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Thread: slow crank.

  1. #1

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    Default slow crank.

    Question about slow cranking (1953 with an O-320). I see many planes that the starter barely turns the engine fast enough to start, including mine. Has anyone tried running a main ground cable directly from the starter to the battery instead of directing the ground path through the engine, engine mount, frame, then to the negative cable and returning to the battery? There are many areas that can aggravate a voltage drop issue in an old plane. It seems like a dedicated ground cable could solve many of them. Is it an issue with legality? Does installing a ground wire become and alteration or would it be considered a repair of existing, even though it would look different than the original?

  2. #2

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    Default Re: slow crank.

    Can't see it being worth the trouble to run a ground. There's only 3 or 4 spots to give you trouble on the ground side. I think I'd start with a quick voltage drop test to confirm your suspicions and go from there. I would think if anything the starter solenoid would be the biggest culprit of a drop if there is one. But that's a quick check too. I believe 0.2V is ideal but some kids are cool with as high as 0.5V.

  3. #3

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    Default Re: slow crank.

    Quote Originally Posted by Electrathon View Post
    Question about slow cranking (1953 with an O-320). I see many planes that the starter barely turns the engine fast enough to start, including mine. Has anyone tried running a main ground cable directly from the starter to the battery instead of directing the ground path through the engine, engine mount, frame, then to the negative cable and returning to the battery? There are many areas that can aggravate a voltage drop issue in an old plane. It seems like a dedicated ground cable could solve many of them. Is it an issue with legality? Does installing a ground wire become and alteration or would it be considered a repair of existing, even though it would look different than the original?
    Do you already have copper cables, or are you still running with the original aluminum cables?


    Sent from my iPhone using Tapatalk

  4. #4

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    Default Re: slow crank.

    Quote Originally Posted by dgapilot View Post
    Do you already have copper cables, or are you still running with the original aluminum cables?
    Sent from my iPhone using Tapatalk
    I know I have excessive drop. .4 to .5 through the original positive cable to the starter and .5 plus (the digital reading was jumping as it cranked) from the starter to the battery negative side. Often times .2 is common through most connections so the stack of connections between the starter and the negative battery can easily be over a .5 volt, if all is working, worse with age and corrosion. I have an automotive background and this issue is common on cars, especially older ones, when the grounds are corroded over time. The best fix for it is to run a ground straight to the block from the battery. It is surprising how much better an old high compression engine will crank once this is done. Airplanes always seem to crank slow, so I was curious if this is a viable fix or a violation because you made it better than designed and someone will be upset because of it.

  5. #5
    Jim's Avatar
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    Default Re: slow crank.

    Hi,

    The question above about still using the original aluminum cables was to see if you may benefit using copper instead.

    https://bogertaviation.com/collectio...aft-cable-kits

  6. #6
    Troy Hamon's Avatar
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    Default Re: slow crank.

    I have had that experience on two different Tripacers. Both times I replaced the battery, battery cable, and starter before it was all sorted out. In both cases the only part that didn't help was the new battery. The cable and the starter can both definitely make a huge difference though. Obviously the battery can as well but it wasn't the issue in either case for me.

  7. #7
    CamTom12's Avatar
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    Default Re: slow crank.

    I added a 2 wide braided ground strap from my block to my battery.

    I also run an earthX battery, and I can almost taxi with my starter.

  8. #8

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    Default Re: slow crank.

    Quote Originally Posted by CamTom12 View Post
    I added a 2 wide braided ground strap from my block to my battery.

    I also run an earthX battery, and I can almost taxi with my starter.
    Don't you have your battery on the firewall? Shorter than back to under the seat...

    Sent from my moto g(7) using Tapatalk

  9. #9
    CamTom12's Avatar
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    Default Re: slow crank.

    Quote Originally Posted by krwill View Post
    Don't you have your battery on the firewall? Shorter than back to under the seat...

    Sent from my moto g(7) using Tapatalk
    True. But you could add a ground strap from the engine to the frame and check/clean/replace your frame to battery ground to get similar results.

  10. #10
    Administrator Steve Pierce's Avatar
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    Default Re: slow crank.

    Troubleshoot, have not seen .5 volt make a difference. I recently trouble shot a Maule that would hit the compression strock and stop. Voltage at the starter was 6-7 volts, none of the connections including the grounds were warm and when I checked the voltage at the battery it was the same as at the starter. That told me my lose was not in my connections. Installed a SkyTec NL starter in place of the LS and it worked great. Have found bad ground straps and connections but I don't replace anything until I troubleshoot and verify what the culprit is. Old school starters draw twice the amperage as the new light weight ones, like 300 plus amps.

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