Analog tach accuracy

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  • Analog tach accuracy

    So I have ordered a new prop and when I try it out I want to be sure of the RPM's. Now I am fretting as to the accuracy of my analog tach. One prop I tried would run 6200 rpm and not hit the rev limiter. Max rpm for my engine is 6000. Not sure when the rev limiter should kick in. I would like to get the merc vessel view mobile but my wife hasn't even paid for the prop yet.
    So, can you guy's please tell me your luck with accuracy with an analog tach?
    Thanks
    Mark

  • #2
    The flywheel will strobe at EXACTLY 1800 and 3600 rpms when you shine a fluorescent light on it in the dark.

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    • #3
      Thanks Billinstuart. How in the world did you figure that out? I'm assuming the fluorescent light is plugged into a 60 hz. outlet ? I have incandescent and led lights that I could plug into my Magnum inverter, but even that doesn't always run a true 60 hz. HHmmmm, thinking. Offgrid- solar-batteries-gen . I do have an old school timing light but don't see how that would work. Maybe the old school diagnostic meter that shows rpm. I could connect it to the coil and compare rpm's.
      Thank you. that is very interesting
      Mark

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      • #4
        Originally posted by HawgU82 View Post
        Thanks Billinstuart. How in the world did you figure that out? I'm assuming the fluorescent light is plugged into a 60 hz. outlet ? I have incandescent and led lights that I could plug into my Magnum inverter, but even that doesn't always run a true 60 hz. HHmmmm, thinking. Offgrid- solar-batteries-gen . I do have an old school timing light but don't see how that would work. Maybe the old school diagnostic meter that shows rpm. I could connect it to the coil and compare rpm's.
        Thank you. that is very interesting
        Mark
        60 cycles is 3600 cycles/minute. An incandescent light doesn't really flash. An LED I don't know about. A fluorescent lite flashes at the rate of the cycles, but we can't detect it. 120v/60 cycles is common power. The frequency cannot vary because all generators are locked in phase together (electrical engineering stuff).

        Home boy has learned some useless shit in his life.

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        • #5
          Installed the merc vessel view mobile and have confirmed that my analog tach is purdy darn accurate
          s.
          Mark

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          • #6
            ... not sure I'd run an OB up to 1,800 RPMs, nevermind 3,600 RPMs ... in my garage. With a proper test wheel and huge water tank - sure, but otherwise ....

            Saw a guy run an OB equipped with a test wheel up to the max RPMs once, to check the WOT timing, very early one morning whilst the boat was tied up to the dock. Too bad he forgot to shift into forward gear first ... yup, he blew the engine ... kaBOOM! High revs in neutral killls!
            Life is too short for an ugly boat!

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            • #7
              DaleH, I agree 100%. I installed the vessel view in the garage, made sure it linked to my phone via bluetooth by just turning the ignition to "on". Then went down to the river and ran the boat, testing a new prop, and verified RPM's. When I read your response my first thought was the guy was gonna pull the dock away. Funny what some people will do , especially when someone else is holding their beer.

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              • #8
                3600 in neutral? No problem. Factory crank learn/relearn on digital engines can be over 5000 rpms in neutral on a new engine.

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