32
1
2
4/5
Chain type
492 (91PX), 290 (90SG),
291 (90PX)
Files and how to work with them
Use a special saw chain round file for sharpening. Standard
round files are unsuitable.
Type 492 (91PX):
Saw chain round file, dia. 5/32” (4.0 mm).
Type 290 (90SG), 291 (90PX):
Saw chain round file,
dia. 11/64” (4.5 mm).
The file should cut only when pushed forwards (arrow). Lift
the file when leading it backwards.
First sharpen the shortest cutter. The length of this cutter is
then the standard for all other cutters of the chain.
New saw teeth must be filed to the exact same shape as the
used teeth, including on their running surfaces.
File depending on chain type (90° to the guide bar).
A file holder makes file guidance easier. It is marked for the
correct sharpening angle of:
α = 30°
(keep the marks parallel with the chain when filing, see
illustration) and limits the cut depth to the correct 4/5 of the
file diameter.
After having sharpened the chain, the height of the depth
limiter must be checked by means of a chain gauge.
Correct even the smallest excess height with a special flat
file (
1
).
Round off the front of the depth limiter (
2
).
α
