How To Get Your Engine Running

If your car refuses to start, even though the starter is turning the engine over normally, there are eight probable causes: tracking in the ignition circuit, a worn contact brush in the distributor cap, a cracked rotor arm, a defective coil, dirty or incorrectly gapped points, poor low tension circuit connections, dirty or defective spark-plugs, and incorrect ignition timing. Another group of likely causes concern problems of fuel supply and include a failed petrol pump, blockages in the supply lines, a blocked carburettor, blocked filters and, of course, no petrol in the tank itself.

Testing The Ignition

If the car will not start the first task is to see if the ignition circuit is functioning properly ; to check, in short, that it is producing a spark. The quickest way to do this is to use one of the HT leads which run from the distributor to the spark-plugs. Detach a lead from its spark-plug and remove any plastic cap which may conceal the metal socket into which the plug fits. If it proves difficult to remove find a nail which has a head that will fit firmly into the socket. Grip the lead by its plastic insulation and hold it no more than 6 mm away from the engine block. With an assistant operating the starter, you should see a series of sparks jumping from the lead to the engine. If not, there is clearly some fault with the ignition system. The engine's failure to produce a spark can result from any of a number of causes, and the way to track down the actual cause is given in the accompanying chart.

Tracking In The Ignition

Tracking is the term used when the electricity is not following its planned route to the spark-plugs, but is short-circuiting to another part of the car. This can be caused by damp settling on certain parts of the ignition system and by the appearance of cracks in the HT leads or the distributor cap, or both. The moisture and cracks both offer the current an alternative path and therefore allow it to leak away from the proper ignition circuit. In damp, misty weather this is a likely cause of non-starting. If this is suspected, take a clean, dry cloth and thoroughly wipe dry each HT lead. With the ignition off, push a corner of the cloth into the sockets at the ends of the leads and wipe them dry too. Also wipe the tops of the sparkplugs dry. Replace the leads and trace them back to the distributor. Unclip the top of this and dry off the inside of the cap. Be very thorough here, as damp can settle in the most obscure places. Make a point of drying inside the sockets holding the HT leads. A good alternative to wiping dry is to spray the affected components with a damp-repellent aerosol such as WD40.

The HT leads should also be examined closely. If any have small cracks in the insulation you may have found the cause of the trouble. Look inside the distributor cap for cracks and forked marks showing the path of the current. If any of the HT leads are found to be in poor condition they should all be replaced. If one has deteriorated, the chances are that the rest will be well on the way, so renewing them all now will save further trouble later. If the distributor cap is found to be faulty this too must be replaced.

Worn Distributor Contact Brush

The contact brush is found on the inside of the distributor cap, right in the centre. It is a small, grey piece of carbon often held in a spring. When the distributor cap is in place this brush makes contact with the rotor arm and carries HT current to it. If it is making less than perfect contact the efficiency of the ignition will suffer. If the tip of the brush is burnt or chipped it must be replaced. Those mounted on a spring should be checked to see that they move up and down freely. If not, replacement is necessary. Distributors whose brush is fixed rigidly into the distributor cap must have the entire cap replaced if the brush has worn flush with the plastic.

Faulty ignition coil

The coil is a small, metal cylindrical component and is always fixed on or near the. engine block. The best way to find it is to follow back the lead which runs to the centre of the distributor. This goes straight to the coil. The coil's function is to boost low tension current (12 volts) from the battery into high tension current (up to 30,000 volts) for the spark-plugs. It is clearly essential that it be in good condition, and a fault in the coil is the cause of many failures to start. The coil has three leads connected to its top surface. One brings LT current from the battery (via the ignition switch). This current passes through the coil and on through the second terminal, to the points. These are held by push-on connectors. The third and largest lead carries HT current to the distributor cap.

