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Thread: Ignition Timing Harley J Model 1926

  1. #1

    Ignition Timing Harley J Model 1926

    I am setting my ignition for the first time, and the Harley literature has the distributor placed in the in the fully advanced position with the point gap at 0.22 inches.
    I am looking for what the timing is in degrees Before Top Center with the distributor fully in the retarded position.
    I believe my distributor has been modified for more advance by extending the slots in the distributor base so that throws the Harley procedure out the window for me.

    Thanks
    Steve

  2. Re: Ignition Timing Harley J Model 1926

    if you go to jd yahoo groups, click on "files," then click on "timing" and you will find 4 different files of very excellent information that will answer all your questions.

  3. #3

    Re: Ignition Timing Harley J Model 1926

    Steve is the authority on timing the electric models Yhprum. I'm unable to get on the yahoo groups anymore though Steve. Us JD fellas should put together a "JD Handbook" that'll walk you through the tuning / set up. Nothing fancy, just helpful.

    I don't think the Harley procedure is out the window for you Yhprum. As long as your points break at around 3/8th at full advance it'll run and you can tune from there. It's probably easier to tune with the slots cut out as you can unhook your timer and slowly rotate it to adjust your timing on the fly. Pulling the cam cover off is the worst job in the world, makes it a good idea to put studs in the cam chest and use nuts to hold it down so you can use an impact to take them off....

    The Shop Dope for the JD's has the exact distance the cylinders should BTDC for optimal firing. I measure my BDTC when the gear marks are lined up, it comes out a .315" BTDC or around there... Good enough to get you on the road for adjustment which I think was the intent.

    I have a Bosch ZEV where the cam had the slot cut out so +- 30 degrees could be attained. I figured it was so they didn't have to pull the cam cover to reset the gear on the mag, good idea in my book.
    27 JD (almost)

  4. #4

    Re: Ignition Timing Harley J Model 1926

    Thanks guys. I had a look at the yahoo site, was helpful. I am guessing fully retarded timing will be close to top dead center. It looks like altering the slots is not unusual after all.

  5. Re: Ignition Timing Harley J Model 1926

    Quote Originally Posted by whp View Post
    Steve is the authority on timing the electric models Yhprum. I'm unable to get on the yahoo groups anymore though Steve. Us JD fellas should put together a "JD Handbook" that'll walk you through the tuning / set up. Nothing fancy, just helpful.

    I don't think the Harley procedure is out the window for you Yhprum. As long as your points break at around 3/8th at full advance it'll run and you can tune from there. It's probably easier to tune with the slots cut out as you can unhook your timer and slowly rotate it to adjust your timing on the fly. Pulling the cam cover off is the worst job in the world, makes it a good idea to put studs in the cam chest and use nuts to hold it down so you can use an impact to take them off....

    The Shop Dope for the JD's has the exact distance the cylinders should BTDC for optimal firing. I measure my BDTC when the gear marks are lined up, it comes out a .315" BTDC or around there... Good enough to get you on the road for adjustment which I think was the intent. i need to add what i am saying was in part, handed down to me from some of the very fine fellows on this forum.

    I have a Bosch ZEV where the cam had the slot cut out so +- 30 degrees could be attained. I figured it was so they didn't have to pull the cam cover to reset the gear on the mag, good idea in my book.
    Will, your description of me is a damn scary one for me to try to live up to. all i really know anything about is the "wasted spark" ignition. one of the critical things i have not seen mentioned in this discussion is once the exact moment points begin to open is found at full advance is to rotate the crank backwards and then rotate it forwards as a means to double check the exact moment points begin to open, factory "Mechanic's Bulletins" cover the entire procedure from start to finish. The June 10, 1926 Bulletin goes over the procedure on pages 9-11. i use a "buzz box" and a dial indicator to "connect" the position of the piston with the moment the points open. elsewhere in the Bulletin it talks about using the compound gear as a means to set timing; my experience is this method is only an approximation. The Bulletin also discusses using a 6 inch scale to measure piston position, which while the 6 inch scale does not lie, aligning my vision with where the mark on a 6 inch scale is relative to where the piston position is relative to where i am sighting the mark on the scale to a mark on some part of the engine is variable and subjective at its best. To get timing dead on the most accurate way is to use a buzz box or a light along with a dial indicator. of course one cannot use a dial indicator if the engine is in the frame. i must add that some of what i am saying was handed down to me by some of the very fine fellows on this forum.
    Last edited by Steve Swan; 12-04-2018 at 05:45 PM.

  6. #6

    Re: Ignition Timing Harley J Model 1926

    After lots of reading on the internet about timing flathead engines, it appears that starting timing (fully retarded) is someplace between 5 degrees before top dead center and top dead center. I will use a continuity light to set my timing (points open) at zero degrees TDC and go from there. It will be awhile before I can report back how it went. Thanks for the suggestions they were all helpful.

  7. #7

    Re: Ignition Timing Harley J Model 1926

    A big twin is about 5 deg BTDC..a sporty is closer to 10

  8. Re: Ignition Timing Harley J Model 1926

    Shop dope says 5/16" BTDC which for a JD is 29 deg according to info in JD yahoo groups and this would be for flat top pistons. i have my timing set at 7/16" = 34.7 deg as i am running domed pistons.

  9. #9
    Join Date
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    69

    Re: Ignition Timing Harley J Model 1926

    The only Fixed point of the ignition timing is full advance, therefore this is the starting point where the ignition should be provisionally set before conducting a road run to prove the setting or adjusted to find the "sweet spot, remembering that much of the fuel we use today is not the same as 90 years ago so of course the original figures for btdc might have changed a tad.
    The amount of retard can be quoted as "it has enough to allow the engine to run smoothly at low revs and under heavy load"

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