M117 Distributor Phasing Adjustment

[73MB280SEL]

Howdy,

Working on my 280 SEL 4.5 and came across a problem. I think I have found a solution so I'd like to pass it along. There may also be the "correct" way to do this that some of you will I'm sure educate me about.

The problem is distributor phasing. Correct phasing is where the rotor pole points directly towards the appropriate cylinder pole in the distributor cap WHEN THE IGNITION FIRES. Incorrect phasing is where the rotor pole is not pointing towards the distributor pole when the ignition fires.

I noticed I had a problem when I replaced the distributor cap and rotor. After a few weeks of duty, I removed the distributor and found that there were arc marks on only the leading edge of the distributor poles. This meant that when the ignition system fires, the rotor hadn't rotated far enough towards the appropriate cylinder distributor pole.

I found absolutely no way to adjust this, so I removed the distributor and dissassembled and cleaned the vacuum advance/points plate. I noticed that there is a ball bearing and retainer that helps hold the vacuum advance (or retard) plate down. This was also rotated all the way over to one side, which would be consistent with a phasing problem.

Here's how I solved the problem: I used a moto-tool to grind out the holes in the vacuum advance (retard) unit. This allowed it to be slid over affectively adjusting the phasing. Some of the end of the foot of the vacuum canister had to be removed in order to get it to slide over far enough.

To set it up, I put the distributor foot in a vise. I then set the point gap to book tolerance when fully open. I then put the rotor and distributor cap back on and marked the point on the outside of the distributor body where cyl no 1 distributor pole is located. After removing the distributor cap again, I then adjusted the vacuum canister mount so that the points just open when the rotor is pointing at the mark.

A few more days of driving have confirmed this to work. Now there are firing marks all over the copper distributor pole instead of just one side.

I suspect that there may be a difference in length of the actuator arm for vacuum canisters. This probably accounts for the phasing problem.

I was wondering if there was an adjustment built into the distributor? I have a book by Christopher Jacobs that uses an old distributor cap to adjust phasing. To do this, you cut a hole in the cap so that the rotor and number 1 cylinder pole is visible. With the distributor on a test bench, you use a timing light to view the position of the rotor relative to the distributor pole.

Sholin