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Pmag Reinstall

J

John Tierney

Well Known Member
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I removed 2 Pmags from my yet-to-fly IO-360 to get the firmware update (Thanks Brad for the quick turn-around). Aerosport Power installed the Pmags on the engine originally (years ago), and it didn't look like there was any kind of sealant on the accessory case or Pmag. I have replacement gaskets for the Pmags; should they be lubricated or sealed with any product?

Also, what torque value should be used for the upper and lower clamping nuts?
 
for devices that do not need to be adjusted/rotated, I use a sealant on both sides of the gasket to avoid seepage. For the mags, I coat one side of the gasket with sealant to allow later movement without gasket tearing.

Larry
 
There is no official call-out for sealant. Best practice is to install magneto gaskets "dry". They seal just fine (paper + oil = seal). The gasket will not be as susceptible to tearing. And your life will be much easier for future removal / installation. If it's tough stabbing the Pmag (or magneto) dry with the gasket falling off the flange put a small dab of DC4 or other lube on a small part of one side of it to get it to stick in place during handling. Or even a small piece of masking tape that can be removed before fully stabbing.
 
I use fuel lube on the gaskets for no other reason than to hold them in place while installing the P-mags.

Make sure that your ground wire (P-mag pin #1) goes to an engine case bolt (different case bolt for each P-mag).
 
This must be the week for Pmag reinstalls.

I sent both of mine off as part of troubleshooting an engine surge issue.

One had axial and radial bearing play and the other had a failure of one of the phases of the built in three phase alternator.

These were older production Pmags but only had 85 hours on them. A little disconcerting that both had some sort of failure. I'm hopeful that the repairs will solve the engine surging issue.

Standing by for the "this is why you should not install two Pmags" lecture...
 
KatanaPilot said:
This must be the week for Pmag reinstalls.

I sent both of mine off as part of troubleshooting an engine surge issue.

One had axial and radial bearing play and the other had a failure of one of the phases of the built in three phase alternator.

These were older production Pmags but only had 85 hours on them. A little disconcerting that both had some sort of failure. I'm hopeful that the repairs will solve the engine surging issue.

Standing by for the "this is why you should not install two Pmags" lecture...
Click to expand...

FYI - the EICommander will pick up the bearing issue and a preflight power check should catch the generator issue.

I'm now at 850 hours on both P-mags and have only had one hardware failure which happened shortly after my prop strike, so I can't rule that out as a possible cause.
 
I just used fuel lube like Bill R. Just to hold them in place. Never had a leak. They have been on 1 year now!
 
Bill - why can?t both Pmags be grounded to the same case bolt? It seems like two case bolts on the same case, just a few inches apart, would be electrically the same. I?m pretty sure both of mine are grounded to the same bolt on the accessory case.
 
Scott Hersha said:
Bill - why can’t both Pmags be grounded to the same case bolt? It seems like two case bolts on the same case, just a few inches apart, would be electrically the same. I’m pretty sure both of mine are grounded to the same bolt on the accessory case.
Click to expand...

Electrically it is the same; however, if that one bolt comes out, you run the risk of both ignitions failing.

Addition:

Why take two completely independent systems and make them dependent on one bolt or a single ring terminal, which are known to fail?

Should that one bolt back out, the P-mags will continue to fire; however, when you land at some "away" airport in the middle of a "dark and stormy night" and your RPM's drop below that magic 800 RPM self powering threshold, your engine will die on the runway and you will be scratching your head as to why. (This scenario has happened before, but not on a "dark and stormy night".)
 
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I'm sure the answer is to avoid a single point failure that would result in engine stoppage if one bolt shears/backs out.

EDIT - beat like a rented mule.
 
I guess I didn’t consider a bolt falling off the engine as a risk - but anything is possible. I’ll check mine to see if I’ve done that. The more likely failure point is the wire/connector and I have separate ring terminals on each Pmag. If the connector fails, it wouldn’t matter what bolt it was attached to - it would still fail. The reason for my question was to see if there is some grounding issue with both ground wires going to the same point and I’m not sure I did that, I was just curious as to the why. Pretty easy to move it over if I did.

Here’s another question concerning grounding - just for my own understanding of the system...... If the ground wire on the connector fails, I’m not sure the engine will quit when the RPM drops below 800. Wouldn’t the chasis of the Pmag still provide a ‘not very good’ ground? It’s not an excuse to not install a ground wire, and disregard the installation instructions, but I think the ground wire in the Pmag connector is there to provide a reliable ground due to poor conductivity of anodized aluminum on the Pmag chasis. If that fateful bolt fell off the engine, you may not know it until you have the cowl off next time and discover it. Isn’t that the way it works? - again, I’m not saying anyone should do that, and I’m not saying anyone should trust a single grounding point on the case for two separate mags, but it seems like the wire is providing a reliable and redundant ground for each Pmag. If so, and it’s redundant, you might not know you had a wire/connector or bolt failure unless you checked it when the cowl was off. Is that correct?
 
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Scott,

The P-mags will ground through their case, as you mentioned; however, there are electronics in the P-mags that would really like a clean ground signal.

