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Magneto help please


JoeM

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65 E model, IO 360 AIA with M20 Turbo and Slick 4347 mag. AOG Yuma AZ. On runup, mag appeared to be completely dead, but at idle it would fire briefly before dying. Believe problem to be with left mag since it dies when ignition switch is closest to "Both" (panel not marked L and R). AP/IA removed left mag after placing #1 cyl at TDC position. On tear down, mag shows no corrosion, gear damage, or wear on points. Points barely separate. IA said he felt they should open further. Mag (and engine) has 375 hours since OH in 2007 so little flying over many years.  Questions....1. Can the mag be field tested to determine if it is good?  2. Do mags require 500 hour inspection / OH for part 91 with Turbo installed? 3. Does it make sense to gap the points, re-install and test op or should I rent a car to get home, order replacement mag and come back for the plane after OH mag is installed next week? 4. What else am I missing? Thanks for any help.

Joe

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You need to do the procedure for setting the internal timing. This adjusts the points to open at the strongest magnetic field. If the cam hasn’t moved, it will set the correct point gap.

Normally, you would set the point gap and then adjust the cam so it opens at the E-gap. After the cam has been set, you can adjust the points gap so they open at the E-gap and everything should be back to the original settings.

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9 hours ago, Mooney79329 said:

On runup, mag appeared to be completely dead, but at idle it would fire briefly before dying. Believe problem to be with left mag since it dies when ignition switch is closest to "Both" (panel not marked L and R).

 

Joe,

Can you provide more detail on this? This doesn't make a lot of sense when I read it. When you turn to the RH Mag (or what you think is the RH mag), the engine just quit or came close to it? 

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9 hours ago, EricJ said:

Yes, the points can be gapped and try it again.   Slick mags are much easier to work on than Bendix.   It can be bench tested if the shop has a test fixture, but not all shops do.

 

What isit that makes Slick mags much easier???   An individual familiar with Bendix Magnetos can disassemble, clean, IRAN and reassembled in well under 4 hrs (I've seen it done quite a bit faster). I've never thought of either design as particularly difficult.  I have strong opinions about which design is more robust (Bendix).  I would happily run Slicks on an airplane that I bought until overhaul time, than I would replace them with Bendix.

Edited by Shadrach
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Since this mag has 400 hours on it, was 14 years old, with cam worn causing points not to open,  and the IA can't test the internal parts, and since the engine is turbocharged (which makes 500 hours inspections more desirable), I was leaning toward replacing it. Aircraft Magneto Service in Montana had a replacement with 500 hour inspection and wear parts replaced for $750. This is half what Spruce quoted and it comes with a 500 hour warranty. This will give me one recently inspected mag, which improves my safety margin.  It's time to rent a car, drive home, and come back in a week.

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1 minute ago, Mooney79329 said:

Since this mag has 400 hours on it, was 14 years old, with cam worn causing points not to open,  and the IA can't test the internal parts, and since the engine is turbocharged (which makes 500 hours inspections more desirable), I was leaning toward replacing it. Aircraft Magneto Service in Montana had a replacement with 500 hour inspection and wear parts replaced for $750. This is half what Spruce quoted and it comes with a 500 hour warranty. This will give me one recently inspected mag, which improves my safety margin.  It's time to rent a car, drive home, and come back in a week.

the cam probably isn't worn, it is probably the follower on the points. It is plastic and wears. If you reset the points, you can easily get the last 100 hours out of it.

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3 hours ago, Shadrach said:

What isit that makes Slick mags much easier???   An individual familiar with Bendix Magnetos can disassemble, clean, IRAN and reassembled in well under 4 hrs (I've seen it done quite a bit faster). I've never thought of either design as particularly difficult.  I have strong opinions about which design is more robust (Bendix).  I would happily run Slicks on an airplane that I bought until overhaul time, than I would replace them with Bendix.

There are fewer parts in a Slick, and I find it much easier to set the internal timing on a Slick than a Bendix, although neither is horrible.   The Slicks just seem to be a lot easier to work on.  As an engineer, I've found the Slick design to be much more straightforward and a lot closer to how I'd have done it than a Bendix, which has a lot of "why did they do that?" moments and extra fiddling during reassembly.   The Bendix is just a more complex design, perhaps because it's older.   I've not had a ton of experience with either, but have done disassembly/reassembly and set timing on both.   My Bendix D3000 is close to due for a 500-hour inspection and I'll send it away rather than do it myself.   Slicks I wouldn't hesitate to do myself.   In the end both are fine, Bendix enjoys a good reputation, although they fail, too.   

