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Thread: Finding top dead center

  1. #11
    Join Date
    Jun 2001
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    Quote Originally Posted by kitabel View Post
    The difficult thing to do is... when, exactly, does the piston stop?...
    Lash is certainly the issue, Kitabel!

    That's why the oil drop in a tube method lets you gently turn the crank back and forth, felt-tip pen at TDC, and one more very slight backward and forward wrenching to that mark lets you set your degree wheel precisely.

    Degree wheels are the easy part. Just print one out to a convenient size.

    ....Cotten
    Last edited by T. Cotten; 10-28-2019 at 04:04 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  2. #12
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    Feb 2011
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    Pa
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    Thank you everyone for all the replies

  3. #13

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    Oil sounds really good, since the oil level will be a large function of the piston motion, by the ratio of the bore^2 ų tube^2. If the bore is 3.25" (Chief) and the tube ID is 1" the oil will rise rise & fall over 10 times as far as the piston.
    What do we learn from this: don't use a small tube, or you'll get your ceiling lubricated.

  4. #14
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    Just get it close to TDC first, Kitabel!

    A tiny tube uses a tiny drop, which you can suck in from a toothpick-full by wrenching the crank backwards a few degrees.
    Then forward again to take up lash and mark it at its extreme.

    Yes, the oil moves quite dramatically, much more than the actual distance the piston moves.

    That's what makes it accurate.

    ....Cotten
    PS: I believe I got this tip on the VirtualIndian mailing list, from Keith Lummus, RIP.
    PPS: I hope I'm wrong, and he's still alive!
    Last edited by T. Cotten; 10-29-2019 at 12:32 PM.
    AMCA #776
    Dumpster Diver's Motto: Seek,... and Ye Shall Find!

  5. #15
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    And don’t look down the bore of the tube

  6. #16

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    Howdy chaps,

    The head/cylinder configuration on a 38 later Four bears no resemblance to HD/Indian flat heads of the era. If you view image #4 on row 5 at my site below the spark plug hole is at the top of these heads positioned upright behind the intake valves. That spark plug hole is a very narrow aperture at the end of a tube below the spark plug (likely to subdue flame propagation?) The intake valves are directly over the exhaust valves. Looking at image #3 you will note how offset all of this is rendering a probe useless.

    Unless you have a through-the-timing-cover oil filter arrangement it takes minutes to loosen the oil gauge and remove the timing cover. As you can see in image #2, #1 rod is right there and with the front valve adjuster cover off you can quickly determine TDC. These motors are in an extremely soft state of tune (for a reason). Though an advance setting for these is published, most just use TDC on full retard. Especially with electronic ignition I am not comfortable going with that format, rather merely using it for a baseline, focusing more on the full advance setting at highway speed which is more critical for those motors prone to run hot anyway, retarded ignition just adding to the challenge of heat rejection.

    http://www.patwilliamsracing.com/1941indianfour/

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