Distributor Points Plate Return Spring Eccentric Post

During our experimentation of the 1966-67 Beetle Distributor (113-905-205K) and other -205 Distributors, we switched from using Original German Bosch Vacuum Canisters to a Reproduction Vacuum Canister to test its viability. Please see this Article.

What we found was that the Reproduction Vac Canister would not allow the 1966-67, -205K Distributor to meet Bosch critical specification requirements. We tested the Reproduction Vac Can on other Distributors of the -205 denomination and found a similar lack of performance. I refer to the 1967 Distributor because we are most focused upon the Distributor which came on the USA Deluxe 1967 Beetles. Please view this YouTube Video.

Perhaps the composition of the Diaphragm material of this Reproduction Canister does not allow the required Vacuum to operate the Points Plate advance and retardation? Since there was/is no manner for testing that material, we looked elsewhere for answers.

Very naturally, we examined the Return Springs of several -205K, M and T Distributors. We could see that they were not “equal” in Spring Turns (and perhaps in terms of wire thicknesses, etc.). In other words, by comparing Original Springs on Original Distributors, we could determine that there are Proprietary Springs for different Distributors in the -205 Series. Switching Springs would change not only the Specifications of a Distributor, it would/could change the Operation of that Distributor.

For example, the proprietary Return Spring for the -205M Distributor is: VW Part Number 113-905-237A. I do not have Part Numbers for others of the -205 series
Distributors.

I produced a quantity of loose Distributor Return Springs from my stockpile of Distributor parts. Still using the Reproduction Vacuum Canister, we substituted unknown Return Springs and were able to achieve differing, and even promising results, depending upon which Spring we substituted. We were onto something essential, for sure.

However—this was, at best, “blind” experimentation. We could find no Bosch guidance to which Springs could be substituted in order to achieve proper operational results.

We examined the rest of the Return Spring “train”. The led us to, perhaps, the last piece in this puzzle—an examination of the fixed Post onto which the Return Spring is looped. This Post is interesting!

It is not a simple Post—it is formed so that the part upon which the Return Spring is attached is not centered. In other words, the Post is an Eccentric Cam. Examination of the bottom side of a Distributor Housing reveals that the Post is an addition to the Housing—not a cast part of the Housing itself.

More research, with help from the larger VW Community, led to a Samba Forum where a short series of entries revealed that the Eccentric Post can be adjusted with the purpose of changing tension upon the Return Spring.

In this Forum, are depictions of at least two Tools created by Bosch for the purpose of adjusting the Eccentric Post to increase or to reduce tension upon the Return Spring.

One Tool is advertised in Swedish (February, 1961). I translate below:

“Special Tool for the Vacuum Controlled Tooth (sic) Distributor on the Volkswagen

In the 2/1961 issue of the Bosch Magazine, we had a description of the new Tooth (sic) Distributor on the Volkswagen where it was mentioned that it has imaged (the) Bosch Tool EF2V 28 with which you adjust the gear adjustment by turning the eccentric bolt where the return spring is suspended. The price for EF2V 28 is Nok 5:75 net.”

A second photo also stems from the Samba Forum:

I posted a Wanted Ad on thesamba.com. Shortly, this was answered by a brother in the VW Community who gave me the Bosch Part Number for (one iteration of) the Adjusting Tool as well as other relevant information. (Bosch Part #EFZV 31)

I was elated.

Now, to locate one of these Tools for further experimentation purposes. One very promising lead ended abruptly–???

Now, it seemed that I was on my own.

Knowing that there are fabricators who use a process known as “electrical discharge machining”, I approached a local, well-known and established shop with this capability. Unfortunately, for me, I was at the bottom of the list of huge contracts with my very small venture. I located a second shop which could work me into its busy schedule. I sat with the owner to discuss what I needed. I took a Distributor, stripped of everything but the Housing and the Eccentric Post. In addition, I took a Post which I had carefully removed from a Distributor Housing. I also took a functioning Distributor.

To remove the Post, I used a drill with a small bit to cut away the bradded end of the Post, (exterior bottom of the Housing) thus releasing it where it extended through the Housing. This released a tiny steel Washer which had reinforced the bradded portion of the steel Post, as well as an additional tiny “wave” Washer between the initial Washer and the Housing.

Once the Fabricator understood my request, I sent him photos of the Tool as well as a depiction of a Tool being used to adjust the Eccentric Post.

The greatest challenge to fabricating this Tool lay in the configuration of the Eccentric Post itself.

First—the Post is placed extremely close to the edge of the Distributor Housing.

Next lay the challenge of the “face” of the top of the Post where the Adjustment Tool would fit. The “face” is not flat! Were it flat, the job would have been simple, in the scheme of things. However, for reasons of its own, Bosch created a very slightly convex face. This means that the Tool must have a concave surface to fit tightly against the convex face of the Post.

OR—for example, had Bosch created the top of the Post in a hex shape, a tiny hex wrench could be used to adjust the Post.

In about a week, I checked to see if there were any questions. In another week, I received a call telling me to come for my Tool! T-Day had arrived!

I hurried to the shop with a Bosch Distributor (ZV/JU4R3) in hand. I wanted to test the Tool on a vintage “virgin” (untouched) Distributor.

While the fabricator and the office manager watched, I applied the Tool and was able to adjust the Eccentric Post.

I am contemplating some minor adjustments to the Tool which will, I believe, make it better. That’s on the docket for a later date.

The proximate step will be to test a known -205K Distributor, with the Reproduction Vacuum Canister installed, by adjusting the Return Spring Tension—using the New Tool. I will present details following tests performed using the Sun Distributor Testing Station.

Notes:

Many thanks go to Kurt Troeger and to Adam Troeger for expending a lot of time and energy in setting up for the experiments with Distributors and Canisters! What is shown on the YouTube video is only a small part of the actual testing.

Adam Troeger, Thank You! for having restored the Sun Distributor Testing Station to superb operational condition.

To my daughter, Janeva Sulman, I extend thanks for coming to our assistance with the videoing. She is a busy person and actually returned home from an event in which she was participating—just to help us.

A thank you to our son, Kevin, who came to my aid when I struggled with a photo. Then, he gave welcomed advice, from his engineering background, about the subject at hand.

To David Brown—again our gratitude for having provided the Sun Distributor Testing Station!

And—to those of the VW Community who provided information about the Bosch Adjustment Tool and other pertinent information—I thank you.