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post #1 of 6 (permalink) Old 03-31-2019, 06:51 PM Thread Starter
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Dura Spark ?

I'm wondering about the advance weights. I've got lots of old Dura Sparks and parts laying around. I always change springs in them to get the curves speed dialed in but I wonder about the weights, there are many different ones, they are marked to identify so it must make some difference but I just don't quite understand, spring tension vs advance weight ? I have never ran into a situation where a simple spring change didn't do the trick.
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post #2 of 6 (permalink) Old 03-31-2019, 08:51 PM
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Cool

Yes there are different weights.

A combination of the OEM light spring and a 925D Mr. Gasket will almost always do the trick.

Over the years I've simply used the weights in the unit I have on the sun machine, bush or change slots as necessary, weld up slot in some cases and play with spring tension.

The OEM curve is two stage with one light spring and one very heavy spring that adds tension from about 3000 to 5500. Toss it.
Add initial advance and make the curve more linear.


Vac advance is a whole other subject.



Duraspark_distributor_recurve_instructions_index


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post #3 of 6 (permalink) Old 04-01-2019, 07:03 PM Thread Starter
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Quote:
Originally Posted by The Mad Porter View Post
Yes there are different weights.

A combination of the OEM light spring and a 925D Mr. Gasket will almost always do the trick.

Over the years I've simply used the weights in the unit I have on the sun machine, bush or change slots as necessary, weld up slot in some cases and play with spring tension.

The OEM curve is two stage with one light spring and one very heavy spring that adds tension from about 3000 to 5500. Toss it.
Add initial advance and make the curve more linear.


Vac advance is a whole other subject.



Duraspark_distributor_recurve_instructions_index


SJ
Yea I have been through all that but I still wonder about the weights. At what point or what conditions should advance weight / weights (2) be altered and why ? I have lots of used weights that are of different weight and I wonder which weights I should be using ? Is there a better acting weight / weights (2) that I should look for in my used stuff ? This is a area that no one I've talked to knows anything about. They say just use the ones that are in it but Ford put different ones in them so it must make some difference ? For all I know I may have some weights in mine that are only suited for a smog situation and there might be something much better in my extra parts that I'm missing out on. So my question is still spring tension vs advance weight ?
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post #4 of 6 (permalink) Old 04-01-2019, 08:31 PM
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Yea I have been through all that but I still wonder about the weights. At what point or what conditions should advance weight / weights (2) be altered and why ? I have lots of used weights that are of different weight and I wonder which weights I should be using ? Is there a better acting weight / weights (2) that I should look for in my used stuff ? This is a area that no one I've talked to knows anything about. They say just use the ones that are in it but Ford put different ones in them so it must make some difference ? For all I know I may have some weights in mine that are only suited for a smog situation and there might be something much better in my extra parts that I'm missing out on. So my question is still spring tension vs advance weight ?


I've never in 19 years needed to address the slight differences in weights. Working with spring tension is enough. No need to make it complicated. I've re-curved and sold thousands of distributors both reman, OEM as well as new. I am on my third distributor machine.

Heavier weights, same OEM springs faster curve???



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post #5 of 6 (permalink) Old 04-04-2019, 09:24 PM
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Heavier weights respond like light tension springs... brings more advance sooner/lower rpm. Like the mad porter, I would use the stock weights (whatever they may weigh) and adjust the advance curve with springs. Maybe... just maybe, tweak the spring tab to fine tune the curve.
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post #6 of 6 (permalink) Old 04-19-2019, 06:23 PM
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Agreed with all of the above. Just to answer your question; the weights may be used to alter the rate of advance similar to staged strength and tension springs, as in the graph below. The weights apply more force the farther from rotational center they get. This means you can also change the travel limiters for different rate effect. The factory may alter the weights in order to have a specific distributor setup work "just right" with standard spec springs, requiring little manual adjustment or tuning. Labor costs, you know.

This all gets to hair-splitting level, as the springs may be combined in different rates and tensions to provide roughly the same effect, so altering weights is rare. An example might be an engine that detonates (knocks or pings) only momentarily on throttle tip-in from idle. One or both weights could be lightened in order to delay advance progression only in that area. But as mentioned, the springs can be changed, mismatched, or tensioned for a similar effect, so

David
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File Type: jpg Dist_weight_effect.jpg (10.2 KB, 8 views)

-= If it was easy, everyone would do it =-

Last edited by PSIG; 04-19-2019 at 06:28 PM. Reason: OEM reasons
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