Dwell Angle

I never was able (probably out of ignorance) to measure the dwell (the angle through which the distributor cam rotates while the points are closed) on my standard distributor using my Allen-Tune Model 50-514 Dwell/Tach meter, although when I ran a Mallory distributor, the Dwell/Tach meter would work, albeit I had (as memory serves) to divide (multiply?) the reading by 2 inasmuch as the 50-514 was only set up for 6- or 8-cylinder engines. As I recall, at least on my SBC's (283's and 327's, always in a Chevy and not a Model A) the dwell specification was 28 to 32 degrees, so, depending on the distributor cam profile and the point gap (reducing the gap will increase the dwell) if you did want to set your point gap by measuring the dwell, it ought to be somewhere around 45 +/-degrees. (If this isn't correct, someone more knowledgeable will chime in.)

However, (a) I wouldn't rely on this and (b) as fordgarage correctly pointed out above, set the gap and then the timing. It isn't that difficult and works pretty well.

And, lastly (and depending on the quality of your distributor cam, the tightness of the upper distributor plate and the condition of the distributor bushings) do not rely on just one lobe to set the points. Instead, pick a lobe, set the point gap (after ensuring the points are reasonably clean and "polished" and are parallel to each other when closed) and then measure the resulting gap at the other three lobes. You might be surprised to discover the variance from lobe to lobe.
 
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Dwell also depends on whether you are using an A cam or a B cam. The B cam is the only one sold and it gives about 9 or 10 more degrees of dwell when the points are set at .020".

I measured the dwell years ago and seem to recall it was about 35 for the A cam and 45 for the B cam.
 
I agree there is no "spec", per se. I carefully set the gap on some new points with a feeler gauge. Then, when the engine is running, I measure the dwell, just to see what it was (for future reference).

I use that number to do a quick check for point "follower" wear. Every time I change the oil, I connect the dwell meter just to see where it's at. It is quick and easy to do. If the dwell has fallen too much from my initial reading, I open up the distributor and set the gap back out to spec with a feeler gauge.
 
Vince,
I would think you could chuck the pencil up in a lathe then bore out the center and then
slide the new guts in with a little Loctite to hold it in place.

Bob
 
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Bob and Vince,

I was thinking the same thing Bob. BUT, were are dealing with Vince, a crafty kind-
a-guy, soooo, Vince you have any photos of this project?
 
After you follow the procedure in the service bulletin ,put it away and set the timing where the engine gives you the best performance with out rattling ( pining ).
 
"Anyway, does anyone have any advice or info on how to modify and convert these into a plastic bodied style, with gel ink cartridge, and a rolling ball tip? "

Hmmm! Let me DWELL on this for a bit.:D:p

Yep, keep it simple and just set them at .020" and enjoy the drive.:)
 
There once was a Model A distributor,
Which required point-gap setting by feeler.
"I tried gapping by dwell,"
"But the ignition went to hell,"
Proving the old way is often times better.
 
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I have some assorted old shop literature that all call out 31 degrees dwell... 31 would be for ORIGINAL distributor cams. the ones available now will run 41 - 47 degrees (my measurement). forget about the dwell and just set the points as previous posts state. I think Napa Skip supplied an excellent summation !
 
My dwell machine must be 40 or more years old. Just thought I would have
Some fun using it again, you know for something to do?

Was easy on old chev motors just connect the leads, start the engine and,adjust distributor with a Allen key.

Next big project I might remove the small stones from the tire treads!

Fredski
 
That is not a measurement you need to waste your time on for keeping the A happy. I think there is a pun in there...

What you do want to measure is the amount of slop between your upper plate and the center bushing area of the dist in the normal operation area. If there is too much play here you get a variation in timing as the plate moves.

I measured mine with a dial indicator about where the points would be. Then slid the top plate back and forth to determine the movement. A couple of thou is not too bad, but at some point beyond that you can start altering the point gap enough to change how the engine is running. More importantly it can vary as the engine runs giving some inconsistancies in the engine running.

A fix is to use a peen and expand the metal a bit near the edge where the hole is larger. This will reduce the movement, but depending on use the points of the squeeze will wear faster over time.
 
One day I had more time then projects. Sooo... I took dist. out and bench set the pionts to .020. Then I used a VOM to check the rotational angle that the points were in contact. I am not sure what I measured but I think you could determine the dwell by this methed. My brain cells leak after a time and it was quite a while ago that I did this so I am not sure what I found the dwell to be. Seems like it may have been about 38*.
 
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Doesn't seem as though it would be too hard to do. Set the points and then check the dwell. If you're like me, you'll have to write it down and then forget where you put it.
 
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I have one of these that I have had for 40+ years.
 

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I used the B cams in both my cars purchased from brattons / swapped out the A cams... Very high quality and a noticeable improvement as well
 
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