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Engine burp

My guess – sorry for being a bit paranoid on this topic – the mag coil is close to be scrap. Do a mag test AFTER an hour´s flight at at least cruise engine speed or higher and listen. You may get decent misfiring when the coil and capacitor are shot. This does NOT show with a cold engine and mag but you could set up a motorized test rig in your oven at 60 to 70 degrees and look at spark lengths after a several hours run. Might come as a shock. Don´t ask how I know . . . . Vic

vic
EDME

Hmmm, yes, could well be. Very interesting.

Thankfully that magneto is now history, and going back to the US for an overhaul. We did a service right after the said flight and the A&P/IA reckoned the impulse coupling didn’t sound right. It was also a bit sticky when rotated by hand. So I put in a spare mag (D3000 single shaft one; can never be too paranoid in this case) and the difference is dramatic in the mag drop amount; improved from some 200rpm (and in spec only if leaning IAW the Lyco instructions) to 120rpm at full rich.

I wonder if any bench test can reveal this? The mags are not tested at an elevated temperature.

Administrator
Shoreham EGKA, United Kingdom

vic wrote:

My guess – sorry for being a bit paranoid on this topic – the mag coil is close to be scrap.

Yep, sounds plausible. Had exactly that in a C210 right in the middle of Australia – Birdsville.

I am informed that the coils are tested under heat, on a mag overhaul. I didn’t know that.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

improved from some 200rpm

200rpm should be a concern already
As far as I remember on run-up, mags check, each mag should not drop more than 150rpm unless you play with LOP on the ground.
More information about LOP on the ground here

ES?? - Sweden

The Lyco procedure includes leaning in order to reduce the mag drop. It isn’t LOP; it is just a slight lean, just a bit back from full rich which is where the mag test is normally done (at 2000rpm).

So it is an acceptable procedure.

Whether the need for it indicates a faulty or mis-adjusted mag, I don’t know. I know the cause of the mag drop (obviously, only one plug firing) but I don’t understand the factors in the magneto which would affect its magnitude. Especially if it is identical on both mags.

Administrator
Shoreham EGKA, United Kingdom
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