Ford Duraspark Recurve
The Ford Duraspark distributor is a great alternative to aftermarket distributors, and for a fraction of the cost. As of writing this article you can find them for about $55.00 if you have a core, if you do not have a core the core charge is usually around $20 depending on which distributor you get.
Spring kits are available (and not very expensive) to fine tune when your full advance is “all in”. One example kit is the Mr. Gasket 925D which can be ordered at many online retailers, including Summit and Jegs for about $4. We will discuss this later in the article.
I am going to show you how I recuved my duraspark distributor to suit my needs. I have never done this before now and the recurving process was pretty simple once you understand what needs to be done. I actually recurved mine while the distributor was installed in the car, it was that simple.
Here is the distributor with the cap, spacer and rotor removed so we can get to work.
Remove the two screws that hold the vacuum advance pot to the main body.
Remove the small C clip that holds the vacuum advance arm to the breaker plate. Be careful not to lose this clip!
Now lets remove the reluctor from the distributor shaft. First we need to mark the reluctor with a pen or marker because there are two positions that it can be installed, and you need to be sure you install back where it was.
Notice the tiny roll pin between the reluctor and the shaft, be cautious when prying the reluctor off so you do not lose the pin! You do not need to try and remove the roll pin first, it will come out when you pry off the reluctor from the shaft.
Now, take two large screwdrivers and gently pry upward on the reluctor from both sides. You do not want to pry on the teeth of the reluctor, place the screwdrivers under the reluctor so you dont break anything. It should slide off the shaft pretty easily and catch the roll pin when it comes off.
Remove the two screws that hold the breaker plate to the main body. You will need to rotate the pickup to access the other screw.
Now you can see which advance slot is being used. This will tell you how much advance your distributor is providing. You can see in mine it had a 21L and 16L. The 16L is the side being used currently. You multiply this number by 2 to get the total number of degrees it is advancing. Since mine is using the 16L, it is advancing my engine 32* on top of what my initial timing is.
I want to limit the advance to be 20* for my application. There are several ways to accomplish this. One way is to get lucky and find a different breaker plate that has 10L. They do exist. I tried several distributors and the lowest I found was a 13L, which is still to much for me. So what many do, including me now, is just weld up the slot a little bit and grind it down smooth so that it becomes the equivalent of a 10L.
First we have to get the advance slot off the shaft so we can work on it. Detach each of the two springs from the advance arm.
In order to pull this off the shaft you will need to remove a small retaining clip that locks it in place. It can be hard to see the spring clip in there and took me a while to figure this one out. With a good flashlight you will see 2 small tangs sticking up. These need to be spread apart (not squeezed together) to remove it. The wife comes in handy here. I had her lightly apply upward pressure on the shaft while I used a small pair of needle nose pliers to spread the tangs apart and voila! its off. Here is a couple of pics helping explain this.
**NOTE** If your advance slot happens to have the correct number you need on the other side, you can simply lift up and rotate the slot around and use the one you want. Keep in mind if you do that though you would would need to pull and re-install your distributor because your timing would be 180* off.
To figure out what the slot width should be for a given advance figure, simply multiply the number of desired centrifugal degrees by .013″ then add .150″ to account for the width of the stop pin. I wanted 20* for my application so that would be 20 x .013 = 0.26 then add .150 = .410″. So to make my 16L slot to a 10L, we need to weld it up a tad so that the gap is .410″ vs. the .566″ that it is now.
Here is the finished grinded product!
For reference here is a little chart to give you slot widths for various degrees of advance.
- 8L slot = 16 degrees centrifugal advance = .358″
- 9L slot = 18 degrees centrifugal advance = .384″
- 10L slot = 20 degrees centrifugal advance = .410″
- 11L slot = 22 degrees centrifugal advance = .436″
- 12L slot = 24 degrees centrifugal advance = .462″
- 13L slot = 26 degrees centrifugal advance = .488″
- 14L slot = 28 degrees centrifugal advance = .514″
Mine being measured after it was grinded down
Now before we put it all back together it is a good time to check and/or replace your springs. These 2 small springs are dictating how soon all of your advance comes in. For my performance engine I want my advance to be “all in” before 3000 RPM. This stock distributor will have the advance “all in” later than that so we can change to a lighter set of springs to achieve this. Like we mentioned earlier you can use Mr. Gasket 925D which is a set of light springs that will bring your advance in between 2000 and 2800 RPM.
Now lets put it all back together. Install the breaker plate, set the wiring harness in place and install the two screws previously removed.
Place the reluctor back on the shaft using the marks we made before so it goes back in the same place. The slots on the reluctor and the shaft make a round hole for the roll pin to go in once you have it aligned correctly. Use a deep socket such as a spark plug socket and gently drive the reluctor back into place. Take it easy, if its correct you should not have to force it on there. I was able to slide mine on without using any tools to drive it down. Once you have it fully seated place the roll pin into place (carefully) lightly tap it with a hammer and a small punch to drive it home.
Install the vacuum advance canister and reattach the arm and the C clip.
Put it all back together and fire that engine up and check your timing with a timing light. Check your initial timing and note what it is. Slowly rev the engine and watch (or have someone watch) your RPM’s while you take note of when your timing stops advancing so you will know at what RPM your timing is “All In”. Once your timing is all in, note the timing mark on your pointer to determine what your total advance is. For example after I did this modification to mine, my initial timing (at idle) was 14*. This of course is with the vacuum advance disconnected and plugged off using a golf tee in the vacuum line. My timing was all in around 2800 RPM, and the total timing was 34* at said 2800 RPM (or any RPM above that). This tells me my distributor is advancing 20* (34-14), exactly what I was shooting for!