Single mag operation: issues?

[LAL]

Without bothering folks with details, I had to run the engine for 30 min or so on single mag. Temps all normal during that operation.. mid 300s CHTs, etc. In general, I have always been curious if single mag operation has negative consequences for an engine. Should mixture be "normal" or richer than normal if one has to do that? Other than the obvious concern around that second mag giving up the ghost, any wisdom for me?
IO360A1A, FI, dual P mags.
Regards,
Len

[airguy]

Aircraft run dual mags primarily for safety in case one mag quits in flight. The differences in the way the engine runs (fuel efficiency, power output, EGT/CHT, etc) are strictly a side effect. You should not have any issues at all from running for a while on a single mag.

[frankh]

Safety reasons aside the only effect is to retard the timing a little...Not because the timing of the mag retards, just that the cylinder is so big and it takes less time for the flame front to go across the cylinder if you light the fire from both sides so to speak.

Thus the maximum cylinder pressure will come up a few degrees later than if both mags are rumming.

As max cylinder pressure is something like 30 degrees after top dead in an ideal case, having the pressure come up later than this is less efficient.

But as to hurting the engine its a non issue.

Now the bigger question is..would you fly home on only one ignition system??..

Frank

[Ironflight]

I was always taught (this is word of mouth - no data to back it up!), that the "non-operating" plugs will foul if you run on one Mag for a long time. I've never had reason to try and prove or disprove this, so I don't know if it is true or not....

Paul

[John Clark]

Originally Posted by Ironflight

I was always taught (this is word of mouth - no data to back it up!), that the "non-operating" plugs will foul if you run on one Mag for a long time. I've never had reason to try and prove or disprove this, so I don't know if it is true or not....

Paul

Not quite a Lycoming, but I once had a mag failure in flight on an R1830 Pratt & Whitney. The failed mag was causing it to run very rough. Switching to the "good" mag cured the roughness. We flew about 45 minutes, landed and had the mag removed and repaired. We looked at a couple of the plugs and decided that it wasn't worth inspecting them all. The engine started normally and the run-up was uneventful. My best guess is that as long as the engine is healthy and the combustion temps are close to normal, fouling the inoperative plugs shouldn't be an issue.

John Clark
RV8 N18U "Sunshine"
KSBA

[LAL]

Thoughts much appreciated!
Len