Mag timing

[NJMac]

Is there ever a time where the serial plate info on the engine would not be correct? Mine says 20 degrees.
 
Here is the back story.
 
A number of threads back I noticed my hottest EGT went from #3 to #2 and i wasn't able to lean it as aggressively.
 
Mechanic guessed it could have been a mag timing issue. At annual they found it had moved 4 degrees.
 
I picked it up from annual on Friday. Topped off the tanks wanting to get to KPOF for my new seats. Sumped 4 tbs of water put of the left tank. Mx said he had no issues. Odd. Started my skepticism.

After that, went and did the run up. Up to 2000 rpms and right mag dropped 150 rpm. Left only 60. Back to right and its still in the 140-150 range.
 
Went back to mx and they found the monkey setting the mags did one of them wrong.
 
Mx insists on doing mag check at 1700 and now they both drop about 125.
 
Frankly I don't feel right flying the plane at the edge of tolerance. Maybe I shouldn't? Thoughts?
 
Oh, and recommendations in OH, KY, or IN for a Mooney shop that knows their stuff? I'm about tp ferry it down to Maxwell for my next and future annuals.
 
 
 
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[Hank]

The nice folks at Attitude Aviation in Huntington, WV did my maintenance when I lived there. They're at KHTS in WV and at KHTW in OH, across the river from each other. Should be about a 35-minute flight south-southeast from Dayton.

[Shadrach]

15 minutes ago, NJMac said:

Is there ever a time where the serial plate info on the engine would not be correct? Mine says 20 degrees.
 
Here is the back story.
 
A number of threads back I noticed my hottest EGT went from #3 to #2 and i wasn't able to lean it as aggressively.
 
Mechanic guessed it could have been a mag timing issue. At annual they found it had moved 4 degrees.
 
I picked it up from annual on Friday. Topped off the tanks wanting to get to KPOF for my new seats. Sumped 4 tbs of water put of the left tank. Mx said he had no issues. Odd. Started my skepticism.

After that, went and did the run up. Up to 2000 rpms and right mag dropped 150 rpm. Left only 60. Back to right and its still in the 140-150 range.
 
Went back to mx and they found the monkey setting the mags did one of them wrong.
 
Mx insists on doing mag check at 1700 and now they both drop about 125.
 
Frankly I don't feel right flying the plane at the edge of tolerance. Maybe I shouldn't? Thoughts?
 
Oh, and recommendations in OH, KY, or IN for a Mooney shop that knows their stuff? I'm about tp ferry it down to Maxwell for my next and future annuals.
 
 
 
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It reads like your mags are well synced and within Lycoming's mag drop specs.  I am not a fan of the 20° timing.  I feel like it corrected a symptom and not a problem.   I think you and your mx are reading too much into a simple mag check. It really does not tell you that much more than the following. 

1) mags are firing somewhere near specified timing

2) Mags are reasonably well sync'd.  

3) Ignition switch continuity

4) spark plug and harness continuity

Hemming and hawing about which RPM to use to minimize mag drop is a waste of time.   

When you say the timing was off by 4°, was it advanced or retarded? 

As a data point for you. My mag drop is about 50 rpm from both to single with no differential.  

Definitely have another set of eyes put on the mags.  You have a lycoming under the cowl you don't need  Mooney specialist nor do you need to go to Texas. You simply need a competent A&P to verify proper mag installation and timing.  When it's time to overhaul mags consider swapping to Bendix if you currently have Slicks.

[NJMac]

It reads like your mags are well synced and within Lycoming's mag drop specs.  I am not a fan of the 20° timing.  I feel like it corrected a symptom and not a problem.   I think you and your mx are reading too much into a simple mag check. It really does not tell you that much more than the following. 
1) mags are firing somewhere near specified timing
2) Mags are reasonably well sync'd.  
3) Ignition switch continuity
4) spark plug and harness continuity
Hemming and hawing about which RPM to use to minimize mag drop is a waste of time.   
When you say the timing was off by 4°, was it advanced or retarded? 
As a data point for you. My mag drop is about 50 rpm from both to single with no differential.  
Definitely have another set of eyes put on the mags.  You have a lycoming under the cowl you don't need  Mooney specialist nor do you need to go to Texas. You simply need a competent A&P to verify proper mag installation and timing.  When it's time to overhaul mags consider swapping to Bendix if you currently have Slicks.

I honestly agree with you. My mags both used to drop 60 each. I do think there is more going and I was hoping these symptoms would shed some light to someone here. I'll ask if they were 4 ahead or behind, not sure.

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[MB65E]

There was an old SB that changed the timing to 20° from 25° this was done to prevent extra heat on the angle valve heads. Legally, if the SB was done, as you state, you should run it there. You can reverse the SB and run 25° but you should correct the data plate. Your tech doesn’t sound that awful, just a bit uninformed.