 

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4 hours ago, EricJ said:

There are fewer parts in a Slick, and I find it much easier to set the internal timing on a Slick than a Bendix, although neither is horrible.   The Slicks just seem to be a lot easier to work on.  As an engineer, I've found the Slick design to be much more straightforward and a lot closer to how I'd have done it than a Bendix, which has a lot of "why did they do that?" moments and extra fiddling during reassembly.   The Bendix is just a more complex design, perhaps because it's older.   I've not had a ton of experience with either, but have done disassembly/reassembly and set timing on both.   My Bendix D3000 is close to due for a 500-hour inspection and I'll send it away rather than do it myself.   Slicks I wouldn't hesitate to do myself.   In the end both are fine, Bendix enjoys a good reputation, although they fail, too.   

 

Do you use that little egap tool to set the Slicks? I looked at a couple of youtube videos and it looked a little imprecise so I just sent it to Aircraft Magneto. Steve told me he uses some sort of large protractor to set it.

Skip

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2 hours ago, PT20J said:

Do you use that little egap tool to set the Slicks? I looked at a couple of youtube videos and it looked a little imprecise so I just sent it to Aircraft Magneto. Steve told me he uses some sort of large protractor to set it.

Skip

Yes, the tool makes it pretty easy.   I think it keeps it within a fraction of a degree if you're careful, and I doubt it needs to be any better than that.   Magnetos don't strike me as precision instruments.  ;)

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Under 500hrs... no real issues are expected...

M20Ks typically use or may use pressurized mags... check while ordering a new one...

Left mag is typically the mag responsible for starting, it has the ability to change timing to 0° BTDC...

If unable to get the engine to start... this circuit in the mag may be mis behaving...

If unable to keep it running... that may be something different...

 

Looks like I’m 23hrs late to the conversation...   :)

PP thoughts only, not a mechanic...

Best regards,

-a-

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After installing rebuilt Slick 4347 left mag from American Magnetos, timing both mags to 25 degrees BTDC on compression stroke, reconnecting P lead and retard lead (engine has a Bendix Starting Vibrator), and checking grounding on ignition switch, engine started once, but won't start again. Mechanic is stumped. American Magnetos says to check all wiring, which we will do tomorrow. Any other suggestions are welcome.  

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79329,

What was/wasn’t working?  When it didn’t start?

What techniques did you try?  Winter has a tendency to need a lot of prime compared to the other times of the year.... what was the OAT?

Are you familiar with the engine already? (Help me out, I don’t remember your whole history)

Start with all the things you tried, and why they didn’t work...

If it was working once already... how much wiring can you check?

Did the starter not work?

Do you have engine monitor data?

Did you get to the point of performing a run-up to see how well the Mags were working independently of each other?

PP thoughts only, not a mechanic...

Best regards,

-a-

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Thanks for all the feedback. The battery had 11.7 volts (may be run down due to all the cranking on FBO ramp with no electricity) so we are charging it to full. Hopefully that will energize the shower of sparks and get the engine running. Will then try to move plane where we have ground power to keep battery charged. Once shower of sparks is working and engine starts, next step is to troubleshoot why new left mag is dead on mag check. (BTW, removing left P lead doesn't work on SOS system. Right mag is disabled on start, and left mag needs P lead connected for SOS system to make the plugs fire. Right mag works on Both, but not on Start ignition switch setting)

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14 hours ago, carusoam said:

79329,

What was/wasn’t working?  When it didn’t start?

What techniques did you try?  Winter has a tendency to need a lot of prime compared to the other times of the year.... what was the OAT? 

Are you familiar with the engine already? (Help me out, I don’t remember your whole history)

Start with all the things you tried, and why they didn’t work...

If it was working once already... how much wiring can you check?

Did the starter not work?

Do you have engine monitor data?

Did you get to the point of performing a run-up to see how well the Mags were working independently of each other?

PP thoughts only, not a mechanic...

Best regards,

-a-

OAT is 70 degrees in Yuma AZ. I have owned this plane for a few months so limited history. This is my first (of three) Mooneys with Shower of Sparks ignition. Initial problem was that engine stopped completely on L mag during runup after working fine previously. Replaced mag with tested good from Aircraft Magnetos so it should work. Engine started but died on L mag so it's the same problem. Starter is fine. No engine data pulled - EI may have some. 

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5 minutes ago, Mooney79329 said:

OAT is 70 degrees in Yuma AZ. I have owned this plane for a few months so limited history. This is my first (of three) Mooneys with Shower of Sparks ignition. Initial problem was that engine stopped completely on L mag during runup after working fine previously. Replaced mag with tested good from Aircraft Magnetos so it should work. Engine started but died on L mag so it's the same problem. Starter is fine. No engine data pulled - EI may have some. 

Engine probably started off the right mag when you released the switch. At that point the prop was still spinning and the right mag could fire allowing the engine to start.  Check your P lead to ground, it should be grounded in the off position but open in both.  
 

Brian

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Actually with the SOS the ignition switch must connect the two leads from the retard breaker mag together. This keeps the points from opening until the retard breaker opens. And un-ground them. If it doesn't connect them together, there will be no energy from the SOS to the mag.

Edited by N201MKTurbo
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