Rotax A reduction drive gear, dog hub, spring washers, and prop shaft update

Aircraft Effected: All ultralight aircraft using the Rotax A reduction drive.

Rotax A reduction drive gear, dog hub, spring washers, and prop shaft update

We have several reported problems from pilots using the Rotax reduction drive.
1. a hard to start engine, or an engine that will start but has a hard time coming off an idle or runs very erratic at idle.
2. the gears inside the gear box disintegrating, especially on engines using large radius propellers.
3. the gear box retaining bolts vibrating loose and or breaking allowing the gear box to in one case come right off the back of the engine.
4. the output shafts on the gear box especially on the 65 hp engines, severing, or the prop shaft hub cracking.
5. the oil slinger located on the end of the output shaft breaking and then getting messed into the gears.
6. the loss of reduction drive gear oil during flight.
7. the stripping of the bolts used to attach the prop to the hub of the gear drive. 

Suggestions: 

Rotax A reduction drive gear, dog hub, spring washers, and prop shaft update

1. There was a problem on early Rotax gear drives where a series of spring washers inside the gear box, over a period of time lost their tension.

This in turn caused the engine to become hard to start, and would not come off an idle. Rotax has an update kit which replaces the eight spring washes, and spacers found in the old style gear drives with a new 12 spring washer system. 

It is recommended that these spring washers be replaced every 150 to 200 hours and that the gear drive oil be checked periodically, and replaced every 100 hours or yearly which ever comes first.

2. The problem with the gears shattering was also an early problem, and there is also a retrofit kit, which replaces the gear with a stronger gear.

3. The problem with the retaining bolts backing off was more common on the 3 bolt pattern adapter plates, the new engines are 4 bolt. This problem was also caused by pilots who were reinstalling the gear box for whatever reason. 

In reinstalling the bolts on the 3 bolt system, there are two different lengths of bolts. Both bolts will go in and appear to tighten the plate against the housings. In fact the longer bolt is bottoming out in the crankcase housing and is NOT tightening up on the adapter plate.

4. The aluminum hub cracking hub cracking problem were also corrected on later model Rotax reduction drives, I am not however aware of a retrofit kit for this at this time. The only suggestion would be to update to the new style steel output shaft and hub.

5. The oil slinger problem has been eliminated by the removal of the slinger completely. New model engines do not come with the oil slinger, and the removal of them is recommended on older style gear drives.

6. The stripping of the prop bolts seems to occur when pilots have taken off and reinstalled their props several times. Some pilot have reported drilling out the holds using larger bolts, with locking nuts, and safety wire.

Other pilots have simply gone to larger bolts and used the other bolt pattern on the redrive. This problem is caused by the pilot over torquing the prop bolts on installation. The recommended torque is 100 INCH LBS.

7. The gear oil existing problem can be cured simply by installing a very small gas line filter on the top of the reduction drive vent cap using a small piece of gas line and some clamps. It is caused by the prop creating a low pressure area above the vent, siphoning the oil out of the gear drive. 

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