Distributor: Problems And Troubleshooting

The distributor is a component of the ignition system. It transmits the high voltage current to the spark plugs of each cylinder according to the ignition sequence. In the battery ignition system, the distributor and ignitor usually settle on the same shaft. They are driven by the camshaft. The distributor also has the ignition advance angle regulating device and capacitor.


1. Function

2. Problems and troubleshooting

    2.1 Distributor shaft and bushing

    2.2 Broken distributor cap

    2.3 Electrical leakage

    2.4 Damaged capacitor

    2.5 Defective diaphragm


1. Function

The role of the automotive distributor is to connect and disconnect low voltage electricity and distribute the high voltage generated by the ignition coil to the spark plugs of each cylinder according to the ignition sequence of the engine.

If the component damages, it is impossible to perform accurate ignition, which causes the engine to work less efficiently or even not to work.

2. Problems and troubleshooting

2.1 Distributor shaft and bushing

●  Mating gap inspection

The mating gap between the distributor shaft and the sleeve is generally 0.02~0.04mm (0.01~0.03mm for some cars). If it exceeds 0.07mm (0.05mm for some cars), the vehicle doesn't work well.

When checking, use a vise to hold the distributor shell so that the contact needle of the micrometre vertically withstands on the upper end of the shaft, along the axis of the contact needle direction to pull the distributor shaft.

The gap between the shaft and the distributor bushing should be in line with the standard. If the swing difference of the contact pin is greater than 0.14mm (0.1mm for some cars), the worn shaft should be repaired, or the bushing should be replaced.

●  Wear and tear of distributor shaft

After the distributor shaft wears out, the diameter increases by the hard chrome plating or the porous chrome and then ground to the standard size for installation. If the shaft is replaced with a new one, the new shaft and bushing must be hardened (i.e. quenched to a certain hardness).

When the bushing of the distributor shaft tears out, a new bushing should be prepared. It is usually made of tin bronze bar stock. 

The interference between the bushing and distributor shell should be between 0.025~0.05mm. The bore should be reamed after pressing in the bushing to ensure the mating gap between the shaft and the bushing.

●  Shaft curvature inspection

Clamp the distributor shell with a vise. The micrometre contact pin vertically withstands the distributor shaft. Rotate the distributor. The maximum swing of the micrometre should not be greater than 0.05mm. Otherwise, it should be corrected or replaced with new parts.

●  Axial clearance check

During the inspection, fix the distributor shell. Use the thickness gauge to measure the clearance between the coupling or transmission gear and distributor shell contact surface. 

Generally, it should be 0.15~0.5mm. If it exceeds the standard, it can be adjusted by adding shims between the transmission gear and shell contact surface until it meets the requirement.

2.2 Broken distributor cap

If there is a crack in the distributor cap, you can see the high-voltage spark jump fire at the crack. And you can hear the noise. The method of determining the crack is as follows.

Remove the distributor cap. Remove the spark plug on the high-voltage line. Take the sub-cylinder high-voltage line in one hand so that each end is 3 ~ 4mm away from the cylinder.

Turn on the ignition switch. Use the other hand to toggle the contact arm. 

There is a high-voltage spark jumping, indicating that the high-voltage main fire line jack and the side jack have problems.

2.3 Electrical leakage

First, insert the main high voltage firewire into a side jack. Put two adjacent jacks into the sub-cylinder high voltage wire so that the other end of the sub-cylinder high voltage wire is 3~4mm away from the cylinder block.

Turn on the ignition switch. Toggle the contacts or use the starter to drive the engine crankshaft rotation. See if sparks are jumping across the block on the two taps. If there are sparks, the electricity between the side jack has problems.

When the distributor cover between the jack has problems, you can scrape the tampering or leakage. Then bake it with a small fire for a while. If it is still ineffective, you can drill a hole for first aid. You can also use candles or melted asphalt scraped from the battery to coat the clean crack to insulate it temporarily.

Good Distributor

2.4 Damaged capacitor

●  Bad capacitor can

When the component loses the possibility of repair, the starter, solenoid and their retaining ring can be used instead. You can put several layers of paper between the generator or starter's retainer and the shell between the pad, so that the retainer and shell insulate.

Then take two wires. One end connects to the fastening bolt of the generator or starter retainer. The other end connects to the low-voltage terminal of the distributor. These two connect in parallel to increase the power capacity.

If the capacitor has a short circuit, disassemble it. Check the broken position on the wax paper. If it is close to the end, cut off the broken part. If it is close to the middle, cut one small wax paper pad and put it in the middle. Then carefully wrap it up to reuse.

●  Broken capacitor wire

The capacitor which connects to the ignition coil is made of two thin strips of aluminium or tin. Both sides are rolled into a cylindrical shape with wax paper clamped in the barrel-shaped shell.

The two pieces of metal sheet are insulated by wax paper and metal sheet respectively with a soft wire lead. One wire connects to the shell. The other (i.e. lead) goes through the outside.

If the capacitor lead breaks from the root, and you don't have any welding repair tool, a needle or a fine nail can be used to thread through the original root and connect the wire.

You can also peel the capacitor shell opening and take off the insulation gasket. Then put the wire outside the insulation gasket hole through the winding lump. Use a small hammer to flatten it so that it will not come out. Put the insulation gasket back on and press it tightly.

●  Short circuit in capacitor

If the capacitor's insulation wax paper is punctured, there is a short circuit in the engine. Disassemble the capacitor, cut out the punctured part of the aluminium foil or insulation wax paper. Then wrap it again.

If the punctured part is at the inner end, the aluminium foil and insulating wax paper at the punctured part can be cut out and then rewound (the two ends of the aluminium foil are staggered).

When finishing the winding, connect to a wire in each of the two layers of aluminium foil. Wrap it with tape. One wire is lapped. The other one connects to the low-voltage terminal of the distributor. For convenience, cardboard or round stick can be the mandrel during the winding.

2.5 Defective diaphragm

When the equilibar regulator diaphragm is defective, there is air leakage. The maintenance is as follows.

●  Remove the vacuum chamber nut and pressure spring. Clamp the bur on the bench vise. Make the regulator's rolled edge mouth to the bur edge. 

Gently hammer the outer circle of the regulator with a small hammer. Turn the regulator while hammering, and gradually crack the rolled edge until the diaphragm can be removed.

●  Remove the defective diaphragm. Trim it with double-layer yellow wax cloth into the original diaphragm style and rivet on the tie rod.

●  To make the vacuum regulator sealed, apply insulating paint or glue between and around the two layers of the wax cloth. Then install it and knock back the original rolled edge with a small hammer until it no longer leaks when checking with the mouth by suction.

When installing the diaphragm, be careful to make the connecting rod just fit on the shaft of the movable base plate of the disconnector.

●  Finally, reinstall the return pressure spring and nut.

Interested in other ignition parts? Visit http://www.delcoribo.com/contact to make an enquiry if you need more motor products.

Lauritz Carolsfeld        September 30, 2021

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