Mag Check!

[Browncbr1]

I was coming back from Nashville and did a mag check on the way and found that operation on the left mag was smooth, but rough on the right mag.   in the image, the left rise is the left mag operating smoothly...  notice #1 drop on the right mag is not as high... and the others rise much more...   RPM mag drop on the right mag is currently max RPM limit on ground run up..   Any suggestions?

 

[N201MKTurbo]

To get meaningful data it would be better if you let the temperatures stabilize on each mag before going back to both.

[Browncbr1]

The left mag was smooth and seemed that egt went up and stayed there.   The right mag was rough and egt went higher, but yea, I switch to both because it was running so rough. 

[N601RX]

How many hrs since the Kelley overhaul on the mags?  There has been a problem with Slick points not holding the initial e-gap setting. There have been numerous reports with the e-gap needing to be adjusted with 25 or less hours.  Once reset then they are usually fine.

Was this LOP or ROP? 

[CaptainAB]

The obvious question. I'm sure you did. Did you lean the engine for ground ops and try the run up again?

AB

[Browncbr1]

On the ground, I lean until it stumbles when giving more throttle.   

This kelley "OH" mag has about 20 hours on it.

the mag check was done at peak.  (#1&2 peak, 3&4 are about 30dF LOP)

[kortopates]

It's really inadequate data- only a single data point on the right mag. May I suggest you go to Savvy Analysis web page and download the Savvy Test profile and follow the test profile instructions. Or google our "Savvy Inflight Diagnostics". When you do it again, keep it on the mag position long enough to collect at least 10 data points - with your 2 sec sampling rate give it a full half min or 30 sec and that includes the both position in the middle. Do the LOP MAG check after the gami spreads at 65% power ( without changing MAP or RPM, just FF) so you how much it is LOP can be verified. enrichen after the gami spreads enough that you have a smooth running engine before you start the LOP (I.e. 50 LOP or less if necessary). Then look for a weak rise or erratic EGT (missing).

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[DXB]

I was struggling to get my head around it, but I suspect the real answer is by kotopates  above.  Just for comparative fun, here's my recent mag check in cruise, leaned to around 25 ROP (I'm carb'd but could probably go leaner), with sample rate on the JPI set to 1/sec, holding each side for about 10 secs.  No major roughness, but  it still wasn't long enough for EGTs to stabilize.

[Browncbr1]

1 hour ago, kortopates said:

It's really inadequate data- only a single data point on the right mag. May I suggest you go to Savvy Analysis web page and download the Savvy Test profile and follow the test profile instructions. Or google our "Savvy Inflight Diagnostics". When you do it again, keep it on the mag position long enough to collect at least 10 data points - with your 2 sec sampling rate give it a full half min or 30 sec and that includes the both position in the middle. Do the LOP MAG check after the gami spreads at 65% power ( without changing MAP or RPM, just FF) so you how much it is LOP can be verified. enrichen after the gami spreads enough that you have a smooth running engine before you start the LOP (I.e. 50 LOP or less if necessary). Then look for a weak rise or erratic EGT (missing).

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Thank you for reminding me.  I'll try to get up later this week and do proper tests.   Usually my Gami spread is about 0.7 gph btw, which is about what this flight logged. 

[Browncbr1]

One thing I realized last night is the mag switch seems intuitively backward.   The placard shows "R" on the left position and "L" on the right position...    So, this means my OP is backward?  The first EGT rise is actually operating the Right mag??..   

[carusoam]

Standards are often quirky and may be less intuitive than expected.  

The two mags are often different from one another. Only One has the set-up for starting.

the left mag is on the left side of the engine block (pilot side). (Guess, based on old memory)

the switch is marked R on the furthest positon to the left. R, L, B... (Memory challenge that creeps in over many years)

The switch gets my vote for being the most quirky.  Hardest to read as well...

when discussing ignition problems with your mechanic, it really helps to know exactly which device is giving you a problem.

at least be able to say what switch position was used when the problem arose.

Since the lower plugs often get fouled before the top ones, it may also be helpful to know which mag operates which plugs.  A JPI (or other) is better than the memory intensive technique.  Make sure the  wire numbers actually match the cylinder numbers. 

