Distributor Rotor Adjustment ?

[Cape Codder]

I have seen a measurement that the rotor end should be x number of thousands from each cylinder pin inside the Distributor Body. My measure:
#1-.022, #2-.014, #3-.012 and finally #4-.010. This Distributor has a NEW shaft and bushings. Also a NEW body and cap along with rotor and cam.

First, can anyone tell me this measurement?
Second, how do you adjust the gap?

Thanks for any information.

[P.S.]

That is close enough! Maybe just a tad too close. You don't want them too close, otherwise, the rotor will strike one of the "button" contacts and knock the cap off. The cap does wiggle around a little when it's running.

If the gaps are too great, then the spark will be affected.

I think the spec. is .035 gap for rotor-to-distributor cap gap. One of the gurus will know for sure. Having a small difference in the 4 measurements is not unusual. Yours sounds just fine.

[sphanna]

I have seen .025 th. in publications I have mine at .030 but most say .025

[Cape Codder]

So...........now how do I get that clearance?

[Fred K-OR]

Originally Posted by Cape Codder

So...........now how do I get that clearance?

If they are to close, file or grind down the rotor or some people say you can bend the rotor to get the clearance.

[Mitch//pa]

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file it ,, beware trying to bend it as it will break out of the plastic. as long as they are not rubbing i wouldn't get to anal on the gap...

[Patrick L.]

If you reset the cap/rotor the numbers will probably change.

But, if you want to change it,,
The rotor tip can be bent a bit, but, thats dicey and I don't like doing it.

Or, if you still end up with one a bit more than the others like the .022" one, then I would file the cap tips of the other 3.

[BILL WILLIAMSON]

On conventional distributor caps, we don't even give it a second thought! We're only concerned if they're OXIDIZED/BURNED away or show evidence of carbon tracks or cracks.
Bill W.

[Tom Wesenberg]

Does the distributor body move side to side on the distributor casting? If so then shim it with tape and recheck the clearances. If they are not even, then file the body contacts to make all 4 even. If you file the rotor, they will still not be even, but all will have a larger gap. If you don't make them all even, chances are you and the car will never know, and it will be fine.

[Bruce,Upstate NY]

I can't find distributer bodies that properly fit the distributer housings. Likewise I can't find rotors that aren't sloppy on the cam. It the rotor to body clearances aren't equal, the ignition timing isn't accurate. That's the way I see it.

[Tom Wesenberg]

At the speed of electricity you'll never be able to measure any lag from a few thousandths difference if the gap. I'd use paper to hold the rotor snug on the shaft.

The last two distributor bodies I bought were at least 10 years ago. I bought one from Bratton's and one from Little Dearborn, and both were a nice snug fit to the cast body.

[MAG]

Tom W.
"At the speed of electricity you'll never be able to measure any lag from a few thousandths difference in the gap."

X2.

[Tom Wesenberg]

Actually it's more than just the speed of electricity. The collapsing magnetic field in the coil needs to build the secondary windings to a higher voltage to jump the larger gap, but a few thousandths difference in gap still won't matter as far as a smooth running even fire engine.

That's why when you hold the coil wire away from the cap and make the spark jump a gap, a fouled spark plug will start firing. The coil now has to build to a higher voltage to jump the gap, and that higher voltage will also jump the plug gap before the voltage is syphoned off to ground by the wet insulator.

[BILL WILLIAMSON]

As a side note: When using the '32-'34 style cap, sometimes the cutaway for the advance lever is TOO NARROW & needs to be filed out, so the advance range is proper for a MODEL A distributor.
Bill W.

[Cape Codder]

What I am trying to do is rebuild a distributor to the best of my ability. Bushings have been replaced and a NEW shaft installed. We all buy the books which are instructing us on how to do a particular repair or rebuild. Late last night I found in the Les Andews book that the gap should b .025" to .030". So with that information I have two positions that are approx. 1/3 of what it should be, one that is only 1/2 of what it should be and there is the .022" which is close to the low side.

I wasn't able to work on the distributor further today as we went on a short trip for lunch to R.I. leaving this morning. A friend lent me his distributor and the car ran well.

So tomorrow my intent is to change distributor bodies, change rotor and see how they measure out. I do want to say I bought all the new parts from A&L and are very good fitting. The distributor body is very tight to the casting as well as the rotor is to the cam.

Thanks to all for your responses and I will get back and let everyone know how I ended up.

[Cool Hand Lurker]

The cap is only as good as the guy who made it and how precise he is in placing the contacts in the mold. If the finished part is put on a truing reamer to make them all equal, the spark timing on all cylinders should be equal. Maybe it doesn't matter but why not make it right?
I say adjust the cap with a file to make all contact's clearances close to each other. It "might" make the firing smoother.

[Terry Burtz, Calif]

Original distributor bodies (A-12105) were made of Bakelite and machined in 3 places after molding to insure that all important interfaces were concentric . These three areas are where the body interfaces with the distributor base assembly (A-12130), the 4 contacts, and where the body interfaces with the distributor cap (A-12115).

Reproduction distributor bodies are made by several manufacturers. Most make a distributor body that is generic, phenolic, have notches to fit '28 through '34, and they are not machined as above which requires filing for rotor gap. One manufacturer makes an exact copy of the distributor body that is made of Bakelite, machined as above to the Ford blueprint, and no filing is required.

Ask your dealer for a "machined Bakelite distributor body".

[Mike V. Florida]

File down the contacts inside the the body to get the correct, and same, gap on all the contact points.

Getting a newer distributor body will only get you a spare bod for the shelf as they are not correct out of the box.

[dnkcurtis]

You said you have a new shaft, check to see if your points open the same gap on all four lobs of the cam. I bought 10 new shafts from an e-bay business a few years ago. I always measure them at the bushing areas, these were all right on.

Then when I started to set the gap I realized the cam was not centered, when I set the gap I notice that the others were off, even one closed when it should have been open. I put this shaft on a mini lathe and found the surface was not centered to the rest of the shaft. Further checking I found 3 of the 10 were off center. This part of the shaft is what you are putting your rotor on and could be off center.

Just some info to check, could be why you are close on one side and away on the others. You can check it fast while you have it out, by checking the point gap on each lob of the cam.

Good Luck DRC

[daveymc29]

I had some old bakelite bodies that had been in boxes for years with other junk piled willie nillie around and on top of them. Most were distorted and a poor fit on the distributor and the gap from the body to the rotor varied considerably. Some looked like Christmas lights were under the hood when I lit her up at night, so be careful what you buy. properly packed originals would be best. Filling will improve most and some are junk. Pays to test in the dark to spot leaks.