FIG 3:1 The coil and the distributor. Lead from terminal 15 goes to ignition switch, from terminal 1 to terminal on side of distributor and from terminal 4 to distributor cap (HT lead). Arrow points to clamp bolt
3:6 Centrifugal advance mechanism
3:7 Checking capacitor (condenser)
3:8 Removing and installing distributor and drive gear
The location of the distributor and ignition coil can be clearly seen in FIG 3:1. The distributor houses a contact breaker with centrifugal advance mechanism and above these a rotor arm distributes high-tension current to the sparking plug terminals inside the cap. This high-tension current is produced by the ignition coil when the contact breaker points open. A cam on the central shaft opens the points and this is the precise moment of ignition by the sparking plug. The ignition timing is automatically advanced by centrifugal weights flying outwards as engine speed increases, the weights altering the position of the cam with respect to the drive shaft.
High-tension current from the coil is conducted to a carbon brush in the distributor cap, the brush making contact with a brass segment on the rotor. As the rotor turns, the segment almost touches a terminal in the cap and the high tension current jumps the gap, passing from the terminal to the plug lead and so to the plug itself. In one revolution of the rotor, four such sequences take place, the sparking plug leads being so connected that the correct firing order of 1, 4, 3, 2 is obtained. Note that the segment on the rotor does not touch the terminals in the cap. Any erosion of the parts is due to the sparking which takes place. All the parts just mentioned can be seen in FIG 3:6.
At 3000 miles and then every 6000 miles or after a major overhaul, put a thin smear of Bosch grease Ft.1v8 on the cam to the left of the arrow in FIG 3:2. The arrow points to a gap in the contact breaker plate. Inject a few drops of engine oil into the gap. It is most important to take care that no lubricant reaches the contact points 9 and 11.
The contact breaker:
After long service the points become dirty and pitted. Do not use emerycloth to clean them, but dress them with a contact file. Move the file between the points while applying light pressure to the moving contact. The contact faces must be parallel and meet squarely when closed. Clean away all filings when finished. A slight pit in one face is not detrimental.
Check the gap to which the points open. Turn the engine until the distributor cam opens the points to the maximum extent and measure the gap with feeler gauges. Correct gap is .400 mm or .016 inch. To adjust, slacken screw 10 (see FIG 3:2) and turn eccentric screw 12 until the gap is correct after the clamping screw is retightened. After adjusting, check the timing as instructed in Section 3:5. This is essential because an alteration of .100 mm (.004 inch) in the gap changes the ignition timing by approximately 3 deg. of crankshaft angle. It will be appreciated that accurate setting of the contact gap will be impossible if the distributor shaft is slack in its bearings.
FIG 3:1 The coil and the distributor. Lead from terminal 15 goes to ignition switch, from terminal 1 to terminal on side of distributor and from terminal 4 to distributor cap (HT lead). Arrow points to clamp bolt
Distributor cap and rotor arm:
These must be clean and dry. Look for cracks and ’tracking’, which will be evident as a black line on the insulating material between two terminals. The carbon brush in the centre of the cap must protrude and must spring out again when pressed in and released. Slight erosion of the terminals and rotor arm is normal, but renew the parts if it is excessive.
Sparking plugs:
Instructions for regular servicing of these are given in Section 3:10.
Starter operates but engine will not start:
1 Check HT lead for good contact at coil (terminal 4 in FIG 3:1). Pull coil lead from centre of distributor cap and hold end about ¼ inch away from a clean metal earth point on the engine (not carburetter). Keep fingers well away from gap. Use the starter. If there is a good spark the coil is in order and the contact breaker working. Proceed with test 5. If there is no spark proceed as follows:
2 Connect a 6 volt lamp between distributor primary terminal 1 and earth. Primary circuit is probably good if light goes on and off as starter is operated.
3 If light remains on, contact points are not closing. Check contact breaker and earth connections in distributor and clean the points.
4 If light remains off, there is a break in the primary circuit or the points are not opening. Check for defective wiring, loose connections, earthed distributor terminal and faulty points. Check ignition switch and primary winding in coil (continuity between terminals 1 and 15 in FIG 3:1).
