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A friend popped over tonight with a timing light. We rigged it up and started the engine. Once it was idling nicely, we turned the dial on the back of his timing gun to 4 degrees advance (I've got civilian ignition/Pertronix). The TDC mark on the pulley then lined up perfectly with the bolt on the engine, so that was good.

However, I thought I'd see how altering the timing changed things so we twisted the distributor cap (up to 20 degrees) but it made no difference at all - why is this? Can't move the actual distributor - it's jammed in tight.

Also checked that the mechanical advance was working - didn't get a number on it, but the mark moved by about 20 degrees with high revs.

spandit wrote:Can't move the actual distributor - it's jammed in tight.

Oh the joy, I spent the better part of 2 hours “gently” taping my distributer back and forth to free it up. That’s after letting penetrating oil soak in over night. Used a 8” by 1” piece of wood doweling and a hammer. When it was finally loosened up I pulled the distributer cleaned the corrosion and greased the surfaces before putting it back.

Ed

But shouldn't twisting the cap alter the timing anyway?

But shouldn't twisting the cap alter the timing anyway?

The timing comes from the relationship of the distributor shaft and the distributor HOUSING; the housing is where the points/Pertronix is mounted. Twisting the housing clockwise/counter clockwise is what changes the timing.

The cap is just the "switch" (through the rotor) that makes the spark go to whatever is the proper cylinder; if the cap is in the proper position then the rotor lines up with the cylinder as the spark is produced. If only the cap is rotated, then the rotor gets further from the proper cylinder terminal, the spark has to jump further, and eventually either can't jump at all or jumps to the adjacent cylinder terminal - not a good thing.

So the timing will never change unless the distributor housing is free to turn.

Jim M.
712W and 710M

I see - makes sense. How can I make sure the cap is lined up in the best position? Turn the engine to TDC & put the #1 electrode in the middle of the rotor electrode?

Usually, the cap is keyed to the proper postion on the distributor so you shouldn't have to deal with it, but since it sounds like you have a Civi kit with the cap on the adapter you could get things out of alignment.

If I recall correctly, the distributor turns clockwise when looking at it. So at idle, with no mechanical advance, the rotor should be almost past the cylinder electrode in the cap when the spark happens. As the spark advances, the spark will happen EARLIER (the rotor is more nearly lined up with the electrode). At full advance, the rotor might be just a little before the electrode when the spark happens. Because the rotor has width, and the electrode also has width, the spark has a good range of angle where it can jump from the rotor to the electrode without an excessive gap.

If you think of the cylinder electrodes at 12, 3, 6, and 9 o'clock then at idle the spark might jump at 12:02 and 24 degrees of mechanical advance would then have the spark jump at 11:58. So the range is not huge.

So use the timing light to determine the idle timing then shut off the engine and hand turn it to the same timing; set the cap to be centered to just slightly counter clockwise to the rotor postion.

Of course if I goofed and the rotor goes counter clockwise you will have to reverse all I've said!

Best of luck,

Jim M.

Oops, 4 minutes of the clock does NOT relate to 24 degrees of timing - because the distributor runs off the camshaft at half the crankshaft speed, TWO minutes of the clock equates to 24 degrees of advance. So 12:01 to 11:59 is 24 degrees of advance. I didn't think of this until after my first post.

So aim the cylinder terminal in the cap right at the rotor; the advance doesn't make much difference.

Jim M.

After reading these posts, I'm going to add a job to the preventative maintenance list..... Every time I take the engine cover/doghouse off, give a good blast of WD-40 or similar to the distributor/engine interface !!

IF I ever have to tweak the timing in the future, at least the dizzy should move without the use of a big hammer and naughty words.


Mike 712M

You can do it through the oil fill section of the cover. I keep a can of WD-40 to spray on the distributor in case I run through a bill puddle and she starts running rough. Works every time.