How to adjust the Points on a Classic Car

How to adjust the Points on a Classic Car
How to adjust the Points on a Classic Car

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.

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

Diagram of Hitachi Distributor on a Classic Car
Diagram of a Hitachi Distributor on a Classic Car

Most watched HITACHI Distributor Parts on eBay


The DUCELLIER M78 Distributor

Diagram of a Ducellier M78 Distributor
Diagram of a Ducellier M78 Distributor

Most watched DUCELLIER M78 parts on eBay


The BOSCH JFU4 Distributor

Diagram of a Bosch JFU4 Distributor
Diagram of a Bosch JFU4 Distributor

Latest BOSCH JFU4 Distributor Parts on eBay


The AC DELCO Distributor

Diagram of an AC Delco Distributor
Diagram of an AC Delco Distributor

Latest AC DELCO Distributor listings on eBay


The MARELLI Distributor

Diagram of a Marelli Distributor
Diagram of a Marelli Distributor

Most watched MARELLI Distributor parts on eBay


The LUCAS 43D Distributor

Diagram of a Lucas 43D distributor
Diagram of a Lucas 43D distributor
Diagram of an early Lucas 43D Distributor
Diagram of an early Lucas 43D Distributor

Most watched LUCAS 43D Distributor parts on eBay


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.

THE LITTLE GREEN SPARK PLUG COMPANY in SCOTTYS Supplier Library
This is a great place to start for further specialist advice.
Click above to shop direct or learn more about them in my Supplier Library

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 two types of Contact Points on a Classic Car
The two types of Contact Points on a Classic Car

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.

Two one-piece contact sets. They are of different manufacture and, because of their shape, are not interchangeable
Two one-piece contact sets. They are of different manufacture and, because of their shape, are not interchangeable

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.

The distributor cam and points (closed)
The distributor cam and points (closed)

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.

Points open at too large a gap
Points open at too large a gap
Points open at the correct gap
Points open at the correct 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.

To change the points, first remove the distributor cap (with the ignition off). Examine the cap carefully for signs of wear
To change the points, first remove the distributor cap (with the ignition off). Examine the cap carefully for signs of wear

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.

Remove the rotor arm. It may pull away easily, or it may need gentle leverage. At all times avoid straining the distributor
Undo the screw or nut connecting the LT and condenser leads to the points. Make a note of the order in which they are fitted
Undo the screw or nut connecting the LT and condenser leads to the points. Make a note of the order in which they are fitted
Pull the leads clear of the baseplate on which the points are mounted, and make sure they are not placed under any strain
Pull the leads clear of the baseplate on which the points are mounted, and make sure they are not placed under any strain
Two screws are usually used to secure the points. One mounts in a slot to adjust them. Remove the other screw first
Two screws are usually used to secure the points. One mounts in a slot to adjust them. Remove the other screw first

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.

Undo the second screw and place both in a safe place ready for reassembly. Be careful not to dr-op them into the distributor body
Undo the second screw and place both in a safe place ready for reassembly. Be careful not to dr-op them into the distributor body
The old points can now be lifted from the base plate. If they are not badly worn. they may be cleaned as an emergency standby
The old points can now be lifted from the base plate. If they are not badly worn. they may be cleaned as an emergency standby
Before fitting the new points. the two faces must be carefully cleaned with petrol to remove every trace of protective coating
Before fitting the new points. the two faces must be carefully cleaned with petrol to remove every trace of protective coating
Having wiped the base plate clean. fit the new points in place with the screws. Do not fully tighten the two screws at this stage
Having wiped the base plate clean. fit the new points in place with the screws. Do not fully tighten the two screws at this stage
Turn the engine over by hand until the distributor cam opens the points. Then insert a feeler gauge of the correct thickness
Turn the engine over by hand until the distributor cam opens the points. Then insert a feeler gauge of the correct thickness
If the points gap is incorrect. it can be adjusted by levering with a screwdriver in a small cut-out at the base of the points
If the points gap is incorrect. it can be adjusted by levering with a screwdriver in a small cut-out at the base of the points
Recheck the gap with the feeler gauge and. when it is correct, with the feeler still in position. gently tighten the two screws
Recheck the gap with the feeler gauge and. when it is correct, with the feeler still in position. gently tighten the two screws
Replace the distributor cap. It can only be located in one way, since a raised square on the cap locates in a cut-out
Replace the distributor cap. It can only be located in one way, since a raised square on the cap locates in a cut-out

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.

For routine maintenance, lightly oil points A and B with clean engine oil, and smear points C and D with a thin coat of grease
For routine maintenance, lightly oil points A and B with clean engine oil, and smear points C and D with a thin coat of grease

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


About this site

Visit SCOTTYS Supplier Library for Classic Car Parts Suppliers.

Visit SCOTTYS Technical Library for Guides and Parts Manuals.

Visit SCOTTYS Artisan Library to find a specialist company.

Regards SCOTTY