The best means of checking the condition of the coil is through this last lead. Unclip the distributor cap and, having checked the contact brush (see above), hold an insulated screwdriver close to, but not touching, the contact brush. Make sure that the shaft of the screwdriver is also touching a good earthing point. Ask a friend to turn the engine over and a series of sparks should jump from the brush to the screwdriver. If so, the coil is in good order. If sparks do not appear check the top of the coil. Wipe off any oil or grease that may have accumulated there. Next disconnect the HT lead from the top of the coil. This is usually held in place by a knurled plastic nut, the whole connection being protected by a thin rubber cover. Ease the rubber away and undo the plastic washer. Be careful here, as it is fragile and will crack if too much pressure is applied to it. If there is no nut the lead will simply be a push-fit into the top of the coil, in which case it can simply be eased out.

With the end of the lead exposed, examine the condition of the wires in the core. If they appear at all dirty or thin the wire must be cut back to expose the full core of wires, then reconnected. Next, disconnect the light leads and check the condition of their terminals. Clean them with abrasive paper if they are badly tarnished. Reconnect all the wires and test at the distributor cap again. If there is still no response, turn the engine so that the contact-breaker points in the distributor are open. Connect one end of a test lamp to the terminal which carries the wire to the distributor. Connect the other wire to earth. Turn on the ignition. If the lamp lights, current is clearly leaving the coil and it is therefore working properly. If it does not, one last check must be made before concluding that the coil is at fault. This will test if power is reaching the coil.

To do this attach one of the test lamp leads to the other small terminal on the coil and connect the second lead to an earthing point. Turn on the ignition. If the bulb lights, power is flowing into the coil and, as the other tests have proved negative, the coil must be defective. The coil is another part of the ignition that is not capable of being repaired, but must be replaced. This is not a complicated exercise as the coil is usually held in place by, at most, two bolts. The one point to watch is that the two light leads are connected to the correct terminals on the new coil�so change them over one at a time.

Cracked Rotor Arm

The rotor arm is carried on top of the shaft in the body of the distributor. It is a thick plastic boss and has a shaped metal plate fixed on its top edge. It performs the highly important function of distributing the HT power to each of the spark-plugs in turn. If the plastic cracks it can provide an alternative path for the current. To check for this, remove the rotor arm and look at it closely. If it appears to be slightly cracked, renew it. A more positive test is to remove the central lead from the distributor cap. With the rotor arm back in position, get a friend to turn the engine while you hold the bare end of the lead close to the centre of the rotor arm. For once the absence of a spark is a good sign, and its presence is a bad one. If a spark is there it is obvious that the plastic body of the rotor arm is not preventing the current from running to earth, so it should be renewed.

Dirty Electrodes

The electrodes which receive the current from the rotor arm are also a potential source of trouble. These are the brass studs in the distributor cap. If any show a slight deposit of carbon, clean it off with a rag soaked in methylated spirits. If these contacts are pitted or badly burned the distributor cap must be replaced. Never attempt to clean the electrodes with an abrasive as this will widen the gap between the rotor arm and electrode.

Faulty Points

The contact-breaker points control the timing of the surges of HT current which the coil sends to the distributor. They also influence the strength of the current. It is therefore essential that they be in good condition. There are two main factors which affect them: incorrect gapping, and an accumulation of dirt. The most important point to remember is that the gap must be measured when it is at its widest point. With the points open, check if they are clean. The slightest trace of dirt on them can be the 'last straw' in an engine that is already reluctant to start, so it is a good idea to clean them even if they do not appear to be particularly dirty. This can be done without removing the points. Rub each side of the contacts with fine emery paper and blow out any dust which this might produce.

If, on the other hand, an inspection of the points shows that they are quite obviously dirty, they can be removed for a more thorough cleaning. In many respects, however, this may be more trouble than it is worth. Points have only a short life and, as they are crucial to the performance of the car, it is a good policy to replace them when they have clearly deteriorated. They should certainly be renewed if they are blackened or pitted.

Poor Low-Tension Connections

The low tension circuit runs from the small terminal of the coil to the contact-breaker points. A fault at any of the connections in between could interrupt the circuit and cause the engine's failure to start. Check for any signs of dirt or corrosion or loose connections. Clean or tighten as appropriate. If you dismantle any of these connections for cleaning, be careful to replace in the correct order the assortment of nylon and metal washers you will find. To be sure of doing this, lay out the washers on the wing of the car in the order in which you remove them.