Best regards,

-a-

[Hank]

Each mag should operate two top and two bottom plugs. If one mag operated only top plugs, and that mag failed in flight, if your bottom plugs weren't nice and clean it could get exciting. Memory isn't exactly clear from last summer's investigative work, but I think the mags are connected to a top and a bottom on each side, but it may be both tops on one side and both bottoms on the other side.

[carusoam]

Thanks, Hank.

I forgot to clean that up in my paragraph.

Each mag operates a top pair and a bottom pair of plugs, for a four cylinder engine. Two left and two right.  Not a cross pattern...

I stopped to consider how things are done with the six cylinder engine.  Then distraction took over my writing...

The six cylinder engine is treated the same way.  Three bottom and three top plugs go to one mag on opposite sides of the engine.

Where the distraction came in...

There are a couple of variations on which mag 'could' operate which plugs (X-pattern,vs LR.) there is no good way to run an engine on one mag or missing one plug.  The bottom plugs have a tendency to foul the most.  It would be bad to have all the good plugs attached to a bad mag.

Thanks again,

-a-

[kortopates]

49 minutes ago, carusoam said:

Standards are often quirky and may be less intuitive than expected.  

The two mags are often different from one another. Only One has the set-up for starting.

the left mag is on the left side of the engine block (pilot side). (Guess, based on old memory)

the switch is marked R on the furthest positon to the left. R, L, B... (Memory challenge that creeps in over many years)

The switch gets my vote for being the most quirky.  Hardest to read as well...

when discussing ignition problems with your mechanic, it really helps to know exactly which device is giving you a problem.

at least be able to say what switch position was used when the problem arose.

Since the lower plugs often get fouled before the top ones, it may also be helpful to know which mag operates which plugs.  A JPI (or other) is better than the memory intensive technique.  Make sure the  wire numbers actually match the cylinder numbers. 

Best regards,

-a-

So very true Anthony. We ask our clients when following the Savvy Test profile for the LOP Mag test to begin with the Left position. But so often we see them backwards and my suspicion has always been its because the leftmost key position is actually the right mag - not left as I suspect many pilots assume without looking closely. With a healthy ignition system though we can readily tell them apart.

The two mags aren't always different though. Those that use impulse coupling will often have two impulse coupled mags which I think is a great advantage. Obviously though you won't see two mags with SOS systems so normally the left mag only will have the starting circuit.

18 minutes ago, Hank said:

Each mag should operate two top and two bottom plugs. If one mag operated only top plugs, and that mag failed in flight, if your bottom plugs weren't nice and clean it could get exciting. Memory isn't exactly clear from last summer's investigative work, but I think the mags are connected to a top and a bottom on each side, but it may be both tops on one side and both bottoms on the other side.

Exactly right but lets not limit it two plugs though!  Best to say in the vast majority of engines that each Mag fires the Top plugs on its side and the bottom plugs on the opposite side (i.e. Left Mag fires top Left side cylinders). Plus we always have Odd numbered on the right and Even numbered on the left. But Continental starts counting #1 from the rear while Lyc has to be different and count #1 from the front. Firing the top of the same side is true for almost all engines with a few exceptions including the 4 cyl Lycoming and continental 300; which does the opposite (left mag fires top right). But if one replaces there Bendix ignition wires on a Lyc 360 they can end up with the conventional Left Mag to Left top plugs - so the Lyc 360 is a uniquely odd in that it depends. But no, the different style wires do not alter firing order at all.

Edited March 3, 2016 by kortopates

[carusoam]

Paul, thanks for filling in the spectacular details!!!

Best regards,

-a-

[Browncbr1]

Some of you may recall my other thread about my mag issue. I have a 4345 on the left and a 4370 on the right.   Timing is set to 20 currently.   

I will be sending the left mag out to get new retard breaker timing and relevant data plate applied when going back to 25 degree timing.   

 

To clarify, when the key was at the far left position (2 clicks left), the motor ran smooth on that mag alone.   I went back to both for a moment, then switch the key to the middle position (one click left).. this is where the roughness set it.   It is shown on the right side of the graph in the OP.

[Browncbr1]

I had a chance to do a slow mag check after a slow gami test at 6500 WOT today...  I pulled all the bottom plugs off and cleaned before flying... 

the left mag (right side of graph) was still pretty rough..   Not as rough as when an injector is clogged, but it the right mag was comparatively smooth.

