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Ignition Tech- Proper Method to Set Gap on a Dual Point Distributor

Discussion in 'The Hokey Ass Message Board' started by phartman, Mar 27, 2010.

  1. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    Can some of you ignition gurus please walk me through the correct method to properly set point gap on a Mallory flattop dual point ignition? I am using a ZC unit with a single condenser and dual points, MAL-24875B. The distributor is on my Ford 223 inliner.

    A couple of topics to cover, if you will please...

    I've read to use a feeler gauge to initially set the gap, and then others have said to not use a feeler gauge. How say you? Some old-timers swear by a matchbook cover to set the gap. Folklore, or ok in a pinch? I tried it and the motor ran terribly.

    For my inline, what is the proper gap? The Ford manual says .032"-.035". On one website, it said .029" for an inline using the Mallory points. What is the proper gap?

    I have a dwell meter and I understand degrees of dwell. How do I set the primary points and then the secondary points? What is the safest way? Block off one set with a piece of cardpaper? What are the correct degrees of dwell for an inline? Is it even necessary to use a dwell meter? Some say "Yes" and other say "No."

    And how often should I re-adjust the point gap?

    Thanks, guys. I need the benefit of a proper education here. Been relying on too much folklore and that doesn't always work so well.
  2. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    So no need to worry about first setting the primary points, then dialing in the secondary???
  3. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    These instructions are off the Century Performance webpage. They on the money?

    Here is the link: http://www.centuryperformance.com/setting-breaker-points-spg-90.html

    For Dual Point distributors there is a bit more effort involved. You can still set the point gap on the "primary" point set in the distributor (see note below), but you might as well forget the secondary point set at this moment.

    NOTE: Primary vs. Secondary (or trailing) point set. The Primary point set is the "first" point to open in relation to the rotation of the engine and it's placement in the distributor housing. If you look into the distributor from the top, you will notice that the pair of points are nested to one side of the distributor housing. No matter the rotation of your distributor, the first point set that opens is called the primary set. The second one that opens is called the secondary (or trailing) point set. When the primary point opens, watch it ... before it closes, the secondary point will open.
    To set dual point ignitions you first block the "secondary" point set. You can block it by either not having it in the distributor, or using a thin piece of cardboard such as a matchbook cover between the contacts of the secondary point set. With the same (Safety Precautions) as above: ignition coil wire removed, the cap and rotor off the distributor, and a dwell meter properly connected to the coil, you can spin the engine. The best way to do this is with a remote starter button. The only other way to do this is with someone assisting you. Crank the engine and watch the reading on the dwell meter. You will be setting ONLY the primary point to the required setting at this time.

    After you have set the primary point set to the required dwell, install or unblock the secondary point set. You will now spin the engine again and by adjusting ONLY the secondary point set, adjust the the secondary point so that the dwell reading matches the "combined" dwell specification. You do not have to touch the primary set again.

    Example: You have a V8 engine application and your dwell settings are 26° (each point), and a combined setting of 33° ± 2°. You will set the primary point to 26° with the secondary set blocked, then by adjusting ONLY the secondary point set, adjust it so the dwell reads 33° (or between 31° and 35°).
  4. carcrazyjohn
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    carcrazyjohn Member

    Matchbook folded in half is 15 thousandths ,Im a young guy of 41 and I was taught that many years ago ,Works great for roadside emergencies,Im getting away from points ,Look into an igniter eventually ,One time points let me down and I didnt score if you know what I mean ,I was on a date,Many years ago..........New years eve pretty gal ,Boke down shaft was wearing down the points ,Had it running a few times but kept dying ,Got towed and she ended up marrying the tow truck driver ,They were friends ,so I didnt have to pay the tow bill.True story
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  5. garcoal
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    garcoal Member

    its not hard first buy a dwell meter find out the combined dwell of the 2 sets of points. take your dist cap and rotor off put a peice of paper between the secondary or trailing points have some one turn the engine over set the first set at 32 degrees. take the paper out of the second set the amount of dwell will be the amount of dwell left hence combined dwell they are set. the guys that tell you to use a matchbook cover seem to like engines that run good enough, then figure out how to really set the timing with a timing light with intial timing and with the full advance you wont believe the difference, point ignitions are not hard to set really well amaze your friends why do it half a**ed when you can do it right . these old cars will respond to a trained hand
  6. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    How do I find which is the primary set of points? Start at top dead center and see which set opens first? I understand the concept, but "opens first" in relationship to what? Sorry to be acting so thick here....
  7. 29nash
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  8. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    Here's what I tried...installed the primary points and set the gap with a feeler gauge. Tried wider settings than the recommended .029" but it didn't seem to make any difference on the dwell reading with the meter, so I went back to .025 which is what is in the Ford manual. Set the secondary points at the same gap, and ran the dwell meter. Meter reading combined was too low. Reset the gap at .028" on both point sets, ran the dwell again and it was 34 degrees which is within tolerance. Road tested, ran great, came back and retested at 34 degrees.

