This guide captures ‘bygone’ advice on how to adjust the points on a Classic Car. It is part of a series I am building that describes what to do on a Classic Car Basic Service.
- Why change the Points on a Classic Car
- How to check a Distributor Cap on a Classic car
- The most common Distributors fitted to Classic Cars
- How to check the Carbon Contact in a Distributor Cap
- How to check the Rotor Arm in a Classic Car Distributor
- What are the Contacts or Points on a Classic Car
- How to check the Points Gap on a Classic
- How to replace the Points on a Classic Car
- How to change One Piece Contacts on a Classic Car
- How to change Two Piece Contacts on a Classic Car
- How to lubricate a Distributor on Classic Car
- What does a Condenser do on a Classic Car
- How to tell if a Condenser is faulty on a Classic Car
- About this site
Useful information for Classic Car and Retro Car enthusiasts, as many of these tasks are no longer required on modern day cars.
Remember folks these are ‘bygone guides’ … useful but the safety and personal protective equipment measures are reflective of bygone awareness. Stay safe.
Why change the Points on a Classic Car
Incorrectly set contact points cause the engine to operate below its optimum performance. The resulting increase in running costs is far in excess of the cost of re-adjusting or replacing them.
Checking, adjusting or if necessary replacing the points is a straightforward job with which the diy mechanic can easily accomplish.
Normally, the procedure is to check the points gap every 10,000 km (6,000 miles) and to replace them when they have done between 16,000 and 20,000 km (10,000 and 12,000 miles).
How to check a Distributor Cap on a Classic car
Before you deal with the points, start by looking inside thedistributor cap.
With the ignition switched off, unclip the cap, wipe both the inside and the outside with a clean rag and then examine the cap closely.
If there are any hair-line cracks in the cap, or any pieces broken from the base or outlet sockets, you will need to renew the cap. Any mechanical fault of this nature tends to encourage damp and dirt to build up and these deposits provide a path to earth for high-tension electricity.
In dry, warm weather such faults may not be noticed-but they will be in misty, cold weather when nearly all the battery’s output is used to turn over a stiff engine.
On top of the cap you will find an HT lead to each of your spark-plugs.
These must be attached to the correct terminals on the cap, or your cylinders will fire in the wrong order-an unnerving experience.
So when fitting a new cap, transfer the leads one at a time from the old cap to the new, working clockwise around both caps. Alternatively, if you have to remove the old cap and take it to an accessory store while you find a replacement, number all the leads in order.
The most common Distributors fitted to Classic Cars
There were obviously many types of distributors fitted to Classic Cars however below are the main ones which should help you identify the type of distributor fitted to your car.
- The Hitachi distributor
- The Ducellier M 78 distributor
- The Bosch J FU 4 distributor
- Various AC Delco distributors
- Various Marelli distributors
- The Lucas model 43D distributor
- The Lucas (early) model 440 distributor
- The Lucas model 23D distributor
The HITACHI Distributor
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The DUCELLIER M78 Distributor
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The BOSCH JFU4 Distributor
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The AC DELCO Distributor
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The MARELLI Distributor
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The LUCAS 43D Distributor
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How to check the Carbon Contact in a Distributor Cap
The carbon contact in the middle of the cap is the connection from the coil. It must be in sound shape to carry electric current from the coil to the distributor and ultimately the spark-plugs.
On Lucas distributors, the contact is a spring-loaded carbon cube or ‘brush’. To work properly, it must be near enough square-ended and at rest at least 3 mm (¼in.) must be protruding. If the contact does not satisfy these conditions or if the tip is cracked or broken, pull the contact and its spring out of their socket and fit a new one.
On other types of distributor the contact is a fixed one and there is a spring tongue on top of the rotor arm which bears against the contact. It is unlikely that there will be much wear on a contact of this type but it should be renewed if broken.
How to check the Rotor Arm in a Classic Car Distributor
Every distributor has a rotor arm on top of its spindle. This is a hook-shaped device with a metal face which almost but not quite touches the four, six or eight contacts in the distributor cap which are connected to the plug leads.
The current from the coil comes through the central connection in the distributor cap, runs along the metal strip on top of the rotor arm, and jumps from the rotor arm face to each plug lead contact in turn.
There is a tiny air gap between the rotor arm face and the contact, which means that a certain amount of sparking is inevitable as the rotor arm passes each contact.
This sparking will result, after some time, in pitting and dis-colouration of the metal on the rotor arm. Discolouration / can usually be removed with a rag or by rubbing the rotor arm against a tyre, but pitting is best dealt with by fitting a new rotor arm.
Although you can usually remove a rotor arm easily by pulling it straight up off the spindle, there are times when it is a tight fit and will not easily come free.
In this case, gently lever the rotor arm upwards from its base with a broad-based screwdriver pivoted on part of the distributor body. Go cautiously as the distributor is easily broken.
What are the Contacts or Points on a Classic Car
There are two contact-breaker points, both metal. One is fixed (but adjustable) and earthed through the body of the distributor. The other is spring-loaded and is moved by an arm operated by the distributor cam
The contact-breaker points are, in effect, an automatic switch to make and break the electrical circuit which indirectly feeds HT current to the spark-plugs.
In a four-cylinder engine running at 4,000rpm, the points open and close 8,000 times a minute. Since they have to open and close completely each time, the gap between them when they are open must be exactly right.
