FIG 3:1 Dual ignition system wiring and components
3:1 Description
3:2 Routine maintenance
3:3 Ignition faults
3:4 Removing and dismantling distributor
3:5 Timing the ignition
3:6 Sparking plugs
3:7 The distributor drive shaft
3:8 Fault diagnosis
Conventional coil ignition is employed, with a distributor of Bosch or Marelli manufacture. All distributors have a centrifugal advance and retard mechanism which advances the ignition timing progressively as engine speed rises. Some units additionally have a vacuum control unit which advances the timing in response to inlet manifold depression.
All Bosch and some Marelli units have the centrifugal mechanism beneath the base plate which carries the contact breaker. In this case the rotor arm is a push fit on the top of the contact breaker cam. An alternative type of Marelli distributor has the centrifugal mechanism above the contact breaker, with a larger circular rotor arm held in place by two screws (FIG 3:6).
Certain models such as the Giulia Sprint GTA are equipped with a dual-ignition system, using twin plugs and coils. The distributor contains two contact breaker units and a twin arm insulated rotor system which fire both sparking plugs in a given cylinder simultaneously, through separate wiring. The circuit configuration of a dual-ignition system is shown in FIG 3:1. It will be appreciated that, for this type of ignition system, the following instructions for maintenance and servicing must be carried out in duplicate where necessary, to cover both ignition circuits.
In all cases the firing order is 1–3–4–2, the cylinders being numbered 1–2–3–4 starting from the front of the engine.
About every 3750 miles, pull off the two spring clips and remove the distributor cap to gain access to the contact breaker points. If the rotor arm is of the pull off type, remove it from the cam spindle. Refer to FIG 3:2 for standard ignition systems and soak the felt 1 with oil and apply a few drops of oil through the lubrication hole 3. Apply a thin smear of grease to the cam. Refer to FIG 3:3 for dual-ignition systems and soak the felt 3 with oil. When lubricating the distributor, ensure that no oil or grease contaminates the contact breaker points.
Refer to FIG 3:2 and turn the engine until one of the cams has opened the points to the full extent, then check the gap at S with a feeler gauge. The gap should be as specified in Technical Data for the version in question. To adjust the gap, loosen the screw or screws securing the fixed contact (2 in FIG 3:2) and insert a small screwdriver between the pins on the contact breaker plate and in the slot at the end of the fixed contact point. Turn the screwdriver in the required direction to obtain a gap as specified. If the contact breaker plate is provided with an eccentric screw for adjustment, turn the screw until the correct gap is obtained. Tighten the locking screw and recheck the gap.
FIG 3:1 Dual ignition system wiring and components
Refer to FIG 3:3 and turn the engine until the cams have opened both sets of contact breaker points to the full extent, then check the gaps at S with a feeler gauge. Each gap should be between .012 and .01 6 inch (.30 and .40 mm). To adjust a gap, loosen the screw 1 then turn the eccentric screw 2 until the specified gap is obtained. Tighten the screw 1 and recheck the gap.
FIG 3:2 Distributor lubrication points and contact point adjustment, standard ignition system
Use a fine carborundum stone or a contact breaker file to polish the contact points if they are dirty or pitted, taking care to keep the faces flat and square. Afterwards, wipe away all dust with a cloth moistened in petrol. The contact points may be dismantled to assist cleaning by referring to Section 3:4.
If the engine runs unevenly, pull back the rubber covers to expose the sparking plug lead connectors. Start the engine and set it to idle at about 1000 rev/min and, taking care not to touch any metal part, earth each plug in turn by placing the shaft of an insulated-handle screwdriver between the plug connector and the camshaft cover. Doing this to a plug which is firing properly will accentuate the uneven running but will make no difference if the plug is not firing, Having located the faulty cylinder, stop the engine and remove the plug lead. Start the engine and hold the lead carefully to avoid shocks so that the metal end is about ⅛ inch away from the cylinder head. A strong regular spark confirms that the fault lies with the sparking plug which should be cleaned as described in Section 3:6 or renewed if defective.
FIG 3:3 Distributor lubrication points and contact point adjustment, dual ignition systems
If the spark is weak or irregular, check the condition of the lead, and, if it is perished or cracked, renew it and repeat the test. If no improvement results, check that the inside of the distributor cap is clean and dry, that the carbon brush can be moved freely against its internal spring and that there is no ‘tracking’, which can be seen as a thin black line between the electrodes or to some metal part in contact with the cap. ‘Tracking’ can only be rectified by fitting a new cap.
Check that the contact breaker points are clean and correctly set, then proceed as follows. Disconnect the thin wire from the coil that connects to the distributor Connect a test lamp between these terminals, turn on the ignition and turn the engine slowly. If, when the contacts close the lamp lights, and goes out when they open, the circuit is in order. If the lamp fails to light there is a fault in the low-tension circuit. Remove the test lamp and reconnect the cable to the coil and distributor.
