In The Shop: The Sounds of "Worn Out"

June 23, 2016 02:45 PM
 
In The Shop: The Sounds of "Worn Out"

Bearings, chains and belts rarely fail without warning. Their final gasp might come with a bang or a cloud of smoke, but they usually offer warning signs attentive operators can look for during the off-season to prevent catastrophic breakdowns in the field. For example:

  • Remove belt or chain tension, then spin shafts by hand. A healthy bearing should spin silently. Any “rumble” suggests rough spots in the bearing’s races that will eventually lead to problems. A “click” or “clunk”—even a faint one—that occurs once per revolution hints the bearing’s lock collar is loose or cracked, allowing the bearing to shift or spin on the shaft. Disassembly often reveals a groove worn in the shaft by the bearing. 

If turning a shaft creates screeching sounds, small puffs of reddish dust or ball bearings dropping onto the ground—well, if you can’t read the message that bearing is sending, you shouldn’t be operating heavy equipment.

  • It’s OK for roller chains to “sizzle” a little as they run, but a harsh “zzzz-ing” sound suggests a chain that’s dry from lack of lubrication. It can also be due to worn, hooked teeth on sprockets snagging chain links rather than cleanly releasing them. 

Disassemble master links on suspect chains. If a master link is dry, rusty and hard to take apart, then all the links are worthy of replacement. 

If a chain passes the master link disassembly test, visually inspect the rollers. The seams on rollers should be tight. The rollers themselves should not taper from side to side, and there should not be excessive gaps between the rollers and the side plates. 

Finally, lay the chain on a flat surface and measure the difference between fully stretched length and fully compressed length. Chain manufacturers say chains should be replaced when they “stretch” 2% of their length. That means a 120"-long (10') chain should be replaced when it has 2.4" of stretch. 

  • Worn belts generally show their age long before they fail. Any single crack that extends more than halfway through a belt signals it’s time for a new belt. Cracks that extend more than one-quarter of the way from the back toward the surface hint replacement might be necessary within 50 to 100 hours of running time. Belts with polished, shiny sides that won’t mark with a fingernail have been overheated and have a questionable future. 

Be sure to rotate and inspect the entire length of a belt and check for “time bombs.” During storage, belts often crack where they’re bent backward or stressed around idlers. Those cracks close when that segment of belt is positioned between pulleys and idlers, making them difficult to spot. 

Belts that “flop” excessively while the machine is running are often the result of a pulley that spun inside a stopped belt. (Remember the slug of crop that plugged the combine at midnight during harvest?) The spinning pulley burned into the sides of the belt, creating a 4" to 10" segment that’s a fraction of an inch narrower than the rest of the belt. The narrow segment drops deeper into the groove when it goes around pulleys. That makes the belt “flop,” sometimes in dramatic ways that shock-load the system and the belt drives, and can create an annoying, mysterious vibration that shakes an entire machine. Simply run your fingers down both sides of belts, and it’s usually easy to feel segments as little as 1⁄8" narrower than the rest of the belt.

Finally, extend all hydraulic cylinders, shut off the machine and listen for several minutes. Occasional “pops” or “clunks”  suggest a leaky hydraulic cylinder is allowing components to settle. Dripping oil identifies culprits, but never ignore the possibility of invisible internal leaks. 

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