How to check the Points Gap on a Classic
The points gap is checked in exactly the same way as the gap in a spark-plug-by sliding a feeler gauge (page 66) between the contacts.
First, however, you must switch off the ignition and turn over the engine by hand until the points are fully open. There are several ways of doing this:
- Use the starting handle (if your car has one)
- Engage top gear, release the handbrake and rock the car backwards and forwards
- If you already have the spark-plugs out, thereby reducing the compression in the engine, pull on the fanbelt (not the fan blades)
- Use a spanner on the crankshaft pulley
The arm which operates the movable point rests against the lobe on the distributor cam in such a way that the points faces separate and reach their maximum opening when the lobe is at its peak. This is the position in which the points gap is checked.
When the points are fully open, it is likely that you will see a small build-up of carbon and possibly a slight ‘pip’ between the two surfaces. These must be removed before checking the gap.
With the points still fully open, gently stroke a points file across the peak of the pip until it has been eased flat.
To remove the carbon deposits, first turn the engine over again so that the points are closed. Then pull back the moving point with your fingertips, and insert a small strip of 400 grade wet-and-dry abrasive paper between the two points. Let the points close up again and move the paper backwards and forwards until all the carbon has been removed.
Once the points have been cleaned up, turn the engine until they are fully open again. Then slide the correct feeler gauge between the two contacts. Ideally, it should be a reasonably tight fit, but not so tight that you have to force it.
If the gap is incorrect, you can enlarge or reduce it by loosening the locking screw which holds the fixed point in position and moving the supporting base plate in the appropriate direction. Finally, tighten the locking screw firmly and re-check the gap.
If the carbon build-up on the points is such that you cannot remove it, or the points themselves are badly pitted, they are due for replacement.
How to replace the Points on a Classic Car
Contact-breaker sets are available either as the one-piece type or as the older, two-piece type.
The one-piece type makes the job of replacing points a great deal easier and, on many cars, it is now possible to swap twopiece contact-breaker sets for the one-piece type, but not generally vice versa. Motor accessory stores usually sell both types.
When buying replacement points, whether one-piece or two-piece, take with you a note of the year, make and model of your car together with the type (and if possible, the serial number) of the distributor.
Before you remove the existing points, compare them with the new set that you have just bought. Unless, of course, you are changing from two-piece to one-piece the new and old points should match exactly.
How to change One Piece Contacts on a Classic Car
Changing a one-piece points set is simple. All you have to do is to remove the rotor arm and disconnect the wire from the points to the distributor body. The locking screws are removed and the set is then free to be lifted up and off.
Before fitting the replacement set, wipe the faces of both points with a rag moistened with petrol to remove any protective coating and make sure that the underside of the base plate is free from any similar coating. Finally, tighten down the new set, check the gap and then firmly tighten the locking screw.
How to change Two Piece Contacts on a Classic Car
There are several different makes of distributor, such as Lucas, Bosch, AC Delco and Ducellier, but the routine for fitting a two-piece contact set is substantially the same for all of them.
Two things will help you to avoid mistakes:
First, when dismantling the distributor, write down how and in which order the various components are removed. Although some contact sets come with an instruction sheet, it is essential to write down the positions of the various washers and insulation items to make sure that they go back in the same way.
Second, make sure that the points assembly-and in particular, the moving point-is fully insulated. You can do this by seeing that all insulation components are in the right place and-most important-right way up, and by looking carefully at the finished job. Failing to do so will result in a short-circuit of such proportions as to cause the wiring to smoulder and char in a very short time.
Generally, to change a two-piece contact set you need to remove the rotor arm and disconnect from the points the wires coming from the LT side of the ignition and the condenser. Then you loosen the retaining screw(s) and carefully lift out the points.
Next, as with one-piece contact sets, you wipe the preservative from the new points with a petrol-moistened rag, and reassemble in reverse order. Finally, you check the gap and tighten the locking screw.
How to lubricate a Distributor on Classic Car
When replacing or checking the points, it pays to lightly lubricate the distributor. Give the faces of the cam a thin smear of oil or grease (for example, 3 in 1 oil).
Then apply a few drops of oil through the gaps in the distributor base plate, and finally lightly oil the pivot post.
Do not over-lubricate the distributor, however. If any grease or oil finds its way between the points, excessive carbon deposits will occur and your car will misfire badly, reducing performance, and perhaps leaving you with the job of having to strip the distributor to clean it up.
What does a Condenser do on a Classic Car
The condenser has two functions. One is to store an electrical charge and the other is to reduce the amount of sparking between the contacts as the electrical flow is interrupted.
Although the spark at the points is a tiny one and the burning effect of each operation can hardly be measured, the burning accumulates over the hundreds of thousands of on-off operations. The condenser’s job is to minimize this.
How to tell if a Condenser is faulty on a Classic Car
If the points show signs of excessive burning and there is a corresponding roughness or hesitation in the running of the engine, the condenser is probably at fault.
Leaving a faulty condenser will eventually result in the points becoming so burned that soon they will not work at all. A new condenser is inexpensive to buy, so if there is any doubt about its condition you should renew it.
The job is straightforward: you disconnect the wire from the distributor, remove the retaining screw, fit the replacement and replace the screw.
Finally, remember that any ignition system-no matter how well maintained-is susceptible to ‘tracking’, especially in damp weather. A monthly wipe inside the distributor cap and around the plug leads and caps to remove dirt and moisture takes only a few minutes and is well worth the trouble
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