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Distributor advance mechanism

Discussion in 'Technical Q&A' started by pernicev, Jan 17, 2006.

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  1. pernicev

    pernicev Karting

    Jun 22, 2005
    134
    #1 pernicev, Jan 17, 2006
    Last edited by a moderator: Sep 7, 2017
    In the ongoing saga of my 78 308's intermittant running front bank, I disassembled the front distributor to gain access to the advance. I do not have experience in this area, so maybe some of the techs here can diagnose what they see. Both halfs of the advance pivot ok and the grease looks ok. Of the 4 weights, 1 is contacting the outside due to spring pressure, the other 3 have play in them, i.e. I can slide them back and forth. Is there something wrong here?
    Vince
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  2. Mike Florio

    Mike Florio Formula Junior

    Jun 19, 2003
    599
    NW Rural Nevada
    Full Name:
    Mike Florio
    #2 Mike Florio, Jan 17, 2006
  3. pcelenta

    pcelenta Karting

    Nov 1, 2003
    216
    #3 pcelenta, Jan 17, 2006
    vince,
    how many miles on your car? low right? check to see if the advance is sticking or siezed. I remember that you had very low milage so I am not sure that the mechanical advance is worn...However, you would still get spark to that bank and it would not cause the whole bank to be dead even without any advance.

    Regards,
    Paul
     
  4. pernicev

    pernicev Karting

    Jun 22, 2005
    134
    #4 pernicev, Jan 19, 2006
    Thanks for the replies.
    I think what I'm asking is if the little spring loaded pins should be touching the outside of the cup at all times. As soon as you turn the shaft, they slide to the outside of the cup even before any centrifugal force compresses the arm against the spring loaded pins.
    I don't see anything in there that looks seized or otherwise worn. Am I correct in assuming that this advance assemply is working as it should?
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    26,931
    30°30'40" N 97°35'41" W (Texas)
    Full Name:
    Steve Magnusson
    #5 Steve Magnusson, Jan 19, 2006
    I think not always touching statically is OK/as intended -- see page 8 of 11 of the link Mike F. posted.

    The bottom line is just measuring what the distributor advance does vs dist RPM using a dedicated dist. machine (or if you add a few extra marks to your flywheel you can get a fairly good idea if you're OK-ish or way bad).
     
  6. Mike Florio

    Mike Florio Formula Junior

    Jun 19, 2003
    599
    NW Rural Nevada
    Full Name:
    Mike Florio
    #6 Mike Florio, Jan 20, 2006
    In each hole you have the pin, the spring and the cup. If you have some old dried grease in the hole it might impede the cup from moving in. Or the cup could be binding.

    The inner shaft has to rotate freely within the outer shaft.

    If either one of these is not correct it will affect your advance curve.

    You could disassemble the advance mechanism, making sure to keep each pin/sleeve/spring set together and remembering which hole they go into (CRITICAL), and also make sure the yellow dot of paint is intact so you can reassemble the correct arm to the correct pivot.

    Clean each part thoroughly and lightly grease (I use a medium weight hi temp synthetic grease) the reaseeemble - make sure the shaft rotates, and each spring is compressable (finger pressure should do).

    This will not guarantee the advance curve is correct, but will be as close as you can get without a Distributor Machine. Last time I did mine there was a "dip" in the middle of the curve on one distributor, which I fixed by shimming the spring with a small brass washer.

    The other issue is that both distributors should have matched curves. With mine, they both reached max advance at the same RPM. but were off by 10 degrees in the mid range. Again, without Distributor Machine and curve plots you can never know.
     

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