5 Remove distributor cap and check for moisture, bad corrosion and ’tracking’. Check plug leads and see that the contact pins penetrate to the wire core. Check plugs and gap. Set to .50 to .60 mm (.020 to .024 inch).
6 If unsuccessful, check ignition timing, and if correct, check the fuel system and mechanical condition of engine.
Engine runs badly:
Misfiring, difficult starting or loss of power may be due to many causes, not necessarily to faulty ignition. Check sparking plugs, coil and capacitor (condenser) by substitution. Check plug leads by running engine in the dark. High-tension leakage will then show up as a discharge of sparks. Misfiring at high speeds may be due to a weak contact breaker spring. Backfiring and spitting back through the carburetter may be due to wrong ignition timing or a loose or bent distributor shaft. Wrong type of sparking plug, excessive carbon or poor fuel may also be causes.
FIG 3:2 View of contact breaker. Arrow points to gap where oil is injected to lubricate centrifugal mechanism
Key to Fig 3:2
1 Primary terminal
2 Capacitor
3 Spring
4 Insulation
5 Insulating washer
6 Insulating block
7 Clamping plate
8 Terminal screw
9 Arm with moving contact
10 Clamp screw
11 Fixed contact plate
12 Eccentric adjusting screw
Refer to FIG 3:2. Remove wire from terminal 1. Slacken second nut and lift off moving contact arm and spring, taking careful note of position of insulators. Put light smear of Bosch grease FT.1v8 on pivot pin and fit new part, locating end of spring in correct place to ensure that the terminal is not earthed. Renew fixed contact plate 11 by removing screw 10. When installation is complete, check gap and timing.
Ignition takes place 5 deg. BTDC (before top dead centre) on all models except 1600S.90 and 1600SC where it is 3 deg. BTDC. For easier setting, the angles are translated into distances round the crankshaft pulley rim, being 6.3 mm (.25 inch) and 3.6 mm (.14 inch) respectively. Mark the distance on the pulley rim, measuring clockwise from the notch which indicates TDC. Before checking the timing, set the contact breaker gap as instructed in Section 3:2.
Remove distributor cap and turn crankshaft until timing mark is aligned with mark on crankcase and rotor arm is in-line with notch on distributor body indicated by arrow in FIG 3:3. This is the position for firing cylinder No. 1.
Connect a 6 volt lamp to earth and terminal 1 on coil or distributor (see FIG 3:2). Slacken distributor clamp screw arrowed in FIG 3:1. Switch on ignition and turn distributor body clockwise until points close. Turn distributor anticlockwise until lamp lights then tighten clamp. Check setting by turning crankshaft. In normal direction of rotation, lamp will light when timing mark lines up with mark on crankcase or at 180 deg. to it.
A simple test of this is to turn the distributor rotor arm clockwise until it stops. When released it should return freely to its original position. If it does not, the springs may be broken or the bearing surfaces seized. A rough check of the action is made with a stroboscope. Make an additional mark on the crankshaft pulley 30 deg. or 37.8 mm (1½ inch) from the timing mark originally made for checking ignition timing as described in Section 3:5. Measure in a clockwise direction.
Run the engine at idling speed. Using the lamp, the timing should coincide with the lefthand mark. The timing should move smoothly to the righthand mark as engine speed increases, until at just over 3000 rev/min it is at the mark. Jerky action or inadequate range indicates a faulty centrifugal advance mechanism.
FIG 3:3 Rotor arm is in position for No. 1 cylinder when it points to notch on distributor body indicated by arrow
This is part 2 in FIG 3:2. A faulty capacitor gives rise to burnt contact breaker points, a weak spark and difficult starting. Without test equipment, check as follows:
1 Disconnect wire from distributor terminal and remove capacitor lead. Connect a 6 volt test lamp across the leads.
2 Switch on ignition. If lamp lights, capacitor is earthed. If lamp does not light, reconnect leads.
3 Disconnect coil lead from centre of distributor cap and hold end ¼ inch away from crankcase, keeping fingers away from gap. Switch on ignition and operate starter. If no spark, try a new capacitor. If still no spark, try for faults elsewhere.
Always use a genuine replacement of a faulty capacitor so that the capacity is correct, or the contact points may be burned.
