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Thread: lycoming 540

  1. #1
    Member ArcherBob's Avatar
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    Default lycoming 540

    I¬ím having an issue with my lycoming 540. It sits on a 14¬í Hull. It has toggle switches to turn off the magnetos one at a time, and the engine should continue to run on half the plugs. For no apparent reason it started doing this thing where I can run with both switches on or one on but if I turn the other off it stalls out. I¬íve replaced the magneto that goes to the switch which was killing the engine, no luck! So without paying for A&P certified work $$$. Is there a mechanic around fairbanks that would work on this airboat and not charge aircraft mechanic prices? I know this isnít about flying so if not allowed here, Sorry. Thanks for any advice!
    Bob

    Become one with Nature......... Then Marinade it.

  2. #2

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    Sounds like you switched out the wrong mag. The switch that was killing the engine was turning off the mag that works...the other one should be the problem.
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  3. #3
    Member ArcherBob's Avatar
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    I put the multi meter on that one and itís doing itís job. Thereís something else going on.
    Bob

    Become one with Nature......... Then Marinade it.

  4. #4
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    Quote Originally Posted by ArcherBob View Post
    I put the multi meter on that one and itís doing itís job. Thereís something else going on.
    it can be difficult to troubleshoot over the internet... P leads are either grounded or not, a grounded P lead shuts off the magneto. An ungrounded magneto is called a hot mag. You need to ascertain whether your mag switches are correctly marked for the mag they are grounding, also if the ground circuit is complete. Next leave the mag that is ungrounded and working alone and remove the ungrounded mag that isnít working. You can make up a small test stand with a battery drill and a vice. Spin up the dead mag to see what is going on. There are two mag manufacturers out there slick and bendix. There can be many reasons why a mag is not functioning. You can also have bad plugs and ignition leads that make you think that your mag is bad. Start with the easy stuff and work your way forward.You need to eliminate the plugs and leads as being a problem, then figure out what type of mag you have. There are two timing settings for a mag, internal to itself and external to your engine. Both of these timing setting are critical to the proper functioning of the engine ignition system. Do you know how to time a mag to the engine? Can you figure out when the #1 cylinder is say 25 degrees before TDC (top dead center), on the compression stroke? If you are not able to follow this conversation, just pay an A&P mechanic to do it for you... NOTE!!! When your mags are not grounded, your engine can start when you move the prop...

  5. #5
    Member ArcherBob's Avatar
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    That is very informative and hopefully helpful! I have done quite a bit of troubleshooting and I know the switches are working correctly and the plugs are good. You have definitely given me some new ideas to troubleshoot so thank you!!!
    Bob

    Become one with Nature......... Then Marinade it.

  6. #6
    Member ArcherBob's Avatar
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    Figured it out, it was my fault. When I put the rebuilt magneto in I had the gear 180* off which threw the timing way off and made the switch do nothing. Running like a champ now. Thank you for the response!
    Bob

    Become one with Nature......... Then Marinade it.

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