When is a roller chain worn out? According to manufacturers, a chain should be replaced when it measures 2% longer than its original length.
To check a chain, lay it on a flat surface and push the links together to shorten it as much as possible. Note the length, then pull the chain to full length. Using the 2% guideline, a 60" roller chain justifies replacement when it has "gained" 1.2" in length and measures 61.2".
Chain wear is unavoidable, but it can be significantly reduced with lubrication. In the old days, it was common for our grandfathers to remove chains from corn pickers, planters and other equipment and soak them during the winter in a bucket of used engine oil.
That strategy is actually a good way to extend the life of roller chains. Tests show that plain ol’ 30W engine oil is an effective lubricant for chains if allowed to fully seep between rollers and side plates. But it takes time to soak chains and it creates a mess when they sling oil after re-installation, so many farmers now use spray-type chain lubricants.
The right way to extend chain life. Spray lubricants work well if applied correctly. Run the machine to warm the chain, then apply lube while the chain is running at a low number of revolutions per minute. Aim the stream of lubricant between the ends of the rollers and side plates and at the edges of the side plates, on the inside of the chain’s "run."
The goal is for the centrifugal force of the chain moving around the sprockets to force the lubricant outward, between the pins, rollers and side plates.
Spraying lube on a non-running, cold roller chain is better than nothing, but it minimizes the opportunity to get lubrication and rust protection deep between pins, rollers and side plates.
How do you know if a chain is well lubed? Disassemble its master link. If the link’s pins slide easily, the chain is in good shape. If the pins are dry, rusty or galled, the chain needs lubrication—and might have suffered enough damage to justify replacement.
Replacement considerations. When replacing roller chains, take care to correctly install half-links and master links. Install half-links with the narrow end toward the direction of rotation. Install master links with the open end of the clip facing away from the direction of travel.
Worn, "hooked" sprockets can dramatically shorten the life of a chain. If the sprockets aren’t visibly hooked and if the chain’s rollers fit snugly between the teeth of the sprockets, it’s a farmer’s judgment call whether to replace the chain.
There are always exceptions to any rule, and planter drive-wheel sprockets are an exception to the "snug fit" rule. Those sprockets, mounted on the sides of planter frame wheels, often run in dirt, trash or mud and are designed with tapered teeth that fit loosely against the chain’s rollers.
In a perfect world, chains would be lubricated daily. In the real world, operating conditions often determine the frequency of lubrication.
- January 2013