Magneto Timing Using Digital Level by Peter Cassidy
Airplay Third Quarter 2011
One of the challenges in timing aircraft mags is getting the angle correct. It needs to be spot on -- within half a degree or less. Close won't do. The time-honored practice is to use a pendulum protractor attached to the prop spinner. Eastern Technologies make one for $59.50 from Aircraft Spruce including the piston stop. The problem with this device is it sticks as you rotate the prop. While there are ways around this problem, I've found a better solution using a digital level. Any digital level will work. I bought one from www.woodworker.com made by Wixey for $40. You also need a synchronizer box, I use an Eastern Technologies E50.
- Fasten digital level to prop (anywhere) using masking tape on all sides.
- Remove all top plugs.
- Find approximate TDC for #1
- Back prop about 90 deg.
- Install piston stop in #1.
- Rotate prop forward till it just touches piston stop.
- Zero digital level.
- Rotate prop backward till it just touched piston stop.
- Read digital level and divide by 2 (e.g. 68/2=34).
- Remove piston stop.
- Rotate prop forward to amount calculated in step 4 (e.g. 34).
- Zero digital level. This is TDC.
- Rotate prop back about 25 deg.
- Attach E50 Mag Sync box to ground, L and R P leads.
- Turn E50 synchronizer on.
- Turn Mags (ignition sw) on.
- Rotate prop slowly forward watching Sync box lights.
- Each light will indicate exact point of closing.
- Adjust mags until both lights are in sync and buzzer changes pitch at the desired setting. (22 deg BTDC for TCM IO550B)