The Ford Barn

Corley · 12-08-2022, 07:24 PM

Dwell isn't magic, and it isn't difficult to understand. The distributor has 360 degrees of rotation for the 4 cylinders of the model A engine. That leaves 90 degrees of rotation for each cylinder. If you look at the distributors cam, you can see that it is going to keep the points closed about 50% of the time, therefore, the dwell is going to be somewhere in the 45 degree range (half of 90 degrees). So just estimating, the dwell should be something between 35-55 degrees.. What I suggest is to set the points at the center of their range (0.020"), measure the dwell, and that would be what I would use in the future. (I run a trouble free Honda electronic distributor, so I can't actually check it for you.)

Note1: I would expect the model B cam to provide a bit more dwell due to it's profile, but...
Note2: If you watch Paul shinn's video on distributor rebuilds, he sets the points at 0.018". I do not buy that setting. The normal wear of the fanalic cam rubbing block on the movable point arm causes the points to naturally close up over time. It just seems wrong to start out with the points set to the minimum setting. I suggest 0.020" as a better setting.
Note3: I built the dial indicator points checking tool seen in the restorer magazine a few months back, and took it and a bunch of distributors to our club meeting. Using feeler gauges, the club members were asked to set the points to 0.020". Every single one of them set the points significantly wider than 0.020", some as wide as 0.030". It seems to be human nature the adjust them wide, or at least a common mistake. A dwell meter would verify correct settings. (A dial indicator can also verify correct adjustment.) I now have very little confidence that the average model A owner will set points at the correct gap.

Y-Blockhead · 12-08-2022, 08:37 PM

Quote:

Originally Posted by Corley

Dwell isn't magic, and it isn't difficult to understand. The distributor has 360 degrees of rotation for the 4 cylinders of the model A engine. That leaves 90 degrees of rotation for each cylinder. If you look at the distributors cam, you can see that it is going to keep the points closed about 50% of the time, therefore, the dwell is going to be somewhere in the 45 degree range (half of 90 degrees).If you watch Paul shinn's video on distributor rebuilds, he sets the points at 0.018". I do not buy that setting. The normal wear of the fanalic cam rubbing block on the movable point arm causes the points to naturally close up over time. It just seems wrong to start out with the points set to the minimum setting. I suggest 0.020" as a better setting.

I can't speak for Paul Shunn but setting the points at .018" will give you more degrees of dwell than setting them at .022".

That said, I also set my points at .020" to allow for some phenolic block wear. Easy to check to see if the points are closing up using a dwell meter.

Rob Doe · 12-09-2022, 08:24 AM

Guyz, I've read through this thread multiple times over the last few days. This time, a memory flashed back. FWIW, I think I read somewhere that the Model A has more dwell than the coil needs or will make use of??? Comments???

60 years ago, I had a 31 coupe. As I recall, the early recommended points setting range was 16-18???

alexiskai · 12-09-2022, 08:43 AM

That's my understanding – 4-cyl engines operating at the relatively low RPM range of the Model A get all the dwell the coil needs quite easily. I always understood the advantage of the B distributor cam to be that it reduces wear on the rubbing block. If you look at the '32 service bulletins, "dwell" is never mentioned in the context of the Model B, only when talking about the V8s. In the Model A service bulletins, dwell is never mentioned at all.

imacrazy · 12-09-2022, 09:07 AM

It’s Christmas Time, don’t dwell on the past, dwell on the future and the good times we have with our Model A each time we climb in and take a good ride. There is enough strife in this world today with out thinking about how we look at different things.

GOD BLESS & Have a VERY MERRY CHRISTMAS & HAPPY NEW YEAR

Bill

Ramman · 12-09-2022, 01:18 PM

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Quote:

Originally Posted by Rob Doe

on
60 years ago, I had a 31 coupe. As I recall, the early recommended points setting range was 16-18???

I going to say your setting from 60 years ago was .016"-.018" gap at high, point cam, not 16°-18° degrees of dwell.

12-08-2022, 07:24 PM	#21
Corley Senior Member Join Date: Aug 2011 Location: Battle Ground WA Posts: 293	Re: Setting points with dwell meter Dwell isn't magic, and it isn't difficult to understand. The distributor has 360 degrees of rotation for the 4 cylinders of the model A engine. That leaves 90 degrees of rotation for each cylinder. If you look at the distributors cam, you can see that it is going to keep the points closed about 50% of the time, therefore, the dwell is going to be somewhere in the 45 degree range (half of 90 degrees). So just estimating, the dwell should be something between 35-55 degrees.. What I suggest is to set the points at the center of their range (0.020"), measure the dwell, and that would be what I would use in the future. (I run a trouble free Honda electronic distributor, so I can't actually check it for you.) Note1: I would expect the model B cam to provide a bit more dwell due to it's profile, but... Note2: If you watch Paul shinn's video on distributor rebuilds, he sets the points at 0.018". I do not buy that setting. The normal wear of the fanalic cam rubbing block on the movable point arm causes the points to naturally close up over time. It just seems wrong to start out with the points set to the minimum setting. I suggest 0.020" as a better setting. Note3: I built the dial indicator points checking tool seen in the restorer magazine a few months back, and took it and a bunch of distributors to our club meeting. Using feeler gauges, the club members were asked to set the points to 0.020". Every single one of them set the points significantly wider than 0.020", some as wide as 0.030". It seems to be human nature the adjust them wide, or at least a common mistake. A dwell meter would verify correct settings. (A dial indicator can also verify correct adjustment.) I now have very little confidence that the average model A owner will set points at the correct gap. __________________ Corley ----------------- Subscribed to the KISS principle!

12-09-2022, 08:24 AM	#23
Rob Doe Senior Member Join Date: Apr 2021 Location: Central Illinois Posts: 496	Re: Setting points with dwell meter Guyz, I've read through this thread multiple times over the last few days. This time, a memory flashed back. FWIW, I think I read somewhere that the Model A has more dwell than the coil needs or will make use of??? Comments??? 60 years ago, I had a 31 coupe. As I recall, the early recommended points setting range was 16-18??? __________________ "It ain't what you know for certain that gets ya in trouble. It's what ya know for certain that just ain't so!"

12-09-2022, 08:43 AM	#24
alexiskai Senior Member Join Date: Apr 2018 Location: Mebane NC Posts: 2,356	Re: Setting points with dwell meter That's my understanding – 4-cyl engines operating at the relatively low RPM range of the Model A get all the dwell the coil needs quite easily. I always understood the advantage of the B distributor cam to be that it reduces wear on the rubbing block. If you look at the '32 service bulletins, "dwell" is never mentioned in the context of the Model B, only when talking about the V8s. In the Model A service bulletins, dwell is never mentioned at all.

12-09-2022, 09:07 AM	#25
imacrazy Senior Member Join Date: Mar 2011 Posts: 163	Re: Setting points with dwell meter It’s Christmas Time, don’t dwell on the past, dwell on the future and the good times we have with our Model A each time we climb in and take a good ride. There is enough strife in this world today with out thinking about how we look at different things. GOD BLESS & Have a VERY MERRY CHRISTMAS & HAPPY NEW YEAR Bill