If that wire fails for any reason, the P-mags will still fire as the path is out one plug and back through the other.

Because of how our EICommander determines if there is a firing angle difference between the two ignitions, it must have a clean signal and we have found that wiring them per the manual eliminates extraneous noise that the EICommander picks up as a timing divergence error.

This is your ignition you are wiring, I cannot express strongly enough that they should be installed exactly as described in the manual.
 
Thanks Bill, and yes I did install them exactly as the manual suggests. I was just questioning the failure mode if the ground wire were to fail, either in the wire
/connector itself, or the attachment to a case ground bolt. You answered my question - there is a redundant ground path in case of one of those types failures. Good to know.
 
Case is anodized ... also non-conductive ... how is it grounded through their case?

Hello Bill

Cans you explain this a bit deeper?

N941WR said:
The P-mags will ground through their case,
Click to expand...

How is this done?

The case is anodized aluminium, this is electrical non conductive!?

Aluminum Anodizing is an electrochemical process that creates a thin aluminum oxide film on the surface of aluminum substrates. The resulting anodized film is electrically non-conductive, protects the aluminum against corrosion and is resistant to wear.

If I where Emagair, I would just cut away the layer of anodisation on the place where the clamps from the two brackets hold them to the engine case. So that there is the first and strongest ground. Maybe change the aluminium alloy to a not so corrosion reactive type.
The benefits would be:
- Two grounds per Pmag
- Fire resistant for many minutes
- If Pmag is mounted correctly, it is grounded
- Bullet prove
 
swisseagle said:
Hello Bill

Cans you explain this a bit deeper?

How is this done?

The case is anodized aluminium, this is electrical non conductive!?

...
Click to expand...
You really must ask Emag as I am not on their design team.

I do know the P-mags are insulated from the case by the gasket; however, the path may be through the hold downs. Check with Emag.

Also, there is a ground path through the sparkplugs, as I also mentioned.
 
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the hold downs will usually scratch the surface

On a flat surface, this will not happen ... inside an anodized thread, if you tighten the screw fairly well, then you have a ground ... but not a proper one ... take at least two screws.

If you want to have this on a flat surface, then the clamping element must have some sharp edges/spikes that break the oxide.
 
John Tierney said:
I removed 2 Pmags from my yet-to-fly IO-360 to get the firmware update (Thanks Brad for the quick turn-around). Aerosport Power installed the Pmags on the engine originally (years ago), and it didn't look like there was any kind of sealant on the accessory case or Pmag. I have replacement gaskets for the Pmags; should they be lubricated or sealed with any product?

Also, what torque value should be used for the upper and lower clamping nuts?
Click to expand...
Do you happen to have the replacement gasket part number?
 
Scott Hersha said:
Bill - why can’t both Pmags be grounded to the same case bolt? It seems like two case bolts on the same case, just a few inches apart, would be electrically the same. I’m pretty sure both of mine are grounded to the same bolt on the accessory case.
Click to expand...

Electrically it is the same but when one bolt is used, should that single bolt fall off or come loose, you run the risk of both ignitions failing to fire.
 
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Do not ground pMags (or anything else) to the engine case. Run separate ground wires to whatever you are using for the common battery ground connection on the firewall. The engine should be connected to ground at only one place; the nice ground lug on the starter (#2 welding cable is perfect for this job).

Reason - if that starter ground wire fails for any reason the engine won’t crank. You will quickly find the problem. If you have a bunch of additional stuff grounded on the engine, the starter will now use these connections to seek a path to ground for all that current. Bad things will happen to all that stuff before you figure out why the engine won’t crank.

Carl
 
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Carl Froehlich said:
Do not ground pMags (or anything else) to the engine case. Run separate ground wires to whatever you are using for the common battery ground connection on the firewall. The engine should be connected to ground at only one place; the nice ground lug on the starter (#2 welding cable is perfect for this job).

Reason - if that starter ground wire fails for any reason the engine won?t crank. You will quickly find the problem. If you have a bunch of additional stuff grounded on the engine, the starter will now use these connections to seek a path to ground for all that current. Bad things will happen to all that stuff before you figure out why the engine won?t crank.

Carl
Click to expand...


Sorry Carl - that is in direct conflict with the instructions provided by the manufacturer of the P-Mag. You are correct that if the ground strap fails, the current will find whatever path necessary to go back to ground - on a traditionally ignited engine, that would be the P-Leads. But for the P-Mags, a far better solution (if you?re worried about the ground strap failing) is to wire two ground straps. Going against the manufacturer?s instructions on an electronic ignition system is generally a bad idea.

You and I can disagree on this, but I want folks reading this thread in the future to understand that the manufacturer of the P-Mags would not agree with your recommendation, and they should do some research.
 
Ironflight said:
Carl Froehlich said:
Do not ground pMags (or anything else) to the engine case. Run separate ground wires to whatever you are using for the common battery ground connection on the firewall. The engine should be connected to ground at only one place; the nice ground lug on the starter (#2 welding cable is perfect for this job).

