Thorp Air Command - T18.net

Had a little excess mag drop on one of the mags - got a little worse on the trip to Visalia. Thought I best check the timing on the mags - got the hangar neighbors timing device and hooked it up.

L was almost 3 teeth retarded and the R was 4 teeth advanced - so far out they could not be timed dead nuts without internally adjusting the setting. Got them within less than a tooth externally tho - internal timing this weekend - amazing how much smoother the engine runs when the mags are timed.

I probably wore 200 hours off the engine running it like that.

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

You wore 200 hours off me just reading it ! [:0]

RB

Fraser,
Did you check the mags internally for point gap and cam follower wear?? Here is a recommendation from the Lycominglist. They are talking about checking a dual mag, but refers to a single. Mahlon knows his Lycomings.



These mags are a bit finicky and I would take them off every 3-400
hours for complete teardown and inspect and repair. Regardless of
symptoms, I would never run more than 500 hours without removing them
from the engine and taking them totally apart. Always replace the
condensers at this time and always make sure you have a good ground
between the points and the mag and the harness cap and the mag and the
condenser and the harness cap. If you see big changes in mag to engine
timing while doing a 100 hour or annual (say more than a couple of
degrees) don't just reset the mag to engine timing..my bet is you will
find the point gap has closed up. If that is the case, replace the
condenser and points and check all the grounds as listed above.
If I were flying behind one of these mags I would check the timing at
every oil change to see if the mag to engine timing has shifted and if
it has shifted more than I would expect, I would do the point,
condenser, ground thing. As you have probably guessed, they have a
problem with point gap closing from melted cam followers on the
points. They say this is from the points overheating due to bad
condenser or bad grounds.
If the mag is set up correctly on the bench then the two of them will
be within a degree of each other when timing to the engine.
If you can do single mag inspection and repair you can do dual mag
inspection and repair, they aren't that much different mechanically.
Good luck,
Mahlon

Bob MO

Hi Frase, these are slicks?? Dan

Dan - Bendix

Bob - the mags were rebuilt by the previous owner about 120 hours ago - they are suspect - this winter will get a rebuild and new condensors and new wiring - much of the wiring throughout the plane is original and needs replacing anyway - the one mag needed an internal adjustment - slicks apparently don't have that issue. I rebuilt a bendix mag myself a few years back - everything checked out - timing and during runnup, then I lost the mag just after takeoff - cost me a pair of underwear - told myself I won't do that again and will leave mags to those who work on them on a regular basis.

_________________
Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)