First gami spread was 0.7...  I did another slow gami test well after the mag check and got 0.4

[Browncbr1]

Here's the first gami if it's helpful.  this was done a couple minutes before the mag check.

[Browncbr1]

Any advice on what I'm looking at ?

[carusoam]

Your EGT#2 is misbehaving when only on the left mag...

When you set it to a particular condition (left mag only), fuel is not burning normally in the cylinder and continues to burn in the exhaust giving a high EGT fingerprint.

From the graphs you are showing, the left mag (right side of graph) is showing the dead/errant plug.

Which plug is connected to the left mag in cylinder #2?  Pull that guy and check it's resistance.  Replace with a good plug and repeat the test.  Using Paul's guidance above (only if I got it right), Top plug on the #2 cylinder is misbehaving on the left mag...

I also see some minor change of the FF that I didn't expect.  It may be related to a change of rpm or MP..?

PP feedback, not from a qualified mechanic...

Let me know if this makes sense.

Best regards,

-a-

[Browncbr1]

Thank you for your help!. I will check the leads and plugs on #2 and come back with findings.. 

[Browncbr1]

I verified the left mag is driving the top plugs on the left bank (#2/#4) ... I pulled the top plugs off and they looked ok.  resistance was just under 1400ohms..  

I guess the only thing to do now is pull the left mag and check internal timing and points while the retard breaker is reset to 25 degrees... probably won't happen for a couple of months at annual..  i'm guessing a retard internal timing would result in higher egt.. 

Edited March 11, 2016 by Browncbr1

[carusoam]

Something is not making sense(to me).  You may want to have a discussion with your mechanic to talk about your graphs. This will help get to a proper and quick resolution.

If it were a mag issue, it wouldn't be showing up on only the one cylinder.  Maybe an ignition wire or the wire's connection at either end? (How old are the ignition wires?)

The risk of waiting for annual...

1) From your graphs, It looks like a plug is not working properly, but it could be something else... (Send your graphs to Saavy for pro advice).

2) there are two plugs per cylinder, one may not be working.  What happens when the other mag fails?  This would leave you flying on three cylinders.

Essentially, the safety net of having two complete and separate ignition systems has recently been removed.  You want to get that back.

3) fixing this problem first will be nearly the same cost as fixing it at annual.  It probably is the same cost if you take the top cowling off yourself in preparation for the mechanic.  If it is an ignition wire not working properly, the mechanic is going to add the troubleshooting time and effort and associated costs on top of the other mag changes you are making.

4) When you pulled the plugs and checked their resistance,  did you put them back in their same places? Swapping their locations would be a second way of confirming that is not the plug itself causing an issue. Some plugs have the screw on cap(?) that have been known to cause issues under actual use but not during bench testing.

 

This is my PP opinion.  The same PP that flew a C152 on a return X-country flight with a dead mag.  I thought it was a spare mag and you only needed one.  I misunderstood something important in the training early on.

Hopefully this gives you some ideas to get to where you want to be.

Best regards,

-a-

[Browncbr1]

#2 is much higher on the right side of the graph, but #4 is also... Actually, the only one that is not higher on the left mag is #1.

I did swap the two plugs on top, but I didn't fly and do another LOP mag check because it was pretty rough air.. 

 

One thing I forgot to mention is that I have fine wires on the bottoms of all jugs.. massives on top.. all tempest with low hours.  Maybe this might be causing part of the issue shown on the graph

[N201MKTurbo]

It looks like all your plugs are firing. Your gami chart shows two cylinders are a bit richer then the other two. The difference between the two mag drops is most likely caused by a timing difference.

As the combustion charge burns it transfers heat to the cylinder to do work. The more complete the combustion when the exhaust valve opens, the lower the EGT. The more you advance the timing the cooler your EGT (all else being equal). When you turn off one mag the charge is burning from one point instead of two. This effectively retards the timing leaving more unburned charge when the exhaust valve opens, raising the EGT.

If any spark plug is misfiring, the EGT will drop on that cylinder when running on one mag. None of yours did that.

The difference in EGT rise can only be attributed to a timing difference.