1958 FIAT 500 low oil pressure

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

After the crankshaft has been reground it is important
that all traces of swarf are removed by constant washing
and then drying with a non-fluffy rag.
The clearance between the main bearings and journals
must be checked before installing the crankshaft in the
engine. It should also serve as a recheck after the
crankshaft has been reground.
Measure the maximum main bearing internal
diameter and the minimum journal diameter using
accurate measuring equipment. The clearance must not
exceed .0039 inch otherwise the journals must be
reground and undersize bearings fitted.
Undersize bearings w i t h .0394 inch stock on the
internal diameter are also supplied unmounted. They
must be press fitted in the supports, the recommended
interference fit being .00039 to .00197 inch. After
pressing the bearing into the support, a hole is drilled in
the bearing in line with the location dowel hole in the
support. The hole is finished with a suitable expanding
reamer, such as Fiat U.0334, and the dowel pressed i n ,
noting that the hollow dowel fits in the flywheel end
support.
The next stage is to heat the assembly in an oven or
oil bath for a period of one hour at 150°C (302°F).
When the assembly has cooled to room temperature,
the bearing is reamed in a lathe to match the crankshaft
journal size.
3
Crankshaft oil seals:
Two inner spring rubber oil seals are located, one in a
special seat in the timing gear cover and the other in the
flywheel end of the crankshaft support and provide oil
tightness. These seals are shown in FIGS 1 :3 and 1 :34.
Whenever the engine is dismantled for overhaul these
seals should be carefully inspected for correct seating and
that the inner seal surface is not worn and that the contact
area is perfect both on the crankshaft and on the fan and
generator drive pulley hub.
Clutch shaft pilot bushing:
A self-lubricating bronze bush is fitted in the end of the
crankshaft as shown in FIG 1 :34 and provides a bearing
for the clutch shaft. Should the bush be worn use Fiat
puller A.40006/1 /2 to remove the worn bush. A new bush
should be fitted using a suitably sized drift.
1:12 Flywheel and starter ring gear
The flywheel should be inspected for wear at the clutch
driven plate contact area. It should be flat and have a
smooth finish.
The ring gear teeth should be cheeked for damage
which if evident, the ring gear must be replaced. To facili-
tate the fitting of a new ring gear on the flywheel, the new
ring gear should be heated in an oil bath to a temperature
of 80°C (176°F). Using a press gently ease the
expanded
ring gear over the flywheel and press fully home.
1:13 The oil pump
Sedan :
A helical-spur gear type oil pump is driven by the cam-
shaft through a front dog drive coupling. The gears are
F50025 To remove the pump from the engine proceed as
follows:Pump removal and reassembly:
Remove the engine rear central support from the timing
gear casing. Remove the filter cover pulley and lift
away the drive belt.
Release the hollow screw attaching the slinger and the
mounting flange of the filter on the crankshaft. Also
release the nuts fixing the timing gear cover to the
crankcase.
Remove the timing gear cover together with the oil
pump assembly and the pressure relief valve.
Lift out the oil pump suction scoop with the filter
screen attached from the sump.
Reassembly of the pump to the engine is the reverse
procedure to dismantling. 1
2
3
4
5 located in a special housing in the timing gear cover and
held in place by a cover plate. The oil pressure relief valve
is mounted on the drive gear shaft guide.
A pump suction scoop fitted with a filter screen is
secured in the crankcase and connects to a duct in the
timing gear case as s h o w n in FIG 1 :36.
2
4
6Key t o Fig 1 :36
Rocker shaft
Ducts, cylinder head oil drain
Oil pressure relief valve
to centrifugal filter
9
with central oil gallery
12Sump cooling air conveyor
indicator sending unitOil filler with vent valve
Line, oil delivery to rocker shaft
Level indicator rod 31
5
7Gear pump
8 Oil duct
Centrifugal oil fitter
1110
Crankshaft
Oil pump intake screen filter
13 Low oil pressure FIG 1:36 Engine lubrication diagram

