Ellery Queen and the Case of the Missing Magneto Gear Teeth

Okay, here's the solution to the mystery.

When I went to take the magneto off for the Nth time, I couldn't find the "red
mark" to time the mag before removing it from the engine. "Funny," I thought.
"It only had 15 minutes since I last had it off."

Then it hit me. What had been bothering me all this time was the way the teeth
on the gear were wearing. See the black marks? And notice the angle wear of the
teeth? This gear has only about 10 hours on it! The gear was not engaging
properly on the metal gear in the magneto.

Now see the photo dated 7/25/2003 at

http://www.fotolog.net/palmer_mp

This is a shot of the copper sleeve bushing in a Bendix distributor block.

The cause of the problem was that the copper sleeve bushing in the distributor
block had worked loose in the block. (About 700 hours since new.) Hard to show
"wobble" in a still shot, but here you can see the bushing deflected to one
side to give an indication of the "play" it had.

Hence the gear was wobbling/shimmying around inside the magneto. The shimmy was
so bad that the gear would occasionally jump off the main gear, skip and change
timing! I'm guessing that the old gear stripped when the rotor arm finally
jammed against one of the four copper posts.

I suppose the only reason we were able to fly for 10 hours since overhaul was
that the repairman put a new felt in the block, which somewhat stiffened the
bushing until the felt became oil soaked and/or crushed a bit from the wobble.
Too bad our repairman didn't notice the loose sleeve in the first place. (I've
taken it to him since. "You don't see that too often" was his reply.)

If anyone has a contact at Bendix (no pun intended) please let me know so I can
send them this block.

Hope this helps,

Mike Palmer
Excellence in Ergonomics