Hot Rods Mallory dual point distributor - They work very well !

That would make sense. You need as much dwell time as you can get when you try to get a lot of sparks out of one ignition coil - there's not a lot of time between each spark so you better make the most of it! Any 8+ cylinder engine running at relatively high rpm would absolutely have some of that issue (maybe not enough to notice, but spark energy will absolutely be tapering off at high rpm). A 6 would handle it much better, and a 4 even more so, so not as much reason for dual points on those - but I do remember seeing some 1970s Datsun 4 with dual points. I suppose overkill never hurt anything.

 

I’m just wondering,,,,does anyone check the clearance between the distributor and the oil pump drive ?
Mopar uses an intermediate shaft,,,,,but even if it connects directly ,,like a Chevy ,,,,,how many ever check the gap or clearance so it doesn’t bind up ?

I decided to trial fit my new distributor with my intermediate shaft today .
I’m glad I did,,,,,it was a little too tight .
After seating on the block ,,, the unit was not fully down,,,,,and there was no clearance in the unit internally .
After I investigated the issue,,,,,I realized the new intermediate shaft was slightly taller than what I needed .
Or,,,,,the new distributor was slightly longer than what I needed,,,lol .

Anyway,,,it stands to reason that a slight tolerance stack up could happen .
The tang was slightly long on the distributor and bottomed in the shaft ,,,,so I trimmed it back about .070 thousandths .
Everything fit perfectly after that and it is dead on the money now .

It always pays to trial fit assemblies,,,,especially when changing things from original .
I’ve caught several calamities before they have happened in the past ,,,,,and I have even missed some and kicked myself later,,,,lol .

My mistakes always seem to cost me money !

Tommy

 

Very nice work! ^

 

In the case of the Datsun, the second set of points was controlled by a switch on the transmission which activated the second set of points and altered the timing in high gear for emission compliance purposes. Chevy LUV Trucks (Isuzu) had the same set up.

 

Some crazy stuff occurred back then in the name of improving emissions. In the seventies, GM increased the rotor tip gap by .060 for the same reason. This one seems a bit extreme.

 

This is true in most cases but some Mallory's are different. These are the ones with half as many cam lobes (I believe they are called the "Double-Life series). They energize the coil alternately, so each set of points fires half as many times as a regular distributor. Because of this and the fact that longer duration can be achieved on each cycle, they produce a hotter spark These can be use with a regular coil. In some cases Mallory made a special coil to be used with these that had two primary windings and one secondary. Each set of points feeds one primary winding which energizes the primary. Sort of a "Poor man's dual coil". And of course, a dual coil distributor works like two separate ignition systems in one distributor.

It is obvious to me now, but I found out the hard way when I had my Seagrave pumper with the Pierce-Arrow derived V12 and two dual coil dual point distributors, of which one didn't work. I initially tried to get it going using the "extended dwell" theory but soon saw the error of my ways.

Here's one of the special coils :

Notice the three primary terminals. I believe that this was originally a 6 volt unit (they were black; 12 volt units were red) with an auxiliary resistor added for use in a 12 volt system.

 

Yes, that is correct. Dual points allow for more coil saturation time while still maintaining a suitably large point gap so as to provide consistent hi-RPM operation.

 

Just curious as to what ballast resistor to use. I'm running a ZC in my 6 cyl Chev with a 28675 coil. I was using the Mallory 700 resistor but burning the trailing set of points after a while. Primary resistance on the coil is .5 ohms as is the resistor.

 

That' obviously not enough resistance. As a rule if thumb, I like to see no more than 4 amps through the points. Ohm's Law states the Current (amps) = Voltage / Resistance (ohms). If you have a 12 volt system, that means around 3 ohms total resistance. For 6 volts, it would be 1.5 ohms. This is a starting place. I am not familiar with those particular components. Is the coil by any means intended for an electronic ignition?

 

This is the old Mallory box style coil. It is not for electronic ign but I do have an identicle one that is. Different part number and says for electronic on the lable. My thought is that the Mallory resistor was meant to be used in addition to the original vehicle resistor. Any help is appreciated. I'm an old Mallory fan.

 

The stock gm resistors measure 1.5, so even that is only 2 ohms.

 

Thanks to all for the help.

 

Is there source for the bushings?

 

I bought a pretty nice Mallory dual point #2548201 for Chevy at a swap meet many years ago. Was thinking I'd use it on a 327 that I was building. But then, oops! I decided the engine had to have vacuum advance. Last time I checked I could still buy points and condenser, but it's been a while.

 

Cool thread !

I have early Mallory point distributors in 3 of my rides. All dialled in to suit each combo with initial and mech advance, with one also having adjustable vac advance.

All work great and have never had an issue.

 

I always thought their vacuum advace mechanism was kinda funky. It's like a mini brake shoe that rides against the rotating advance plate proportinal to the amount of vacuum applied.
quaint

 

I had a Mallory duel point Marine distributor in several of my small block Mopar’s. The cap was two piece and didn’t use the clips to hold it on. It had a rubber gasket between the distributor and base of the cap that screwed on. Then the top of the cap didn’t have nipples. It had a rubber gasket and flat plastic plate with holes for the wires and screws to clamp it down. Made it 100% waterproof. Extra cool factor for an 18 year old kid, it looked like a magneto. Yes it worked well.

 

I am using a YC Mallory in my avatar with a MSD box; since it is a 4 lobe unit you need both sets of points , however I don't have a condenser. As pointed out already, the points pass very little current because they just trigger the MSD which controls the primary side of the coil. The contacts don't seem to to wear; however the follower on the dist. cam still does.... slightly.

 

I have an early style, 2pc cap design that uses vacuum only advance and only has one set of points. I think it might have been a marine application.