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Thread: Why?

  1. #1
    cgoldy's Avatar
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    Why?

    Why (often) does the engine start when I release the key?
    And why does it often take 6 blades to start with the key and only one when hand propping?
    I think I have noticed this with cars as well.

    Or am I imagining this?

    One mag and one Emag


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  2. #2
    storm_pilot's Avatar
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    Take a look at your mag and ignition switch set-up. In the crank position most ignition switches are set up to utilize only the mag with the impulse coupling installed which retards the timing and increases spark output. Usually this is the left mag. Then when you release the switch both mags fire. You say that you have one mag and one Emag. Where is each mounted? Left or Right? The Emag will produce great spark at low RPM since it is powered by the battery and is programmed to automatically retard timing at low rpm. I suspect that you are running the standard mag on the left and that it may be weak, improperly timed, or that the impulse coupling may be malfunctioning. Personally I would set it up to start on the Emag and eliminate the impulse coupling altogether.
    Buying parts is CHEATING!
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  3. #3
    cubdriver2's Avatar
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    Mags fire better at a slower speed

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"

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    hotrod180's Avatar
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    Starter might be spinning the engine too fast for the impulse to work correctly?
    Cessna Skywagon-- accept no substitute!
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    PerryB's Avatar
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    You probably have a points-related issue on the impulse mag. The other mag is shunted out while cranking but wakes up when you release the key. If pulling the P-lead off the right mag makes the issue go away, you have your culprit, left mag is dying. CAUTION-- the engine will always be hot with a mag lead disconnected.
    After Monday and Tuesday, even the calendar says WTF !

  6. #6
    Eddie Foy's Avatar
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    ????????????



    Quote Originally Posted by cubdriver2 View Post
    Mags fire better at a slower speed

    Glenn
    "Put out my hand and touched the face of God!"

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    cruiser's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    Mags fire better at a slower speed

    Glenn
    To quote from The Magneto Ignition System by John Schwaner “the amount of primary current is determined by how strong and how fast the rotating magnetic field crosses the primary windings”. Page10.

  8. #8
    cgoldy's Avatar
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    Quote Originally Posted by hotrod180 View Post
    Starter might be spinning the engine too fast for the impulse to work correctly?
    You might be onto something here Hotrod. Since I fitted the light weight prop and earthx batery it cranks faster but does not start as easily.

    Mag on left and Pmag on right and wired correctly. When hand propping I start it on the impulse only.
    Back Country O-375 wide body extended wing cub

  9. #9
    www.SkupTech.com mike mcs repair's Avatar
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    yup, check your impulse coupling health.. you will break the starter off if impulse fails to engage and retard spark/attempt to kick back....

  10. #10
    PerryB's Avatar
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    Quote Originally Posted by cruiser View Post
    To quote from The Magneto Ignition System by John Schwaner “the amount of primary current is determined by how strong and how fast the rotating magnetic field crosses the primary windings”. Page10.
    The FASTER the field crosses the coils, the more voltage is produced. Mags get hotter with speed until you reach the point that saturation time becomes an issue. That's why the drag racers use them. As speed increases and saturation time diminishes, induction voltage continues to climb so spark intensity stays relatively constant. With our low RPM engines the spark intensity is hotter all the way to redline. We don't get anywhere near plateau speed.
    After Monday and Tuesday, even the calendar says WTF !
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  11. #11
    cgoldy's Avatar
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    Quote Originally Posted by mike mcs repair View Post
    yup, check your impulse coupling health.. you will break the starter off if impulse fails to engage and retard spark/attempt to kick back....

    All I I know is that it clicks when turning by hand. How else do you check it Mike?

    And that doesn't explain why it fires on first blade when hand propping.
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  12. #12
    cgoldy's Avatar
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    I wonder if my tach reads when starting. I'll check to see what rpm the starter runs it at. Any one know what RPM impuls couplings work up to?
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    cgoldy's Avatar
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    Quote Originally Posted by PerryB View Post
    You probably have a points-related issue on the impulse mag. The other mag is shunted out while cranking but wakes up when you release the key. If pulling the P-lead off the right mag makes the issue go away, you have your culprit, left mag is dying. CAUTION-- the engine will always be hot with a mag lead disconnected.

    I might just swap the wires on the back of the switch and test if it starts better on the emag.
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  14. #14
    skywagon8a's Avatar
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    Quote Originally Posted by cgoldy View Post
    You might be onto something here Hotrod. Since I fitted the light weight prop and earthx batery it cranks faster but does not start as easily.

    Mag on left and Pmag on right and wired correctly. When hand propping I start it on the impulse only.
    If the engine is turning enough faster the impulse will not engage because it thinks that the engine is already running. The impulse fly weights will be centrifugally disengaged. So the spark will be advanced to the run setting rather than being retarded for starting. That is why it starts when hand propping as it's not turning too fast.

    If you have both a P-mag and an impulse coupled magneto you should remove the grounding connection on the back of the mag/starter switch. Then when you select start, both will be firing.
    N1PA

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    Quote Originally Posted by skywagon8a View Post
    If the engine is turning enough faster the impulse will not engage because it thinks that the engine is already running.
    The mag should still fire once or twice as the cranking speed comes up.

