Anyone know how to i.d. the correct advance springs , that came in the old m.p. race distributor 4120942 ? looks like i have one thats pink and one that has no color/paint marking on it. What springs came in that dissy for full/quick advance ?

Get the lightest set, I use just one to bring back to start, full in at 800 up. Bring up to 1500, then set at where you want full advance degrees to be. Full advance at idle

I like and use the Mr. Gasket real light weight advance springs, part number 925B
Those springs work well on the street and strip only cars with BB motors

Race deal with a big cam? I just lock it out so I don't have to make it idle 13-1500. 800 in gear.

o.k. , anyone know what springs were used in a New chrysler Aluminium race distributor ? 1970's era

IIRC, they were Mallory. You can find them at Summit but they ain't cheap.

From the "Don't Never Throw Nothing Away" dept - This has been in my tool box for longer than I can remember.
I never thought someone might be looking for them.

those look exactly like the Mr. Gasket 925B springs

Same springs hanging on the peg board at the speed shop, ONE company makes them all

Do you happen to know which company that is? I've tried to find out who was making them but never could figure out who is making them.

TIA

There may have been changes in springs used for the tach drive race distributors over the years, but if so, they would be small changes.
Break out your calipers and magnifying glass. Measure the wire, the coil od. and the over length inside the loops.


Spring______Wire Dia. Coil O.D. Coils Spring Rate Length
.Light Spring 1: 0.018", 0.230", 12.5, __1.26 #/in, 0.72"
HeavySpring 2: 0.053", 0.293", _5.0, 174.41 #/in, 1.086"

MP P2932675
Super Light pr: 0.015", 0.225", 11.5, __0.68 #/in, 0.7"

The original combination was designed to:
a. compensate for delays that made the effective timing retard in the higher rpms.
b. provide easy restarting with high compression engine.

I suspect the super light springs were originally for racing with dual point distributors.

Wow, VERY GOOD INFO !!!!!

If it means anything....the color of the springs look like the paint color on the old mopar purple shaft cams . I will end up testing the advance curve , to verify .

If you haven't seen the first before, its from the DC Engine Book.

The second is a small block version of that distributor I ran on Sun 404.

The heavy spring loop is part of the secret sauce that keeps timing steady or slightly rising depending on how quick the pulse amplifier is.

Are you sure the value you give for the heavy spring lbf/in is correct?

Yes. As a calculation anyway. Feel free to run the numbers. I subtracted 1/2 coil for active coils and used 11,000 K for elastic shear modulus.
Measurements make a big difference when there are few coils.

But as a comparison, it should be ballpark correct.
When looking at the effect on the advance, its the rate multimplied by the distance moved. Because of the long loop, it doesn't extend much. And when used with light primary spring, it gets little assistance.

Hard to believe it is 174 lbf/in spring

On springs that I have spring rates from the manufacturers, my calcs based on the measuremens are in the ballpark - often very close.
So I have no reason to suspect these are far off.

As mentioned above, the difference in force between secondary and primary springs is not as great as the difference in spring rates appears.
For example, here's a pair from a semi-generic A1 Cardone rebuild. Who knows what the original application was.
Primary spring 8 lbs/in, 0.72" long
Secondary spring 45 lbs/in, .92 in long.

When the springs are installed, they are stretch to approximately .79"
So here's the force restraining the weight (ignoring the mounting angle which changes as the weights swing out)
Distance - Force Primary - Force Secondary
0.79" - 0.56 lbs - 0 lbs
0.82" - 0.80 lbs -
0.86" - 1.1 lbs -
0.89" - 1.4 lbs
0.95" - 1.8 lbs - 1.4 lbs
1.00" - 2.2 lbs - 3.6 lbs
1.05" - 2.6 lbs - 5.7 lbs


All this only goes so far. What we really want to know is what happens when we spin the distributor up!
But it does save some time when looking at which spring is most likely to cause the change in rate or force wanted.

I guess your confusing me with calculation versus a measured spring rate.

You state the long spring is rated at 175 lbs per inch. I really doubt you could hang a 175 lb weight on it and not have it come apart. This is in the range of Valve springs.

The spring is slotted to allow the lighter spring to control low rpm advance. Higher rpm with greater centrifugal force from the weight and a slower rise of advance required to get to total is where the heavy spring comes in.

I never measured them but I do have a distributor scale for point setting, and an old larger scale for heavier objects so I guess I will do a pull test to see the rating.

Are you sure your not missing a decimal point and it is 17.4lbfs/in. The light spring is only 1-2 lbf/in.

Maybe its the way I wrote the posts. It may take a few posts to straighten out.

The dimensions of the springs were used to calculate the spring rates. That's where all of the spring rates posted come from. I do have a few springs with rates from the manufacturer but did not post those. But they back up the general accuracy of the calculated rates.

In the post immediately above, the numbers in the two right hand columns represent spring force. Pounds force.
This is the force of each spring pulling on the weight.

With the wieghts engage into the advance slots, the primary spring is slightly stretched.
So it provides a restraining force on the wieght.
That force(red arrow) is the spring rate multiplied by distance stretched.
.79"-.72" = 0.07" stretched
8 lbs/in x .07" = .56 lbs force
The secondary spring is free to move, so it applies no force.