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Can I use an Autometer "diesel" tach?

Discussion in 'The Hokey Ass Message Board' started by DocsMachine, May 23, 2011.

  1. DocsMachine
    Joined: Feb 8, 2005
    Posts: 279

    DocsMachine
    Member
    from Alaska

    Years ago I put a cheap JCWhitney 2-1/6" tach in the dash of my '66 Toronado, in place of the factory clock. (More than a decade later, Jay Leno did the same thing with a boost gauge. :D )

    The tach has long since died, and I'd like to replace it with a slightly larger 2-5/8" unit. I'll have to mill out the potmetal dash pod for it, but that's part of the plan.

    Problem is, the car's a daily driver with a very mild engine build and tall gears- 60MPH is only about 1800 RPM. I'd like to use a 0-5000 tach, rather than a 0-8000, but the 5K ones only come in "diesel only". They apparently have a sensor or pickup that attaches to the alternator somehow, to feed the signal to the tach.

    Is there a way I can use this (or one like it) with a spark ignition? (HEI, in this case.)

    I don't know what the sensor/pickup is or does, or what kind of signal the tach needs to properly read. Over a hundred bucks is a bit much to just buy one and try it out, so I'm hoping someone here can help me out.

    Doc.
     
  2. Willy301
    Joined: Nov 16, 2007
    Posts: 1,426

    Willy301
    Member

    I have one on my diesel, it takes some tuning to get it correct, but yeah, it should work fine.
     
  3. DocsMachine
    Joined: Feb 8, 2005
    Posts: 279

    DocsMachine
    Member
    from Alaska

    Thanks, but I was actually wondering if there was a way to use it with a spark ignition, and not use the alternator pickup.

    What, exactly, is the pickup? Is it an "eye" that counts the fan blades, or an inductive pickup that works off the rotor, or what? And what do you mean by 'tuning'? Do you have to check the engine RPM with an external tach (like on an engine analyzer) and adjust something on the dash tach?

    Doc.
     
  4. The alternator pick-up connects to the stator terminal. Most car alternators do not have
    a stator tap, but one can be added. We used to have it added at the local rebuilder when a replacement engine did not have a take-off for mechanical tach drive. The tachs have a series of dip switches that are adjustable to match signal to proper rpm reading. Somewhat involved to get adjusted; but work OK.
     

  5. Have you looked at what the marine (boat) guys use? Their RPM range is limited to 3000 to 5000 RPM in most cases.
     
  6. medicinal_marinara
    Joined: Nov 24, 2009
    Posts: 139

    medicinal_marinara
    Member
    from Oregon

    If you run an 8k tach in 6 cylinder mode on a V8 and it will read 1.333x the actual reading. You can make a new face for it. Or run it in 4 cylinder mode and it will read twice as high, 4000 rpm will read 8000 on the gauge. Again, make a new face.
     
  7. DocsMachine
    Joined: Feb 8, 2005
    Posts: 279

    DocsMachine
    Member
    from Alaska

    -Ah ha! Thank you. I'd looked at Summit and didn't see that one. I saw the same 2-1/16" and 3-3/8" ones, but must have missed that one somehow.

    -Actually, that's exactly what I used to do with the old JCWhitney tach before it croaked. I wanted to make a new face years ago, but the gauge bezel was roll-crimped in place.

    Is there a trick to getting crimped-shut gauges open?

    Doc.
     
  8. Willy301
    Joined: Nov 16, 2007
    Posts: 1,426

    Willy301
    Member

    The pickup on my tack is a small round piece fixed in a metal bridge, that bridge is clamped to the outside of the stator ring on the alternator, no wire to hook to ignition. It really is a reliable set up IMO
     

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