Mag check issue

[bonal]

2 minutes ago, DonMuncy said:

It has always been dyslexic to me too. You can read up on it, or check with an ohmmeter.

And while I'm at it I will learn how to spell dyslexic 

[bonal]

So reading up confirms what I thought selecting L is grounding the right mag since there is no drop in rpm I'm thinking my right mag is the problem. And if so is the right mag on passenger side i.e. Right facing forward.

[DonMuncy]

Look at that mag and see if the small wire is attached to the stud. If so, pull on the wire to see if it is crimped well on the terminal. If so, clip a jumper wire from the terminal to a known ground and see if the mag is still hot. If it is not, look for a bad connection on the ignition switch, or (unlikely) a broken wire between the switch and the mag. Using the RPM drop is OK, but seeing if the engine will run with the key in the off position, is the absolute test.

[bonal]

It definitely ran with ignition off going to inspect wires if nothing visible will be going into LASAR for repair.

[bonal]

Went and opened up right side found P lead broken at back of mag. Made up fresh end and re connected. Did not want to drag out into rain so we'll see what happens next run up but should be good to go.

[Shadrach]

I do a mag and prop continuity check at taxi power, very rarely do I do a run up. If departing a field under 2000' I run to full power as I release the brakes. If EGTs are where they should be, I know the mags are doing their job.  I have had two in flight mag failures over 20 yrs of flying several different aircraft. Neither were revealed by a mag check in flight or otherwise; they revealed themselves on the EGT gauge.  I was over the Chesapeake when the last one happened and I did not bother to verify with a mag check as it would have needlessly terrified my passengers. As it turned out the coil fired well enough under 2100 as to be undetectable during a run-up. I needed to go to full power to determine the bad mag.  I think the old 1500 or 1700 or whatever rpm run up is almost always a waste of time. It is however excellent if your objective is to suck pebbles into the prop. Can anyone conceive of a mag failure that would be revealed in a mag check that would not be just as obviously revealed on an EGT gauge? 

[bonal]

I wonder if the single EGT gauge would be a real trustworthy source plus I need to bring RPM up to cycle the prop. I think I'll stick to a pre flight run up and mag check. Haven't been on too many run up areas that have much debris that could get sucked into the prop but I agree it sucks to have FOD repairs 

[Shadrach]

3 hours ago, bonal said:

I wonder if the single EGT gauge would be a real trustworthy source plus I need to bring RPM up to cycle the prop. I think I'll stick to a pre flight run up and mag check. Haven't been on too many run up areas that have much debris that could get sucked into the prop but I agree it sucks to have FOD repairs 

Actually, the prop will show an RPM drop if it's cycled while taxiing 1000 RPM just as easily as it will at 1800rpm. It's just a gentle way of establishing control continuity. You really  need not be concerned with getting fresh oil up to the hub until you move up to something with a big Pratt or Wright hanging out front turning a Hamilton Standard prop...

And yes,  I think I could identify a mag issue with a single probe EGT as long as it was well marked and easy to read.  All of my EGTs climb several hundred degrees when running on a single mag.  

[Seanhoya]

On 1/2/2017 at 6:57 AM, Andy95W said:

I don't understand why the engine would fail just by doing a mag check on a reasonably well maintained airplane.

How about this: You accidentally turn off the engine when you are done with the check, vice returning to the Both detent.  Nothing has to fail - just pilot error.

Does anyone have specifics regarding this course?

[neilpilot]

25 minutes ago, Seanhoya said:

How about this: You accidentally turn off the engine when you are done with the check, vice returning to the Both detent.  Nothing has to fail - just pilot error.

Does anyone have specifics regarding this course?

No specifics, but IIRC if engine does stop you need to retard throttle before you restart.  Same action is required before you restart if you happen to run a tank dry.  If you don't, you can potentially cause a backfire and blow apart your muffler.

[captainglen]

I will address the hot mag problem first. Early C models use a shower of sparks system and can not be started unless the ignition switch is activated to the start position. Later models have an impulse coupled mag in the left position and rotating a hot mag past the point where a loud click is heard can result in an inadvertent engine start, injury and even death. Others have noted the possibility of an open P lead but it is even more likely that the ignition switch is to blame. Check to continuity of the P leads and check that in the off position both leads are grounded which will adjudicate the switch.

[Patto]

I'm dealing with this same issue right now. During run up mag check, no drop when checking the right magneto.

I just finished putting in an overhauled artificial horizon, so I wonder if I pulled on something inadvertently.

Thanks for the info everyone.

[gsxrpilot]

1 minute ago, Patto said:

I'm dealing with this same issue right now. During run up mag check, no drop when checking the right magneto.

I just finished putting in an overhauled artificial horizon, so I wonder if I pulled on something inadvertently.

Thanks for the info everyone.

Simple... disconnected P lead on the Left Mag?

[Patto]

Simple... disconnected P lead on the Left Mag?

Exactly what I will check tomorrow morning. Thank you!

[Guest]

3 hours ago, Patto said:

I'm dealing with this same issue right now. During run up mag check, no drop when checking the right magneto.

I just finished putting in an overhauled artificial horizon, so I wonder if I pulled on something inadvertently.

Thanks for the info everyone.

If the P lead is open or disconnected, you should also have a live mag along with no drop during run up.  If so use caution around the propeller.

Clarence

[carusoam]

@Patto verify what @M20Doc mentioned regarding safety around the live engine....

P wires have a tendency to cause some unexpected issues.  Unexpected by ordinary people.  Not so unexpected by trained magneto guys... 

Best regards,

-a-

[Patto]

I took a look at it today. The metal plate on the left magneto with the negative lead coming out of it was loose. All four bolts were partially unscrewed. I applied some Loctite and refastened the plate. Mag check successful after that.

Thank you, gents! Saved me some cash and frustration with your expertise!!

[carusoam]

That was pretty quick!

MS works in some pretty awesome ways.

Thanks to all that participate!  

Best regards,

-a-

[DXB]

On 1/2/2017 at 11:05 AM, bonal said:

Yes this I know my question is if the key is aligned with L which is giving no rpm drop which mag is not grounding pilot side or pax side. I'm thinking that when checking mags and the key is on one L or R that is the one that should be grounded and you are running on the other. I hope I'm making sense since this has always been kind of deslexic to me.

Right one is grounded when key is on the left.