drive FIAT 500 1967 1.G User Guide

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

sections of the air conveyor securing with seven
screws, seven toothed washers and five nuts.
22 Slide the fuel pump control rod into its seating,
assemble the insulator between oil wetted graphite
gaskets and fit the pump to the crankcase using nuts
and toothed washers.
23 Fit the air conveyor cover complete with the accelera-
tor control relay lever and rod. Secure using eight
mounting screws, eight toothed washers, eight plain
washers and eight nuts. Fit the fuel line retaining clip
which is secured by one of the air conveyor upper
screws. Install the generator and fan drive pulley
having first placed four adjusting rings between the
pulley halves and the thrust ring on the outside.
Secure the pulley to generator shaft using three
screws and three toothed washers. Fit the generator
fan drive belt.
24 Refit the carburetter having first positioned the
bakelite heat shield between the t w o oil moistened
graphite gaskets. Secure the carburetter using t w o
copper washers and t w o self-locking nuts. Fit the
exhaust silencer and secure to the exhaust manifolds
with nuts and spring washers. Place the t w o graphite
gaskets between the manifold joints. Fit both exhaust
silencer upper mounting brackets and secure them
on the top side to the brackets already in place w i t h
nuts and toothed washers on the bottom side w i t h
screws and toothed washers.
25 Carefully position the distributor at a 10 deg advance
setting and secure w i t h a
nut, plain washer and
spring washer. Fit the fuel pump to carburetter line
complete w i t h mounting bracket rubber lining and
secure the line with two clamps. If difficulty is
experienced in positioning the fuel line into the pump
or carburetter funnels it is suggested that the line
ends should be heated in hot water and thoroughly
dried before installing.
26 Install the air cleaner elbow and rubber hose assembly
on the top of the carburetter using a graphite gasket
in between and secure w i t h nuts, plain washers and
spring washers. Carefully position the air cleaner, line
and hose assembly and connect it to the elbow.
Secure the cleaner to air conveyor cover using screws
and toothed washers.
27 Fit the spark plug cables complete with the rubber
grommet for cable mounting bracket on engine
cowling and connect the cables to the distributor
and spark plugs. Fit the oil pressure gauge sender
unit together w i t h its sealing washer.
28 Install the cylinder head cover and oil breather pipe
assembly w i t h a cork gasket inserted between.
Secure w i t h self-locking nuts and fibre washers.
Connect the accelerator control relay lever rod to the
carburetter and secure with the clip.
29 Fill the oil pan with the correct grade and quantity of
oil, insert the dipstick and the engine is ready for
refitting.
1:18 Engine assembly (station wagon)
Reassembly of this engine is straightforward as it is
the reverse procedure to dismantling. It is recommended
that Sections 1 :5 and 1 :17 are studied as the assembly
technique is similar for both the horizontal and vertical
F50031 cylinder engines. The following points should however
be noted:
1 Refer to FIG 1 :45 for the correct positioning of the
connecting rod-piston assembly on the 120.000
engine.
2 The sequence of tightening the cylinder head nuts is
different, the new order being given in FIG 1 :46.
Key to Fig 1 :47 1 Suspension arm 2 Screw,
rubber pad to bracket 3 Bracket-to-engine nut
4 Nut, arm to bracket 5 Arm bracket 6 Spring
7 Arm pin-to-support nut 8 Screws, pin to support
9 Pin arm to supportFIG 1 :47 Power plant rear suspension FIG 1:46 Cylinder head stud nut tightening sequence.
500 D. F and L Sedan and Station Wagon

