During normal operation of a chain, pins and bushings contact and slide against each other as it engages and disengages from the sprockets. This causes some metal to metal contact even when properly lubricated and under ideal conditions. This wear, along with any overloading and metal fatigue will eventually cause pitch elongation. Pitch elongation limits the life of the chain, leading to chain replacement.
The number of teeth in the large sprocket determines the amount of wear that can be tolerated before irregular chain and sprocket contact occurs, making chain replacement necessary. Pitch elongation should be measured periodically to avoid damage to the drive or any of its components.
Pitch elongation is measured by placing a certain number of pitches under tension. The chain length must be measured with a load applied (Table VII). This can be done by removing the chain from the sprockets and hanging in a vertical position or placing on a flat horizontal surface and applying the weight needed for each individual size chain. If the chain is measured on the sprockets, apply sufficient tension to keep chain taut.
When chain is properly tensioned consult Table VI for the number of pitches that should be measured. This number is determined by chain size and number of teeth in the large sprocket. Measurement should be taken from pin center to pin center. Do not include offset links in the segment to be measured. Count the number of teeth in the large sprocket and find the appropriate column in Table VI. If measurement taken is equal to or exceeds the figure in Table VI, the chain should be replaced.
Please note if the chain breaks or fails due to broken parts, the complete chain should be replaced. Used chain and new chain should never be connected and used in the same strand. Sprockets should always be inspected before a new chain is installed. If the sprocket's teeth are worn or hook shaped, the sprocket should be replaced. Always check that sprocket alignment is correct after replacing chain and or sprockets.