    Here is what is throwing me off. When I block the secondary set and spin the motor for just the primary, I can't get more than about 20 degrees no matter how I try and set the primary points. Ideas? Am I doing something wrong? As long as the combined is within tolerance, is everything ok?

    Car seems to run better. The only other adjustment I had to make was to bump up the idle screw a little on the carb. Other than that, the road test seems good. Certainly better than with the burned up points.

    But again, why is the primary dwell reading low?

    And again, sorry for being so thick here. I really appreciate the help.
  9. 29nash
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  10. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    That's the part I'm not understanding. :confused: I thought that the dwell for the primary points had to be first set at 29 degrees. But I can't get that much dwell. Close, but not 29 degrees. The point gap is dead on for the primary and the secondary sets, and the combined dwell is in range. I just figured I was goofing up somewhere. :eek:

    I'm ok then, even though the primary point dwell is less than what Mallory recommends, but the gap is where they suggest? The car is running much better, but I don't know yet how long the point sets will last. My plan is to keep after it every couple hundred miles and readjust as the sets wear down.

    Let me know if I've goofed up here somehow...It's been know to happen. ;)
  11. mj40's
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    mj40's Member

    Years ago I had a Mallory dual point in my 53 Mercury flathead. I set the primary points then went to the secondary with a piece of cardboard in the primaries. Worked great. A couple years later I though I better check my points out and only had to replace one because the cardboard was still in the points. And I thought old people were forgetful.
  12. GMC BUBBA
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    GMC BUBBA Member

    Some good thought here guys , however be carefull as the designs of different distributors may cause a problem.

    I would suggest using in all cases the manufacturers suggested setting for the contacts.

    After reading this thread for a couple days i had a customers old mallory in for a tune up this afternoon and spent a extra minute with it.

    This particular unit had a factory ( mallory) tag that stated to set each point set at .020. When set at .020 the dwell was 26 degrees . Combined was 36 degrees. And remember that dwell is a average of a complete cycle. You can have different dwell settings between cam lobes and still come out with a good number. A syncograph or distributor machine is the only way to actually see this..

    On another mallory ( YC Rev pol) using a four cam design it is entirely different.
    My advise is to find and use the specs provided......:D:eek:
  13. 36-3window
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    36-3window Member

    on my Accel dual point for a sbc, the instructions says to set the primary points at 26 degrees while the secondary points are disconnected. then hook up them back up and set the total dwell to 36 degrees. normal dwell for a sbc is 28-32. so you can see that the first one is less dwell , but overall there is more dwell.

    this is very easy to set on my distributor machine , maybe you can find someone in you area with one
  14. Alfster
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    Alfster Member

  15. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    Jim (GMC Bubba) you raise a really good point. I have two vintage Mallory distributors for this motor, a Rev Pol and a conventional dual point and I did notice the difference in the profile of the cam lobe. They are not the same. Also. I was not spinning the motor for several cycles. I'll readjust according to what is on the distributor cam and report back.

    I assumed the cam lobes are all the same and obviously they are unique to the distributor. Duh. Should have known that.
  16. DanBabb
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    DanBabb Member

    Please teach a newbie to points.

    What's Dwell?
  17. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    rmt, you are a genius! That is exactly correct. Car still wouldn't run the way I wanted, so I dug back into the Mallory site. Here's what I came up with FOR AN INLINE 6 ONLY!!!

    Gap .020"
    Dwell (each set) 24 degrees
    Total Dwell 48 degrees

    Here is additional info straight off the Mallory site on "old" distributors:

    Old Mallory Distributors - Double-Life, Rev Pol, YC, ZC, 10, 11, 14, 15 Series
    Dual Point

    Dual Point Gap Dwell-each Point Set Total Dwell
    8 Cylinder .018" 17 Degrees 34 Deg +/- 2


    Dual Point Gap Dwell-Each Total
    6 Cylinder .020" 24 Degrees 48 Deg +/- 2



    Dual Point Gap Dwell - Each Total
    4 Cylinder .022" 35 Degrees 41 Deg +/-2

    AND ON YOUR DWELL METER, MAKE SURE YOU ARE READING THE RIGHT SCALE!!!

    I am a complete and total idiot, because a few times, I was reading the 8 cylinder scale on the dwell meter, not the 6 cylinder and it does make a difference. After the readjustment, car ran pretty good, but the idle was off. Turns out that there was a little trash in the fuel line and the carb needed a thorough cleaning out. Readjusted the idle and the timing and now- finally- the car runs unbelievably better.

    Like so many other problems, mine had a couple things wrong. Burned up points was the first big problem, but the trash in the carb and the timing a little off made it confusing where to start.

    And not paying attention to the correct scale...geez. More coffee next time.
    Last edited: Apr 2, 2010
  18. phartman
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    phartman Member
    1. Virginia HAMB(ers)

  19. GMC BUBBA
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    GMC BUBBA Member

    Gotta watch the scaling....happens to me all the time on the distributor machine.....oops......
  20. phartman
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    phartman Member
    1. Virginia HAMB(ers)

    Jim, I'm pretty embarrassed. Maybe I need to drop that family obligation and attend your class in April, sooner rather than later. :eek:

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