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Slick mag problem

planenuts

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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
 
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
 
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.
 
^^^Switch pointing at left mag should mean left is hot right is not. (and visa versa) unless I missed something....
 
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
 
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.
 
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

Happy New Year

Glenn
 
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
 
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
 
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
 
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
 
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.
 
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.
 
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
 
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.
 
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.
 
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...
 
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
 
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
 
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.
 
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
 
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
 
mag ign switch.jpg
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.
 

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New guy here, J3 owner.

Having some puzzling issues with a new-to-me A7 mag switch and new P-leads for the Slick mags (fairly new; maybe 125 hrs). The new P-leads ( from here: https://bogertaviation.com/products/p-leads-slick-style) come with the P-lead shielded wire and a ground wire for each mag. The P-lead terminals were connected to the P-lead connectors (with wafer insulation washers) on each mag and then to the appropriate posts, L and R, on the A7 mag switch. The ground wire terminals were connected to the GND screws on each mag and then both other ends were connected to the ground post on the mag switch.

Everything worked great for several days and flights and then the engine would not turn off when the mag switch was turned to the “off” position.

Disconnected the wires at the mag switch, cleaned the posts with Scotchbrite, checked continuity, reconnected the wires and all worked fine for another few days. Then, it refused
to turn off.

Disconnected the P-leads and ground wires at each end (mag switch and at the mags), checked continuity of the wires and the mag switch again, all Ok. Reconnected, and all worked fine for a few more flights. Then, it again wouldn’t turn off.

Remived the A7 mag switch and cleaned/serviced it according to this: https://www.shortwingpipers.org/forum/attachment.php?attachmentid=8258&d=1428156785
Then checked continuity, reassembled, and again it worked fine for a couple of test starts but then wouldn’t turn off at the end of the first flight.

Any ideas?? I’m at a complete loss and totally mystified. I spoke with a guy at Champion Aerospace before installing anything and he suggested (if I recall correctly) leaving one ground wire disconnected. The local A&P didn’t do that and connected them to the mag. Not sure if that’s a contributor or not. Regardless, I’m open to any insight at all.

This Cub came to me with some ugly toggle switches as mag switches. Wanting to restore it to “original” as much as possible I found and had the A7 installed. Almost ready to go back to the toggle switches as I’d prefer to go back to the toggle switches. This really should t be this difficult, should it?!
 
By your description you have done the proper things. It sounds as though your A-7 switch is tired. Perhaps the spring contacts are weak and sometimes not making contact?
I'm certain that you know this, but it is worth repeating: Magnetos continue to run with an open in the Plead wire or no Plead wires at all. Continuity between the magneto points through the switch back to the magneto case closes the point circuit shutting off the mag. This sometimes is confusing for those who are used to turning on a light by closing a circuit. Magnetos turn on by opening a circuit.

There is nothing wrong with toggle switches. Hot mags are extremely dangerous, particularly when you think they are off. By your description, that A-7 is unreliable and even if it appears to be functioning properly it can not be trusted.

An engine does not even need to be turning to start running. It is possible if everything is lined up perfectly and the impulse coupling on the mag happens to snap, the engine could start. I have seen this happen on a radial engine but not on a Cub 4 cylinder. Still don't take a chance.
 
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