  16. #16
    cubdriver2's Avatar
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    I have propped a bunch of engines going back to 1911. 20 hp thru a 400 V12 Liberty. Mag speed is important to generate current. The 50 hp Franklin in the Honroit had to be propped closes to the hub to get enough speed. But others like a B5R Kinner on a Fleet will " never " start moveing the prop fast, starts better hardly moving it. We had an Oliver tractor with a mag that we converted to 12V and it spun so fast it wouldn't start till when you released the starter button and it slowed down. The 400 Liberty just like the 680 in the Stearman fired with one hand slowly pullinging the blade. But what do I know?


    Glenn
    Last edited by cubdriver2; 03-31-2018 at 09:22 AM.
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  17. #17

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    “I have propped a bunch of engines going back to 1911.”

    Man Glenn, you look great for your age! (If I didn’t say it, you know darn well someone would...)
    Mark

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    Is the mag Slick or Bendix?
    DENNY
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    PerryB's Avatar
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    Quote Originally Posted by cgoldy View Post
    I wonder if my tach reads when starting. I'll check to see what rpm the starter runs it at. Any one know what RPM impuls couplings work up to?
    To my knowledge, they typically disengage at about 300-350 engine RPM. I don't think any starter is going to get past about 200 BUT... If you have weak springs (or one broken) in the IC, that number is going to come down. I'd been thinking about it some more and I think you have 1) an internal timing/e-gap issue in the left mag and - 2) a failing IC. Basically time to overhaul lefty.
    After Monday and Tuesday, even the calendar says WTF !
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  20. #20
    Hardtailjohn's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    But others like a B5R Kinner on a Fleet will " never " start moveing the prop fast, starts better hardly moving it.
    Glenn
    I was just gonna say....watch someone that doesn't know how, try to start a Kinner!!
    John
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  21. #21
    cubdriver2's Avatar
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    Quote Originally Posted by Hardtailjohn View Post
    I was just gonna say....watch someone that doesn't know how, try to start a Kinner!!
    John
    Most time I'm too stupid to understand the why's and what's that make it work. But I'm lazy enough to figure out what it likes to make it work, my bad

    Glenn
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  22. #22
    aktango58's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    I have propped a bunch of engines going back to 1911.

    Glenn
    That makes you older than EATON! Now I am impressed.
    I don't know where you've been me lad, but I see you won first Prize!
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    Quote Originally Posted by mam90 View Post
    “I have propped a bunch of engines going back to 1911.”

    Man Glenn, you look great for your age! (If I didn’t say it, you know darn well someone would...)
    Dang, I was just going to say something similar.

  24. #24
    cruiser's Avatar
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    When someone asks a question about some special technique to get this or that started and the secret start system begins with driving around the hangar in a clockwise direction but under a full moon you must go in a counter clockwise direction or some such BS I always believe that the real answer is basic preventative maintenance. Fuel, air and ignition is all it takes. In the correct proportion. Some folks are too smart for that.

  25. #25
    hotrod180's Avatar
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    Quote Originally Posted by skywagon8a View Post
    .....If you have both a P-mag and an impulse coupled magneto you should remove the grounding connection on the back of the mag/starter switch. Then when you select start, both will be firing.
    FWIW I much prefer a off/left/right/both key switch with a separate starter button.
    Cessna Skywagon-- accept no substitute!
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  26. #26
    WhiskeyMike's Avatar
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    I had this problem after an overhaul and it turned out that the "new" left mag was bad, so it started when you let go of the key to hit both. Make sure it's working. After that the mag check was weird and we weren't getting any drop on right, so we knew something was up.

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    Quote Originally Posted by hotrod180 View Post
    FWIW I much prefer a off/left/right/both key switch with a separate starter button.
    If you have a separate starter button, and 2 impulse mags, is there anything wrong with cranking the starter first to get up to speed and then switching the mag switch to both to start the engine? I know the usual method is to switch on and then crank to start.

  28. #28
    cgoldy's Avatar
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    Quote Originally Posted by PerryB View Post
    To my knowledge, they typically disengage at about 300-350 engine RPM. I don't think any starter is going to get past about 200 BUT... If you have weak springs (or one broken) in the IC, that number is going to come down. I'd been thinking about it some more and I think you have 1) an internal timing/e-gap issue in the left mag and - 2) a failing IC. Basically time to overhaul lefty.

    I think I am seeing 300 rpm with the starter only. But I have a crappy little tach so hard to be sure that low down. But you might be onto it Perry.

