Rotax MMH-912 Series Maintenance Manual page 116

3.9.12) Gear set inspection
Effectivity 912/914 Series
Edition 1 / Rev. 2
BRP-Rotax
Maintenance Manual
The gear set is inspected to detect any damage to the gear-tooth
system.
◆ NOTE: The gear set can be inspected with the gearbox
installed by using an endoscope with flexible shaft. This
must be done in such a way that the condition of the
gear flanks can be precisely evaluated - which re-
quires experience.
■ CAUTION: Inspect all gear tooth contact surface for signs of damage
and pitting.
Gear set pitting can cause high frequency vibration. This vibration may
result in severe problems. As it is transmitted throughout the engine
and its attached components:
– fuel pump damage
– gearbox wear (splines and contact area)
– external alternator wear
– exhaust system wear
– crankcase mating surfaces
◆ NOTE: This vibration can be detected with dynamic propeller
analysis equipment. Normal vibration level for the
engine is approx 0.5 to 1.0 inch per seconds or ask the
aircraft manufacturer for the figures for the particular
installation.
Pitting can take many forms, from tolerable break-in pitting to
spallation. To assist your judgement, please read the following.
General note on pitting:
Pitting is the breaking off of smaller or larger material particles from the
active gear tooth contact surface. Whereas the fracture of a tooth
results in gearbox failure, pitting will not normally influence the running
of the gearbox. There are different degrees of pitting.
◆ NOTE: Fine pitting or areas of pitting hardly influence the
operation of the gear-tooth system.
However, pitting will normally increase with the period of operation.
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page 44
July 01/2008