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Magneto confusion/Ignition issue


Greg Ellis

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Can someone please clear up a little confusion for me. 

When you move the ignition key to the R position, is this grounding out the Right mag or grounding out the left mag?  And vice versa? 

Also, I am having an issue with the ignition.  When I turn the key to the R position and push the key in the prop turns.  Won’t start but turns.  When I put it in the L position and push it in nothing happens. In the both position and push it in nothing happens and of course when I turn it to the start position and push it in the engine starts in less than 1 turn of the propeller usually.  Is this a problem with the switch, or the magneto or something else? 

The right mag always runs rough during run up and I have to run the rpm up and lean it way out for a minute or 2 to clear it so I am not sure if that has something to do with it as well because it all points to the R mag. 

Anyways,  any help is appreciated.  Plane goes in for annual in September and I would like to be armed with some information before it goes in. 

This is a 1963 C model with an O-360-A1D. 

Thanks, 

Greg Ellis

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Does your plane have a Shower of Sparks or an impulse coupling?

Do you hear a buzzing sound when you start the engine?

Eithir way, only one mag is used while starting. It retards the timing to TDC either with a retard breaker or an impulse coupling.

The mags can not generate enough power at starting speeds, so they need help to make extra power. 

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It sounds like you have two separate issues, neither of which is really all that complicated.

In the R position, the left magneto is grounded.  Since you say the right mag always runs rough until you run it up and clear it, that is probably not a magneto problem, it is probably a bad, dirty, or mis-gapped spark plug that is connected to the right magneto.  The only magneto problem which may contribute to this would be if the timing was off.  No problem- that is checked every annual.  I am assuming your magnetos have been checked every 500 hours- if it hasn't, then there is the possibility you may need magneto work. If you have Slick magnetos, you may have a coil going bad.  Bendix magnetos are usually okay, but still need to be checked.

The starting issue when in the R position is your switch, and is one of the indicators that your switch may not pass the AD check on it.  There are a lot of contacts on the back side of the switch and yours is making contact when it shouldn't.  You may need a new switch, but there are rebuild kits if your shop is willing to do the work.  New switches are $350 for the proper one.  I thought Rich @N201MKTurbo had mentioned the rebuild kits at some time in the past, although it may have been someone else.

 

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Thanks for the info.  Just sounds like I need switch and mag work.  These are slick mags.  No SOS.

The timing may be off as well.  I sent in data from my JPI to Saavy and was told that it looked like the mags were not timed correctly.  They gave me a long explanation of how they could tell from the engine monitor data so hopefully that will get corrected at annual.  Thanks for the responses.

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There is only one impulse coupling on left mag. The fact that the right position will allow you to go to start seems odd and I don’t think it should. Sounds like switch is worn. If that switch allowed you to crank it over in left only it would start. Don’t try it in right only because if you do get a spark from the mag at cranking RPM it will fire at about 20 degrees before top dead center. It will then kickback and might get an induction fire. Only crank in both. All sounds okay as long as you don’t try to start in right.


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30 minutes ago, Mjknick@gmail.com said:

There is only one impulse coupling on left mag. 

Greg and Mjknick-

Unless your M20Cs has been significantly modified, you do not have an impulse coupling, you have shower of sparks (SoS).  Slick magnetos can also use the shower of sparks, or a replacement box known as SlickStart.  

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6 hours ago, Greg Ellis said:

Can someone please clear up a little confusion for me. 

When you move the ignition key to the R position, is this grounding out the Right mag or grounding out the left mag?  And vice versa? 

Also, I am having an issue with the ignition.  When I turn the key to the R position and push the key in the prop turns.  Won’t start but turns.  When I put it in the L position and push it in nothing happens. In the both position and push it in nothing happens and of course when I turn it to the start position and push it in the engine starts in less than 1 turn of the propeller usually.  Is this a problem with the switch, or the magneto or something else? 

