BRP-Rotax
Maintenance Manual
Effectivity 912/914 Series
Edition 1 / Rev. 0
72-00-00
page 45
May 01/2007
d02622
Pitting is damage caused by material fatigue. The latest insights reveal
that its formation is influenced by exceeding the permissible Hertzian
stress for the material, tangential stress on the surface (friction) and
temperature strain. This means that in addition to the material and heat
treatment of the material, the surface quality and structure, the surface
treatment and the lubricant (viscosity at operating temperature and the
additives used) are also important.
Pitting can be divided into the following categories according to the size
of the pitted area, the type of pitting involved and the number of areas
affected.
– minor pitting (breakin pitting)
– advanced pitting
– spallation (large zones of the tooth surfaces have broken off)
Minor Pitting: See Figs. 72-44, 72-45 and 72-46.
Characteristics:
Isolated small areas of pitting (up to approx. 0.5 % of the flank area)
or porelike zones of pitting, usually only found at the root of the flank.
The formation of this type of pitting may stop once the gearbox wearin
period is over.
Causes:
High local pressure on new gears which have not yet been broken in can
cause isolated pitting. With increased wear, the stress on these areas
is relieved and the pitting may stop. In the same way, changes in the
operating conditions can stop the progress of pitting formation.
Conclusion:
This type of pitting does not prevent safe operation. The gear set can
remain in use.
â—† NOTE: Figs. 72-44 to 72-46 show gear flanks with minor
pitting.
â—† NOTE: Because of the small size of the pitting shown and the
copying process, the pictures may not show the pitting
clearly enough. If you are in any doubt, seek assistance
by studying technical publications or consult your au-
thorized ROTAX distributor or Service Center.
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