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Dial-back timing light?

Discussion in 'The Garage' started by 77crewcab, Aug 17, 2005.

  1. 77crewcab

    77crewcab 1/2 ton status

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    I'ver read this term many times but have no idea what it means. Could someone explain or give a link to a good article about timing a BBC for street/towing. I am just starting to try and understand the whole timing mystery better. My timing light simply flashes with each firing of #1 cylinder. Can someone also explain how to determine intial, mechanical and total timing and approx what they each should be.
     
  2. southernspeed

    southernspeed 1/2 ton status GMOTM Winner

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    Right, well a dial back light is one where you can set the amount of advance on the light and use your tdc mark as your timing line. ie: if you wanted to set your max advance to occur at say, 5000rpm (or where ever) you can set the light to your max figure (say 36'btdc) then rev the motor to 5000rpm. Turn your dizzy untill your timing mark lines up with the 0' timing line.
    Initial is where you set the static timing (0' on tbi trucks, around 8' on carbed non ecm trucks. Mechanical is the amount of advance you'll get from the bob weight advance mechanism and total is those two plus the vaccum advance all together. :D
     
  3. Beast388

    Beast388 1/2 ton status

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  4. 77crewcab

    77crewcab 1/2 ton status

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    Thanks for the links I'll take all the info I can get. Let me make sure I get the idea here. Dial-back--set the total advance you want per rpm, rev engine adjust dist to line up on 0. Intial--mark showing at idle with vac advance disconnected. Mechanical--set using spring adjustment on weights. Vaccume advance determined by the vac cannister on dist and adjustable by buying adjustable cannister. So when setting it up you would do so in the following order intial,vaccume, and adjust mechanical to get to desired advance or would you do mechanical and then adjust vaccume? Does it mater which is done first as long as desired advance is reached?
     
  5. 77crewcab

    77crewcab 1/2 ton status

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  6. SUBFAN

    SUBFAN 1/2 ton status

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    You get your 'total' advance number more from the wieghts and springs used, not necessarily from turning the distributer to get the desired results....Otherwise you could end up with a crap load of initial advance, which could be bad....

    After you get the total advance and the curve where you want them, recheck the initial advance and make slight tweaks if needed....

    The dial back timing light is a very useful tool for graphing your timing curve, and finding total timing, since many factory dampeners are not marked for that high a reading
     

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