Technical Mallory Four Lobe Service

Lately there has been some discussion regarding the use of a Mallory 4 lobe or 8 lobe distributor cam. After rebuilding 2-3 the last couple days i felt i could help this discussion a bit.
(I am not getting into the different operations and coils etc with the two cams as i just dont have the time )
On this working example i set both sets of points at .018 with a feeler gauge using my very best bench procedure. In many cases this may be as good as it gets from shop to shop.
I then put the distributor on a distributor machine and ran it. You can see the timing between cylinders is off by 5 degrees . ( Thats 10 degrees engine timing), then by adusting the contacts nwe can adjust the sync of the point set to exact cylinder timing. The only way to get one of these perfect is on a machine. To me 10 degrees of timing difference is way too much!! The old Sun testers allowed only 3 degrees .
Note the factory Mallory jumper used on the four lobe......

 

Please, can we have some more? I like posts like this one.
r

 

I wonder what the dwell variation is between the two sets of contacts, when the timing is the same?

 

I'll second that question, I'd like to know also.

 

Jim, In a perfect world the dwell would be the exact same per set . I have built a few using a feeler gauge and then put it on a tester and the timing was so close i didnt change any thing. When ran as a pair one set breaks the circuit and the other set makes the circuit. So only the break set controls the timing.

 

Jim didn't you offer distributer tuning classes at one time? I have an old Sun distributer machine that I'd love to know how to use correctly!

 

I think I'm a little "late to the party" here. Does this setup use one of the special Mallory "Rev-Pol" coils or a regular coil (as the jumper wire suggests)?

 

Me, too!

 

Great stuff, interesting as all get out, taught by the best. But it makes my brain hurt.

 

Yes we did a Hot Rod ignition class with 10 guys for two days , it was great and a lot of fun and everyone got to rebuild their distributor. I have tons of requests to do it again and may get around to it . However it takes a lot of time to set up and do again. Right now i just done thave the time, but stay tuned as i may do it again some day.......

 

Hmmm....here you are talking about a dual point distributor for a V8, with an 8 lobe rotor. But in the example I asked about, you were talking about a dual point distributor for a V8, with a 4 lobe rotor. In this type of distributor, one set of points operates every other cylinder. And you showed that the timing was different for each set of cylinders operated by each point set, then corrected it by adjusting the dwell on one set to make the timing match the other set. I'm curious how much you had to change the dwell, and how different they are now.

 

Jim,

I have a few in the shop to get done, i will check the dwell for each set on the next one i do. Almost all the units i do with the four lobe cam come in the door with the factory red jumper lead installed . If not i usually add it as the dual primary coil is kinda hard to find, and even harder to understand. for some.
I ran a dual primary Mallory on my GMC six powered dragster for some time and it worked very well.
Attached is a diagram of the first version Mag Spark coil set up , came in yesterday for rebuild , flathead Ford eight lobe cam. Points NOT wired together??

 

Jim, You guys seem to enjoy this stuff , heres some more explanation of the early Ford Mallory Mag Spark ...When someone figures it out write a post so i can understand it. I just dont have the time......rbg :>)

 

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The coil with the kit is a regular coil.........NOT the Rev Pol unit.........

 

OK, I think I have it. The points are jumpered together and each set alternatively energizes the single conventional coil. When you gapped the two sets of points the same, the alternate point sets didn't fire exactly 90 degrees apart, so you adjusted the gaps to bring the points back in phase. Is this a fair summary of what's going on?

I have a complete (6 volt!) RevPol set up for an Olds Rocket. If you don't mind, I think it might be informative for me to post a few pics of it so people can see the difference. Whadya' think?

 

I'm in...never too much info that can help us out..

 

Love the question Jim. But wouldn’t that be equal to asking what timing works for all applications? I think the answer would be differant if one was fortunate to have a hand full of those distributors to test. Meaning, if you built 6 BBC exactly the same, would they all have the same dyno results?

 

I think "Squirrel" may have a point. If the manufacturing tolerances on one of these would stack up completely the wrong way, It might be impossible to get the points "in phase" (firing exactly 90 degrees apart.) And if you did, it may have taken a disparity between the alternate point gap such that one may be down to .008"-.012", rather than, say a recommendation of .016" on each set. This would significantly reduce the dwell, and therefore coil saturation, and consequently spark strength. Hopefully these units were built with sufficient precision that this wouldn't happen. I think Jim said he is going to check a few. The results should be interesting.

 

Yea we got it down pat and the lesson here is that a dwell meter is the very best way to set these up!! Also remember dwell is a average reading of the complete circle.

 

That is what I have been playing with on my switched duel point.

 

Let’s dwell. Bubba didn’t have time so he used others time to teach us instead. Yet, there was time to review?

 

I think your points are closed.

 

Yep that works well some times, start the discussion and stand back someone will lead on. Saves personal energy, thats what old guys do.... rbg :>)

 

Do you still have that old 6 powered dragster??

 

And also negative grounded.

 

Jim had me thinking something wasn’t equal some where. But where, and how could dwell correct a flaw that’s perhaps in the distributor. That would never work. The flaw turned up else where to what I was try to say. No two things will create the same result no matter how well machined or matched.

 

No , wish i did. We traded it off its in Minnesota with a Chevy v8 in it now.