Distributor Body notch

Ford Service Bulletin page 480 August 1930, provides the following information, the notch should allow the plate lever to travel 20 degrees.

See attached Ford Service Bulletin August 1930 page 480



picture.php
 
The notch in my distributor would allow the Plate Lever to travel 38 degrees. Too much. Using some 180 grit sandpaper i roughed up the area at the edges of the notch in the distributor then used JB Weld to built the edges of the notch to get it to the 20 degrees listed in the Service Manual. Problem solved. ken
 
I have the correct control rod length (some vendors' are incorrect) and the bulletins, but how is the 20 degrees translated into the width? Is it measured at the end of the plate lever ball to the other end? The dimension can change across the arc by sliding dividers in or out. The bodies I have are all a little different and don't have an original to compare to be able to set the fully retard accurately for timing.
I read somewhere that the early bodies were about 7/8" and later ones were 31/32" depending on lever width and not sure which lever I have that corresponds to the widths..
 
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Since the distributor plate moves 20 degrees, That means there is 40 degrees of advance possible since the crank is moving twice the distance of the distributor and advance is generally measured at the crank, not at the cam/distributor.

If this is the case, then when you time the engine (removable pin in the cam gear depression, points set so they just break) it must be somewhat retarded and not at TDC.
40 degrees when fully advanced would be far too much.

Also, it makes sense to time a Model A somewhat retarded since it is a hand crankable engine.

How retarded is the spark when timed by the book? I'd guess about 10 degrees, but does anyone know the actual number?
 
Timed by the book, the spark should be exactly TDC when #1 plug fires with the spark lever full UP. But, as you say, 40* is too much, so I never pull my spark lever down more than about 2/3rds.
 
Thanks KATY, you answered the question, and that seminar info I now remember.
The opening dimensions listed will help to be able to retard the spark lever for initial timing and by comparing if the housing notch is centered properly. Then one can advance as driving conditions dictate.
 
Tom Wesenberg said:
Timed by the book, the spark should be exactly TDC when #1 plug fires with the spark lever full UP. But, as you say, 40* is too much, so I never pull my spark lever down more than about 2/3rds.
Click to expand...

Thanks, Tom.

I wonder why Henry allowed 40 degrees of advance when doing so doesn't seem like a good idea (at least to us).

I wonder if somehow moving the upper plate 20 degrees doesn't change the timing at the crank by 40 degrees. It would be interesting to put a pointer and some timing tape on the crank pulley to see the timing change at the crank as the advance lever is moved. Has anyone done this?
 
I believe you would get less than 40 degrees, as the arm occupies some width in the slot. If you measure how much movement there is with the arm, you will find it less than 20 degrees arm movement, or 40 degrees of crank rotation. I could be wrong on this as I have not measured mine, but if I remember, I will look at it tomorrow.
 
It wouldn't be hard to calculate out if one knows the ID of the distributor, the width of the slot and the width of the arm where it fits in the slot.
 
dave in australia said:
I believe you would get less than 40 degrees, as the arm occupies some width in the slot. If you measure how much movement there is with the arm, you will find it less than 20 degrees arm movement, or 40 degrees of crank rotation. I could be wrong on this as I have not measured mine, but if I remember, I will look at it tomorrow.
Click to expand...

Dave,
I'll look at mine also. At a minimum I'll get the dimensions katy needs to calculate the angle.

In the article that 160B posted, it appears that the 20 degrees is not the full with of the slot. It looks like it is just the angle at the ball end of the arm when at the opposite sides of the slot.
 

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katy said:
It wouldn't be hard to calculate out if one knows the ID of the distributor, the width of the slot and the width of the arm where it fits in the slot.
Click to expand...

Here's the measurements from mine. I believe the distributor upper plate to be an original, but I can't be sure about the distributor body.

Diameter of distributor body (inside at base) 2.88"
Width of slot in body .985"
Width of arm at the slot .409"

Using this triangle calculator...

http://www.calculator.net/triangle-calculator.html?vc=&vx=1.441&vy=1.44&va=&vz=.576&vb=&angleunits=d&x=62&y=25

...I come up with 23.074 degrees.
 
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I've never measured or worried about the slot. I simply advance the spark half way as soon as the engine starts, then move it down to about 2/3 when driving. Once the engine no longer gains speed when advancing the spark, it's time to quit advancing the spark, as too much advance is hard on the bearings.
 
Dick Steinkamp said:
Here's the measurements from mine. I believe the distributor upper plate to be an original, but I can't be sure about the distributor body.

Diameter of distributor body (inside at base) 2.88"
Width of slot in body .985"
Width of arm at the slot .409"

Using this triangle calculator...

http://www.calculator.net/triangle-calculator.html?vc=&vx=1.441&vy=1.44&va=&vz=.576&vb=&angleunits=d&x=62&y=25

...I come up with 23.074 degrees.
Click to expand...