Remove distributor cap and thin wire from distributor terminal. Remove nut to left of arrow in FIG 3:1. Lift distributor away from crankcase. Do not disturb clamp.
FIG 3:5 Correct position of offset driving slot in distributor drive shaft with No. 1 piston at TDC and both valves closed. Slot is offset towards pulley
Removing drive gear:
Remove fuel pump, flange and pushrod (see Chapter 2). Insert finger in pushrod aperture and lift drive shaft upwards, turning it to the left. Take great care not to drop the drive shaft thrust washer into the timing case. There is a small spring in a bore at the top of the drive shaft.
Clean the parts and inspect for wear. If the gear is worn, renew the shaft and the bronze pinion.
Installing drive shaft:
Feed the thrust washer onto a screwdriver or length of rod, insert the rod into the hole which takes the distributor and let the washer fall down into place. Take care it does not fall into the timing case. Set No. 1 cylinder at TDC with both valves closed. Insert the drive shaft as in FIG 3:4 so that when it has finished engaging, the slot is parallel to the timing case joint and the small segment is adjacent to the pulley. The offset of the slot is shown in FIG 3:5. Drop the small spring into place down a length of rod.
Installing distributor:
This is a reversal of the removal procedure. Set the rotor to point towards the notch on the distributor body as shown in FIG 3:3 and fit the distributor, turning the arm to and fro to engage the coupling. Secure the clamp to the crankcase. Check the ignition timing (see Section 3:5).
The components of the distributor are shown in FIG 3:6, and apart from small deviations in design as new models were introduced, the basic functions of the parts remain the same. Dismantle the distributor as follows:
1 Remove cap 70 and rotor arm 60. Take off the low-tension lead from terminal 42 (see also part 1 in FIG 3:2).
2 Dismantle the terminal. FIG 3:2 shows the assembly quite clearly, but whilst withdrawing the various washers and leads, make a note of the positions of the parts so that they may be reassembled correctly.
3 The spring of the moving contact 38 is hooked under the head of the terminal, and with the terminal loose, the moving contact assembly may be lifted off its pivot pin. Note the insulating washer underneath the arm.
4 Remove screw 37 to release fixed contact 36. From sides of body 1, remove screws 40 and lift out breaker plate 35.
5 Before dismantling shaft 15, make a note of the correct relative positions of driving dog 31 and the slot for the rotor arm at the top of camshaft 29. The dogs are offset and could be reassembled 180 deg. out. Remove spring retaining clip 33 and drive out pin 32 so that the driving dog may be lifted off the shaft.
6 Push out the shaft assembly 15. There are shim and fibre washers on the shaft (see parts 26 and 25) and also on the camshaft (see parts 28 and 27). These control end play. Before parting them, note relative positions of camshaft and drive shaft.
Clean all the parts except the body in a solvent. The reason for not using a solvent on the body is that the self-lubricating bushes for shaft 15 will lose their properties if soaked or immersed in it. Check the springs 24 and renew if rusty or worn at the eyes. Check the fits of the camshaft on the drive shaft and the drive shaft in the body. New bushes may be pressed into the body by an agent, or the body renewed. If the contacts are deeply pitted or badly worn, renew them as a pair. If serviceable, simply file off the pip on one of them and finish them both so that they are clean, flat and will meet squarely. A small pit in one of the points will not affect the working efficiency. Scrap the contact breaker if the moving contact spring is rusty as it will almost certainly break due to the pitting.
When satisfied with the condition of the parts, reassemble as follows:
1 Put engine oil on the shaft and fit to the body with the shim and fibre washers correctly fitted. Fit the driving dog and check the end play of the shaft. Fit shims until the play is negligible. Fit the cross-pin after checking the relative positions of the dogs and the rotor arm slot.
2 Fit the contact breaker plate, not forgetting the shim and fibre washers on the camshaft. Fit the fixed contact.
3 Reassemble the terminal with the insulating block 44 on the inside. Fit the capacitor lead and leave the terminal loose until the moving contact is fitted on a pivot pin which has been very lightly smeared with Bosch grease. Do not forget the insulating washer under the arm. Fit the spring under the clamping plate and tighten the first terminal nut (FIG 3:2 shows how the parts are located). Fit the low-tension wire and second nut. Remember that the terminal and its metal parts must all be insulated from the distributor body.
