Ryobi RY40800 Operator's Manual page 66

 Replace the chain cover.
 Replace the chain cover lock knob; rotate knob
clockwise to tighten. The bar should still be free
to move for tension adjustment.
 Remove all slack from the chain by turning the
chain tensioning knob clockwise until the chain
seats snugly against the bar with the drive links
in the bar groove.
 Lift the tip of the guide bar up to check for sag.
 Release the tip of the guide bar and turn the
chain tensioning knob 1/2 turn clockwise.
Repeat this process until sag does not exist.
 Hold the tip of the guide bar up and tighten the
chain cover lock knob.
The chain is correctly tensioned when there is no
sag on the underside of the guide bar, the chain is
snug, but it can be turned by hand without binding.
NOTE: If chain is too tight, it will not rotate. Loosen
the chain cover lock knob slightly and turn the
chain tensioning knob 1/4 turn counterclockwise.
Lift the tip of the guide bar up and retighten the
chain cover lock knob. Ensure that the chain will
rotate without binding.
MAINTENANCE
CHAIN
TENSION PIN
HOLE
26 - English
CHAIN DRIVE
LINKS
BAR
GROOVE
BAR STUDS
Fig. 28
CHAIN
COVER
CHAIN
COVER LOCK
KNOB
CHAIN
TENSIONING
PIN Fig. 29