Using Dick's measurements, I come up with 22.9°
 
I'm starting to think that 40 degrees of advance is not unrealistic under certain conditions for our As. Here's an article that helps explain this...

http://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/

I know it is focuses on a more modern engine, but the principals are similar on any internal combustion engine.

You need more spark lead as RPM increases (to a point) in order to light the charge in time to create maximum cylinder pressure at the ideal point after TDC. For the engine in the article, this is about 35 degrees before TDC at 2600 RPM and above when the engine is pulling and there is little or no vacuum. At light throttle conditions over 2600 RPM (like steady state cruising) even more advance is required since the throttle is barely cracked. the A/F mixture is lean and not tightly packed and will burn slower because of this. In order to hit maximum cylinder pressure at that ideal point after TDC, the charge has to be lit even earlier. In the example in the article, about 45 degrees of total (initial + centrifugal + vacuum) advance is required. Since there is plenty of vacuum at these conditions, the vacuum advance adds the required additional advance.

All forms of advance in a modern engine (initial, centrifugal, vacuum) are handled by the driver with the spark advance lever on stock Model As. Advance is retarded to TDC to start the engine, and advance is added as RPM and load conditions require. Theoretically, we should be constantly "fooling" with the advance lever in order to maximize performance and fuel economy. This would be a pain in the butt and probably result in only minor gains, so we move the lever to the position that we have found is the best compromise and go for a drive.

So, my current (unproven) theory, is that there is a use for the 40 degrees of advance that is obtainable (also unproven) when the spark lever is pulled all the way down. This would be during light throttle, steady state cruising at high (for our cars) RPM. Let's say 40-50 MPH on level ground.

I tried this with my 30 Tudor. I run with the spark lever about 2/3 advanced. At 40 MPH when I pull the lever all the way down I do note a slight increase in RPM and smoothing (slight). Maybe not enough to worry about. The downside of doing this is that if I forget I've done it and then don't retard the spark when the engine is pulling again and I'm into the throttle, preignition (detonation) could occur which is bad for any engine...especially one with a babbitt lower end.

If our engines are capable of 40 degrees of advance, I believe Henry knew it and made it possible for a reason. My next step would be to measure how many degrees of advance are actually occurring at the crank during full movement of the advance lever. Any good ideas on how to do this?
 
Dick Steinkamp said:
I'm starting to think that 40 degrees of advance is not unrealistic under certain conditions for our As. Here's an article that helps explain this...

http://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/

I know it is focuses on a more modern engine, but the principals are similar on any internal combustion engine.

You need more spark lead as RPM increases (to a point) in order to light the charge in time to create maximum cylinder pressure at the ideal point after TDC. For the engine in the article, this is about 35 degrees before TDC at 2600 RPM and above when the engine is pulling and there is little or no vacuum. At light throttle conditions over 2600 RPM (like steady state cruising) even more advance is required since the throttle is barely cracked. the A/F mixture is lean and not tightly packed and will burn slower because of this. In order to hit maximum cylinder pressure at that ideal point after TDC, the charge has to be lit even earlier. In the example in the article, about 45 degrees of total (initial + centrifugal + vacuum) advance is required. Since there is plenty of vacuum at these conditions, the vacuum advance adds the required additional advance.

All forms of advance in a modern engine (initial, centrifugal, vacuum) are handled by the driver with the spark advance lever on stock Model As. Advance is retarded to TDC to start the engine, and advance is added as RPM and load conditions require. Theoretically, we should be constantly "fooling" with the advance lever in order to maximize performance and fuel economy. This would be a pain in the butt and probably result in only minor gains, so we move the lever to the position that we have found is the best compromise and go for a drive.

So, my current (unproven) theory, is that there is a use for the 40 degrees of advance that is obtainable (also unproven) when the spark lever is pulled all the way down. This would be during light throttle, steady state cruising at high (for our cars) RPM. Let's say 40-50 MPH on level ground.

I tried this with my 30 Tudor. I run with the spark lever about 2/3 advanced. At 40 MPH when I pull the lever all the way down I do note a slight increase in RPM and smoothing (slight). Maybe not enough to worry about. The downside of doing this is that if I forget I've done it and then don't retard the spark when the engine is pulling again and I'm into the throttle, preignition (detonation) could occur which is bad for any engine...especially one with a babbitt lower end.

If our engines are capable of 40 degrees of advance, I believe Henry knew it and made it possible for a reason. My next step would be to measure how many degrees of advance are actually occurring at the crank during full movement of the advance lever. Any good ideas on how to do this?
Click to expand...

Would the quality/octane of gasoline back then have anything to do with why Henry thought 40* would be good?
 
Following this post, I have check measured 3 distributor tops that I have and found them to be all within 5 thou of 0.972".
Cheers, Ross
 
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