If the fault lies in the low-tension circuit, use the test lamp to carry out the following tests with the ignition switched on.
Remove the wire from the ignition switch side of the coil and connect the lamp between the end of this wire and earth. If the lamp fails to light a fault in the wiring or connections between the battery and coil is indicated. Reconnect the wire if the lamp lights.
Disconnect the wire from the coil that connects to the distributor and connect the test lamp between the coil terminal and earth. If the lamp fails to light it indicates a fault in the primary winding and a new coil must be fitted. Reconnect the wire if the lamp lights and disconnect its other end from the distributor. If the test lamp does not light when connected between the end of the wire and earth it indicates a fault in that section of wire.
The best method of testing a capacitor (condenser) is by substitution. Disconnect the original capacitor and connect a new one between the low-tension terminal on the side of the distributor and earth for test purposes. If a new capacitor is proved to be required, it may then be properly fitted. The capacitor is of .23 to .33 microfarad capacity
Pull off the two spring clips and remove the distributor cap. Refer to FIG 3:7 and turn the engine until the timing marks on the crankshaft pulley and reference plate are aligned as shown and the distributor rotor is pointing towards the front. This will facilitate the refitting of the distributor.
FIG 3:4 Bosch distributor components
Key to Fig 3:4
1 Retaining clip
2 Contact breaker points
3 Securing screw
4 Spring washer
5 Connector tongue
6 Contact breaker plate
7 Fibre washer
8 Lubrication felt
9 Cam
10 Spring clip
11 Flyweights
12 Intermediate plate
13 Insulating washer
14 Shim
15 Fibre washer
16 Shim
17 Securing screw
18 Spring washer
19 Plain washer
20 Spring washer
21 Securing screw
22 Spring
23 Ball
24 Shim
25 Flyweight spring
26 Distributor shaft
27 Spring washer
28 Securing nut
29 Plain washer
30 Retainer
31 Insulating bush
32 Insulating washer
33 Washer
34 Screw
FIG 3:5 Marelli distributor components
Key to Fig 3:5
1 Retainer
2 Contact breaker plate
3 Distributor shaft
4 Thrust washer
5 Vacuum unit
6 Circlip
7 Securing screw
8 Plain washer
9 Plastic washer
10 Securing screw
11 Spring washer
12 Securing screw
13 Distributor housing
14 Felt ring
15 Plastic washer
16 Spacing washer
17 Driving dog
18 Locking spring
19 Distributor cap
20 Centre carbon brush
21 Distributor rotor
22 Securing screw
23 Spring washer
24 Oiler
25 Oil wick
26 Spring clip
27 Spring washer
28 Securing screw
29 Clamp screw
30 Insulating lug
31 Insulating bush
32 Washer
33 Capacitor
Remove the vacuum hose from the distributor connection and disconnect the low-tension cable. Loosen the clamp bolt on the distributor mounting bracket at the crankcase and withdraw the distributor and drive shaft.
Refer to FIG 3:4 for Bosch distributors or FIG 3:5 for Marelli distributors. Remove the securing screws and detach the vacuum unit. Pull off the rotor from the top of the cam. Using a suitable punch, drive out the retaining pin from the drive dog and remove the drive dog and washers. Withdraw the contact breaker plate complete with the centrifugal advance mechanism from the distributor body. Collect the thrust washers from beneath the plate. Loosen the terminal screw on the contact breaker and disconnect the leads, then remove the contact breaker assembly. Remove the securing clip from the moving contact point arm and separate the contact breaker points.
Check all parts for wear, the moulded cap for tracking’, the condition of the points and the moving contact spring for satisfactory tension. The contact breaker points should be cleaned as described in Section 3:2 or renewed if they are badly burned or pitted. Renew any parts found to be unserviceable. Clean the inside and outside of the distributor cap and make sure it is dry and free from grease and oil.
Reassembly is a reversal of the dismantling procedure, noting the following points. Make sure that the thrust washers are positioned onto the drive shaft before it is fitted to the distributor body. Refit the thrust washers to the bottom of the drive shaft before securing the drive dog with the retaining pin.
This is the reverse of the removal instructions. On completion, check the contact breaker points gap as described in Section 3:2 and the ignition timing as described in Section 3:5.
FIG 3:6 Marelli distributor with centrifugal mechanism above contact breaker. The rotor arm is shown removed
FIG 3:7 Alignment of the engine and distributor timing marks
Make sure that the contact points are correctly adjusted then align the timing marks on the crankshaft pulley and reference plate as shown in FIG 3:7 with the distributor rotor pointing towards the front. Loosen the distributor clamp bolt and connect a 12-volt test lamp in parallel with the contact points. One lead will go to the terminal on the side of the distributor and the other to earth. Turn the engine until the static timing mark F on the crankshaft pulley is in alignment with the reference mark on the crankcase as shown in FIG 3:8. Switch on the ignition and turn the distributor body in an anticlockwise direction until the test lamp goes out. Now turn the distributor body back very slowly until the lamp lights, which indicates that the points are just opening. Carefully tighten the distributor clamp bolt without disturbing the setting.