FIG 1:37 Lubrication diagram of engine 120.000
Key to Fig 1:37 1 Oil dipstick 2 Oil filler with vent valve 3 Centrifugal oil filter
4 Crankshaft, with central oil gallery 5 Low oil pressure indicator sending unit 6 Oil pressure relief valve 7 Gear pump
8 Camshaft, with central oil gallery 9 Oil suction filter from sump 10 Oil sump drain plug
11 Oil delivery line to rocker shaft 12 Rocker shaft 13 Head cover
Pump dismantling, inspection and reassembly:
Remove the lock ring and withdraw the pressure relief
valve and spring. Remove the oil pump cover plate and
ease o u t t h e gears and shaft.
Thoroughly clean all the parts and blow clean using a
compressed air jet. Inspect the timing gear cover for
cracks or distortion. Check that the inner duct for oil
delivery to the pump is clear of obstruction. Use a
compressed air jet to clean the passage.
Check the oil pump gear teeth for damage or excessive
wear and fit new gears if necessary. The recommended
backlash is .0059 inch w i t h a maximum wear limit
giving a backlash of .0079 inch. Check the clearance
between the gear teeth and the housing walls in the
timing gear cover. The recommended clearance is .0012
to .0035 inch w i t h a maximum of .0047 inch. Ensure
that the drive gear is firmly attached to its shaft. Upon
assembly there is a pinch fit of .0016 to .0031 inch
between the t w o parts.
The driven gear to shaft clearance upon assembly is
.00079 to .00236 inch with a maximum wear limit of
.0039 inch. Also check the width of the drive and driven
gears which when new should be .3937 to .3928 inch
with a minimum width of .3917. In service a spare drive
gear is supplied complete with its shaft.
26 4 3 2 1
Station wagon:
A helical-spur gear type oil pump is driven from the
lower end of the distributor drive spindle which is in mesh
w i t h the camshaft. The gears are located in a special
housing in the bottom of the timing gear housing and are
held in place by a cover plate. The oil pressure relief valve
is located at the driven end of the camshaft.
A pump suction oil filter is fitted in the sump and this
connects to a duct in the timing gear case so supplying oil
to the pump (see FIG 1 : 3 7 ) .
Pump gears removal, inspection and reassembly:
To remove the pump gears from the timing gear cover
proceed as follows:Inspect the filter screen on the end of the pump suction
scoop and remove any obstruction. If the screen is
damaged it must be renewed.
Check that the pump drive dog is a good fit on the cam-
shaft and that the dogs are not badly worn so as to
impair the pump operation.
Reassembly of the pump is the reverse procedure to
dismantling. Ensure that the pump cover piate is
correctly located by means of the dowel on the timing
gear cover. 5
6
7

Drain the oil sump to ensure that the oil does not syphon
out. Thoroughly clean the area around the pump body
(see FIG 1 :37).
Remove the end cover plate by releasing the retaining
bolts and washers. Carefully ease t h e driven gear down-
wards followed by the driving gear and shaft
Clean all parts removed and blow clean using a com-
pressed air jet. Inspect the timing gear cover pump area
for cracks or distortion. Check that the inner duct for oil
delivery to the pump is clear of obstruction. If in doubt
remove the drain plug and filler cap and use a com-
pressed air j e t to clean the passage.
Check the gear teeth for damage or excessive wear,
ensure that the drive gear is firmly attached to its spindle
and that the end cover plate is not badly scored or pitted.
Fit new parts as necessary.
Reassembly is the reverse procedure to dismantling,
taking care that all parts are assembled clean and the
end cover plate seating correctly with a new gasket. 5 43 21
1:14 Lubrication, oil filter, relief valve
Description :
The engine is pressure lubricated through a gear type
pump which is incorporated in the timing gear cover and
driven from the camshaft by dogs or gears. The lubrication
circuits are shown in FIGS 1 :36 and 1 : 37.
The pump draws oil from the sump through a suction
horn fitted with a filter screen which is fixed to the crank-
case by a d u c t in t h e timing gear cover. This
supplies oil
to the pump.
Oil passes f r o m the camshaft rear seat o n t o t h e crank-
shaft rear support where it flows into an adjacent chamber.
From here the o i l flows through ducts in the crankshaft
from end to the centrifugal oil filter. The centrifugal filter,
which also acts as a pulley for the generator and blower
drive, rotates w i t h the crankshaft.
Oil from the filter enters a passage in the crankshaft,
where it lubricates the main and connecting rod bearings
and passes f r o m a special groove in the front main
bearing and ducting in the crankcase into which is
inserted the oil pressure warning sender unit, and also
the delivery pipe for oil to the overhead valve gear.
The pushrod sleeves provide the return path for the oil
from the cylinder head and delivers oil to the tappet gear
and the camshaft cams. The tappets are suitably drilled
to allow correct circulation of the oil. The tappets are
located in t w o casting cavities, one of which com-
municates w i t h the timing gear housing and the other
one to the crankshaft front drain support drain.
The oil pressure is regulated by a pressure relief valve 5
(see FIG 1 : 3 8) mounted at the rear end of t h e camshaft.
It comprises a hubbed disc which slides on a guide 6 of
the oil pump drive shaft 7. Under spring load 9 the valve
disc circumferentially closes an annular chamber which
communicates w i t h the lubrication circuit. Excessive o i l
pressure causes the disc to uncover the chamber.
Centrifugal oil filter:
The oil filter is of the centrifugal type comprising of
two flanges and an oil slinger. The filter is attached to the
rear end o f t h e c r a n k s h a f t a s s h o w n i n FIG 1 :38. The
outside diameter of the oil slinger (see FIG 1 :39) is
smaller in diameter than that of the flanges but of such a
F50027
Key to Fig 1:39 1 Drive pulley 2 Rotor hub
3 Seal ring 4 Oil slinger 5 Lockplate
6 Hub-to-crankshaft hollow screw 7, 8, 9 Pulley-to-hub
mounting screws, toothed washers and plain washers FIG 1:39 Centrifugal oil filter components Key to Fig 1 :38 Suction scoop 2 Hole in crankcase
3 Duct in timing sprocket cover 4 Timing sprocket cover
5 Oil pressure relief valve 6 Drive shaft guide and oil
pump cover 7 Oil pump driving gear shaft 8 Camshaft
9 Oil pressure relief valve spring FIG 1:38 Engine longitudinal section through oil pump

