dual point distributor

-
furydan

furydan

not so junior member
Joined
Sep 19, 2006
Messages
356
Reaction score
2
Location
east of cincinnati, ohio
So I have this dual point dist. from my 65 formula s that shuts off the motor as soon as I hook any vacumm to it. It has been rebuilt and the vac diaphram is in good shape. I even made sure it has the spring in the vac housing. what is going on? I have since switched to electronic ignition, but I have another 65 that I was thinking of putting this in. Anybody have experience with these things?
Dan
 
Sounds like the ground wire between the 2 plates are broken and your points lose ground when the vacuum pulls the plate. I believe it is called the breaker plate but not sure.
 
chryslerfat said:
Sounds like the ground wire between the 2 plates are broken and your points lose ground when the vacuum pulls the plate. I believe it is called the breaker plate but not sure.
Click to expand...
X2....or the point gap is so far off that when the point plate is rotated by the advance, there's just enough side movement to close the points.
 
I had to re-wire the top of mine about 2 years ago. The points were grounding out completely.

I agree with cudamark, it could also be dwell on one side is set too narow and when RPM's go up enough it causes it to act as grounded.

Check the wire around the breaker plate for cracks and grounds. Use a meter to check to make sure you have continuity and non-continuity. when points opened or closed.

If wiring checks out, Try getting it to run/vac/rev with just one set of points first. I usually take a paper match stick, or a piece of a match-book and place between the set of points I'm not working to. Adjust one-side and then the other. I like to get them to exactly 30 on each side. Then when combined, total dwell should bump up to about 38.
 
chewy said:
I had to re-wire the top of mine about 2 years ago. The points were grounding out completely.

I agree with cudamark, it could also be dwell on one side is set too narow and when RPM's go up enough it causes it to act as grounded.

Check the wire around the breaker plate for cracks and grounds. Use a meter to check to make sure you have continuity and non-continuity. when points opened or closed.

If wiring checks out, Try getting it to run/vac/rev with just one set of points first. I usually take a paper match stick, or a piece of a match-book and place between the set of points I'm not working to. Adjust one-side and then the other. I like to get them to exactly 30 on each side. Then when combined, total dwell should bump up to about 38.
Click to expand...
Chewy,
Do you do that while the car is running? blocking off the 2nd set of points i mean. The car runs until i apply vac. to it. Then it just shuts off.. I dont really get the point of the dual point ignition. Is electronic ign better? I would assume so. I do like have the original dist that came with the S car. I looked at the wires last night and saw very good tight connections and no corrosion or dirt...I spun it and watched the points and one would close just as the other would open, but thet were never both open at the same time. Does that mean anything?...I didn't put a guage on them to measure the gap...I'll do that tonight.
 
Take a close pic from the top of the breaker plate and post it. Maybe we can see something with it then.
 
furydan said:
Chewy,
Do you do that while the car is running? blocking off the 2nd set of points i mean. The car runs until i apply vac. to it. Then it just shuts off.. I dont really get the point of the dual point ignition. Is electronic ign better? I would assume so. I do like have the original dist that came with the S car. I looked at the wires last night and saw very good tight connections and no corrosion or dirt...I spun it and watched the points and one would close just as the other would open, but thet were never both open at the same time. Does that mean anything?...I didn't put a guage on them to measure the gap...I'll do that tonight.
Click to expand...

You block one side when the engine isnt running. Have to have cap off. If you have one set blocked off, and the vacuum still kills the car, It really sounds like a wire short within the distributor.g

Vacuum advance moves the breaker plate, which if you have an intermittet short, when it moves, it could either be breaking a connection, or shorting a connection.

Dual Point Vs Electronic ignition is a debate that has pro's and con's on both sides. Personally, I like the way the dual point runs better. ONce dialed in, point adjustment for me was 5 years in-between.

Initial setting, .017 or .018, but still have to dial in the dwell.
 
furydan said:
Chewy,
Do you do that while the car is running? blocking off the 2nd set of points i mean. The car runs until i apply vac. to it. Then it just shuts off.. I dont really get the point of the dual point ignition. Is electronic ign better? I would assume so. I do like have the original dist that came with the S car. I looked at the wires last night and saw very good tight connections and no corrosion or dirt...I spun it and watched the points and one would close just as the other would open, but thet were never both open at the same time. Does that mean anything?...I didn't put a guage on them to measure the gap...I'll do that tonight.
Click to expand...
If you know someone or a shop that has an old distributor machine, that's the easiest way to get it adjusted. The opening and closing of the points should overlap....before the first set closes, the 2nd set should open. You can check the dwell on each while the engine is running by putting a piece of thick paper between each set, one at a time, and adjust as necessary. Then check the combined dwell reading and compare it to the factory specs.
 
furydan said:
.. I dont really get the point of the dual point ignition. Is electronic ign better?
Click to expand...

Several things.

The Autolite/ Prestolite dists normally had better bushing life than the aluminum Mopar dists, and I believe the breaker plate rotates on a bearing instead of "sliding" like a Mopar

In other words, better build quality, and usually, better high RPM operation

So far as dual points, they were used to increase "dwell time" --the time that the points are closed-- which helps make a little hotter spark.

You cannot just simply increase on single points because as the points gap close up (to create more dwell) they CAN "go shut" at certain RPM, but because they don't open as far, they will burn out faster. Think of it as the points are "jumping" open at wider gaps

Electronic ignition is of course generally better for reliability, but "back then" there were some awesome work arounds for hotter spark. The big huge rectangular Mallory coil comes to mind. Stuff like "duo coil" (can't remember the spelling) where the system used two coils to fire alternate cylinders. This allowed each coil to generate more spark.

Mallory used to make a real oddball called "rev-pol" which used a special coil.

You'll notice that none of this stuff is around, much, anymore.
 
67Dart273 said:
The big huge rectangular Mallory coil comes to mind. You'll notice that none of this stuff is around, much, anymore.
Click to expand...

I used to run one of those with my 273 dual point & my Mallory dual point. I'd almost forgot about it! I bet it's still around here somewhere...
 
So I was wondering, maybe I have the wrong cap for this distributor? There is a specific cap for the dual point, am I right?
 
Try to post a pic from the top with the cap off so we can see what we are dealing with because I still believe the trouble is a broken wire between the two plates causing it to lose ground when the advance is pulled.
 
chryslerfat said:
Try to post a pic from the top with the cap off so we can see what we are dealing with because I still believe the trouble is a broken wire between the two plates causing it to lose ground when the advance is pulled.
Click to expand...

I tend to agree. I pulled one of those distributors off of a car in 1975 & the ground wire between the two plates was in poor shape even way back then. Don't know what the mileage was on the car but I'd imagine most of what you find now days has more.
 
You must log in or register to reply here.
-

Back
Top