Stihl 009 Instruction Manual - Page 38
As it warms up to normal operating temperature the chain
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Worn chain sprocket 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 necessary 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. 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. 125BA023 LA