Oregon Harvester Handbook page 16

Operational Recommendations
Automatic Tensioning Systems
An automatic tensioning system is the most effective means
to keep proper saw chain tension, especially if it is designed to
compensate for the saw chain's high speed around a guide bar
(the saw chain will lengthen as its speed increases) .
The system can be optimized to respond to the changing loop
length as your saw chain goes from rest, to full speed, to rest .
As your saw chain speeds up, your guide bar will need to move
forward to maintain proper tension . Otherwise, tension will
decrease as much as 50 percent and can result in a thrown loop
of saw chain . As your saw chain slows to a rest, the chain will
decrease in length, and the guide bar will need to move back .
Otherwise, the excessive tension will potentially damage your
cutting system .
Refer to our Technical Data Tables (page 7) for the
recommended amount of force applied to the guide bar to
properly tension your saw chain .
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Mechanical Timber Harvesting Handbook