3. Roller Link Care should be taken to avoid repeated impact loads over the allowable load as fatigue breaks may occur. The roller should be checked in the same way as the link plate. If foreign objects interfere with the engagement of the roller and sprocket, the roller may be damaged and a crack may develop. Chains damaged by fatigue breaks must be replaced.
Figure 9-3: Crack Produced on the Roller
4. Sprocket Chain and sprocket engagement can be checked by observing the roller and sprocket tooth surfaces. A proper margin (A) and improper margin (B) are shown in Figure 9-4. Installation should also be checked. Normal margin position is slightly above the tooth bottom. If tension remains on the slack side, the roller will touch the tooth bottom slightly. If an idler or tightener is used, the margin will be at the center of the tooth bottom. 5. Chain Elongation
Figure 9-4: Areas to Check for Sprocket Wear
Chain stretch is calculated as the total amount of elongation caused by wear on the pin and bushing, not including deformation of the link plate. Measuring chain elongation can help estimate the remaining life of the chain.
Measuring Chain Elongation 1. Stretch the chain slightly. 2. To get distance (L), use a vernier to
measure the distance of the inside (L 1 ) and outside (L 2 ) of the rollers at both ends of the measured links. L = (L 1 + L 2 ) 2 3. Use the following equation to calculate chain elongation: Roller
Figure 9-5: Measuring Chain Elongation
Chain Elongation (L) = (Measured Length – Standard Length)
X 100(%)
Standard Length
Where: Standard Length = Chain Pitch X Number of Links
Note: Measure at least six to ten links to minimize errors. A tape measure can be used if a vernier is not available. Because tape measures are less accurate, the measured length should be as long as possible.
RS R OLLER C HAIN C HECKPOINTS 17
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