FIG 1 :48 Power plant front support cross-section
FIG 1 :49 Checking the generator and blower drive
belt tension
1 :19 Power plant mountings
The combined power and transmission unit is elastic-
ally mounted on two supports.
The front of the unit rests on a crossmember which is
secured under the car floor through two rubber block
mountings that are bolted to the gearbox casing as
shown in FIG 1 :48. The position of the rubber blocks
on the crossmember is adjustable so that the assembly
can be correctly aligned.
W i t h t h e rear of the unit the engine crankcase is sprung
to the b o d y rear crossmember through an articulated
swinging arm that compresses a coil spring as shown in
FIGS 1 :47 and 1 :49. A rubber bump pad is mounted
inside the spring to give a progressive action.
Whenever the power and transmission unit is being
serviced the condition of the mountings should be
checked and any worn or damaged parts renewed.
1 :20 Adjustment of generator and fan drive belt
The centrifugal oil filter cover/pulley on the crankshaft
transmits the drive through a V-belt to the generator and
centrifugal fan pulley.
32
(b) Engine stalls
1 Check 1, 2, 3, 4, 10, 1 1 , 12, 13, 14 and 15 in (a)
2 Sparking plugs defective or gaps incorrect
3 Retarded ignition 1 Defective coil
2 Faulty distributor capacitor (condenser)
3 Dirty, pitted or incorrectly set contact breaker points
4 Ignition wires loose or insulation faulty
5 Water on sparking plug leads
6 Corrosion of battery terminals or battery discharged
7 Faulty or jammed starter
8 Sparking plug leads wrongly connected
9 Vapour lock in fuel pipes
10 Defective fuel pump
11 Overchoking
12 Underchoking
13 Blocked petrol filter or carburetter jets
14 Leaking valves
15 Sticking valves
16 Valve timing incorrect
17 Ignition timing incorrect
(a) Engine will not start 1 :22 Fault diagnosis
Since its introduction the Fiat new 5 0 0 model has
been continually developed. The main modifications that
have been made are as follows:
1 Heating system safety device
2 Recirculation device for the blow-by gases
3 Cylinder head modified to incorporate item 1
4 Double valve springs fitted
5 Cylinder barrels modified to incorporate item 1
6 Flywheel modified to incorporate new type diaphragm
spring clutch mounting
7 Larger air cleaner container.
Details of these modifications are to be found in the
relevant sections if they necessitate a change in service
overhaul procedure. Other information is to be found in
Technical Data.
1 :21 Modifications
When the V-belt has been correctly adjusted the belt
should sag 13/32 inch under a hand pressure of about 22 lb
as shown in FIG 1 : 4 9.
Should the belt be too slack the generator and
centrifugal fan will not operate at the correct speed
causing overheating and a discharged battery. Also the
belt will slip causing rapid wear of the belt. Conversely
if the belt is too tight excessive loading will be placed
on the generator bearings causing excessive bearing
wear and noisy operation.
To adjust the belt tension proceed as follows:
1 Remove the three nuts ' B ' (see FIG 1 :49) on the
generator pulley and this will split the pulley into two
parts between which are spacer rings.
2 The tension of the belt is increased or decreased by
either reducing or increasing the number of spacers.
3 Place the spacer rings removed from between the
pulley halves on the pulley outer face so that the rings
may be re-inserted when fitting a new belt.
4 Tighten the three nuts to a torque wrench setting of
14.5
lb ft.
Key to Fig 1 :49 A Normal give-in: about 13/32 inch under
a 22 Ib pressure B Nuts securing the pulley halves with
spacer rings

4 Mixture too weak
5 Water in fuel system
6 Petrol tank vent blocked
7 Incorrect valve clearance
(c) Engine idles badly
1 Check 1 and 6 in (b)
2 Air leak at manifold joints
3 Slow-running jet blocked or out of adjustment
4 Air leak in carburetter
5 Over-rich mixture
6 Worn piston rings
7 Worn valve stems or guides
8 Weak exhaust valve springs
(d) Engine misfires
1 Check 1, 2, 3, 4, 5, 8, 10, 13, 14, 1 5, 16, 17 in (a);
2, 3, 4 and 7 in (b)
2 Weak or broken valve springs
(e) Engine overheats
1 Generator and fan drive belt too loose
2 Shutter or thermostat seized in closed position
(f) Compression low
1 Check 14 and 15 in (a), 6 and 7 in (c) and 2 in (d)
2 Worn piston ring grooves
3 Scored or worn cylinder bores
(g) Engine lacks power
1 Check 3, 10, 1 1 , 13, 14, 15, 16 and 17 in (a), 2, 3, 4
and 7 in (b) 6 and 7 in (c) and 2 in (d). Also check (e)
and (f)
2 Leaking joint washers
3 Fouled sparking plugs
4 Automatic centrifugal advance not operating
(h) Burnt valves or seats
1 Check 14 and 15 in (a), 7 in (b) and 2 in (d). Alsocheck (e)
2 Excessive carbon around valve seat and head
(j) Sticking valves
1 Check 2 in (d)
2 Bent valve stem
3 Scored valve stem or guide
4 Incorrect valve clearance
(k) Excessive cylinder wear
1 Check 11 in (a) and see Chapter 4
2 Lack of oil
3 Dirty oil
4 Piston rings gummed up or broken
5 Badly fitting piston rings
6 Connecting rods bent
(l) Excessive oil consumption
1 Check 6 and 7 in (c) and check (k)
2 Ring gaps too wide
3 Oil return holes in piston choked with carbon
4 Scored cylinders
5 Oil level too high
6 External oil leaks
7 Ineffective valve stem oil seals
(m) Crankshaft and connecting rod bearing failure
1 Check 2 in (k)
2 Restricted oilways
3 Worn journals or crank pins
4 Loose bearing caps
5 Extremely low oil pressure
6 Bent connecting rod
(n) High fuel consumption (see Chapter 2)
(o) Engine vibration
1 Loose generator bolts
2 Blower blade assembly out-of-balance
3 Incorrect clearance for rear engine mounting rubber
F50033

