Jul 7

Testing a Royale Dual Point Distributor on a Machine

As we get my car ready for Pebble next month one of the things we wanted to do was get the distributor on to the machine and synchronize the dual points. In this topic I'm going to go through the process with pictures and video.

The machine in the shop is a rare distributor tester. Made by Electro Products. The back shelf is designed to carry 4 of their other automotive testers. They made 10 different pieces of test equipment.

You more typically see Sun testers or once in a while an Allen.

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Jul 7, 2026

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Replies (32)

· Jul 7

Before doing anything you need the specs on the distributor. For most common applications the manual with the machine probable has the specs. For our Royale DELCO-REMY TYPES 660 AND 662 Distributor the only place you will find that information is in the 1934 National Data Service Manual. None of the other manuals have the information. I put a copy in the library. Thanks to Ed Minnie for that information.

DESCRIPTION:—This type distributor is designed for use on eight cylinder engines. It is fitted with two
sets of contacts operating on a four sided cam. The contacts open alternately at intervals of 45 degrees
corresponding to the 90 degree firing interval of the engines on which it is used. Both sets of contacts
are connected in parallel in the primary circuit of the ignition coil. One condenser mounted on the side
of the distributor shaft housing is used for both contacts. The breaker arms are designed so that one set
of contacts closes immediately after the other set opens which provides a longer period of time for
building up the coil primary current. Both sets of contacts must open to secure a spark at the plugs.
CONTACT ADJUSTMENT:—Contacts should be set at .022 inch and must be held within limits

of .018-.024 inch. Set contact gap by loosening the lock screw on the stationary contact mounting plate
(directly behind the breaker arm) and turning the eccentric adjusting screw. The breaker gap must be
measured with the breaker on the lobe of the cam. Tighten the lock screw. Contacts can be resurfaced
when necessary with a fine flat contact file or on a medium hard oilstone. The contact gap must be set
before the contacts are synchronized and should be checked after the synchronization has been
completed. If synchronization has affected the gap sufficiently to throw it outside the limits of .018-.024
inch, reset the gap at .022 inch and repeat the synchronization.

· Jul 7

Once you have the specs you need to figure out the rotation of the distributor. Many distributors will have a mark on it. Our does and it is clockwise. If not you need to look it up somewhere.

(edited)

· Jul 7

Once mounted on the machine the first thing we did was gap the points to .022.

· Jul 7

Great description of the process.

· Jul 7

I tried to get good video and ask a million questions.

· Jul 7

Yes. Excellent topic!

· Jul 7

With a dual point system you need to determine which is the primary and which is the secondary. The primary is fixed in place and the secondary will have two set screws allowing for movement to synchronize with the primary points.

· Jul 7

Once mounted the distributor machine has a electric motor which will turn the shaft emulating the unit being installed in the car. The speed of the motor can be adjusted. We did our tests at idle or a low rpm. I'm assuming you can crank it up and see if you get float or breakdown at higher RPM but this wasn't something we did.

· Jul 7

Am I missing something? Seems to me that the coil saturation time is determined by the number of cylinders it is firing (and engine speed) and not by the number of contact sets.

· Jul 7

Keeping in mind I only half understand this stuff. 2 sets of contacts divides everything by 2. Each set of points is now dealing with 4 cylinders.

So twin points allows for longer dwell.

· Jul 7

These single coil, 4 lobe, dual point setups are weird. I have the same setup on my car and after two years of studying it, all I know for sure is that the rotor spins and the engine runs.😀

· Jul 7

I'm just a carpenter, but...I think the advantage of this set up is that each contact set is doing half the work so it doubles the service interval. The contace set is just a switch, in this case they take turns turning the coil on and off. The coil doesn't know how many switches are in the circuit, it only knows how often it has to produce a spark. In theory you could have a seperate contact set for every cylinder, I think.....

· Jul 7

And I know so little I'm not even dangerous! But I think there might be a performance improvement at higher RPM because the points are opening and closing at 1/2 the interval. With the 1/2 an interval you lower the risk of point float which will reduce dwell and cause ignition break up.

