57 Johnson 35 hp – Tachometer?

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  • John Link
    John Link
    US Member - 1 Year
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    #172542

    I have a 1957 Johnson RDE-19 35 hp, with magneto but no generator. I have standard wiring harness and standard junction box, all working. Can a current model Faria in-dash tachometer be made to work with my motor? Thanks for any help you can give. John Link

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    frankr
    frankr
    US Member - 1 Year
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    #172548

    Modern motors / tachometers work by counting the AC pulses from the alternator. Since your motor has no alternator, you are somewhat limited in what will work on it. You need something that counts the pulses from the magneto, or one that counts the pulses at a spark plug. Tiny Tach is a popular one of the second type.

    John Link
    John Link
    US Member - 1 Year
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    #172549

    Thanks frankr. Can you tell me how my motor keeps the battery charged? And whether there is something there that could be intercepted to provide a signal to the tach?

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    garry-in-tampa
    Lifetime Member
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    #172565

    I don’t believe it will. I think they are set up to run off pulses from the sense coil. If I am wrong you may be assured I will quickly be corrected. . .

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    garry-in-tampa
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    #172566

    Actually it doesn’t – it also does not use the battery except for starting so it will go a while with intermittent use. Hand cranking turns the motor over twice. The electric starter will double that with a click of the switch. A well tuned motor will start almost instantly. If the boat and motor are kept in the water, be sure to tilt the motor to lessen electrolyses damage to the lower unit. If you get caught with a low battery that can’t turn the motor over – this draws massage amounts of current, overheating the starter. LET THE STARTER COOL. Then pull the starter cord out to engage the compression relief – this reduces starter effort 25%. Some use a shore powered trickle charger. If you go with this, Disconnect the battery from the motor AND BOAT, to avoid electrolysis. I recently heard someone was making a boat cover with a solar panel in it. The cost would buy a couple spare batteries – but who knows ? ? ?

    olcah
    olcah
    US Member - 1 Year
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    #172573

    If all you use the battery for is starting, my experience with a 1956 Johnson 30 HP is that a car battery does not require recharge for weeks of use. My battery came from an old Mustang, size 58 I believe. I take the battery out and recharge it ashore every 2 or 3 weeks just to keep it topped up.

    lindy46
    lindy46

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    #172591

    Or get a small solar trickle charger. You won’t have to manually charge all summer.

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    chris-p
    Canada Member - 1 Year
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    #172616

    I agree with the solar charger, if you leave the boat out on the dock, keeps it fresh, as long as you don’t use it a ton!

    John Link
    John Link
    US Member - 1 Year
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    #172620

    Since posting the question I have found a “Universal Tach Adapter” called “Widget Man” on eBay that employs the wire-wrapped-around-a-spark-plug-wire just like the TinyTach. However, the device resides inside the motor shroud (or attached to the transom) and provides a wire with a signal any ordinary tachometer can use. You can view it here: eBay posting here

    Anybody know anything about this one? Here is what the seller says about it:

    “Doing a plug-wire wrap is usually the best approach with mags of all sorts. The Schmitt input on the adaptor even makes it “tunable” by changing the number of turns — getting a reliable pulse is a simple matter of fiddling until you find a number that admits the initial spark pulse at all speeds, but excludes all the ring noise. If you have a lighting coil, the AC signal from one phase of the coil will also make a very clean trigger, and the BTA has ratios for nearly every configuration of alternator. For the output, depending on the vintage and make of the tacho, you may need to add a booster to the BTA output. Many marine tachos are back-EMF types that won’t trigger at 12V, even some recent ones. You can generally check by bouncy-bouncing the tach signal wire on battery+ to see if the needle twitches. If it doesn’t, then chances are you’ll also need a booster (see our listing# 142171581596). We do bundle shipping if you need both, just pay full shipping at checkout and we’ll refund the excess when the items ship. Thanks for your interest!”

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    frankr
    frankr
    US Member - 1 Year
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    #172702

    That certainly is interesting and I wish them success. But that info is way over the average bear’s head. Over mine too. If they can bring it down to earth speak, they may have a viable product. Changing a light bulb baffles some people.

    John Link
    John Link
    US Member - 1 Year
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    #172730

    Well, I ordered one of the converters. I will check it out via the “bouncy bouncy” technique, but suspect it will work as is. The booster he refers to is basically a transformer that ups the voltage delivered to the sending wire to 30 or more, something that is required for some auto tachs. But the marine tach I am looking at is designed for 12 volts. Since I have an OMC big twin, all the manipulation of the BAT should not be necessary, inasmuch as wrapping one plug wire will generated 1 pulse per revolution. I am restoring a 56 Yellow Jacket and want the instrumentation to be consistent, but not digital. (TinyTach is digital.) Will wind up with speedo, tach with hours, and battery condition meters on the dash, all analog.

    Adding a generator, assuming I could find all the parts, would be expensive, as it appears from my searching around. The 55 Johnson 25 horse we had on our 50s Yellow Jacket never caused any problem with a run down battery that I can remember. But then I had a heck of a dad who just took care of stuff like that while we teen-agers had all the fun..

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    TonyB
    US Member - 1 Year
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    #176054

    Did the widget man device work?

    John Link
    John Link
    US Member - 1 Year
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    Topics: 1
    #176055

    I have not hooked it up yet.

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