This method is used to check the timing with the engine running. Set the static timing as just described, then connect a stroboscopic lamp into the ignition circuit in accordance with the instructions supplied with the lamp. An accurate tachometer is also required. Disconnect the distributor vacuum pipe, if there is one, run the engine and direct the lamp beam at the timing marks. At 800 to 900 rev/min, the timing mark F should appear in line with the reference mark. At a higher speed, 5100 rev/min for 1300 and 1600 models, 5300 rev/min for early 1750 versions, or 4600 rev/min for later 1750 and 2000 models, the M mark (for maximum advance) should appear aligned as shown in FIG 3:9. If necessary, slacken the distributor clamp bolt and carefully turn the distributor body, a little at a time, to align the marks. Then retighten the clamp. Always adjust the maximum advance timing correctly, even if it means disturbing the original static setting, as the timing is most criticial at higher engine speeds.
FIG 3:8 Alignment of the static timing marks on the crankshaft pulley and reference plate
FIG 3:9 Alignment of the maximum advance marks when using a stroboscopic lamp
To maintain peak engine performance, sparking plugs should be inspected and cleaned at regular intervals. Before removing plugs, ensure that the recess around each one is clean and dry so that nothing can fall into the cylinder. The most effective way to clean sparking plugs is to use an abrasive blasting machine. Failing that, deposits can be gently scraped or wire brushed off, taking care not to damage the ceramic insulator, provided that the plug is not too heavily fouled. It is anyway a false economy to continue to use the same set of plugs for a high mileage.
Some models use Lodge 2HL plugs which have four earth electrodes; on this type the electrode gap cannot be adjusted. Lodge HLN plugs should be set to .020 to .024 inch (.50 to .60 mm). Lodge RL 47 plugs to .015 to .018 inch (.35 to .46 mm) and Bosch plugs to .020 inch (.50 mm). For other types, refer to the plug manufacturer’s recommendation. The gap must always be set by bending the earth electrode. Do not try to bend the centre electrode. Lightly file the electrodes until they are bright and smooth to facilitate setting the gap accurately.
Before refitting the plugs, clean the threads with a wire brush. Clean the threads in the cylinder head with a tap if the plugs cannot be screwed in by hand. Failing a tap use an old sparking plug with crosscuts down the threads. Plugs should be tightened to a torque of 18 to 25 lb ft. Do not exceed the torque figure quoted, due to the possibility of stripping the threads in the light alloy cylinder head.
Inspection of the deposits on the electrodes can be helpful when tuning. Normally, from mixed periods of high and low-speed driving, the deposits should be powdery and range in colour from brown to greyish tan. There will also be slight wear of the electrodes. Long periods of constant speed driving or low-speed city driving will give white or yellowish deposits. Dry, black fluffy deposits are due to incomplete combustion and indicate running with a rich mixture, excessive idling and possibly defective ignition. Overheated plugs have a white, blistered look about the centre electrode and the side electrode may be baldy eroded. This may be caused by poor cooling, incorrect ignition or sustained high speeds with heavy loads.
Black, wet deposits result from oil in the combustion chamber from worn pistons, rings, valve stems or guides. Sparking plugs which run hotter may alleviate the problem but the cure is an engine overhaul.
Renew high-tension leads if they are defective in any way. Inspect for broken, swollen or deteriorated insulation which can be the cause of ‘tracking’, especially in wet weather conditions. Check the condition of the rubber covers on the sparking plugs and the terminal nuts and renew them if perished. Thread the new lead through the rubber covers and the terminal nuts before refitting the lead and connections.
The distributor drive shaft is removed with the distributor as described in Section 3:4. The distributor drive dog can then be renewed if it is worn or damaged. The drive slot into which the drive dog engages is at the end of the oil pump shaft and, if wear at this point is suspected, reference must be made to Section 1:9 for oil pump removal and servicing instructions.
(a) Engine will not fire
1 Battery discharged
2 Distributor contact points dirty, pitted or maladjusted
3 Distributor cap dirty, cracked or ‘tracking’
4 Carbon brush inside distributor cap not touching rotor
5 Faulty cable or loose connection in low-tension circuit
6 Distributor rotor arm cracked
7 Faulty coil
8 Broken contact breaker spring
9 Contact points stuck open
(b) Engine misfires
1 Check 2, 3, 5 and 7 in (a)
2 Weak contact breaker spring
3 High-tension plug and coil leads cracked or perished
4 Sparking plug(s) loose
5 Sparking plug insulation cracked
6 Sparking plug gap incorrectly set
7 Ignition timing too far advanced