Honda CRF50F 2007 Owner's Manual page 111

Drive Chain
5. Replace the drive chain if chain slack is
excessive when the rear axle is moved to the
farthest limit of adjustment. Excessive slack
indicates the chain is worn beyond its service
limit.
To check the chain's service limit, remove
the drive chain (page
the distance between a span of
from pin center to pin center. If the distance
exceeds the service limit, the drive chain is
worn out and should be replaced.
102
Servicing Your Honda
105 ). Then measure
77 pins,
Measure a span of 77 pins
New Chain: 38.5 in (978 mm)
Service Limit: 39.3 in (997 mm)