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  1. #1
    Join Date
    Jul 2008
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    near Warragul, Victoria
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    Default Distributor advance curve

    hi

    I need to test or calibrate a vintage automotive distributor advance curve against the specs. , this is a mechanical advance only, no vacuum involved . There are two weights and springs that move and rotate a plate according to the applied RPMs.

    I can easily spin the shaft with a drill and I have a cheap digital tacho device.

    So if I mark the plate and the outer housing with a marker pen at a reference zero or RPM zero and also mark degrees around the circumference of the housing. I should then simply watch to see how far the plate moves at a given RPM.

    Any thoughts ?
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  2. #2
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    Jul 2008
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    near Warragul, Victoria
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  3. #3
    Join Date
    Oct 2004
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    Southern Highlands NSW
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    Default

    A strobe lamp triggered by spark event could help, if a degree wheel were attached to the same shaft as drives the dizzy.
    Note that you should double the tacho reading to translate to rpm at crankshaft.

  4. #4
    Join Date
    Jul 2008
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    near Warragul, Victoria
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    3,738

    Default Ok

    Quote Originally Posted by nadroj View Post
    A strobe lamp triggered by spark event could help, if a degree wheel were attached to the same shaft as drives the dizzy.
    Note that you should double the tacho reading to translate to rpm at crankshaft.
    OK yes, basically, that is the method the article I linked to is describing.

    Somebody on a forum described a method of testing the advance curve using a dual trace oscilloscope, he compared the two signals and worked out the degrees of delay, he used a opto coupler to trigger the CRO.
    Years ago, there were special distributor testing machines made by SUN Co. Tuning business/garages used to use the SUN machines to check the advance curve and other parameters. Some of the more expensive digital readout timing lights you can buy these days have a built in advance readout mode, it displays the advance on a screen.

    These days cars have on-board computers that do it all , the computers do the timing adjustments automatically !

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