123 Ignition Retrofit for 4 Cam Distributors

[Bill Sargent]

Last year, after conversations with Jacques, I decided to try and design a no mods kit to retrofit 123 Ignition electronics into an original 4 cam distributor body. Along the way I ended up making a CAD model of the distributor body so Jacques can machine the distributor bodies he has casted.

Distributor body CAD screen shot

CAD was the only way to do the design as space is tight in the original distributor body to fit all the parts. After many design iterations I determined that the only solution was a new shaft, magnet plate and internal electronics mount ring.

Prototype parts were 3D printed using the SLA procrss where a laser solidifies a resin. This process was needed for the required dimensional accuracy. The prototype parts were then assembled, along with 123 electronics, into an original distributor body and tested on Jacques distributor test machine. All worked as it should.

The next step was to make a small run of production parts. The new shaft and magnet plate are shown below.

Retrofit parts

Disassembly of the original distributor is the first step. Assembly of the retrofit kit is then fairly straightforward as shown in the photos below.

Bare distributor body with condenser wire taped out of the way

Electronics mount ring installed. Radial Position is located by a groove present in the internal side of the distributor body. Vertical position is set by a step present in the distributor body.

The lower shaft and Electronics plate are then installed followed by the magnet plate - which is held in place by a roll pin.

The shaft assembly is then lowered into position and the electronics plate is screwed down.

Finished retrofit. Original cap and rotor are used.

As of this morning I have proof of concept . I set the 123 retrofit distributor up last night and then started the car this morning. Everything worked perfectly.

The motor I am testing on is a 587/1 rebuilt to 904 specs. Ignition system prior to the 123 retrofit consisted of 2 original distributors with mechanical advance and Pertronix 1 in place of points. The distributors are run in a master/slave arrangement with two Winterburn CD boxes. The motor ran well with this system and never fouls plugs.

After calibrating the 123 electronics as they recommend I started the car and it started easily. Timing was about 3 to 4 degrees out but quickly fixed with a timing light.

Observations:

• There is far less jitter in the timing mark - rock steady. This is compared to a stock mechanical advance distributor with a Pertronix 1 with the mechanical advance functioning properly.

• Upon startup it idled steady at 800 rpm. With the stock distributor it would idle at 600 until warm. When warm it idled at 1000 and came down to that rpm smoothly. No slowly wandering down.

• The engine seemed more responsive and seemed to have more torque at low rpm’s - probably due to the stock distributor advance curve not following the stock curve - ie, not enough advance early enough.

All in all I am very happy. Now I need to put a few more miles on the system to make sure it is reliable before offering retrofit kits for sale.

One thing I would recommend potential buyers consider is to retrofit only 1 distributor and use it in combination with the Winterburn twin CD master/slave set up. That way only 1 distributor needs conversion, there is redundancy in being able to quickly rewire to reverse the master/slave relationship and the system eliminates plug fouling and other problems.

I mounted my CD boxes inside the car on the rear firewall which gives me very short wire runs.

CD box placement

But this is not practical for most people. And there is not a lot of room in the engine compartment. I corresponded with Fred Winterburn and he confirmed that placing the CD boxes in the passenger footwell would work fine as long as 2 of the wires were separated for the run back to the engine compartment.

If anyone is interested in future purchase of a retrofit kit please let me know offline and I will keep you posted. Please feel free to email me questions.

[Martin Benade]

Bill, you sure are cooking up some beautiful four-cam products, done very beautifully.

[Jacques Lefriant]

Hi Bill
since the 123 system does not position the rotor as a function of the curve to the same alignment to the cap posts and since the original rotors are quite pricey maybe we should research an alternative(less expensive) rotor with a wider blade.
j

[Martin Benade]

Jacques, that’s a great idea. With your not so American name, can we still call this Yankee ingenuity?

[Bill Sargent]

Hi Jacques - changing the rotor mount on the upper shaft would not be difficult. The only constraint would be finding a rotor of the right height to place the blade and coil contact at the right level within the assembly. I did not model the cap and rotor since I was designing to use the original cap and rotor.

Below is a cross section from the CAD model showing the main components. Red is the lower shaft, yellow is the upper shaft and magnet plate, green is the distributor body, blue is the electronics mount ring and magenta is the electronics board. Note that the electronics are on 2 boards, the main board sits horizontal while a small board hangs down off the main board.

CAD X section

X section 2

[Jacques Lefriant]

Hi Bill
I really like using the original cap and either the old bodies or new bodies but i think we could explore a different rotor.
since it is hidden and the original resistor one is not available.
j

[Harlan Halsey]

Bill Doyle used to replace the resistor with a solid conductor in the original rotors. I suggest that the new rotor idea is a good one, but I would look for a non-resister one.

[Jacques Lefriant]

Hi Harlan you can always remove the resistor and replace with a rod.
j

[Harlan Halsey]

Of course, that is what Doyle did, and I do.

[Jacques Lefriant]

hi Harlan
what i meant that a resistor one would be what i was sourcing and you would have the option.
j

[Martin Benade]

As long as it’s not failed, it’s preferable to have a resistor? Only for radio noise suppression?

[Bill Sargent]

Thought I would post an update now that I have a couple of hundred miles in the 123 Ignition retrofit. Everything is still working perfectly. I pulled the distributor yesterday to check inside and there were no problems. I specifically checked to see if oil was migrating up into the distributor and there was none. The distributor is now reinstalled and timing reset.

I checked for oil migration into the distributor since, unlike 356 pushrod motors, the distributor drive housing on a 4 cam motor is slightly pressurized since it is fed with oil from the motor. Speedco makes a replica 4 cam distributor with 123 Ignition electronics that uses the same 10mm diameter shaft as the regular 123 Ignition distributors. The shaft in the 123 and Speedco distributors lack the spiral groove that acts to push oil migrating up back down and some users of the Speedco reproduction distributors have reported oil migration up into the distributor body.

Both the 356 and 4 cam distributor shafts have the anti oil migration spiral groove. These shafts are also 12.45mm diameter vs the 10mm shaft in the 123 distributor. See photo below.