Mag Check!

[Browncbr1]

Thank you,... yea, Mike had mentioned internal timing has been known to drift within 25 hours of a kelly mag.. I'm thinking that the graph shows that too.. 

[N201MKTurbo]

Just now, Browncbr1 said:

Thank you,... yea, Mike had mentioned internal timing has been known to drift within 25 hours of a kelly mag.. I'm thinking that the graph shows that too.. 

The internal timing will effect the amount of power the mag will produce. It is obviously making enough power to fire the plugs. The internal timing will change as the cam follower on the points wear. Most likely just "breaking in". If the internal timing changes the engine timing will change by the same amount.

Just resetting the engine timing of the two mags should fix your problem.

[N201MKTurbo]

Just now, Browncbr1 said:

Thank you,... yea, Mike had mentioned internal timing has been known to drift within 25 hours of a kelly mag.. I'm thinking that the graph shows that too.. 

The internal timing will effect the amount of power the mag will produce. It is obviously making enough power to fire the plugs. The internal timing will change as the cam follower on the points wear. Most likely just "breaking in". If the internal timing changes the engine timing will change by the same amount.

Just resetting the engine timing of the two mags should fix your problem.

[carusoam]

Hey, that is an eye opener.  

1) #4 is a bit low on the left side.  Raw EGT data can be affected by probe positioning.  (Hold that thought for a second) Raw EGT data gains meaning by comparing between cylinders, or related to FF.  In this case between L&R mags is showing something.

follow the behavior of #2 and #4 they both increase significantly going from one mag to the other.  1&3 are more stable between mag tests.

2) #2 peaks first when you did the GAMI test.  Close to #3.  #2 shows up a bit later.  Number #1 appears to be late to the LOP party.  How late he is, depends on his FF at peak.  Raw FF data gains meaning by comparing between cylinders.

3) what are the FFs at each peak? I am unable to get the numbers off the graph.  The actual GAMI spread may give something to look at in terms of FF through each injector.  Balance is a key factor in smooth running engines

4) Another oddity about the EGT graph is #2's plateau at peak isn't as flat or defined like the other three.  They run out of burnable mixture and flatten out, Descending with the increase of excess air.  #2 is different with it's angled surface.  It really doesn't show the defined plateau as nicely as the others.

It does seem like something is quirky going on between the individual mags.  Both EGTs on one side a rising differently, in a similar way, when the mag changes from L to R.

Having #2 peak first may be an indication of less FF through it's injector...

These are only PP observations.  There is too much data here for me to understand and give valid advice.  Sharing what I see.

Best regards,

-a-

 

[Browncbr1]

I'm not sure if maybe the color is off on your screen.  cylinders always peak in the same order. 4, 3, 2, 1.    the rear two cylinders peak nearly together and the front two peak nearly together.   #2 has never peaked first.

 

FF at each peak always varies with altitude (WOT)  ..  usually somewhere around 8gph or slightly less.

 

BTW, someone asked about my wire harness..   It is a new harness i bought when the kelly "overhauled" mags were installed.. 

[carusoam]

Follow up questions:

1) Why does the mag check really stand out on one bank of cylinders more than the other?

Is this possibly showing a combination of two things...

- Mag timing (the 'alleged' thing that is causing the issue)

- fine wire plugs (Picking up some slack for the errant timing in the other mag)

Thanks for staying with me on these additional observations and questions...

2) CHTs are usually hotter when an engine's mag timing is increased further before TDC.  Would Mr. Brown be able to see this using the data from the inflight mag test?  Or while operating on the ground collecting more data?

3) how many maintenance hours is involved just checking and adjusting the timing of a single suspect mag?

Best regards,

-a-

[Browncbr1]

My thinking is that the internal timing on mag 2 is retarded...   On the right bank, the fuel shoots directly on to the bottom plugs (fine wires) and on the left bank, the fuel shoots to the opposite side of the cylinder.. with massive plugs on top..    I think there may just be some slight internal mag timing difference... and probably the different plugs on top and bottom doesn't help the way things look.

Either way, I'm going to reset timing to 25 degrees and have the left mag inspected during the process.

 

 

[carusoam]

Your patience must be really strong.   Once making the decision to go 25° I would want it done yesterday...

Just an NA power thing I have.

Cost analysis...  Two months of an annual tossed in the trash for impatience vs. waiting two months for the usual annual.   2000/12X2 = $333.   Hmmm.......... Tough choice.....

Best regards,

-a-

[Browncbr1]

I'm a CB, what can I say.

I even start annuals on the last week of the month, so I can get an extra month out of the cost.

Edited March 11, 2016 by Browncbr1

[Browncbr1]

Well, I sent the left mag out to get converted to a 4347.  The guy did this and tested everything and sent it back for $75.  He said the internal timing was at 11 degrees.   I guess that explains quite a bit of what was going on.    

Its going back back together this week and I can't wait to fly it with 25 degree timing! 

During the course of undoing SI1325a, it was unclear regarding data plate legal requirements.   I have written documentation from Lycoming and Nashville FSDO confirming that vibropreen over 20 and stamping 25 next to it with logbook entry is legal if anyone needs it.  

[MB65E]

Nice work! Enjoy the 25°!! Thanks for the note info from BNA & Lycoming. 

 

-Matt

[Browncbr1]

Update: so glad I went to 25 degrees timing.  Smoother ground ops, smoother in flight, noticeably more power and speed, albeit, I just gave it a nice cleaning and wax though.   Temps have risen enough to scavenge lead, but not too hot.   I'm really glad folks on here encouraged me to undo si1325a!  Thanks!