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BC12-D A65 to A75 Conversion

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  • #61
    Re: BC12-D A65 to A75 Conversion

    Staggered timing fires the lower plugs first. The reason is because the lower plugs are closer to the exhaust valves and the mixture there is weaker. A weaker mixture burns slower, so you want to light it earlier.
    John
    New Yoke hub covers
    www.skyportservices.net

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    • #62
      Re: BC12-D A65 to A75 Conversion

      On the timing issue, early A65's had both mags set to one degree setting. The mags fired one set of lower plugs and one set of upper plugs. If you changed wiring and had a single mag firing all upper or all lower plugs, then the timing split.

      I have seen one case( a C series) that had the cylinder holes bored to A65 size, it had no Data plate and I was told it was an A65-12 from a M18 Mite.

      I had a Cessna 140 with a C85-14.

      I still can't find information that an A65-14 was ever produced or installed into any airframe. If nothing exists my congratulation for acquiring engineering approval for installation of an engine that doesn't exist.
      EO

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      • #63
        Re: BC12-D A65 to A75 Conversion

        Then we have another reason: the 28 on left mag ( lower) and 30 on right was done with no impulse mags to let the engine start easier with the left firing first. In fact if she kicked back then you went to left mag only for starting. I timed my first set of Case mags on an A-65 in 1950 at age 8.... I can discuss flame front and all those other comments with the best of them, the slow turning little engines (and there are many of them ) will run okay if they are close on timing
        Any body ever flame tune a Model A Ford aircraft engine at night just watching the flame coming out of the short stacks?
        Taylorcraft Foundation, Inc
        Forrest A Barber 330-495-5447
        TF#1
        www.BarberAircraft.com
        taylorcraft@neo.rr.com

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        • #64
          Re: BC12-D A65 to A75 Conversion

          When I was I kid I watched dad tune his 1/4 midget that way. Memories I had forgotten, thanks Forrest. Larry
          "I'm from the FAA and we're not happy, until your not happy."

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          • #65
            Re: BC12-D A65 to A75 Conversion

            Originally posted by Forrest Barber View Post
            the 28 on left mag ( lower) and 30 on right was done with no impulse mags to let the engine start easier with the left firing first. In fact if she kicked back then you went to left mag only for starting.
            Forrest, Technically, you want to retard timing for improved starting. So you need to start on the mag which fires later. I understood what you meant, but some might get confused on this.
            Terry Bowden, formerly TF # 351
            CERTIFIED AERONAUTICAL PRODUCTS, LLC
            Consultant D.E.R. Powerplant inst'l & Engines
            Vintage D.E.R. Structures, Electrical, & Mechanical Systems
            BC12D, s/n 7898, N95598
            weblog: Barnstmr's Random Aeronautics
            barnstmr@aol.com

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