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Thread: Slick mag problem

  1. #1

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    Slick mag problem

    I have a Titan IO370 on my experimental cub under construction. One Slick mag on the left side and an Emag on the right. After mounting the engine, timed the mags, and thought I was through. In a discussion with a friend, about on is off and off is on for a mag switch, I grabbed up the mag toggle switch for the Slick, still just hanging by the wires, and was going to show him that when the switch was on, it grounded the mag, and when off it allowed the mag to run. With a volt meter I hooked to both poles of the toggle switch, and found that in either switch position, the mag was grounded. So removed the switch, it was working fine, checked the p-lead wire and found it went to ground, so removed it from the mag, and found the stud that is on the mag for the p-lead shows ground. Had not found this before I timed it, but just not sure when was the last time I checked the switch. I am stumped as to why it shows ground on the p-lead stud. My thinking is it should not be grounded until the it is switched off. Any thoughts.
    Thanks Bruce
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  2. #2
    wireweinie's Avatar
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    Voltmeter or ohmmeter? Two VERY different settings. You can't usually check a mag accurately with an ohmmeter. It can read back through other circuitry. When the points are closed, you'll read directly to ground (0 ohms of resistance). When the points are open, you'll read through the primary coil (very low resistance, just a few ohms). Then if you have capacitors or start vibrators or retard breakers in the system, you could also read through their circuits. If you want to accurately check the P-leads and master switch, connect the timing box. It is made to sense whether it's reading directly to ground or through the primary coil. Go back and set up your timing box with no P-lead connected to the mag (SAFETY!!!! HOT MAG AT THIS POINT! Take precautions) You'll be able to make the light and buzzer activate as you rock the prop to open/close the magneto points. Now connect the P-lead, with the master switch in the 'on' position (switch open). You should have identical results as before with the timing box. Now place the master switch in the 'off' position. The timing box should now show the P-lead grounded regardless of prop position.

    Web
    Life's tough . . . wear a cup.

  3. #3

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    What Web says.

    Also, if you are using one of those rotary switches, pay attention to which lead goes where. I am not smart enough to figure out whether L means left mag grounded or left mag hot, and neither are a lot of other mechanics. When a mag fails, diagnosing it with that mag switch only will get you the wrong mag about half the time.

  4. #4
    skukum12's Avatar
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    ^^^Switch pointing at left mag should mean left is hot right is not. (and visa versa) unless I missed something....
    "Always looking up"
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  5. #5
    wireweinie's Avatar
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    Quote Originally Posted by bob turner View Post
    What Web says.

    Also, if you are using one of those rotary switches, pay attention to which lead goes where. I am not smart enough to figure out whether L means left mag grounded or left mag hot, and neither are a lot of other mechanics. When a mag fails, diagnosing it with that mag switch only will get you the wrong mag about half the time.
    That's a good point about the rotary switches. It's confusing because 'on' is an open switch for mags. The easiest way to not get messed up is to keep it simple; Left P-lead always goes to the 'L' terminal and the right P-lead always goes to the 'R' terminal. (forget about Slick Starts, vibrators, and retard breakers for the moment)

    If you need to troubleshoot the switch, disconnect the P-leads first. THEN go ahead and use an ohmmeter to see when the contacts open and close. Selecting 'L' or 'R' means selecting that mag will to be 'on'. 'On' = open contacts

    I think it's safe to say that all of us that have turned wrenches have removed the wrong mag at some point due to bad info or over thinking the switch. A good tip is to take both mags with when rescuing a stranded aircraft and double check that the left & right P-leads actually go to the correct mag. Sort the rest of the issues out in the shop.

