care that no weight
is allowed on any of the attachments.

STUD REMOVAL
PULLER 40010
FIG 1 :12 Removal of stud from crankcase by puller
A.40010
FIG 1 :13 Engine without blower cowling and cylinder
head cover.SPACER A N D CONNECTION
FOR ROCKER SHAFT
LUBRICATION TUBE
OILVAPOR
.VENT PIPE
CASINGS FOR PUSHRODS
(AND OIL RETURN
TO CRANKCASE
21 To ensure no damage occurs to the long cylinder
barrel mounting studs these may be removed using
Fiat puller A.40010 or a universal stud removal as
shown in FIG 1 :12.
1 :5 Engine disassembly (station wagon)
To dismantle the engine proceed as follows:
1 Remove the exhaust silencer and manifold by releasing
the four nuts holding the two flanges from the cylinder
head. Also disconnect the two silencer mounting
brackets and lift away the exhaust system (see
FIG 1 : 2).
2 Place the engine on a firm wooden top bench. Release
the clip holding the tappet cover and lift away together
with the drip tray. Disconnect the fuel line and throttle
linkage at the carburetter and carefully lift away the
carburetter together with its insulator joint and gaskets.
3 Remove the generator drive belt by releasing the three
nuts so splitting the semi-pulley. Lift away the drive
belt.
16
FIG 1 :14 Tool A.60084 for valve and valve springremoval
TOOL A . 60084
4 Remove all the bolts securing the air conveyor ducting
to the cylinder head and to the crankcase, carefully
separate the panels and lift away the separate panels
ensuring no damage is caused to the mating faces.
5 Release the ignition distributor retaining bolt and lift
away the distributor.
6 Remove the fuel pump retaining bolts and also the
three fuel pipe retaining clips and lift away the fuel
pump assembly together with the insulator, gaskets
and control rod.
7 Release the t w o valve rocker retaining nuts, note the
order of assembly of washers and ease away the rocker
shaft assembly from the top of the cylinder head.
Carefully lift out the valve rocker pushrods noting
their relevent positions for correct reassembly.
8 Slacken the four cylinder head cap nuts and the four
conventional nuts in the order shown in FIG 1 :46. Lift
the cylinder head away from the barrels. If difficulty is
experienced it is essential to use Fiat tool A.40014 or a
similar drilled plate as shown in FIG 1 :9, otherwise
serious damage could be caused if other means are
used.
9 Remove the four pushrod sleeves and the casing con-
taining the oil ducting to the overhead valve gear.
10 Remove the six screws holding the centrifugal oil filter
pulley cover and lift away the cover. Remove the
centrifugal filter mounting flange by unscrewing the
crankshaft central bolt. Also remove the timing cover
f r o m t h e rear of t h e crankcase. Note carefully the posi-
tion of the nuts, toothed and plain washers for correct
reassembly.
11 Release the four camshaft sprocket retaining bolts
and lift away the sprocket and timing chain. Using
Fiat puller A.46020 or a large universal two-leg puller
as shown in FIG 1 : 1 0 remove the crankshaft
sprocket and its key
12 Carefully lift out the rocker pushrod tappets making a
note of their location and gently pull out the camshaft
making sure that the front bearing bore is not
damaged by the cam lobes.

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.

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