Timing
the Rotax Ducati CDI Aircraft Engines
Several years ago Rotax changed the
ignition system they used on their aircraft engines
from points and condensers to capacitor discharge
ignition or CDI for short. On the first engines the TRIGGERS
were bolted into place, allowing for NO adjustment in
the timing of the engine. Current models 
have
slotted ends on the triggers which means that the
engine timing can be checked and adjusted if
necessary.
To properly set the triggers a dial indicator with
extensions and rollers is required - Rotax has a kit
which while expensive does the job - part # 414-1047.
To set the TRIGGER in the correct
location requires the insertion dial indicator into
the magneto spark plug hole - the dial indicator MUST
has a roller contact or roller ball on the end of the
extension arm, due to the angular spark plug hole.
You only need to install the dial indicator into the
magneto hole, since it is used to set both sides of
the engine. Once the indicator reads correctly for the
engine you are working on you simply move the TRIGGERS
so that they are as indicated in the above diagram.
Once set in the proper location, set the trigger gap
by using a feeler gauge, and set gap to .45 - .55mm
(0,018-0,022 in.). Tighten taplite screws to 6Nm
(53in.lb).
Rotax 447 - 1.65mm
(.074in.) BTDC measured vertically
Rotax 503 - 1.73mm
(.069in.) measured at a 30 degree angle
Rotax 582 - 1.95mm
(.078in.) BTDC measured at an 18 degree angle
Rotax 618 - 1.48mm
(.059in.) measured at an 18 degree angle
Caution:
Whenever doing the ignition timing always check the
triggers for continuity to make sure that they are not
grounding out. The red trigger should measure 50 ohms
while the red/white rigger should measure 130 ohms.
To do an Ohms check on the CDI system refer to service
bulletin 999-695 which has all the OHM measurements to
troubleshoot the Rotax Electronic box.
WARNING:
Do not cranks the engine over while the spark plugs
are not grounded or you could blow your electronic
boxes!
Preflight Check of Ignition:
You can do a quick preflight check of the ignition by
bringing your engine up to 3,000 rpm and turning one
ignition off then the other - you may notice a drop in
rpm on one side and a gain on the other this is normal
- a drop or increase in the tach reading does not
indicate a problem with your ignition!
