Incident report:
Various MX pilots have reported vibration in their aircraft, upon further examination it
was found that a collar inside the root rube which the top pulley shaft goes through had
begun to wear, allowing the bearing which it retains to move causing the vibration.
It was generally found that all these aircraft had more than 100 hours on them.
Suggestions:
Drill a hole through the root tube directly in front of the bolt that holds the collar and
install a bolt. What this does is holds the collar in place and takes the strain off of
the bearing and collar. Of course if you have already started to feel the vibration then
the bearing is probably gone and must be replaced.
If you have access to a machine shop the suggested retrofit below
replaces the round bearing retaining collar with a new aluminum
insert which fits snuggly into the root tube eliminating the need to
drill the second hole, and prevents bearing and collar wear in the
future.
The two bolts and the way the insert fits into the
root tube gives the drive shaft a solid base, preventing it from
moving up and down.
You can see the bearing cannot move in any
direction.
The part that we are replacing is 10220. It is
a round bearing housing that has one bolt going through it from one
side of the root tube to the other.
With vibration, load and time the cylinder pivots on the bolt.
The retrofit above stops that from happening.
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