    Web
    Life's tough . . . wear a cup.
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  6. #6

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    There you go. I have heard nightmare stories of aircraft grounded in strange places and they overhaul the wrong mag. I like toggle switches. I still verify which wire goes where.
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  7. #7
    cubdriver2's Avatar
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    Quote Originally Posted by wireweinie View Post
    That's a good point about the rotary switches. It's confusing because 'on' is an open switch for mags. The easiest way to not get messed up is to keep it simple; Left P-lead always goes to the 'L' terminal and the right P-lead always goes to the 'R' terminal. (forget about Slick Starts, vibrators, and retard breakers for the moment)

    If you need to troubleshoot the switch, disconnect the P-leads first. THEN go ahead and use an ohmmeter to see when the contacts open and close. Selecting 'L' or 'R' means selecting that mag will to be 'on'. 'On' = open contacts

    I think it's safe to say that all of us that have turned wrenches have removed the wrong mag at some point due to bad info or over thinking the switch. A good tip is to take both mags with when rescuing a stranded aircraft and double check that the left & right P-leads actually go to the correct mag. Sort the rest of the issues out in the shop.

    Web
    During this Christmas Season we thanked the good Doctor who holds us while we stand on our toes and makes us cough

    Web, you are a treasure chest that just keep giving. You are always trying to excite electrons in all of our brains to understand how the juice flows. You always take the time to break it down so we are able to understand and learn something new. If I get up to visit Stu in Ak again I will look you up and be honored to shake your hand.

    Thank You

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  8. #8
    wireweinie's Avatar
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    I thank you Sir and I'd be happy to shake your hand.

    I also always look forward to meeting other members during get togethers like the trade show and New Holstein.

    Web
    Life's tough . . . wear a cup.
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  9. #9

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    Thanks for the explanation, I guess I have always called a muti meter, a volt meter. The function that I was using was continuity. Checking continuity between ground and the plead stud on the mag. Will retime the mag today, with out the plead and with it, and switch on and off.
    I am using toggle switches, as was on the original Super Cubs I believe. Thanks again for the help, the electrical portion of the build often gets above my pay grade.
    Bruce

  10. #10
    www.SkupTech.com mike mcs repair's Avatar
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    Just make sure you have really good switch guards if you use toggles, so your coat sleeve don’t switch them off while you are spinning the trim handle


    Sent from my iPhone using SuperCub.Org

  11. #11
    wireweinie's Avatar
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    Oh yes!

    Had a customer caught in rough weather. While he was bouncing around the sleeve of his coat hooked the toggles and shut his mags off. Figured it out when he was going through a 'mad minute' checklist.

    Web
    Life's tough . . . wear a cup.
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  12. #12

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    Bruce - sounds like you missed the point. Doesn't make any difference what you call it, a multimeter will not help at the mag. An ohm meter will read zero at the p-lead no matter what.

    Borrow a buzz box. Re-read Web's first post. You are dealing with reactance, not resistance.
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  13. #13
    skukum12's Avatar
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    Better yet, buy a buzz box. They don't cost much and you won't get that buyer's remorse of having an expensive tool that hardly gets used. Additionally, your buddies will be impressed when they need to borrow it.
    "Always looking up"
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  14. #14

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    http://www.brewingtontech.com/

    Buy your own kit for $25 and have fun. They work just as good as the big$ ones.

    JP

  15. #15

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    Thanks all. I do have the timing light box that I used to time the mag. Just got a little off track thinking that the plead was grounded even with the switch open as shown on the ohm meter. . I retimed the mag yesterday with out the plead hooked on, and it was right on. So I then tried the pull through test on number one cylinder, and the plug fired. So seems it is working fine. The mag switch guards are the stock Super Cub covers that I picked up surplus some where
    I still have to check it to see if the switch grounds it out. Will let you know what I find, but I think it will be working fine.
    Bruce

  16. #16
    skywagon8a's Avatar
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    Now that that is resolved, I would throw out that Slick and replace it with a second E-mag. The E-mag has variable timing which is related to manifold pressure and RPM. This is one of the advantages of the E-mag. The Slick runs at just one timing point. So the timing will vary between the two ignition spark generators. You are losing some of the efficiency which the E-mag offers. It would be better to have all of the spark plugs operating in the same sparking cycle. If you are concerned about hand propping with a dead battery just wire in a small 9 volt battery to excite the E-mags for starting purposes and low rpm operation.
    N1PA

  17. #17
    hotrod180's Avatar
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    Quote Originally Posted by eskflyer View Post
    http://www.brewingtontech.com/
    Buy your own kit for $25 and have fun. They work just as good as the big$ ones.
    "Big $ ones" ?
    Spruce has buzz boxes for $67.

    https://www.aircraftspruce.com/catal...4aApeQEALw_wcB
    Cessna Skywagon-- accept no substitute!

