Timing the Rotax Ducati CDI Aircraft Engines

Reprinted by permission of David loveman

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 dcditim.gifhave 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 (.066in.) 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. Some details shown at bottom of page.

Do not crank 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!

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