· Jul 7

On the subject of point float watch how fast the points open and close at what is a low RPM and then imagine 3k or higher. If that spring starts to fade you can imagine ignition degrading.

· Jul 7

I think there is some truth to that in more modern higher reving engines, but not sure these engines turn fast enough for that to be a factor. I could be wrong. Where's ShawnG, he oughta know!

· Jul 7

100% Shawn will know. @ShawnG you want to weigh in here?

(edited)

· Jul 7

What rpm was the machine turning the distributor? It would probably never turn any more than 1600 rpm or so on that engine anyhow.

· Jul 7

It was rotating on the slow end. Mike said we were emulating idle.

· Jul 7

That’s definitely the case with the single coil/ dual point wired in series systems. They don’t know whether there’s one point set or eight. Dual coils would be a different story.

· Jul 8

lol thanks...

I've always been told that point bounce is really only a problem after about 5000rpm so 2500 distributor rpm.
That's the reason for dual point systems on multi-cylinder engines. It cuts that figure in half again because there's now only four lobes on the cam instead of eight. It also allows for more dwell for more coil saturation and better spark.
That being said, I received a set of points for a Chevrolet 235 I6 that had very weak spring. The engine wouldn't rev past about 2000rpm before the spark became too erratic.
This is why having a distributor synchrograph is important. Mine is an Allen.

(edited)

· Sep 11

Wood, if it has two sets of points and four lobes on an 8-cylinder engine and only one coil, here is the advantage: it provides for longer dwell. (dwell is the degrees of rotation that the points are closed, charging the coil) Longer dwell increases the saturation time of the coil, creating a hotter spark. The two sets of points take turns making and breaking the flow of current to the coil. When one set of points opens, firing the coil, the other set of points can close just a degree or two later and start charging the coil again. If you just had a single set of points on eight lobes, you couldn't close the points that soon after it opens. Because of the physical limitations, they have to open about .018" and then close again to prevent arcing, and that takes a lot more than a couple of degrees of rotation to accomplish.

· Sep 11

Thanks Joel! Excellent explanation. I sort of understood why. On the Royale a lot of guys have swapped in a Cadillac single point distributor to get around the synchronization issue. If you have access to a machine it takes 10 minutes.

· Jul 7

Separating the points out and setting the primary first.

· Jul 7

First try at setting the primary had the strobe walking. The issue ended up being the distributor was not properly mounted in the drive.

· Jul 7

The dial on the strobe rotates. You identify where the flashing red light is and rotate the zero point to that spot. Then you isolate the secondary set of points and in this case put them 45 degrees behind the primary. Counting the degrees on the dial is wasy.

We ended up being 3 degrees advanced, i.e. the secondary was only 42 degrees behind the primary.

The paper might be a bad insulator as it left debris that had to be cleaned.

· Jul 7

In this video Mike adjust the secondary set of points to bring them exactly 45 degrees behind the primary.

· Jul 7

Mike explains what the second set of points being out of synch means to the actual performance of the engine.

· Jul 7

We installed the distributor back in the car and it was running worse than before. When the cap was displaced to remove the distributor, there was a slight tug on the wires which disconnected one of the spark plug connectors. Mike noticed this and when he tugged on the other 2 more disconnected. Happy we figured this out in the garage and not on the side of the road.

· Jul 7

Two final things. My friend George Ktsanes sent me what I consider the bible on point based ignition systems. I'm trying to digest all of it. "Mallory Ignition Course".

Last thing, the "Mike" in the video is Mike Leveillee of KMLifestyle who I consider an electric genius.

https://mykmlifestyle.com/

· Jul 7

Did you do anything with the mechanical advance curve on the distributor machine?

· Jul 8

Yes! Inquiring minds want to know!
If you did , did you need to change the advance springs and where did you find specs and replacements for those.

· Jul 8

This distributor has 2 weights with 2 springs and 2 pins. As the distributor spins faster the weights force the cam to advance the timing. The spec for this distributor is only 8 degrees of advance at full RPM. Unfortunately I was not there when he checked the curve to get a video but it did advance to the 8 degrees when he spun it up. If we put it back on I'll try to do a video.