FIG 2:5 Starting device (choke) diagrammatic section
KeytoFig2:5 A Device fully inserted B Device partially inserted C Device disinserted 2 Air inlet 16 Bowl
19 Throttle 21 Primary venturi 24 Secondary venturi 26 Mixture duct 27 Mixture leaning air orifice
28 Transition duct 29 Transition mixture orifice 30 Starting mixture orifice 31 Transition orifice
32 Starting mixture orifice 33 Starting valve 34 Mixture duct 35 Starting device air orifices 36 Rocker
37 Lever return spring 38 Starting device control lever 39 Control wire screw 40 Cover with support for starting
device control bowden 41 Starting valve spring 42 Spring casing. 43 Starting jet emulsion air orifice
44 Air emulsion reserve well orifice 45 Starting reserve well 46 Starting jet
F50037
FIG 2 : 4 Diagrammatic section of Weber 26.IMB
carburetter
KeytoFig2:4 1 Air corrector jet 2 Air inlet
3 Idle speed mixture duct 4 Idle speed jet holder
5 Idle speed air orifice 6 Filter cover 7 Filter
8 Fuel inlet connection 9 Needle valve seat 10 Needle
11 Float pivot 12 Float 13 Idle speed jet
14 Main jet holder 15 Main jet 16 Bowl
17 Idle speed mixture adjustment screw 18 Idle speed
mixture orifice 19 Throttle 20 Transition hole
21 Primary venturi (not interchangeable) 22 Emulsion
orifices 23 Emulsion well 24 Secondary venturi
(not interchangeable) 25 Main nozzle
design with a 1.0236 inch diameter throat measured at the
height of the throttle shaft. The amount of charge passing
to the manifold is controlled by a throttle butterfly valve
from an accelerator pedal operating a lever secured to the
throttle valve shaft via a cable. The carburetter is fitted with
a progressive action starting device which enables the
driver to suit the mixture richness to the most arduous of
starting conditions, and will enable the engine to run
evenly until it reaches its normal operating temperature.
A dampened needle valve ensures a smooth running
engine as it is not affected by engine vibrations and there-
fore giving a constant fuel level in the carburetter bowl. A
secondary venturi is incorporated in the single casting of
the carburetter body and this has a diameter of 0.8268 inch.
Carburetter operation:
Filtered air flows through the venturi 24 (see FIG 2 :4)
where it mixes w i t h fuel flowing from the nozzle 25 and
the charge is then conveyed to the cylinders through the
primary venturi 21 and throat, where the throttle butterfly
19 controls the amount of charge.
Petrol flows from the main fuel line to the bowl 16
through a gauze filter 7 and needle valve 10, where the
float 12 pivoting at point 1 1 , controls the opening of the
needle 10 so maintaining a constant fuel level. From the
bowl 16 fuel reaches the emulsion well 23 via the metered
main jet 15 where, after having been mixed with the air
coming from the metered air corrector screw 1, through
the emulsion orifices 22 and spray nozzle 25, it finally
reaches the Venturis where it mixes w i t h the air stream