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.

5 Using the graduated sector check that all the valve
timing angles are as detailed in Technical Data.
Readjust the valve stem to rocker arm clearance to the
correct setting.
1:16 Valve stem-to-rocker clearance adjustment
It is important that the clearance between the valve
stem and rocker is kept to the recommended figure
of .0059 inch, measured when the engine is cold.
If the clearance is excessive operating noise will occur
and if less than recommended the valves will stay open
too long which will result in damage to the valve face
and its seating.
Inspect the contacting surfaces for scoring or pitting:
if it is excessive, new parts must be fitted. Also check
the condition of the rocker-to-valve and rocker ball
head-to-pushrod contact surfaces are free from wear or
pitting. The faces must have a mirror finish.
The oilway in the rockers and shaft must be thoroughly
inspected and free from sludge, otherwise lubrication
failure will occur.
The assembly clearance between the rocker arm and
shaft should be .00063 to .00217 inch and the clearance
between the rocker shaft and the shaft support should
be .00020 to .00138 inch with a maximum wear limit of
0039 inch.
Turn the engine until the valves of one cylinder are in
balance, that is, the inlet valve opening and the exhaust
valve closing. The other cylinder will now have both valves
fully closed. Adjust the valves on this second cylinder by
loosening the locknut, and turning the
adjuster as shown in
FIG 1 : 43 to obtain the desired clearance measured with
a feeler gauge. Adjust the clearances on the other cylinder
in the same manner.
1 :17 Engine assembly (sedan — all versions)
To reassemble the engine proceed as follows:
1 Thoroughly clean and dry all the parts, ensure that all
drillings are free from dirt or sludge and place on a
clean dry surface.
2 Carefully install the cylinder-piston-connecting rod
assemblies w i t h new paper gaskets between the
cylinders and crankcase seats.
3 Refit the big-end bearing shells to the connecting
rods, ensuring that they are free from any dirt or
metallic particles. Carefully ease t h e crankshaft into
the crankcase, lubricate the main journals with clean
engine oil, place a new paper gasket between the
supporting member and the flywheel end of the
crankcase. Install the supporting member and bearing
assemblies. Secure the supporting members with the
screws and special toothed washers.
4 Locate the connecting rod big-end half onto the
crankpin journals, liberally lubricate the journals with
fresh engine oil, fit the remaining shell half, matching
bearing end cap and tighten the bearing cap nuts to a
torque wrench setting of 23.9 Ib ft.
5 Inspect the camshaft bearing bores and remove any
burrs w i t h a hand scraper wetted with oil. Carefully
slide in the camshaft ensuring the cam lobes or gear
teeth do not score the front bearing bore.
6 Fit a new timing gear cover paper gasket held in
place w i t h a little grease. Install the outer thrust ring,
F50029 inner thrust ring, shoulder washer and slide on the
camshaft drive sprocket, locking it with the Woodruff
key. Assemble the timing chain and driven sprocket,
ensuring that the timing marks on the sprocket are
indexing as shown in FIG 1 :41. Secure the driven
sprocket with six screws and lockplates and care-
fully bend down the lockplates.
7 Install the timing gear cover, the oil pump, oil pressure
relief valve and seal assembly. Secure w i t h nuts,
special toothed washers and plain washers located
in the same manner as was noted on dismantling.
Locate the oil pump suction horn and secure with the
nuts and toothed washers.
8 Install the flywheel in the same relative position to the
crankshaft as was noted on dismantling. Replace the FIG 1 : 4 3 Adjusting the rocker clearances using the
optional service tools. Refer to Technical Data for the
correct clearance on early and late engines FIG 1 :42 Graduated sector C.673 for valve gear
timing
TIMING MARK

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