Reason - if that starter ground wire fails for any reason the engine won’t crank. You will quickly find the problem. If you have a bunch of additional stuff grounded on the engine, the starter will now use these connections to seek a path to ground for all that current. Bad things will happen to all that stuff before you figure out why the engine won’t crank.

Carl
Click to expand...

Sorry Carl - that is in direct conflict with the instructions provided by the manufacturer of the P-Mag. You are correct that if the ground strap fails, the current will find whatever path necessary to go back to ground - on a traditionally ignited engine, that would be the P-Leads. But for the P-Mags, a far better solution (if you’re worried about the ground strap failing) is to wire two ground straps. Going against the manufacturer’s instructions on an electronic ignition system is generally a bad idea.

You and I can disagree on this, but I want folks reading this thread in the future to understand that the manufacturer of the P-Mags would not agree with your recommendation, and they should do some research.
Click to expand...
Well said Paul!

With P-mags, you want them electrically grounded to the engine case. We are not talking about the P-lead ground but rather the ground return wire for the P-mags internal electronics.

We are not trying to keep the firewall running, just the engine. Thus, if the engine ground strap fails in flight, the engine will continue to run.
 
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Im not disagreeing with Bill and Paul, but Im one of those guys that like to know the reasons for the rule. Because the manufacturer says so just isnt very satisfying. I know from the Aeroelectric Connection that a common ground point is generally good practice, but somehow that doesnt apply here? I cant believe the reason is really to protect against an engine ground strap failure. That just shifts the onus to the dedicated pmag ground wire, and frankly, I would rather bet on my big fat engine ground strap. So whats the real reason?

erich
 
From what I can read, Carl logic is some what correct but has got it backward.

My understanding is to ground the PMAG to the engine case and not the firewall. The logic is that if you have a less than good ground strap from your engine block to the FW, the starter may use the ground that is provided by PMAG to the FW as a path and since the current is too high, it may fry your PMAG or hide the issue of faulty ground strap.
 
erich weaver said:
Im not disagreeing with Bill and Paul, but Im one of those guys that like to know the reasons for the rule. Because the manufacturer says so just isnt very satisfying. I know from the Aeroelectric Connection that a common ground point is generally good practice, but somehow that doesnt apply here? I cant believe the reason is really to protect against an engine ground strap failure. That just shifts the onus to the dedicated pmag ground wire, and frankly, I would rather bet on my big fat engine ground strap. So whats the real reason?

erich
Click to expand...

You can ask P-Mag directly, and I bet they?ll tell you straight up. I?ve operated enough digital flying machines in my life that I have experince with little digital ghosts that are usually related to grounding issues, so the P-mag instructions don?t seem unsustainable at all. I find it really easy to follow their instructions and equally easy to make sure I am not going to lose the engine ground due to mechanical issues - use good quality crimps, and if you don?t trust them buy a commercial ground strap...or use two.

In my experince it is really rare to have a ground strap fail - much more common for a builder or mechanic to forget to attach it.
 
Bavafa said:
From what I can read, Carl logic is some what correct but has got it backward.

My understanding is to ground the PMAG to the engine case and not the firewall. The logic is that if you have a less than good ground strap from your engine block to the FW, the starter may use the ground that is provided by PMAG to the FW as a path and since the current is too high, it may fry your PMAG or hide the issue of faulty ground strap.
Click to expand...

Ok - I stand corrected.

Considering the pMag case provides a ground connection to the engine block, disconnecting the engine to firewall ground would create a path for the starter through the pMag. So the normal thumbrule of being wary about grounding stuff to the engine is not applicable for pMags.

Carl
 
P-mag grounding

Forget about the main engine/battery ground strap, the p-mag (pin1) ground has to connect to the engine case as per instructions.
I think of the engine/p-mag as being an independent ‘electrical system’ (which it is due to the built in alternator) so the main airframe ground, disconnected or not, will not impact the P-mags if the engine is running. That’s why the P-Mag ground HAS to be connected to the engine case.:)
 
Don't forget, that should the ground strap fail and you have braded stainless steel fuel and oil pressure lines running between the engine and the firewall mounted "manifold", they create secondary and tertiary ground paths.

With the number of customers we have with our EIC's, we have had customers who wired their P-mag grounds to the firewall and there was enough noise caused by the aircraft systems that the EIC would trigger a Timing Divergence Alarm.

When it comes to one's igntion, it is best to follow the manufactures directions and not diverge in any way! Remember, this is your igntion, the thing that keeps you engine running, unless you happen to be running a diesel.
 
Sorry Carl, I was replying, got distracted & then continued & have just seen after hitting reply saw that you had too :rolleyes:
 
Engine Ground

I was working on a Cherokee years ago that had slow turning starter issues that the owner had thrown lots of money at over several years trying to fix. I had him crank it over while I was under the cowling watching and I seen the Bowden cable for the carb heat box glowing red hot!
The way the factory had the engine ground strap attached to the engine mount was through a bare aluminum adel clamp to a 1 inch section of steel tube that was not painted!
 
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