The right mag always runs rough during run up and I have to run the rpm up and lean it way out for a minute or 2 to clear it so I am not sure if that has something to do with it as well because it all points to the R mag. 

Anyways,  any help is appreciated.  Plane goes in for annual in September and I would like to be armed with some information before it goes in. 

This is a 1963 C model with an O-360-A1D. 

Thanks, 

Greg Ellis

Glad to know I'm not the only one confused by the L/R thing! :D

Just to be nitpicky, I assume when you say "R position" you're talking about the left position that is labeled "R", correct?  It took me five years before I noticed those switches have the right position labeled "L" and the left position labeled "R"...

6 hours ago, Andy95W said:

The starting issue when in the R position is your switch, and is one of the indicators that your switch may not pass the AD check on it.  

IIRC, the AD check is just to see if both mags are fully grounded in the OFF position.  That doesn't mean, of course, that there isn't an issue with the switch...

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Magneto switches are normally labelled, left to right.  OFF, RIGHT, LEFT, BOTH, START, either push to start or twist to start

In the OFF position both P leads are grounded.

In the RIGHT position the left P lead is grounded and the Right is open or live.

In the LEFT position the right P lead is grounded and the Left is open or live.

In the BOTH position both P leads are open or live.

In the START position for most independent magneto engines the RIGHT P lead is grounded and the LEFT P lead is open or live.

Clarence

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3 hours ago, jaylw314 said:

 

IIRC, the AD check is just to see if both mags are fully grounded in the OFF position.  That doesn't mean, of course, that there isn't an issue with the switch...

Yes, absolutely right.  I jumped to the conclusion that if he can engage the starter in anything other than the start position he got some funky things goin' on back there.

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Nice explanation, Clarence...

followed by more questions...

When you really want to know your engine well... (trouble shooting is a good reason)

The left mag is on the pilot side (?)

and it operates the top plugs on one side of the engine and the bottom plugs on the other side (?)

So many details to know...

I used To know these details for my crusty O360...

It helps to know this much detail when a single plug stops working and you’re JPI points you to what plug it (sort of) is... 

Best regards,

-a-

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1 hour ago, carusoam said:

The left mag is on the pilot side (?)

and it operates the top plugs on one side of the engine and the bottom plugs on the other side (?)

The left mag is on the pilot's side 

each mag fires the lower plugs on the same side and the upper plugs on the opposite side, so left fires top 1 & 3, bottom 2 & 4

It's diagram 5-1 in the Lycoming O-360 Operator's Manual.  I don't have a scanned copy of just that diagram to post, anyone have that?

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8 hours ago, RLCarter said:

Use extreme caution when the "P" leads are disconnected, the mag('s) will be HOT. I recently discovered the "P" leads were reversed on my 172, right mag issue turned out to be a left mag, easy to ck while your there

With the P leads disconnected from the magnetos, connect your Eastern magneto synchronizer the the P leads, aim it at the windshield and turn ON.  Put the key in the switch, if the P leads are correct left and right,  when you turn the key the lights on the syncronizer will match the switch label, off, right, left, both and in start the righ light should go out.

Clarence

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10 hours ago, RLCarter said:

Use extreme caution when the "P" leads are disconnected, the mag('s) will be HOT. I recently discovered the "P" leads were reversed on my 172, right mag issue turned out to be a left mag, easy to ck while your there

My mags have the safety...  When the P lead is out, the springy thing grounds them out

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19 minutes ago, Yetti said:

My mags have the safety...  When the P lead is out, the springy thing grounds them out

Ok I have too...   "the springy thing"  is that the technical term?   I want FAA proof of that one.  I called the engine a motor and got ripped....  your turn:D

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1 hour ago, Yetti said:

My mags have the safety...  When the P lead is out, the springy thing grounds them out

The P leads on mine are spring loaded ends but I don't think they ground the mag when disconnected

Edited by RLCarter
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