How to Disassemble a Defective Distributor

Technically Speaking

James Berry Nov 8, 2013 0 Comment(s)
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Removing the Distributor from the Vehicle

  1. Unplug the battery wire, tachometer wire, and pick-up-to-ignition-coil three-wire harness from the distributor cap.
  2. Remove the plug wires. On Corvettes it is sometimes difficult to see which cylinder each plug wire feeds without removing the wire completely. It is a good idea to mark the wires, so you will know where they go on the distributor cap.
  3. Remove the distributor cap.
  4. Crank the engine slowly until the rotor blade aims at a fixed point on the engine or firewall. This will allow you to mark exactly where the rotor button is pointing, to use as a reference point when reinstalling the distributor. As a result, you’ll be certain that your timing is accurate, and the oil-pump drive is in the correct location.
  5. Before loosening the distributor hold-down, mark the exact position of the vacuum advance. Once the hold down is loosened, the distributor base can be rotated. Again, put a mark on the engine or firewall as a reference point, so you’re sure to reinstall the distributor the base in the exact same position. This will ensure that your base timing is close.
  6. Remove the distributor hold-down bolt and clamp.
  7. Remove the distributor from the vehicle. Notice how far the rotor button moves in a counterclockwise motion when pulling the distributor up. This will be important when reinstalling the distributor.

Distributor-Shaft End-Play Test

It seems that most HEI distributors have excessive shaft-end play. This unnecessary clearance on the thrust bearing allows the shaft and gear to move up and down during operation. This movement can cause variations in timing, due to the position of the distributor drive gear at any given rpm.

To calculate the timing changes, simply apply one degree of timing for every 0.013 inches of end play.

Distributor Shaft 2/12


The correct clearance for most distributors is 0.010 inches of shaft-end play. This would keep any variation of timing due to end play to less than one degree. You can use a feeler gauge to measure the amount of play present (Image D). Shim kits to adjust this clearance are available at most local parts houses.

Disassembling the Distributor

The first step in disassembling and rebuilding any distributor is the removal of the drive-gear roll pin from the distributor shaft (Image E). This will allow the shaft to be removed from the distributor housing. Use a wooden block to support the end of the drive gear, and a thin punch to tap the roll pin out of the gear. Then, pull the gear and thrust washers off the shaft.

If the drive gear seems to be stuck on the shaft after the roll pin has been removed—or the shaft assembly won’t come out through the top of the distributor—there may be creosote buildup on the shaft itself. This gummy buildup may need to be removed using a chemical cleaner, such as carburetor cleaner, before the gear can be freed from the shaft.

Notice that the distributor drive gear has an index mark. This mark should line up with the point of the rotor button on reassembly (Image F).

Whether you’re installing a distributor-curve kit or just replacing the distributor springs and weights, take care when removing the springs and E-clips from the shaft. Sometimes these parts will fly off, never to be found again.

When reinstalling the distributor weights, the numbers on the weights will normally face up (Image G).

After removing the E-clips, carefully pry off the advance cam with a small screwdriver. You may need to work back and forth between the ends, prying up a little at a time. After the cam has been removed, the reluctor/stator may be slid off the shaft (Image H). The reluctor/stator should be replaced if any of its teeth are broken, or if the component is rusty.

To test the vacuum advance install a vacuum pump on the assembly and apply vacuum. Make sure the vacuum-advance pushrod moves smoothly throughout its entire operating range. If the pushrod does not move, or the vacuum-advance pod will not hold vacuum, the component should be replaced.

Now remove the vacuum advance; it’s attached with two screws. Pry up on the rear of the vacuum advance (where it attaches to the distributor housing) until it loosens, then pry the pushrod down with a pocket screwdriver (Image I). Rotate the vacuum-advance assembly clockwise to remove the attaching arm from the distributor plate.

The pick-up coil assembly is held on the distributor with a thin snap ring covered by a fiber washer. Carefully pry out the snap ring (Image J). The pick-up coil may then be lifted out of the distributor housing.

Ignition Control 9/12


The ignition-control module (Image K) and capacitor are secured to the distributor with three screws. Inspect the wiring harness for wear or cuts.

Next month we will cover checking the centrifugal and vacuum advances, installing your distributor, all of the timing variables, EST distributor testing, and converting a points distributor to HEI.

If you get started on rebuilding your distributor before next month’s segment, remember to purchase OEM or equivalent parts. You get what you pay for, and cheap distributor parts are just that. Remember, you only want to do this job once.


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