Mag drop....what is acceptable on run up?
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timwinters
Ejection Handle Pulled
What does the POH say?
ebykowsky
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goalstop
Isn't it 125rpm on the Lyc 360s? I normally like to see roughly 100rpm drop for each, no more than 50 on the cross-check.
You seem to be well within limitations.
And how in the world are you reading the rpm drop that accurately? Do you have a digital tach?
You seem to be well within limitations.
And how in the world are you reading the rpm drop that accurately? Do you have a digital tach?
Read your POH. I've seen numbers in various planes I've flown from 75-125 total and varying left-to-right differentials.
Note well that you want to see SOME drop always. No drop means something wrong in the switch/p-leads or seriously mistimed ignition. Either way it behooves you to figure out why before you attempt to commit aviation. Sometimes it's not things that you don't expect to happen that do that are the problem but also things you expect to happen that don't! Anything unusual behooves a checkout rather than just assuming things will work out. We lost a few lives in the space program over that.
Note well that you want to see SOME drop always. No drop means something wrong in the switch/p-leads or seriously mistimed ignition. Either way it behooves you to figure out why before you attempt to commit aviation. Sometimes it's not things that you don't expect to happen that do that are the problem but also things you expect to happen that don't! Anything unusual behooves a checkout rather than just assuming things will work out. We lost a few lives in the space program over that.
Most engines split the top and bottom plugs between the two mags. That's not to say that one of the bottom plugs on the lower reading mag isn't fouled. This is when an engine analyzer really helps.
Dan Thomas
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Continental has one mag drive the top plugs, the other drives the bottoms. Lycoming splits theirs up, with each mag driving the tops on one side and bottoms on the other.
The smaller Continentals are famous for fouling the bottom plugs. The plug is very low in the head and oil can run directly into it. When the engine is cold on startup, the clearances allow plenty of oil past the rings and it will foul those bottom plugs. Using REM37BY plugs helps a lot.
Lycoming's bottom plugs are high enough to escape being filled up like that.
The OP's mags might need checking out. Very few magnetos get the internal inspections they need, in my experience. It's not just accumulated hours; it's accumulated years, and things get rotten in there. Mags need attention just like the old cars did with their points and condensers and distributor caps and rotors. We have become really spoiled by electronic distributorless ignition in our vehicles, systems that run for the life of the car, and we now seem to think that our airplanes don't need any more attention than our cars. I run into considerable reluctance from owners when I suggest that those mags need opening up.
Dan
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FastEddieB
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Fast Eddie B
That sounded contrary to my experience with the Continental IO-550 in my Cirrus.
From the SR22 POH:
"Two engine-driven magnetos and two spark plugs in each cylinder provide fuel ignition. The right magneto fires the lower right and upper left spark plugs, and the left magneto fires the lower left and upper right spark plugs."
poadeleted20
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A typical manual gives both a max drop and a max difference. You have a Lycoming O-360-A engine, right? I'll bet if you look at the Lycoming O-360-series Engine Operator's Manual (as I just did), you'll find it says max drop 175, max difference 50. If the Piper POH says max drop 125, I'd take use that more conservative number for that Piper, but in the absence of any guidance from Piper on max difference, I'd stick with the max 50 difference that Lycoming gives. Since you're seeing a difference of 40, that's within limits, but I'd recommend keeping an eye on it and asking your mechanic to look into it if the difference increases further.
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Dan Thomas
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timwinters
Ejection Handle Pulled
Mine's a 1958, O470L and the left mag fires the lower 1, 3, 5 and upper 2, 4, 6.
Right mag fires the others.
I guess "newer" is a relative term
Jthamilton
Line Up and Wait
Toga says no more then 150 drop, and no more then 50 rpm drop between the two for my Lycoming
poadeleted20
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Saratogas have different engines than Archers.
Lots posted here about many different engines from different manufacturers in different aircraft, and the answers vary accordintly. The OP needs information about the Lycoming O-360-A (-A4M, IIRC) installed in a 1979 Archer.
ARFlyer
En-Route
I've always used 175/50. If it's any larger or feels rough I'll lean it back to burn off the carbon. Normally that fixes the issue. If you really do have a bad mag you will notice it.
BillTIZ
Final Approach
it really should get your attention if there is no drop on a mag check. Either the P lead is screwy or the mag is not working.
If the P lead is screwy, you have a hot mag when you shut down!
Make sure to leave a hot prop sign and head directly to the maint office!
If it is not working, you'll know when you check the other mag and the engine quits or runs really rough.
Do not attempt to commit aviation in either situation.
gismo
Touchdown! Greaser!
Or the mag timing is overly advanced. Miss-timed mags are also the most common cause for a noticeable difference in the drop between the two mags if the engine runs smoothly on the low RPM mag.