How to install a distributor

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by: Cobalt327, Jon
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[edit] Overview

This is a tutorial on distributor installation that will work for many engines including the small block and big block Chevy. This is an important step when breaking in a new flat tappet cam, because you want the engine to fire up immediately, so as to not wipe off all the cam lube that was applied... you DID remember to apply moly cam lube to the lobes and bottoms of the lifters, right?? Not using cam lube and having to crank the engine excessively to get it to start up the first time can cause the cam to fail within the first few minutes of running. Correctly installing the distributor and setting the timing to allow a quick start up is the aim of this article.

[edit] Distributor installation

  • Put the distributor cap on the distributor. Make a mark on the distributor housing that lines up with spark plug terminal post #1 of the distributor cap. You can use a Sharpie. On a coil-in-cap "regular" HEI, #1 will be the 2nd. spark plug wire terminal clockwise from the square part of the plastic coil cover that sticks out.
  • Pull the cap back off, line up the rotor with the mark that was just made on the distributor housing. Now look at the other end of the distributor, pick a groove between two teeth, and mark the housing there. Now, rotate the shaft counterclockwise (from the top) till the bottom of that groove is lined up with your mark on the bottom of the housing. You could make secondary mark on the distributor at the top again in case it gets disturbed in the process of dropping it in.
    • Another way to do this is to make the mark for #1 on the distributor body like explained above, then with the distributor out of the engine, turn the rotor counterclockwise about 2" from the #1 mark made earlier. This is about how far the rotor will turn back clockwise as the distributor is installed, because of how the distributor gear is cut.
  • One thing that may prevent the distributor from fully seating is the oil pump drive shaft. If you look at the bottom of the distributor shaft, you will see what looks like a wide flat blade screwdriver blade just inside of the gear. This is what engages with the oil pump drive shaft, and if the pump shaft isn't aligned with the distributor shaft, the distributor cannot fully seat.
    • To remedy this, take a long screwdriver and insert it down through the distributor hole in the intake and turn the pump drive shaft. It may take a couple tries before the distributor shaft and the oil pump drive shaft mesh, but they will, eventually. Take your time and be patient. When everything is correct, the rotor will be pointing at the line on the distributor body made earlier, and the distributor mounting "collar" (what the distributor clamp bears down on from above, and what seals the distributor to the intake with a gasket on the bottom side) will be resting on the intake (don't forget to use a gasket!)- NOT suspended above the intake.
  • Another thing that can cause the distributor to not fully seat is if the distributor is bottoming out against the oil pump drive shaft. This can be caused by incorrect parts but is most likely caused by excessive milling of the heads and/or block. More on measuring and correcting this here.

[edit] Top dead center timing check

Make sure your motor is on TDC on compression stroke, put the timing mark on whatever you want your initial timing to be, let's say 12° for instance. If you happen to have your timing cover off, dot to dot is TDC for #6, TDC for #1 is when both dots are at 12 o'clock.

More at Determining top dead center.

So, now the motor is sitting with the timing mark at 12° BTDC, and your distributor shaft is about a 1/16th of a turn before that, so it will rotate into position as it drops down and engages with the cam. Once it goes down till it's sitting on top of the oil pump shaft, there will be about a 3/8" gap between the mounting flange and the intake surface. If all your marks are pretty close to lined up, push down slightly on the distributor, (not hard, don't force it), and have somebody bump the key till it drops all the way. Some folks like to turn the oil pump shaft with a long flat screwdriver to line up the oil pump shaft as well, I generally don't bother, if everything else is right, it will drop right where it needs to be the first time you bump it over. If you want to re-check your installation, or make sure it will fire the first time, bump the balancer on back around to 12° BTDC on #1 again and make sure your rotor still lines up with your #1 cylinder mark. If it doesn't pull it out and repeat. When your marks line up like they should, go ahead and turn the distributor housing to line up your #1 mark with the rotor, install the distributor clamp and snug it down, put the cap on and connect the wires, because it WILL fire the first time, and be within 2° or 3° of your target initial timing.

[edit] Another method for setting timing for start up

  • Hook your timing light to #1 wire and power.
  • Pull the #1 plug and put your finger in the hole.
  • Crank the engine until it blows your finger out of the hole.
  • STOP cranking.
  • Rotate the engine by hand in the same direction the starter was turning it while watching the timing marks.
  • At 18 degrees BTDC (BEFORE the marks line up at TDC), STOP. Most factory timing tabs go to 12, so it will be a little BEFORE that.

Warning Note: You can use the page How to make a timing tape to easily make a temporary timing tape that will allow you to set the initial and total timing without the need for a dial back timing light.

  • Turn the key to RUN (do not crank the engine)
  • Loosen the distributor bolt enough so you can turn it.
  • Turn the distributor clockwise a bit. (vac can toward the firewall)
  • While holding the trigger on the timing light and looking at it, rotate the distributor counterclockwise until the light flashes.
  • STOP, and lock it down.

This will work with ANY ignition. Your timing will be perfect, and the motor will fire right up.

[edit] Procedure for points from GM manual

The following is procedure copied from a GM shop manual with added clarification. It should be viewed as typical of GM cars and any other distributor equipped engines.

  1. Locate #1 piston in firing position by either of two methods described below.
    1. Remove #1 spark plug and, with a finger on plug hole, crank the engine until compression is felt in the #1 cylinder. Continue cranking until timing mark on the crankshaft pulley lines up with timing tab attached to the engine front cover. OR
    2. Remove rocker cover (left bank V-8 engine) and crank engine until #1 intake valve closes and continue to crank slowly until about 1/3 turn until timing mark on pulley lines up with timing tab.
  2. Install distributor in a position consistant with the original attitude of the vacuum advance device and toward the #1 plug wire position on the distributor cap.
  3. Position the rotor to point toward the front of the engine (with the distributor housing held in it's installed attitude), then turn the rotor counter-clockwise approximatley 1/8 turn more toward the left cylinder bank and push the distributor down to the engine camshaft. It may be necessary to rotate the rotor slightly until the cam shaft engagement is felt.
  4. While pressing firmly down on the distributor housing, kick the starter over very briefly to make sure the oil pump shaft is engaged. Distributor will drop down to the flange. Install hold down clamp.
  5. Turn the distributor body slightly until the points just open and tighten the hold down clamp.
  6. Place the distributor cap in position and check to see that the rotor lines up with the terminal #1 spark plug wire.
  7. Install cap, check all high tension wire connections and connect spark plug wires if they were removed. Wires must be installed in the correct locations.

[edit] Resources

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