Mag and Starting Issues

[thomas1142]

A bit of background. When I first bought 30FM I had a horrible time with engine starts. Hot, cold, flooded normal start, did not matter. I was stranded three different times at a fuel stop. I was ready to sell till maintenance finally took a good look and determined that both mags were not performing correctly and one was even loose and could not hold timing. Mags were replaced and for the next five years I’ve had absolutely no problems staring under any condition .

Fast forward, I picked up 30FM from MX after its annual. It was time for the 500hr mag inspection. Did an IRAN on both. Now I have a 120RPM drop on both, before the IRAN the drop was 90-100RPM.
 

Another issue was with the spark plugs. I was told they were not performing correctly when hot. MX had a hard time starting the airplane when it was hot. For five years I had no issue. They did not have any new plugs but did have a used set that were check out as good. I said to go ahead and replace the plugs with the used ones. When I did the run up the engine ran terrible on either plugs, left or right did not matter. Replaced with original plugs and it ran as before, but with the 120RPM drop on the mags.

Question(s);

Mag drop is not acceptable for redone mags, correct?

Could the plugs be causing my issues with starting? (I had them recheck the timing)?

How do I know plugs are bad?

Any special considerations when changing plugs?

 

thanks

Angelos

[Bartman]

If it ran well before the maintenance to L+R Magnetos, I would start there.  Did they get the timing correct ? 

A new set of plugs may be a good idea but if it ran good before maintenance on those plugs I would look at the area of maintenance.

Another consideration is the RPM drop.  Is this based on the ship tach, electronic tach, or something else?

[thomas1142]

Timing was spot on when it was checked the second time. I have an EDM 900 for engine instrumentation.
 

If they did not keep the plugs in some type of order (which I’m sure they did not since they didn5 think they would have to reinstall them), and they didn’t get the plugs in the same location that they were removed from, would that creat an issue?

[Shadrach]

Reads like a timing issue. Given the drop is equal but but out of limits It sounds like the timing is retarded. the Question is whether it’s external or internal.

[thomas1142]

5 minutes ago, Shadrach said:

external or internal.

???

[Bartman]

I am sure someone like @Shadrach or @N201MKTurbo or others with more knowledge than me will be along soon to explain, but I do understand there is internal timing in the magneto.  There was a recent thread where it was the problem on a freshly installed IRAN/Rebuilt magneto.

[Shadrach]

37 minutes ago, thomas1142 said:

???

Mags have internal timing that is set to spec during IRAN/Overhaul. The fact that they have an identical drop makes me suspect that the timing was precisely but incorrectly set when the mags were installed.

[LANCECASPER]

1 hour ago, thomas1142 said:

A bit of background. When I first bought 30FM I had a horrible time with engine starts. Hot, cold, flooded normal start, did not matter. I was stranded three different times at a fuel stop. I was ready to sell till maintenance finally took a good look and determined that both mags were not performing correctly and one was even loose and could not hold timing. Mags were replaced and for the next five years I’ve had absolutely no problems staring under any condition .

Fast forward, I picked up 30FM from MX after its annual. It was time for the 500hr mag inspection. Did an IRAN on both. Now I have a 120RPM drop on both, before the IRAN the drop was 90-100RPM.
 

Another issue was with the spark plugs. I was told they were not performing correctly when hot. MX had a hard time starting the airplane when it was hot. For five years I had no issue. They did not have any new plugs but did have a used set that were check out as good. I said to go ahead and replace the plugs with the used ones. When I did the run up the engine ran terrible on either plugs, left or right did not matter. Replaced with original plugs and it ran as before, but with the 120RPM drop on the mags.

Question(s);

Mag drop is not acceptable for redone mags, correct?

Could the plugs be causing my issues with starting? (I had them recheck the timing)?

How do I know plugs are bad?

Any special considerations when changing plugs?

 

thanks

Angelos

A good reason for not sending both mags off at the same time for IRAN and staggering them a year apart if possible. 

[philiplane]

1 hour ago, thomas1142 said:

???

Internal magneto timing determines the output voltage available for ignition.

External timing determines when that voltage is available at the spark plug.

So, late internal timing produces a weak spark, which manifests as hard starting, or fouling of plugs at low speed & idle. 

[Bartman]

10 minutes ago, LANCECASPER said:

A good reason for not sending both mags off at the same time for IRAN and staggering them a year apart if possible. 

Good point. This a disadvantage of the A3B6D

[thomas1142]

Can a MX shop check both internal and external timing, or does it have to go back to the shop for internal timing adjustment?

[Ragsf15e]

24 minutes ago, thomas1142 said:

Can a MX shop check both internal and external timing, or does it have to go back to the shop for internal timing adjustment?

It definitely sounds like the mags aren’t perfectly timed.  Curiously, my 1968 poh says up to 125 rpm drop is ok, no more than 50 different between mags.  The timing changes the drop a lot.

Nobody answered your question about identifying a bad plug… the normal 1700rpm, rich runup isn’t a very good test of the ignition. An inflight lean mag check is better, but either way, switching to one mag you will see all the egts rise, but the bad plug will rise much more. If the plug is really bad, egt will drop off (no ignition) and engine will be really rough.

Many people look more at even egts rising during the mag check and not as much at the rpm drop, but both are reasonable indicators.