  18. #18
    algonquin's Avatar
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    ATS has the box for 49.99 right now. I made one of those kits boxes and it does work great, and the battery low it plays taps on the speaker.

  19. #19
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by planenuts View Post
    The mag switch guards are the stock Super Cub covers that I picked up surplus some where
    Bruce
    the crash I was referring to had those installed...... might make bigger ones..

  20. #20

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    Put them in the wing root. I too dislike those left elbow controls and switches.
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  21. #21
    fobjob's Avatar
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    One fine day on planet Udah I had both Slicks go out on me at the same time...on the ground.....one was a cap, the other was the coil. Dang near had to push the bird back to the hanger...They had 450 or so hours. My IA said, never try to take a Slick all the way to 500. I like the idea of having a mag make a nice blue sizzley snappy spark ripe with menace, and the slicks always disappointed me in that respect, but otherwise seem to be pretty reliable...if...
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  22. #22

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    I finally got the time yesterday to do what Web suggested, timed the mag, with out Plead, then made a new cable up, with the shield being used to carry the ground from the mag case to the mag switch, installed and then checked the timing again, with the mag switch in the open position, it showed as before, with the switch closed it showed no lights or buzz. The Emag was much easier, just blow on the tube and you are good to go. Thanks for the advise to change out the Slick, when the pocket book recovers a bit, think I will do just that. Now to figure out a good switch cover to keep from accidentally turning one or both off, and also to keep from knocking one open unintentionally.
    Bruce
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  23. #23
    wireweinie's Avatar
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    I have some customers that like the locking style toggle switch such as the MS24658-22D. My opinion is that the switch guards should always be installed, but the locking feature adds a lot of security.

    Web
    Life's tough . . . wear a cup.

  24. #24

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    web, what on-off mag switch do you like? without the lock.

  25. #25
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    I like a key switch, preferably off-left-right-both (with a separate starter button if required).
    Hard to accidently turn off, plus I like being able to remove the key and hang it on a knob or whatever--
    IMHO that makes it less likely for the mags to be left on.
    Cessna Skywagon-- accept no substitute!

  26. #26
    wireweinie's Avatar
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    Quote Originally Posted by tempdoug View Post
    web, what on-off mag switch do you like? without the lock.
    I agree with Hotrod on this one; I like a key switch. Drill one hole in the panel and you cover both mags and start circuit.

    If you go with toggles, I'd avoid the original switches. They were lamp switches. Literally.

    Electrically almost any toggle will work. The current that runs through the P-lead is almost to small to measure. I've installed lots of NKK brand, #S302 full size toggles. If you want to go MIL-spec try MS35058-23. I realize that these are single pole, double throw but they can still be used as a single pole, single throw switch by just leaving the third terminal unconnected. If you want to go with the miniature toggle style (smaller target to cause damage to) try TE Conectivity (formerly Alcoswitch) A101SYCB04 or similar.

    A tip for the float guys. If your aircraft stays on floats for most of it's life or is flown/stored near salt water, for any application, chose a switch that is listed as 'sealed'. And if it has a boot available for installing over the switch, use it. This will extend the life of the switch.

    Web
    Life's tough . . . wear a cup.

  27. #27
    www.SkupTech.com mike mcs repair's Avatar
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    I Always put in key switch with start position.

    Placement of switch and primer is very important, so when you are in start position the ball of your right hand operating the key switch can feed primer if needed

  28. #28

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    Click image for larger version. 

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    These antiques come up for sale kind of regular. The batt position was for a points, distributor, and coil ignition. Mag was for a magneto. Used on an aircraft with a radial engine- Cessna 195 maybe? When it is on "both" the batt is hot and the mag is open. When it is "off" the batt is open and the mag is grounded. Neighbor thought it would look cool in his Pietenpol but no way could it operate two mags.
    You can't get there from here. You have to go over yonder and start from there.

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