Chain Tension; Worn Chain Sprocket - Stihl 9 Instruction Manual

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Apart from chain lubrication, chain tension is the factor that
has the greatest influence of the cutting attachment's useful
life. It is therefore necessary to check chain tension before
starting work and at regular short intervals during cutting
work. Chain tension is correct in the cold condition when the
chain fits snugly against the underside of the bar and can
still be pulled along the bar by hand (wear gloves!).
As it warms up to normal operating temperature the chain
expands and sags noticeably. The saw chain must be
retensioned when the drive links begin to come out of the
groove on the underside of the bar. If this is not done, there
is a risk of the chain jumping off the bar.
If the chain is retensioned during cutting work it must always
be slackened off again after finishing work. This is neces-
sary because high contraction stresses would otherwise
occur as the chain cools down to ambient temperature,
especially at extremely low outside temperatures, and
cause damage to the crankshaft and bearings.
A new chain must be retensioned more frequently than a
used one because it stretches during the initial break-in
period.


Worn chain sprocket

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The stress and strain on the chain sprocket are particularly
high. If the wear marks on the teeth are very pronounced
(about 0.5 mm/0.02 in deep), the sprocket should be
replaced. A worn sprocket reduces the service life of the
saw chain. The chain sprocket should be replaced as a
matter of routine with every second Oilomatic chain. It is
best to use saw chains alternately with one sprocket.