Modern points plate shortcomings explained

[ctlikon0712]

I was reading through the sticky's and was checking out Pluck first entry. I went to the Nurex website and was reading their tech articles. I have always read members advice not to use the newer type points and condenser plates but never really had it explained to me. This Tech article does a fantastic job. I thought I'd share it here.

http://www.nurex.com/archive.asp


IGNITION FAILURE & FAULTS
B.W. Abrams Distributor Upper Plate with Modern Points

The "distributor upper plate with modern points and condenser" is in use by many Model A owners. A basic design and construction fault has been discovered. Tests on both cars and a distributor stand were made on ten different units from five suppliers.
The problems were initially revealed during timing tests of four cars at two 'A' Meets. The Ignition Timing Kit described in the Jan/Feb 1992 MODEL A TRADER, pgs 2-3, uncovered the faults and causes of the malperformance.

The specific ignition performance symptom observed was:

• The spark control full range could not be used and
• The engine stopped when the control was moved beyond some setting

The owners thought the problem was just mislocation of the timing gear dimple, piston # 1 Top Dead Center.
The malfunction was instead found to be improper location of the point assembly on the movable distributor plate. The rubbing/ actuator block was thus changed with respect to the cam-rotor slot.
The relation between the rotor extended brass conductor and distributor fixed button conductor was consequently not proper at the extremes of the movable plate rotation. At some extreme (full advance or retard), the two conductors were so separated that the spark could not jump the large air gap. The spark failed - the engine catastrophically stopped!
The above observations were strikingly visible using the cut-out cap, timing light, and procedures referenced in the Ignition Timing Kit described in the Jan/Feb 1992 MODEL A TRADER article.
The original Ford point plate, points, cam, rotor, and distributor were properly designed to work on the distributor 20° advance-retard plate rotation. The distributor button is a nominal 5 degree width additionally. The movable point arm rubbing block was positioned, relative to the rotor slot on the cam, so that a portion of the rotor conductor was always opposite the distributor button throughout the advance to retard extremes. This provides the smallest spark air gap. Figure 1A shows the proper conductor relations.
Supplier chosen "modern point assembly" does not duplicate the pivot and contact points relation of the Ford original design. This is not a prime requirement but it does also affect the point dwell time (the time the points are closed). The fabricators have chosen to use some existing holes in the standard point plate, presumably for ease of modification.
The existing plate hole chosen for the assembly pivot location changed the rubbing block position so that the cam slot improperly locates the rotor brass conductor relative to the cam high point for point opening and subsequent spark.
On some assemblies tested, this caused the rotor-distributor contacts to be separated by as much as 3/8 to 1/2 inch in the full retard position (Figure 1B). The spark could not always jump this large air gap. The engine then stopped!

There were other aspects to these "modern point assemblies." The plate hole chosen for the point pivot was unmodified or drastically modified. The point assembly consequently was not flat on the plate or had no fixed position on the plate. The assembly mounting/ hold-down screws also were involved in the point opening adjustment so adjustment was very difficult.
One possible "fix" was drilling the pivot point hole for clearance and adding a chamfer to both positively locate the pivot and allow the point assembly to be flat on the movable plate. It also separated the opening adjustment from the screw hold down functions. On plates which were drastically modified, neither of the above changes were possible.
A point plate modification and assembly that attempted to solve some of the foregoing observations was described in an article by Paul N. Sund, Pacific Grove, CA, in The Restorer - March/April 1990, pgs 19-21.
Visual examination of one of these units appeared to be a proper alteration. It was not tested on the Test Stand shown in Figure 3 or on a car.
A simple "fix" for those owners who have already installed a "modern plate" and want to make a simple and inexpensive correction is shown in Figure 2.

It consists of an extension to the rotor brass conductor. This extended tip is installed on the rotor and can be located for either retard or advance correction. Installation consists of drilling a hole in the rotor contact and bolting the extender in place.

To determine the need and extender position:

1. 1) Temporarily replace the distributor cap with the cut-out of the Timing Kit
   2) Idle the engine
   3) Advance and retard the spark timing-full ranges
   4) Observe the relation between the rotor tip and fixed distributor button

The extender should be mounted on the rotor so there is always overlap of the conductors throughout the full range of advance and retard spark control.
Many tests were made on "original standard point plates", "modern point plates", and distributor cams using the Test Stand of Figure 3.

The findings of those tests are to be published in several forthcoming MODEL A TRADER articles. The tests included performance as a function of point opening, spark timing, cam dwell time, production cams, and rotor contact-distributor contact relations.
The Rotor Tip Extender and Timing Crankshaft Degree Kit were designed for and are being produced by Nu-Rex, Box 9332, Akron, OH 44305. The items will be available from leading Model A parts suppliers. For additional information, call (216) 784-5334 between 4 P.M. and 10 P.M.

