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mag checks

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mag checks

Postby acropilot » Fri Mar 08, 2019 8:29 pm

Jabiru 2200a not getting any discernable mag drop on either left or right on :twisted: :?: mag test .Both P wires are ok and I can shut engine down fine when both mags off.Anybody any ideas ,my flying buddy an airline captain with 20000+ plus hours is now a jibbering wreck because we don't get a drop
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Re: mag checks

Postby Admin » Fri Mar 08, 2019 8:59 pm

No mag drop is pretty normal on a Jab engine.

Spark plugs are very close together. Turning one mag off does not neccessarily result in a drop in RPM. if engine is ticking over, you may notice a slight rumble but that is it. As long as engine runs while on right and left only, then you are fine. It is a good idea to also try a mag check when engine is hot as some of the mag issues only seem to be detectable when engine has reached full operating temperature :D
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Re: mag checks

Postby acropilot » Sat Mar 09, 2019 12:31 pm

Thanks for that info doubt if I can get my flying buddy of the tranquilisers though ,he's gotten a taste for them.
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Re: mag checks

Postby Matt » Sat Mar 09, 2019 4:17 pm

Change flying buddy. Found satis
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Re: mag checks

Postby PKnight » Sun Mar 10, 2019 3:23 pm

I agree.
A mag check at 2000rpm is barely detectable, if at all. You may just be able to detect a slight change in the 'feel' of the engine running but if I see an actual mag drop it is usually the first sign of a duff spark plug.
A mag drop is far more noticeable at idle speed. If you set the rpm to about 800 and turn each mag off in turn you should detect a noticeable change in the running of the engine and a drop in rpm.. I have always assumed that this is the result of the spark from the mags being noticeable weaker at low revs so if one mag is switched off then the engine is running on a single rather weak ignition spark.
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Re: mag checks

Postby skypics234 » Sun Aug 18, 2019 3:02 pm

A better mag check per Mike Busch is to look at the EGTs. When you switch to one mag you should see the EGTs increase. Assuming they have stabilized during the run at 2000 RPM.

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Re: mag checks

Postby diablo » Mon Aug 19, 2019 1:58 pm

That's interesting. Why would EGTs increase while running on a single mag ? What's the theory behind it all ?
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Re: mag checks

Postby skypics234 » Sun Aug 25, 2019 3:02 pm

With only one plug firing on each cylinder more heat energy is being dumped out of the exhaust. Two plugs firing is more efficient so less wasted energy.

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