Delco mechanical advance dilemma - Chevelle Tech
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post #1 of 8 (permalink) Old Sep 13th, 19, 6:12 AM Thread Starter
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Delco mechanical advance dilemma

I picked up a few swap meet Delco points distributors to replace my HEI. The best one was a 1112844, dated Oct of 73. It appeared to be a clean unaltered, low mileage with original points rotor and condensor. The original vacuum can starts at 4 and is all in by 6" of vacuum. I replaced the vacuum can with a new B28 and installed a Pertonix III. After installing I am only getting 6-9 degrees mechanical advance, depending on what springs are in it. Before I take it out to look at, what do you think is going on?
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post #2 of 8 (permalink) Old Sep 13th, 19, 2:19 PM
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Re: Delco mechanical advance dilemma

1973 pass, Nova, Chevelle, Camaro, Monte Carlo, 350/145 horsepower, A/T.

1112844 uses a stock GM vacuum advance of 1973502. B28 is a good performance addition, but needs at least, the rubber tube bushing on the pull pin, or it will give too many degrees of advance. Better yet, add a metal stop, instructions, with pictures, ask for them, [email protected] - they are free.

Some of those engines are very emissons laden, and do not use much mechanical advance. Problems can be from gunk/grease loading up between the distributor main shaft and points cam, other mechanical advance parts, and/or wear on the weights and center scroll.

Test, pull the springs, weights off the top of the advance, and move the plate through its travel, does it run free, or is there resistance? Resistance, grease is stopping the free movement of the advance, clean shaft and advance parts.

Test, take the advance and move it clockwise, and let it go, if it moves freely, good, if not, dirty grease, other issues are in play, disassemble and clean.
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post #3 of 8 (permalink) Old Sep 13th, 19, 6:43 PM Thread Starter
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Re: Delco mechanical advance dilemma

Thanks Dave. I pulled that distributor. It has hardly any mechanical built in. I replaced it with a 69 year rebuilt one that works as it should. Right now I'm at 18 initial 38 total with the can stopped at 10, for a max of 48 cruise.. I will probably try to stop the can at 8 next time around to be safe.
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post #4 of 8 (permalink) Old Sep 13th, 19, 11:29 PM
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Re: Delco mechanical advance dilemma

I'd drop the initial to 14, leave the vac adv to 10, full manifold vacuum.

How did you stop down the vac adv?
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post #5 of 8 (permalink) Old Sep 14th, 19, 6:22 AM Thread Starter
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Re: Delco mechanical advance dilemma

I used the Crane stop installed as you as you suggest.
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post #6 of 8 (permalink) Old Sep 14th, 19, 5:56 PM Thread Starter
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By the way, I found that the 844 distributor head has slots for the stop pin on both sides. I swapped it to the larger slots so it should be fine. I guess I’ll set it up with points for a spare until I can afford to have a Dave’s small body HEI built. Thanks.
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post #7 of 8 (permalink) Old Sep 14th, 19, 6:20 PM
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Re: Delco mechanical advance dilemma

I'd keep the points and use them to trigger a MSD6AL or any other decent CD box out there, that's one of the best ignitions going. This way if the box goes out you can connect up the condenser and drive home on just the points, 14 volts won't kill them..

You could even pick up a vintage Mark 10 CD box and have your under hood looking like it came from Yenko and be modern at the same time.. The CD box I have has a switch to convert it back to points only..

I love how easy those single point distributors are to work on..

Last edited by hydro462; Sep 14th, 19 at 6:43 PM.
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post #8 of 8 (permalink) Old Sep 15th, 19, 2:12 PM
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Re: Delco mechanical advance dilemma

aimhard, that is the way the points distributors start/limited their mechanical advances, length of the slot the pin is in, along with a resin plastic thrust bumper that usually rotted, and fell off after a decade or so (that is why MSD started making metal bushings for them).

As you have already seen, there are a bunch of point distributor points cams with different slot lengths, some of the later ones don't give much advance, they were the last of the points distributors in the emissions eta. now, if you have a radically cammed engine, and find one that has slots for 9 distributor degrees, you get egg roll, 18 crankshaft degrees, and add that to an initial of 18, 36 total, 20, 38 total, bonus.

Large HEI mechanical advance units look the same as the points, but function much, much differently in start/limit, and other factors.
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