12) Examination Of The Drive Gear Set - Rotax 914 F Maintenance Manual

12.3.12) Examination of the drive gear set

The inspection of the gear set helps to detect possible damage on the
gearing.
Remove propeller in accordance with installation instructions of the prop
manufacturer.
Remove prop gear box. Refer to chapter 14.4.
Clean drive gear and dog gear for inspection.
At formation of pitting distinguish between tolerated seasoning pitting and
spallation. To assist your judgement please read the following.
General note on pitting:
The term pitting can be interpreted as spalling of more or less material
particles from the active tooth flank. Whereas fracture of a tooth results in the
complete gearbox failure, formation of pitting normally will not stop operation
of gearbox.
Distinguish between various grades of damage.
But normally pitting will increase with period of operation. The pitting progress
depends on lubricant and load. The zone of pitting might increase to such an
extend, that the remaining unharmed tooth flank can not transmit the load any
more. Further operation will result in the complete ruin of the gearing.
Pitting is damage caused by fatigue of the material. According to the present
knowledge, decisive for formation of pitting is the exceeding of pressure,
tangential stress on the surface and temperature strain. Besides material
properties and heat treatment, surface texture and finish and of course
viscosity of the lubricant at temperature of operation are of importance.
Depending on size, grade and number of pitting distinguish between the
following:
Modification no.
- 0 -
ATTENTION: It is also feasible to scrutinise the gear set by Endoscope but
ensure the exact inspection of all tooth flanks.
ATTENTION: Inspect all tooth flanks for damage and pitting.
NOTE: Tiny pitting or zones of pitting will hardly influence opera-
tional behaviour of the gearing.
NOTE: The preferred zone of pitting formation is the root flank of the
driving gear. Therefore check first the driving gear.
tiny pitting (seasoning pitting)
progressing pitting
spallation over a wide zone
Reference Main Date
914 F 1997 02 01
Page
97