Distributor Cap Advance Lever Slot

[mrbilman]

Is the slot in the distributor cap supposed to act as the stop for the advance lever? On the one I was working on yesterday the stop in the distributor body was off from the slot in the cap when fully retarded. Should this be left as is or is it better to file the slot to better match with the stop in the distributor body?

[P.S.]

Originally Posted by mrbilman

Is the slot in the distributor cap supposed to act as the stop for the advance lever? On the one I was working on yesterday the stop in the distributor body was off from the slot in the cap when fully retarded. Should this be left as is or is it better to file the slot to better match with the stop in the distributor body?

That slot is indeed there to act as a stop at each end of travel of the upper plate. If there were no stops, it could be possible to over-rotate the upper plate and it could pop out of the slot in the housing because of the spring pushing up from underneath.

Some of the repro distributor tops have the slot way too short. If you have one of those, you'll know because the spark adjustment will not be able to move all 10 notches on the column before the upper plate linkage arm hits the ends of the slot in the top cap. A Dremel tool makes quick work of that to open the slot.

[Big hammer]

It’s possible with a two tooth steering gear box that the column is off, I was adjusting the gear box and on the test drive it started running crappy. When I got back to the garage I found the column had turned, I forgot too tighten the clamp

[1crosscut]

My thought is that the slot is not a stop but indicates the limits of the full range of the spark advance lever.
Most likely if you have a two tooth steering column the column will need to be rotated for the correct range of motion. If it’s a 7 tooth you may need to bend the arm on the steering column that the linkage fits onto. A pair of pliers will bend it.
I’ve bent several of them and have not had one break on me.

[Bob C]

Here is a link to the Service Bulletin.
https://modelagarage.com/service_bulletin/distributor/

[bobbader]

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Simply put ............. DO NOT FILE THE OPENING IN THE DISTRIBUTOR CAP BODY!!!!!

If the car has a Two Tooth Steering Column (usually 1930/31) where the outer column tube is held on to the steering box with a clamp just above the top of the box, loosen that clamp as well as the clamp holding the tube inside the car. Now, you can rotate the column tube clockwise or counterclockwise so that the distributor plate lever can be made to hit both stops on the distributor body cap at either end of the spark lever travel at the steering wheel. Once this is done, it is necessary to reset the timing with the timing pin and rotational setting of the distributor cam. Good luck in your endeavors.

[P.S.]

Originally Posted by bobbader

Simply put ............. DO NOT FILE THE OPENING IN THE DISTRIBUTOR CAP BODY!!!!!

If the car has a Two Tooth Steering Column (usually 1930/31) where the outer column tube is held on to the steering box with a clamp just above the top of the box, loosen that clamp as well as the clamp holding the tube inside the car. Now, you can rotate the column tube clockwise or counterclockwise so that the distributor plate lever can be made to hit both stops on the distributor body cap at either end of the spark lever travel at the steering wheel. Once this is done, it is necessary to reset the timing with the timing pin and rotational setting of the distributor cam. Good luck in your endeavors.

What about if you have one of the repro caps where the opening is not wide enough? The poor repro opening is only 3/4 the width of the factory cap opening.

[Jim/GA]

Originally Posted by Bob C

Here is a link to the Service Bulletin.
https://modelagarage.com/service_bulletin/distributor/

That picture is nice, but does anyone have an original Ford drawing with the actual dimension of the slot?

I went out and measured 3 different distributor bodies just now and got 3 different widths! And one was far off (smaller) than the others. The largest was 1 inch.

Then people could measure the slot width on their caps and decide if it needs to be widened.

I have the Service Bulletin below but it does not mention width.

Thanks!

[bobbader]

P.S. You bring up a good point. My take is that, if you have a distributor body with the wrong dimension width of the slot, when you go to set the steering column tube, you may get the distributor plate lever to hit both stops ............ BUT ............ you won't get full travel at the spark lever at the steering wheel. So, to set the timing 100% correctly, the distributor plate lever has to hit both stops AND the spark lever at the steering wheel has to have full travel from fully retarded position (all the way up) or fully advanced (all the way down).

FYI, I've been in the Model A parts business for 45 years and I don't believe I've seen a distributor cap body where the slot is 3/4 the size of the slot in an original cap. Not saying it's not possible ....... lots of different manufacturers over the years. I now sock distributor bodies from 2 available manufacturers and both have the correct dimension slot. My reason for being adamant about not filing the slot is that the distributor plate lever not touching one of the two stops in the slot does not indicate that the width of the slot is wrong. It usually means the steering column tube is mis-aligned.

[Jim/GA]

Originally Posted by bobbader

FYI, I've been in the Model A parts business for 45 years and I don't believe I've seen a distributor cap body where the slot is 3/4 the size of the slot in an original cap. Not saying it's not possible ....... lots of different manufacturers over the years. I now sock distributor bodies from 2 available manufacturers and both have the correct dimension slot.

So, what is "the correct dimension slot"?

Thanks!

[P.S.]

Originally Posted by Jim/GA

So, what is "the correct dimension slot"?

Thanks!

Excellent question, Jim!

I just measured an original cap. The slot is 1-1/32" wide.

Here is an original cap and a good quality repro next to each other. The original is on the right side of the photo. Notice the difference. A poor repro that came from a club member had an even smaller slot that this repro!

[mrbilman]

Thanks to everyone who chimed in! As a result I understand how this should be set and I have no doubt that the 2 tooth steering column will have to be rotated to get the correct setting.
As a follow up-
i inspected my car (a 1931) and it was set up correctly. i did some math by measuring the diameter of the Distributor Housing (3.165") and figured out that 20 Deg. is equal to .552" on the circumference. The spark advance arm is about .455" wide at the slot so adding these two numbers equals a theoretical
slot width of 1.007" on the circumference. The slot width on this housing is .998" (straight across) and the arm just touches on each end of travel before the advance lever hits it's stop.
My conclusion is that the slot should measure very close to 1.00" and be concentric with the centerline of the spark terminals.
Thank again!

[alexiskai]

I have five in my collection; on four of them the opening measures .975” and on one it measures .875”.

[Terry Burtz, Calif]

Originally Posted by P.S.

Excellent question, Jim!

I just measured an original cap. The slot is 1-1/32" wide.

Here is an original cap and a good quality repro next to each other. The original is on the right side of the photo. Notice the difference. A poor repro that came from a club member had an even smaller slot that this repro!

Paul Shinn, Ford drawing A-12105 released under EI 17641 on Sept 19, 1930 specifies a slot width of 31/32 inch. I suspect that the repro is correct and your original distributor body with the 1-1/32 slot has been modified.

[Fullraceflathead]

I wonder what the tolerance is on the ford document plus or minus 1⁄32 of an " isn't that much.

[Jim Mason]

Hard to read. No tolerance noted as it's not a critical measurement

[Fhane]

I would go with Terry’s measurement.

[Kurt in NJ]

The model B cap superceded the A , it had a more narrow opening that on the inside had the A dimensions and was to be filed when installed on the A

[alexiskai]

Originally Posted by Kurt in NJ

The model B cap superceded the A , it had a more narrow opening that on the inside had the A dimensions and was to be filed when installed on the A

To be clear, it is shorter top-to-bottom, not reduced in the range where the arm swings. The shorter gap sits right on top of the B plate arm.

[Bob C]

Originally Posted by Kurt in NJ

The model B cap superceded the A , it had a more narrow opening that on the inside had the A dimensions and was to be filed when installed on the A

That information is in the July 1932 Service Bulletin.
It says to increase the height of the opening from 5/16"
to 7/16".