I looked, but could not find...what's a good tach diagnostic tach for a 318?
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Thread: I looked, but could not find...what's a good tach diagnostic tach for a 318?

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    Display Name: Randy

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    I looked, but could not find...what's a good tach diagnostic tach for a 318?

    I've been wanting one of these for a long time but never got one. My fine tuned hearing tach just isn't as accurate as I'd like it to be. Any suggestions on a decent diagnostic tach for $100 or less?

    Thanks!

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    Try Amazon, I bought a non contact tach for around $25. It uses a reflective tape to count the revs. They also have tach/hour meter combos that can be permanently mounted and use on external power source, just a wire wrapped around spark plug wire.


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    Only for use during repairs? Whadda you have for a multi-meter, and/or anything else that can measure frequency on the switched side of the ignition coil? Figure out how many times the coil fires per crankshaft revolution (Probably one for most of the machines on this site, but double check), measure the pulses per second (herts) on the frequency meter, multiply by 60 to make that into minutes, and divide the whole thing by the number of sparks per crankshaft revolution.

    Some sound analyzing apps for Android (and I have to assume Iphones) are quite capable of "listening" to an engine and working out the RPM. I can't tell you which ones they are, but a couple of guys at work do it this way. One of them uses a full on sound analyzer to work back from frequency, the other (again, sorry, no names...), is a dedicated app that as far as I know, only measures engine RPM and nothing else, but it comes up in a digital readout.

    Google Phototach, Photo Tach, and "Non Contact Tachometer". (Kleenex vs Facial Tissue). Those are fiddly, and you've got to use it for a bit to get a feel for what it will and won't pickup accurately, but they're kind of cool, and very economical. Remember to get the reflective tape, or be sure it's included.

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    I bought one off Amazon for $30.
    It just wraps around the plug wire.
    Has a total hr function and service interval as well.

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    Try Tiny Tach - they make one for gasoline or Diesel engines. I have one on my 332 and it works great!.
    1939 John Deere Model H (Hand Start), 1974 John Deere 112 Electric Lift, 1987 John Deere 332 Special Edition, Brinly Plow, Brinly Cultivator (11 tine), JD spreader, 43 Snow/Dirt blade with Angling kit, 54 4 Way front blade, 47 Mower, 6 cast wheel weights, 4 suitcase weights.

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    I did look at a few of those non contact types but decided they wouldn't do what I wanted on the 318. I was just wondering how everyone here checked their rpm during tune-ups? Any specific brands better than others? I want something reliable and accurate and easy to use. I would also use it on my Harley I guess. It's set up with a single fire ignition. I'm not sure yet how the Onan fires (actually I have the Linamar, same thing only different I guess).

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    It uses a wasted spark system. So google that term.

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    That would be a normal (old) Harley engine. One coil in the system has two wires and fires once each revolution of the engine and the cylinder on the compression stroke uses the spark. The other spark goes unused unless the engine is running very rich, at which point it backfires out the exhaust. It also pops during deceleration due to a rich condition (throttle closed and extra fuel being sucked in because of high vacuum at high rpm's).

    So if these engines work the same way, that makes finding a tach a little easier. Thanks!

    I always seem to think lawn mower/GT engines are some sort of mystical unicorn. They aren't. Just a smaller version of what I'm used to working on. I'll get over my intimidation of them someday. To me, they are like working on a modern car...my hands are too big to get in the little spaces, and when I do get them in I break something that's unseen. Then, like this issue, I have to spend days trying to figure out what I did. Give me a 70's GM engine in a pickup any day! Crawl into the engine bay, rest your feet on the frame and tear into it, you can't break anything because there's nothing in there that can't be seen. 3 or 4 vacuum lines, a few electrical wires, and not much else.

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    I have heard of Harley coils being used on our Onan tractors.

    Give me a 70's GM engine in a pickup any day! Crawl into the engine bay, rest your feet on the frame and tear into it, you can't break anything because there's nothing in there that can't be seen. 3 or 4 vacuum lines, a few electrical wires, and not much else.
    I remember doing this. It was a 71 302 with three on the tree.
    "Everybody is a genius.
    But if you judge a fish by it's ability to climb a tree, it will live its whole life believing it is stupid."
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    Quote Originally Posted by dhager4692 View Post
    I have heard of Harley coils being used on our Onan tractors.



    I remember doing this. It was a 71 302 with three on the tree.
    Actually my 84 Evo Softail now has two coils and a Crane single fire electronic ignition. Nothing fancy. I'm sick of it's temperamental attitude however and think I'm going to put points back in it with the wasted spark setup. I ran points for nearly 15 years in it and never a problem. Never have cared much for this electronic ignition on my Harley, maybe because I just don't understand it very good. Setting advance curves electronically is not my area of expertise. Changing weights and springs is easy. I can get points to work excellent and then have to rely on my finely tuned sense of eardrum rev limiter. I set this electronic unit rev limiter at 6,000rpm and I feel like it's always shutting the engine down at 3,000rpms. I'm wrong, but that's what it feels like.

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