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Mag drop change


Cruiser

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pre-flight mag check showed a drop of 100 rpm on the L mag, R mag dropped 50 rpm as both have been doing previously. The change was very noticeable on the L mag. 

In flight LOP at 6000' I did another mag check with this result. L mag first then R mag.1301889657_LOPmagcheck.thumb.JPG.5605a1ae71c3a0c0ec8a8346c0c7e09f.JPGAny reason for concern? Why the sudden change in rpm drop on pre=flight check? Spark plugs are Tempest massive about 500 hours old. 

Ideas?

Suggestions?

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Not a lot of data points in there... but definitely showing something is different...

When the two peaks are different heights... that may be timing related...

One mag is more retarded than the other...

More before TDC results in the lower peak..

Closer to TDC results in the taller peak...

 

PP thoughts only, not a mechanic...

Has there been any timing or mag change lately?

Best regards,

-a-

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13 hours ago, Yetti said:

What mags? hours on mags?  if they are Slick, then they have a higher than Bendix failure rate

Agree.  Tom should have Bendix mags in his Ovation unless they were changed out.

@Cruiser Tom, I would seriously consider switching to iridium fine-wire plugs...specifically, the Tempest URHB-32S.  Not cheap, but so much better.  With fine-wires, a CMI Gold Seal ignition harness, and Bendix mags, you’ll have the best ignition system available for the IO550 platform.  How recently did you notice the mag drop?  Did you have any other work done on the engine recently...and if so, what type of work?

Steve

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The mag drop isn’t excessive, but if it’s a sudden change from the usual, it’s worth looking into.  I’d start with condition of the plugs, check the magneto timing per MSB94-8D, high tension check of the ignition harness.  How many hours on the magnetos?  Your Bendix mags are much more robust and reliable than Slick mags and will go much further than the 500 hour period without concern.

Clarence

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Impossible to tell with only 2 or 3 data points on the first/left mag - a proper mag test requires 10 data points to see what's going on. But if the left mag peaks remains higher than all the right mag peaks that is an indication of split timing. What ever you monitors sampling rate is, multiple that by 10 for the time needed to isolate the mag and perform the test in flight at about 50F LOP to provide the most informative results.

regardless of what Mags you are equipped with, the first step should not be to replace with bendix mags :)  

Edited by kortopates
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