Timing Light Accuracy

Electrical and Ignition

  1. mopowers

    mopowers Well-Known Member

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    Do inductive timing lights ever go bad and give off inaccurate flashes? I've got a vintage Craftsman chrome inductive light that I'm questioning because of how much initial timing my 340 wants. I've verified the TDC mark - it's spot on. Maybe this 340 just an anomaly because it seems to want 30* initial adv.

    Without having a second timing light to check it against, I'm curious if these thing ever go bad.

    images?q=tbn:ANd9GcQKezUYSrl66b90mVhMUeMmdRlkvWqEMKYKXd7ylj82a_PPKMrSQw.jpg
     
  2. toolmanmike

    toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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    Is it a dial advance light. Those can get out of calibration. The plain ones usually not.
     
  3. mopowers

    mopowers Well-Known Member

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    Good question. No, it's just the plain jane model that everyone probably has.
     
  4. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    I have the same light. I have been using it for 40 years, only thing I have ever had to do was re-solder a joint inside.

    if you want to do a rough calibration / check, find a computer controlled car and check its advance. this may or may not work. I had an older car that I could do this with.

    I would think you have other problems like no vacuum advance?
     
    Last edited: Apr 10, 2019
  5. Syleng1

    Syleng1 Karma is real and Life is short... FABO Gold Member

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    I’ve got that same lite and every so often it goes out of wack. Dampness or dropping.
    It’s a pretty simple system inside.

    When it goes crazy just put it back on the shelf and grab the other one. They are like 25 years old.
     
  6. Dana67Dart

    Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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    Open it up and look for bad solder joints. Mine did the same thing.
     
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    • dgibby

      dgibby Well-Known Member

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      Some lights have an arrow on the plug wire clip and if pointed the wrong way it will give erratic readings.
       
    • brian6pac

      brian6pac Well-Known Member

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      Electrolytic capacitors have about a 10 year life then they start drying out, breaking down inside and not working as well as they should. After 25 years you could change them, they are very inexpensive if you really like the lite or just buy a new one
       
    • mopowers

      mopowers Well-Known Member

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      I guess I'll have to see if one of my neighbors has one I can borrow to see if it'll give the same reading. Thanks guys.
       
    • Murray

      Murray FABO Gold Member FABO Gold Member

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      Had a nice Fox Valley I used for years until I built a race car and started to question the accuracy of my old light because of a comment by MSD. Bought a new MSD light. Don't know if it is better- But I feel better.
       
    • toolmanmike

      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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      What ignition system are you running. Multispark can mess with most lights.
       
    • mopowers

      mopowers Well-Known Member

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      The ignition is a GM HEI module, Mallory-style MP electronic distributor, and MSD blaster SS e-core coil.

      Did you ever check one light against the other?
       
    • Demonracer

      Demonracer 71 Demon 00 Ram 16 Chrysler 300S 05 Caravan FABO Gold Member

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      I've had that same timing light for over 30 years & mine is still dead on. Just FYI, I keep it in the box with a desiccant bag that I change out a couple of times a year.
       
    • mbaird

      mbaird mbaird

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      I have an OTC dial back that goes awry and another digital one (made by OTC as well) with a tach that gets funky on occasions...
      I would like to know how to fix or send them back to OTC for repair.
       
    • brian6pac

      brian6pac Well-Known Member

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      They feel better because they got your $$$, I have a old fox Valley also and I still like it better than any other because the advance wheel is at your finger not a dial on the back
       
    • mopowers

      mopowers Well-Known Member

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      When they start to go bad, what are the symptoms? Erratic timing? stable timing, but a given amount off? non-functioning light bulb?

      Mines pretty stable, so it's hard to believe that it would just flash at the wrong time, but who knows... I just wish I had another hot rodder who lived near me. Hell, someone who even knows what a timing light is would be nice. lol
       
    • Mike69cuda

      Mike69cuda 64 is the new 17 FABO Gold Member

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      Probably cheaper to buy another one than send back. Seems like if you send something back for an intermittent failure they won’t find it and will just send it back to you, unless you are lucky and they send you a new one. You eat the postage and fees and get nothing.

      You may be able to take them apart and spray the switches ( and probably all of the insides) with some contact cleaner. Most of the time it seems like it is the moving parts that go bad.
       
    • toolmanmike

      toolmanmike FABO MODERATOR Staff Member FABO Gold Member

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      You may want to check with OTC. If it's a older model many repair parts aren't available but they may offer a new model for a discounted price.
       
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      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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        does it kick back during cranking?
        Every combo is different, but 30 seems to be a lil much at a normal 750 idle.
        But you can't always give her what she wants at idle, because it will be too much everywhere else. Actually I would say that you can rarely give a street engine the idle timing it might like. And there is nothing wrong with that, especially if she's an automatic with a hi-stall. Just be sure the power timing does not exceed the ability of chosen fuel to withstand detonation. Which usually falls around 36*@3600 depending .....
         
      • doug 371

        doug 371 Well-Known Member

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        I think it would be more likely for the flash to be retarded than advanced...
         
      • KitCarlson

        KitCarlson Well-Known Member

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        There are possible errors in timing lights. The trigger mechanism for the flash can introduce delay. A flash tube is supplied a voltage of a few hundred volts by a charged capacitor, a third connection provides trigger at a few thousand volts.

        A scope with two channels can be used to measure delay between the real ignition event, and photo transistor signal resulting from flash event. Delay error increases with RPM.

        Inexpensive clamp-on lights are often polarity sensitive at the clamp. Clamps are typically marked to show side that goes to plug. Incorrect clamp, results in failure to trigger, or significant error.
         
        Last edited: Apr 10, 2019
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        • RustyRatRod

          RustyRatRod Bla de blizhibliz de blatde blizi bla bla FABO Gold Member

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          My biggest problems with timing lights through the years has been those whose wiring harness plugs into the light and is detachable. Seems the plugs always get loose and then make poor contact. Then, that's when you start having trouble with loss of signal, weak signal, inaccurate or no flash.

          Now, I will only buy timing lights that first, have the wiring harness made into the light and secondly do not have a dial back feature. The engine is the best dial back unit you have. Simply use it for that feature.

          Believe it or not, I found a vintage tuneup kit at a yard sale a while back. It has timing light, dwell meter, vacuum gauge, compression tester and a hand held remote starter switch. Made by Dixco. Remember them? The light thus far has worked well. It seems to be accurate based on the vehicles performance I have used it on.
           
        • harrisonm

          harrisonm Well-Known Member

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          Here is my $0.02. Timing lights are not very expensive. If yours is old and you no longer trust it, get a new one.
           
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          • mopowers

            mopowers Well-Known Member

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            I found a buddy with a timing light. I'm going to snag it this weekend and check it against mine. I'll report back with results.

            It does not kick back at all with 30-32* initial - even when hot. Cranking compression is 162-168 lbs. I've run it WOT with up to 40* total (with my light) and no signs of detonation.
             
          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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            With what fuel,heads, and Q; might I ask?
             
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