FIG 2 : 9 Weber 26.IMB carburetter cover components
Key toFig 2 : 9 1 Float 2 Carburetter cover 3 Float pivot 4 Needle valve gasket 5 , 6 Needle valve seat and needle valve
7 Cover gasket 8 Filter strainer 9 Gasket 10 Filter inspection plug
Carburetter cleaning:
To thoroughly clean the carburetter proceed as follows:
1 Passages. All fuel passages have a diameter that is
specially calibrated to ensure best operating conditions.
It is therefore essential that any dirt or scale that has
been deposited by petrol must be removed. Thoroughly
clean with petrol and blow dry using a compressed air
jet directed through all the passages in the castings. It is
essential that no drills or other metal objects be passed
through the jets or the passages otherwise these could
alter the finely calibrated diameters.
2 Calibrated parts. Idling and main jet holders, and the
relevant bayonet coupled jets are easily removed by
using a suitably sized wrench or screwdriver. To clean
the different calibrated parts, thoroughly wash in petrol
and blow dry using a compressed air jet. Do not use any
fine drills or metallic points as these may alter the fine
calibration of the orifices. Should it be necessary to dis-
mantle the carburetter adjustment components for
inspection always ensure that after reassembly of the
parts that they are seated correctly to avoid possible
operating troubles in the future.
3 Filter. To clean the filter unscrew and remove its plug
10 (see FIG 2 : 9) located on the top of the carburetter
cover and then gently ease o u t t h e filter. Wash the filter
carefully in petrol, also ensure that the filter seat is clean
and then blow dry using a compressed air jet.
2:7 Modifications
The Weber 26.IM B carburetter has undergone a number
of minor changes during the development of the Fiat 500
models, but no changes in servicing procedure are made
necessary. Jet sizes and other calibrations are detailed
in Technical Data.
From 1970, the mounting flange of the carburetter is
slightly modified to incorporate a different mixture
adjustment screw, as shown in FIG 2:11.
40
Throttle valve components:
The throttle valve shaft should rotate freely in its guides
and this should be checked when the engine is at its
normal operating temperature. Any excessive clearance
caused by wear or the throttle valve butterfly distorted are
liable to cause irregular engine operation which will be
more pronounced at idling speed. Should the above con-
ditions be evident then the throttle valve butterfly and the
shaft assembly together with its sealing rings must be
renewed.
FIG 2:10 Jets, jet holders and choke valve
Key to Fig 2:10 1 Choke valve 2 Spring
3 Spring retainer and guide 4 Lock ring 5 Air bleed jet
6 Emulsion well 7 Choke jet 8 Idling jet holder and jet
9 Main jet holder and jet 10 Main jet holder gasket

FIG 2:12 illustrates the starting device fitted to
26.IMB.4 and later carburetters. It differs from earlier
units in detail, principally in having fewer starting mixture
orifices 30 and 32 into the mixture duct 26.
2 : 8 Carburetter operation and adjustment,
Weber 26. OC
The new 500 station wagon is fitted with the Weber
26.OC carburetter which is of a horizontal draft design to
suit the engine which is fitted in the horizontal position.
The carburetter is fitted with a progressive action starting
device which enables the driver to adjust the mixture rich-
ness to the most arduous of starting conditions, and will
enable the engine to run eyenly until it reaches normal
operating temperature.
A dampened needle valve ensures a smooth running
engine as it is not affected by engine vibrations and there-
fore giving a constant fuel level in the carburetter bowls.
A secondary venturi is incorporated in the single casting
of the carburetter body.
Carburetter operation, starting device:
The petrol from bowl 23 (see FIG 2:13) reaches the
starting jet 37 through the duct 35. By operating the choke
lever 31 to the end of its stroke, the valve 30 is lifted from
its seat and brought to the 'fully open' position as shown
in diagram 'A' (FIG 2:13). Under these conditions the
valve 30 uncovers both the starting mixture ducts 28 and
29. With the throttle set in the idling speed position the
engine vacuum created by the operation of the starter
motor causes the fuel contained in the recess of j e t 37 in
the jet and the reserve
well 36 to be mixed with the air
coming from the air jet 38.
The mixture arrives through the ducts 28 and 29 at the
same time as air from holes 34, past the throttle so per-
mitting easy starting of the engine.
A
B
C
FIG 2:12 Section of later starting device
Key to Fig 2:12 A Cold starting position B Warming up position C Normal running position
2 Air inlet 21 Primary venturi 24 Secondary venturi 26 Mixture duct 27 Air bleed 30,32 Starting mixture orifices
33 Valve 34 Mixture duct 35 Air orifices 38 Rocker 39 Lever return spring 40 Control lever 41 Control wire screw
42 Cover and cable support 43 Valve spring 44 Spring guide and retainer 45 Starting jet emulsion air duct 46 Emulsion
air reserve well duct 47 Reserve well 48 Starting jet
F50041 Once the engine has initially fired the starting device will
deliver a mixture whose petrol/air ratio is such that the
engine will run regularly even though it is cold. As soon as
the engine warms up this rich charge would be excessive
and therefore it becomes necessary to gradually ease back
the operation of the starting device. As this is occurring,
the valve 30 gradually covers up the mixture duct orifice 28
so as to weaken the mixture while by closing the duct 29
gradually. It also reduces the amount of mixture delivered
by the carburetter as shown in diagram ' B ' (FIG 2:13). FIG 2:11 Mounting flange modification: A earlier, B
later (dimensions in mm)

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.