Some method of tensioning the chain is always recommended by the manufacturers
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Page 229
Chain Adjustment
To obtain full chain life, some form of chain adjustment
must be provided, preferably by moving one of the shafts.
If shaft movement is not possible, an adjustable idler
sprocket engaging with the unloaded strand of the chain is
recommended. Generally the idler should have the same
number of teeth as the driver sprocket and care should be
taken to ensure the speed does not exceed the maximum
shown in the Quick Selector Chart (see page 234).
The chain should be adjusted regularly so that, with one
strand tight, the slack strand can be moved a distance
“A” at the midpoint (see diagram below). To cater for any
eccentricities of mounting, the adjustment of the chain
should be tried through a complete revolution of the large
sprocket.
A = Total movement
C = Horizontal center distance
Total movement “A” (in.) = C (in.)
K
Where K = 25 for smooth drives
50 for shock drives