Ignition distributor for your car

Your Ignition distributor worn out? » Read more about common malfunctions • Repair • Replacement manual

Synchronising the ignition with the ignition distributor

The ignition distributor is an electro-mechanical component transferring the ignition voltage from the ignition coil to the corresponding spark plug. It goes all the way back to the beginning of the multiple cylinder engine in automotive construction. Initially mechanic, this component is nowadays replaced by electronic controlling and regulating systems.

Ignition distributor: construction and function

Until halfway the 1990ies the ignition distributor was a standard component in automotive construction. With the appearance of central engine control it lost many of his functions and is now present in the engine in a rudimentary form. The traditional ignition distributor consists of the following components:

• ignition cable
• distributor cap
• distributor rotor
• interrupter contacts
• housing.

The ignition cables are orderly connected onto the distributor cap. The amount of ignition cables is always equal to the amount of cylinders in an engine. Therefore there are distributor caps with 3, 4, 5, 6, 8 or 12 connected ignition cables leading to the spark plugs. Additionally, another ignition cable runs from the ignition coil to the distributor cap. This cable is often plugged in the centre between the other ignition cables, arranged in a circle. The distributor cap has copper or brass contacts on the inside. These absorb the ignition current and transmit it to the spark plugs. The ignition voltage is transmitted in a circular fashion by the distributor rotor. Still, a small distance between rotor and contact on the cap exists. This generates a flashover, additionally stimulating the ignition. The interrupter contact, situated under the distributor rotor, has a similar function, interrupting the ignition circuit for a short time and conducting it back to the ignition coil. By doing so it generates the exact voltage peak which is required for the ignition. The distributor rotor sits on a small deflecting gear, driven directly by the camshaft or crankshaft.

Ignition distributor: defects

The traditional ignition distributor had three weak points prompting a regular replacement. These were:

• the contact points in the distributor cap
• the interrupter contacts
• mechanical damages such as cracks.

Both contact points have their own function: the high-voltage flashover causes an additional transfer of material. This material oxidises on its route from one contact point to the other and gradually builds an insulating layer. When this layer gets too thick, the ignition is no longer guaranteed. The oxidation can be scratched from the contact points on the distributor cap with a small screwdriver. For the interrupter contacts replacement is the only option. Corroded contacts in the distributor cap make themselves noticed by reluctant starting. A defective interrupter stalls the car almost immediately. Cracks in the distributor cap allow moist to penetrate. In that case the car no longer starts or has ignition failures. TIP: When the engine stalls during driving despite plenty of fuel still available in the tank, the ignition is generally the cause. However, it does not necessarily mean that the interrupter contact is burnt. In this case, let the car roll to a halt into the parking lane and switch on the warning signalling. Check the engine compartment. There are two errors causing practically the same effect.

• plug of the ignition coil unplugged
• torn or loose earth cable.

When the ignition cable of the ignition coil is no longer plugged into the distributor but dangling on the side, simply put it back in its place. Driving on will be possible now. The second option is the torn earth cable. This is the thick, black cable connecting battery and bodywork. If it is visually ruptured, it can be provisionally bridged by a thick bolt. It should however be replaced as soon as possible.

Repairing the ignition distributor

Repairing the ignition of an older car is one of the easier exercises. It is always recommended to replace all ignition components completely. This creates a reliable new condition for the entire unit. This includes:

• ignition cables
• spark plugs
• distributor cap
• distributor rotor.

When replacing these components, please observe reconnecting the ignition cables in exactly the same order as they were before. A new interrupter is cheap and easy to install. Nevertheless it must be precisely adjusted after installation. This requires a strobe as a special tool.

Buying a new ignition distributor

A complete set for the repair of an ignition costs ca. 50 EUR (± £45).