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Incident report:
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:
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 torqueing
the prop bolts on installation.
7. The gear oil existing problem can be cured simply by installing
a very small gas linefilter on the top of the reduction drive vent cap
using a small piece of gas line and some clamps, or updating to the new
style vent cap 941 115 and 931 200 gasket.
It is caused by the prop
creating a low pressure area above the vent, siphoning the oil out of the
gear drive. |