-Matt

[Shadrach]

6 minutes ago, NJMac said:

I honestly agree with you. My mags both used to drop 60 each. I do think there is more going and I was hoping these symptoms would shed some light to someone here. I'll ask if they were 4 ahead or behind, not sure.

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If someone had previously set the timing to 25° on both mags, the new 20° setting would make for a lower mag drop.  Retarding the timing will decrease RPM all other things being equal. retarding the timing and using a single ignition source (like during a mag check) will exacerbate said RPM drop.

Edited June 24, 2019 by Shadrach

[NJMac]

I'm told it was 4 degrees advanced, set at 24.

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[NJMac]

There was an old SB that changed the timing to 20° from 25° this was done to prevent extra heat on the angle valve heads. Legally, if the SB was done, as you state, you should run it there. You can reverse the SB and run 25° but you should correct the data plate. Your tech doesn’t sound that awful, just a bit uninformed.
-Matt

Thanks for your feedback. Encouraging to hear

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[Hank]

Check your plugs, wires and magneto caps, too.

[Shadrach]

1 minute ago, NJMac said:

I'm told it was 4 degrees advanced, set at 24.

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So if both mags were set to 24 (odd number).  You may notice a slight increase in take off roll and decrease in ROC. This may be contributing to your feeling that something is not correct.

[NJMac]

Check your plugs, wires and magneto caps, too.

Hank, kinda dense here. What am I looking for?

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[RobertGary1]

Some of the factory service centers will still set them to 25 even if you have the later data plate that shows 20. Many believe it runs much better at the old 25.

 

-Robert

[NJMac]

Some of the factory service centers will still set them to 25 even if you have the later data plate that shows 20. Many believe it runs much better at the old 25.
 
-Robert

Which is better? Sounds like 25 Will produce greater performance. Will 20 lead to longer engine life?

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[Shadrach]

8 minutes ago, NJMac said:

Which is better? Sounds like 25 Will produce greater performance. Will 20 lead to longer engine life?

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The engines were certified at 25.  They run well at 25 degrees. Some applications ran hot and retarding timing helped make temps more manageable. It also reduced power to small degree. Does not make much of a difference in cruise (though may be more noticeable above 10K).  It does make a noticeable if not significant difference in climb and take off roll.  I don't think it has any bearing on engine life if temperatures are healthy.

[NJMac]

The engines were certified at 25.  They run well at 25 degrees. Some applications ran hot and retarding timing helped make temps more manageable. It also reduced power to small degree. Does not make much of a difference in cruise (though may be more noticeable above 10K).  It does make a noticeable if not significant difference in climb and take off roll.  I don't think it has any bearing on engine life if temperatures are healthy.

My CHTs have always been low. I'll keep it at 20 and see how it goes. Just got an official POH for my bird and it says runup at 1700 rpm. Guess it's in spec.

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[Shadrach]

1 minute ago, NJMac said:

My CHTs have always been low. I'll keep it at 20 and see how it goes. Just got an official POH for my bird and it says runup at 1700 rpm. Guess it's in spec.

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I'm not surprised. I have a 67 F with the same engine timed to 25 and my CHTs are always low.  In the winter it's a challenge to keep them above 300 at some altitudes.  Though I'd never retard my timing, I can imagine they's be even lower after doing so.  

[Hank]

2 hours ago, NJMac said:

Hank, kinda dense here. What am I looking for?

Check the resistance of your plugs. One multimeter probe on the center electrode, the other inside the other end. Best is < 5000 ohms.

Check resistance / continuity of plug wires. Resistance should be a small number. 

Examine plug wires visually, especially where they go through, around or under something. Look for cracks / breaks in isulation.

Breaks like here, going into doghouse and bending to attach to the plug.

What isn't visible is where it was pinched between battery box and doghouse . . . .

New plugs, new wires, old copper antiseize cleaned out of plug holes, now using graphite antiseize. No more problems. 

Edited June 24, 2019 by Hank

[PT20J]

9 hours ago, RobertGary1 said:

Some of the factory service centers will still set them to 25 even if you have the later data plate that shows 20. Many believe it runs much better at the old 25.

 

-Robert

Well, that wouldn't be legal and the next mechanic would just set it back to match the data plate. Also, if you do it correctly, it's more than just setting the timing. When Lycoming changed the timing, it also changed the impulse coupling to one with a reduced lag angle. That's why the IO-360-A3B6D remained at 25-deg --- the Bendix dual mag lag angle couldn't be changed.

SI1325 Timing Change for IO-360 Series Engines.pdf

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[PT20J]

Here's Lycoming's current recommendations for mag checks. Essentially, it says that low power rich mixture mag checks are pretty worthless for determining the health of the ignition system. 65% power and lean mixture is better. I generally check the mags during runup on the first flight of the day and watch for all the EGTs to rise. If it's running smoothly, I don't pay a lot of attention to the rpm. I like to do an in flight mag check at cruising power and lean mixture once a flight because that's a better stress test.

SI1132B Magneto Drop-Off.pdf

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