Faulty Spark-Plugs

For the engine to start reliably the spark-plugs must be clean and correctly gapped. If the HT lead held close to the block eventually produces a spark, yet the engine still refuses to fire, there is a good chance that the plugs are neither clean nor correctly gapped. Remove the plugs, connect one to its HT lead and hold it against the engine - do not, of course, hold the plug itself, but the HT lead. Once the engine is turned over sparks should appear across the gap. If not, the plugs must be cleaned and gapped. If this produces no improvement the plugs will have to be replaced.

Other Possible Faults

If all the tests described above prove that petrol is reaching the engine and that the plugs are sparking, then all that is left is a major fault such as slipped timing or a disconnected drive to the distributor or even faulty valve gear. A quick check of the timing - a rough one, but it will do - is to remove No. 1 plug and bring the engine round until No. 1 piston is at the top of its compression stroke. Check this by holding your thumb over the plug-hole to feel for compression. When the piston is at TDC on its compression stroke, the rotor arm should be pointing towards the lead to that cylinder with the points just about opening. If it is widely out, then the timing has slipped for some reason and it will need much closer investigation to find out why.

Similarly, the valve timing may also have slipped and if no compression can be felt then a serious fault has arisen in the valve train. Mechanical faults are not the only reasons for cars failing to start. Driver error is as frequently responsible. On most older cars the choke should be pulled out fully and the starter operated without touching the accelerator. The common habit of wildly pumping the accelerator� as much out of frustration as in a belief that it will help to start the car - will only swamp the engine with petrol and saturate the points of the plugs. If your car is proving reluctant to start, do not keep the starter turning as this will rapidly flatten the battery. Operate it in short, sharp bursts of about five seconds. On cold mornings the viscosity, or thickness, of the engine oil increases significantly, thus increasing the work of the starter motor. In such circumstances, let the clutch in when you turn the starter. This will take the weight of the gear-box off the load the starter motor is turning.

Using Jump Leads

If the battery will not turn the engine over at all, jump leads can be used to connect a sound battery to the flat one. Bring the car with the good battery as close as possible to the non-starter. First connect the jump leads to the terminals of the flat battery. Then start up the car with the good battery. Connect the other ends of the leads to the terminals of this battery, making sure that positive terminal is connected to positive terminal, and switch on the ignition of the breakdown. Never let uninsulated jump leads touch each other while they are connected to a good battery, or you will weld them together.

Wielding A Starting Handle

Some Veteran and Vintage Cars are equipped with starting handles, which engage with a notch on the pulley on the end of the crankshaft. Actually getting the handle on is often awkward, but lifting the bonnet and peering down between the engine and the radiator allows you to see a little better. Have an assistant in the car with the ignition turned on and ready to press the throttle when the engine fires. Once it is in position, grip the handle in one hand and ease the engine round until you feel its resistance becoming stiffer. This will mean that one of the pistons is coming up on to compression. Pause, then swing the handle over with as much momentum as possible.

Bump or Push Starting

Bump or push starting also allows a flat battery or broken starter motor to be by-passed. It can be used, however, only if the car is standing on a hill or you have a group of volunteers willing to push the car. If so, turn on the ignition, pull out the choke and see that the car is in neutral. Then let off the handbrake and either allow the car to roll off down the hill or signal to the pushers that they should get going. Get the car up to about 5mph, engage third gear and let out the clutch. See that your assistants keep pushing after you have let the clutch out, as the momentum of the car alone is unlikely to be sufficient. Once the engine fires, let in the clutch, stop the car, and rev the engine to keep it from stalling.

Tow Starting

A car can be towed into life in much the same way, only with another car towing the non-starting car. There is a correct way to attach the towing rope: it must be tied to a point on the car which is capable of taking the strain that towing will put on it. So do not attach the rope to any part of the steering or suspension, nor, on a front-wheel-drive car, to the drive shafts. Bumpers are also a bad fixing point. Look under the car before you decide where to fix the rope, as some manufacturers provide towing points. Many transverse engined cars, for example, have hook-ended bolts where the sub-frame joins the body. If there is no obvious towing point available put the rope around an engine mounting bracket.