It is no exaggeration to say that roller chains and associated drive sprockets can perform their jobs long, long after they are worn out. I’ve seen roller chains with rollers missing from the chain links and the sprockets worn to nubs that were still merrily--though very noisily--driving their machinery. So I can’t say that every chain or sprocket showing wear has to be replaced at the first signs of wear.
And “wear” is the operative word. Despite what everybody says, chains don’t “stretch.” Any slop or “stretch” in a chain is simply minor wear on each pin, roller and side plate, multiplied by the number of pins, rollers and side plates.
An engineer at a chain manufacturer once told me chains should be replaced when “stretch” reaches 2 percent of length. That means a chain that was 10-feet long (120 inches) when new is technically “worn out” when it has 2.4 inches of “stretch.”
In the real world, I usually see other reasons to replace chains long before they wear enough to meet those manufacturer’s replacement guidelines. I may recommend replacing a chain if I disassemble its master link and its pins are dry and rusty because that warns me that all the pins are dry and rusty. And I usually recommend replacing chains that have rollers that are tapered from side to side, or with rollers that are “spread” and exceptionally loose on their pins.
Yes, it’s possible to soak rusty, worn chains with lubricant and get them to keep running. But it’s not my job to squeeze every last second of life out of a machine’s components, until one of the aged components finally disintegrates in a cloud of rust and metal shrapnel. I can do that if the machine’s owner insists, but my preference is do maintenance and repairs to avoid unexpected, inopportune breakdowns that occur in a cloud of rust and metal shrapnel.