[Shadrach]

45 minutes ago, Ragsf15e said:

It definitely sounds like the mags aren’t perfectly timed.  Curiously, my 1968 poh says up to 125 rpm drop is ok, no more than 50 different between mags.  The timing changes the drop a lot.

Nobody answered your question about identifying a bad plug… the normal 1700rpm, rich runup isn’t a very good test of the ignition. An inflight lean mag check is better, but either way, switching to one mag you will see all the egts rise, but the bad plug will rise much more. If the plug is really bad, egt will drop off (no ignition) and engine will be really rough.

Many people look more at even egts rising during the mag check and not as much at the rpm drop, but both are reasonable indicators.

Mine says the same, but I’d not be happy with it. Currently I see about a 50 rpm drop and no difference from mag to mag.

now that I reread the OPs post, chasing an extra 30-40 rpm drop is not worth the effort if all else is well.

[Ragsf15e]

1 minute ago, Shadrach said:

Mine says the same, but I’d not be happy with it. Currently I see about a 50 rpm drop and no difference from mag to mag.

Yeah I agree, I was just pointing out that he might have someone telling him it’s fine.

[N201MKTurbo]

The internal timing sets the breaker cam so the points open at the E-Gap. The E-Gap is where the magnetic field is strongest during the rotation. The cam on the dual mag controls both points and therefore both mags. So both are right or both are wrong. You can adjust it quite a bit with the point gap, but sometimes the point gap gets very small trying to get the e-gap right. If you adjust the cam, you have to buy a new screw. They are only allowed to be torqued once. If the E-Gap is off by more than a few degrees, the mag output drops a lot.

The mag output should be tested on a spark gap tester. It should make a spark across a specified gap (3/8 inch or so) at a specified RPM (500 or so), so it should have been functionally tested before it was sent to you.

[thomas1142]

On 8/29/2023 at 10:08 PM, Ragsf15e said:

Yeah I agree, I was just pointing out that he might have someone telling him it’s fine.

Nope, definitely not acceptable even though it’s within POH margins. 
 

On 8/29/2023 at 10:42 PM, N201MKTurbo said:

so it should have been functionally tested before it was sent to you.

Sounds like it they will be going back to the shop.

Thanks

[N201MKTurbo]

BTW,

You can check the internal timing on the plane, with a mag timer and an inspection mirror.

[skykrawler]

Get magneto educated...

 

 

Edited August 31, 2023 by skykrawler

[N201MKTurbo]

15 minutes ago, skykrawler said:

Get magneto educated...

 

 

The video gets a couple of things wrong. For one, the cam pushes the points open not closed. The other is the function of the capacitor, but everybody gets it wrong. It forms an L-C parallel resonant tank circuit. When the points open, the collapsing magnetic field induces an oscillation in the tank circuit. this AC signal is coupled into the secondary windings. If you look at it on a scope you will see that it actually fires the plug 4 or 5 times in microsecond time scale. With the capacitor removed it only fires once, and does arc across the points because most of the energy is dissipated in the point arc instead of being coupled to the secondary.

[thomas1142]

Tried to do some trouble shooting today, couldn’t even start the engine. Normal, hot, even flooded start procedures would not work. It would turn over, cough like starting a few times, never actually starting. Really frustrated, memories from when first bought it.

[LANCECASPER]

On 8/29/2023 at 6:17 PM, thomas1142 said:

A bit of background. When I first bought 30FM I had a horrible time with engine starts. Hot, cold, flooded normal start, did not matter. I was stranded three different times at a fuel stop. I was ready to sell till maintenance finally took a good look and determined that both mags were not performing correctly and one was even loose and could not hold timing. Mags were replaced and for the next five years I’ve had absolutely no problems staring under any condition .

Fast forward, I picked up 30FM from MX after its annual. It was time for the 500hr mag inspection. Did an IRAN on both. Now I have a 120RPM drop on both, before the IRAN the drop was 90-100RPM.

So at the annual it was running ok and then after you picked up the airplane you sent off the mags for the 500 hour inspection?  Was the mechanic that did the annual the one who took them off and reinstalled and timed them?  What shop did you use to do the 500 hour inspection?

[thomas1142]

2 hours ago, LANCECASPER said:

So at the annual it was running ok and then after you picked up the airplane you sent off the mags for the 500 hour inspection?  Was the mechanic that did the annual the one who took them off and reinstalled and timed them?  What shop did you use to do the 500 hour inspection?

The mags were taken off during the annual and sent away for the 500 inspection, then reinstalled. Same mechanic did the work. They were sent to Maxwells Magnetos, Palm Coast FL

 

[thomas1142]

Mags were removed and sent back to the shop that rebuild them. Received them yesterday and were reinstalled. I was told that “brushes” were changed out on the starting mag. 
 

Airplane started up right away, and I turned it off and waited various time lengths for restarts. All went well.

Question,  Is a 90 to 100 RPM drop acceptable for rebuilt mags?

[N201MKTurbo]

The mag drop has more to do with the timing than the mags, unless the mag is really weak, then you will get a big drop and rough running. As long as it runs on all four cylinders on either mag, the mags are fine. if the drop is inconsistent between them, it is the timing.

[tmo]

On 8/30/2023 at 3:12 AM, LANCECASPER said:

A good reason for not sending both mags off at the same time for IRAN and staggering them a year apart if possible. 

And what is the consensus on the electronic magnetos? As in send one off for IRAN, replace with a SureFly/eMag (if the latter is applicable)?