    So just to recap. Last month before I replaced my heavy borer with the whirlwind and lead acid with an earthex and moved the battery location from rear seat to fire wall, she would start on the second or third blade religiously.
    Last edited by cgoldy; 03-31-2018 at 02:19 PM.
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  29. #29
    WhiskeyMike's Avatar
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    Quote Originally Posted by AK81 View Post
    If you have a separate starter button, and 2 impulse mags, is there anything wrong with cranking the starter first to get up to speed and then switching the mag switch to both to start the engine? I know the usual method is to switch on and then crank to start.
    . That is standard operation in radial engines to get some of the oil cleared out of the lower cylinders to avoid liquid lock. I frequently do it on four-cylinder opposed engines as well when I have a separate starter button I don’t know who invented this key switch start thing but I hate it. For example how in the heck are you supposed to crank a loaded engine through with the throttle open and the mixture lean with the mags off It looks to me like a combination of slick marketing and security theater in that having a key is somehow supposed to keep people from stealing airplanes. That said I also hate cars with a new computer style on off button. it strikes me as one more way to remove competence - and responsibility- from people. Crabbiness aside I’d like to wish everybody a joyous Easter

  30. #30
    skywagon8a's Avatar
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    Quote Originally Posted by cgoldy View Post
    So just to recap. Last month before I replaced my heavy borer with the whirlwind and lead acid with an earthex and moved the battery location from rear seat to fire wall, she would start on the second or third blade religiously.
    Colin, That is why I said in post#14 that it is turning too fast for the impulse to do it's job. Try exchanging the P leads on the back of the mag switch so that the mag is shut off and the Pmag is on during starting.


    Quote Originally Posted by WhiskeyMike View Post
    . I don’t know who invented this key switch start thing but I hate it.
    This key start thing showed up when they started using the "shower of sparks" for starting instead of impulse couplings. They wanted to ensure that one mag was dead and that the "shower of sparks" was properly turned on only while the starter was engaged.
    N1PA

  31. #31
    aktango58's Avatar
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    Quote Originally Posted by cgoldy View Post
    I think I am seeing 300 rpm with the starter only. But I have a crappy little tach so hard to be sure that low down. But you might be onto it Perry.

    So just to recap. Last month before I replaced my heavy borer with the whirlwind and lead acid with an earthex and moved the battery location from rear seat to fire wall, she would start on the second or third blade religiously.
    Change in prop weight changed the speed it turns, and time to spool up.
    I don't know where you've been me lad, but I see you won first Prize!

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    AkPA/18's Avatar
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    Hello Cgoldy
    Is your keyswitch an ACS. If so that is a common symptom of it going bad. I believe there might be a repair kit for that key switch. Also I believe there is a service bulletin or possibly an AD on that switch. This is just from several of my friends that have had that problem. You are not the only one. If not an ACS disregard

    Mark
    Last edited by AkPA/18; 04-01-2018 at 05:28 PM.
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  33. #33
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by AkPA/18 View Post
    Hello Cgoldy
    Is your keyswitch an ACS. ... I believe there might be a repair kit for that key switch. .

    Mark
    http://www.aircraftspruce.com/catalo...?clickkey=7224

  34. #34
    cgoldy's Avatar
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    Yes! I have an ASC!

    Thanks Mark. The depth of knowledge on this site never ceases to amaze me.

    Col Goldy



    Quote Originally Posted by AkPA/18 View Post
    Hello Cgoldy
    Is your keyswitch an ACS. If so that is a common symptom of it going bad. I believe there might be a repair kit for that key switch. Also I believe there is a service bulletin or possibly an AD on that switch. This is just from several of my friends that have had that problem. You are not the only one. If not an ACS disregard

    Mark
    Back Country O-375 wide body extended wing cub
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  35. #35
    AkPA/18's Avatar
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    Hopefully that is the problem. Everything that was written above also makes perfect sense though. Just another direction to try. Your issue does mirror the keyswitch failure---starts on key return and handprops fine. Best of luck. If i remember right there was visible carbon tracking in the switch?

    Mark
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  36. #36
    Eddie Foy's Avatar
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    One reason the Magneto switch is coming out of my 180. I prefer the mag toggles and a button.
    "Put out my hand and touched the face of God!"

  37. #37
    cgoldy's Avatar
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    Quote Originally Posted by Eddie Foy View Post
    One reason the Magneto switch is coming out of my 180. I prefer the mag toggles and a button.
    So if I was to do the same, replace with switches and a button, how could I disable the aircraft to satisfy CASA's. (FAA) security concerns?


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  38. #38
    hotrod180's Avatar
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    "Security" of any mag switches is kind of a joke, since you can bypass them by just cutting the p-leads.
    But I will admit that I am more comfortable with a key switch vs toggles.
    You can't stop a determined thief, but like most locks, they keep the honest people honest I guess.
    Cessna Skywagon-- accept no substitute!

  39. #39
    Eddie Foy's Avatar
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    Put a keyed switch in the master to master solenoid line is one way. A hidden kill switch is another way. Old Cubs have no keys.



    Quote Originally Posted by cgoldy View Post
    So if I was to do the same, replace with switches and a button, how could I disable the aircraft to satisfy CASA's. (FAA) security concerns?




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  40. #40

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    This post makes me realize, that since I went to a mechanical master switch (mounted on the inside firewall, inches away from the EarthX battery) that uses a 16" pushrod with a T handle that I can easily access like the other panel mounted controls, I have failed to placard it's function. Good security I guess, lousy keeping to the regs, even for an experiemental type like me. I do have a keyed ignition also, but the keys, like all my vehicles, stay in all the time. One new placard coming up.

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