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Thread: Lazy tachometer

  1. #1

    Lazy tachometer

    Hi all, just got my 78 SR running after sitting for years. Every thing worked great except that the tach is VERY slow to respond. Maybe it will come out of it with more use. Any suggestions?

  2. #2
    Senior Member MadMax's Avatar
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    Carefully lube the cable with light oil, try not to let any up inside the tacho when you refit the cable, the needle is operated by a revolving magnet which pulls a disc around, this disc is resisted by a hair spring. If lubricant gets up inside the mech', it can "mask" the magnetic attraction and response will be even worse.

    A new cable may be a better bet, they're cheap enough.

    Max

  3. #3
    FORUM SUPPORTER pineywoods's Avatar
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    What Max said, plus the original lubricant in these old gauges stiffens with age and the gauges get sluggish. I've had good luck with removing the gauge from it's bucket and then warming it gently with a heat gun, or even just placing it on a furnace vent in your home to let some warmth penetrate the unit. As the old lubricant warms things will loosen up and begin to come around. You can spin the input shaft with a variable speed drill (reverse?) (check the rotation of the driven cable on your bike to see which way it should turn) to see if it's coming around.

    roy
    Unis Est Satis



    Bikes in the barn; 78'SR500E, 77'XS650D, 78'XS650SE, 98'Honda Magna

  4. #4
    Twice over the years (once in a car and once on a bike), I have traced a lazy tach to a spider web inside the bell housing. Both times on vehicles that had been sitting. That strand of spider web was enough to alter how the magnet pulled on the steel bell. You might try vacuuming out the bell to see if it helps. FWIW.

  5. #5
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    The guts if you are curious.

    Mine had a broken needle, so got the dremel through the body treatment. Figured couldn't make it worse, and lacked the patience to do the other method. Glued the needle back together, but the spring is stuffed.
    Last edited by red dragin; 12-06-2017 at 05:20 AM.
    1978 SR500E 2U8

    Confused about your frame number?
    http://xt500.free.fr/technique/numerosr.html

  6. #6
    Quote Originally Posted by red dragin View Post
    Mine had a broken needle, so got the dremel through the body treatment. Figured couldn't make it worse, and lacked the patience to do the other method. Glued the needle back together, but the spring is stuffed.
    If you're into electronics much......you could use the original tach housing and face and put in LEDs every 500revs and build an electronic tach. Just a thought.

  7. #7
    Wow, you guys are awsome. Max, cable is good. Was'nt sure how the internals worked but now I know. Pineywoods, thought about the heat gun thing. May still try that. Hexrod, I hate spiders. Red dragon, nice pics. Not afraid to tear into it if I have to. Solo2racr, I'm trying to stay original if I can but there is always that option. Thanks to you all.

  8. #8
    Quote Originally Posted by solo2racr View Post
    If you're into electronics much......you could use the original tach housing and face and put in LEDs every 500revs and build an electronic tach. Just a thought.
    I'm pretty sure that the tachometer I have on my boat is a direct fit into the original housing. Go electric and get away from the cable drive. The same brand also does a GPS speedo which I have on my boat too.
    1978 SR500E 2U8

    Confused about your frame number?
    http://xt500.free.fr/technique/numerosr.html

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