4 Adjust the contact breaker points to the correct gap (see Section 3:2). Fit the rotor arm and the distributor cap, making sure that carbon brush 71 is correctly fitted and is free to spring in and out.
5 Install the distributor and time the ignition as instructed in Sections 3:8 and 3:5.
FIG 3:6 Components of a typical Bosch distributor as fitted to Porsche cars, with minor variations according to model
Key to Fig 3:6
1 Body
2 Capacitor
3 Screw
4 Washer
15 Shaft
17 Screw
18 Spring washer
19 Washer
20 Centrifugal weight damper
21 Centrifugal weight
22 Washers under weights
23 Weight retaining clip
24 Springs
25 Fibre washer
26 Shim washer
27 Fibre washer for camshaft
28 Shim washer
29 Camshaft
30 Felt pad
31 Driving dog
32 Cross-pin
33 Retaining clip
35 Contact plate and breaker
36 Fixed contact
37 Screw
38 Moving contact
39 Washer
40 Screw
41 Spring washer
42 Terminal screw
43 Clamping plate
44 Insulating block
45 Insulating strip
47 Insulating washer
48 Washers
49 Spring washer
50 Nut
51 Terminal tag
52 Insulating sleeve
60 Rotor arm
70 Cap
71 Carbon brush and spring
72 Clips for cap
73a Clip bracket
73b Clip bracket
78 Clip for lead
79 Rubber grommet for lead
85 Cover
FIG 3:7 Gap between sparking plug electrodes is indicated at A. It must be .50 to .60 mm (.020 to .024 inch)
These should be examined every 3000 miles and renewed at 10,000 miles. As they are relatively cheap, it is false economy to continue running on old and worn-out plugs as they will adversely affect starting and fuel consumption.
The appearance of the sparking plug will help in assessing the working conditions of the engine. If the points or electrodes are a light brown or tan colour, the plug is firing properly and the fuel strength is correct.
If the deposit is white, the plug is running at a high temperature, probably due to weak mixture. On the other hand, a soft black deposit is due to rich mixture or a plug which is running too cool.
If the plug is fouled by a wet, black deposit, there is too much oil about and the engine is probably so worn that oil is getting past the pistons.
The best way to clean sparking plugs is to have them shot-blasted on an official machine so that they may be tested under pressure. Plugs may spark quite well in the atmosphere and yet fail under compression pressure. If cleaning by hand, use a wire brush on the threads and electrodes but clean the insulator and internal surfaces with a piece of wood and not a sharp metallic object.
File the electrodes to a bright metallic surface and set the gap between them by bending the outer electrode. Do not attempt to bend the central electrode. Use a gauge which gives a gap setting of .50 to .60 mm (.020 to .024 inch) as shown in FIG 3:7. When refitting the plugs, fit new sealing washers and do not overtighten.
The correct type of sparking plug is Bosch W.225.T1 or the equivalent in other makes.
Sparking plug leads may deteriorate by cracking or chafing. Problems of poor starting or erratic ignition may be due to high-tension leakage and this may often be detected by running the engine in the dark and looking for a discharge from the lead to an adjacent metal object. Renew leads which are faulty, and always at a major overhaul.
(a) Engine will not fire
1 Battery discharged
2 Contact breaker points dirty, pitted or out of adjustment
3 Distributor cap dirty, cracked or ’tracking’
4 Carbon brush inside distributor cap not touching rotor arm
5 Faulty cables or loose connections in the low-tension circuit
6 Distributor rotor arm cracked
7 Faulty coil lead to distributor, faulty coil
8 Broken contact breaker spring
9 Contact points stuck open
10 Faulty capacitor (condenser)
11 Faulty ignition switch
(b) Engine misfires
1 Check 2, 3, 5 and 7 in (a)
2 Weak contact breaker spring
3 Plug and coil high-tension leads cracked or perished
4 Loose sparking plugs
5 Sparking plug insulation cracked
6 Sparking plug gap incorrect
7 Ignition timing too far advanced or retarded