[Tom Wesenberg]

Thanks for all the information Craig.

So, what it boils down to is there is now a fix for the non-fix originally installed.

[ctlikon0712]

Right Tom , and in a subsequent article titled
“A NEW DISTRIBUTOR UPPER PLATE ASSEMBLY”
They now say a proper plate is manufactured......
Which is great but I'll stick to my original one.

[Richard Wilson]

Thanks Craig. On the other hand, I have run a modern upper plate in all of my tour cars for the last twenty years with no problem. Probably drove over 10,000 miles. I have found that the modern points work better with a .015 - .016 gap instead of the .018 - .022 of the old style points. I set the timing by the book and then fine tune it by going for a short drive in the car, stopping after about a mile, slightly adjust the distributor, drive the car for about a mile, stop, adjust distributor, etc. until I find the "sweet spot" for that particular car. Once set this way, I seldom have to recheck the points or timing for several years.

[ctlikon0712]

Good to know and thanks for sharing Richard.

[lindy williams]

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The article cited in Model A Trader is over 20 years old. Are we sure these problems haven't been corrected since then?

[Tom Wesenberg]

Richard, when you close the gap down you increase the dwell time, and also change the relationship of the spark timing and position of the rotor tip to the cap terminals.

[Richard Wilson]

Originally Posted by Timothy Kelly

Richard:

What prompted you to replace the original point system with the modern upper plate?

Was there a particular problem you were looking to solve?

Timothy

Way back when I changed over to using the modern style points and condenser we were having a very bad problem with the condenser that all the Model A parts dealers were selling for the original distributor set up. This condenser was made in India and would get hot and short out easily. With the condenser in the original location near the exhaust manifold you might get an hours drive time in the summer and the condenser would go bad. Now that they have better quality condensers for the original systems I don't really have a preference of one over the other. I am down to only two Model A's now. One has the modern plate and the other has the original ignition system. Both work fine.

[Richard Wilson]

Originally Posted by Tom Wesenberg

Richard, when you close the gap down you increase the dwell time, and also change the relationship of the spark timing and position of the rotor tip to the cap terminals.

Yes Tom you are right. Most points gaps for modern cars are set closer than the old gaps from the 30's and 40's. I think the modern style points are designed for the closer gap. Changing the timing is really not a problem in my Model A's. That is why I take the extra time to adjust the distributor while driving the car for best performance.

[hardtimes]

Originally Posted by lindy williams

The article cited in Model A Trader is over 20 years old. Are we sure these problems haven't been corrected since then?

X2...
Didn't have to hit those boys over the head twice for them to get after it,eh!
I have the newer version 'upper plate/condensor' in use for 6 yrs now and nary a miss and no adjustment since first installed. To each their own !

[JBill]

I've used the modern set up in both my cars, one for more than 20 years, with no problems whatsoever.

[john in illinois]

I use Accel USA Ford V8 points (modern points) and never have a problem. They hardly wear or need adjustment.

John

[BILL WILLIAMSON]

On Minerva, I used the modern upper plate with the extended pig tail wire & NEVER had a problem. That SAME distributor is going into Vermin tomorrow! Bill W.

[Mitch//pa]

i see problems with the modern lower plate with the brass contact instead of the pig tail

[marc hildebrant]

Interesting article and it continues to make sense to me to keep the Model A as original as possible.

Marc

[BILL WILLIAMSON]

Originally Posted by Mitch//pa

i see problems with the modern lower plate with the brass contact instead of the pig tail

RIGHT, Mitch, I have a wireless lower plate, but never used it. I COULD modify/improve it, but what's to be gained over using a longer pig tail wire?
I compared my stock dist with the other one with a modern upper plate. The positioning of the rubbing block, in relationship to the plate is identical to stock & WOULDN'T affect the position of the rotor tip to the contacts in the distributor body, (cap). If some of the previous dialogues are correct, then someone must have manufactured some plates with the points mounted cock-eyed!
I use the modern points as they're less prone to pitting & causing mis-firing. Some have said they're too hard to adjust???? I have no problem with that.
Yes someone will say, "Even used original will last forever, dang, I've run the same old points I picked up at a swap meet, 27 years ago"!! PSHAW, get real, points wear/burn out in the REAL world! Bill W.

[Tom Wesenberg]

Bill, I'll let you know when my original points wear out.........if I'm still around.

[Flathead]

I'm thinking the originals had some of that very rare ingredient known as QUALITY.