Seat-of-the-Pants Diagnostics

 
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After weeks in the seat of a combine, any odd noise or budding vibration grates on a veteran operator like fingernails on a chalkboard. Recognizing there’s a problem is the easy part. The challenge is identifying where the disturbance is coming from and what to do about it.

Use a process of elimination to identify the general location of the problem. Start the machine, engage all systems and go to full throttle until the noise or vibration is evident. To pinpoint which system harbors the vibration or noise, systematically turn off the header/feeder house, then the unloading system, then the separator until nothing is running except the engine.

If vibration is most evident when the separator is engaged but fades the longer the machine runs, be suspicious of imbalance due to dust buildup. Dust inside cylinders, beaters and large sheaves or pulleys can fall to the bottom when the separator is shut off. Centrifugal force pins the dust to one spot in the component when the separator is re-engaged, throwing it off balance.

Over time, the dust load will redistribute itself, or the operator can turn the separator on and off at low rpm to redistribute and rebalance the dust load.

Damaged belts, especially variable-speed drive belts, can cause vibration. If a cylinder, rotor or straw chopper has been plugged and its drive belt slipped and “burned” in one spot, that spot is probably  measurably narrower than the rest of the belt. Every time that burned, narrowed spot passes around a pulley, idler or sheave, it sends a pulse through the system that can magnify into a significant vibration.

Straw choppers spin at high speed and are very sensitive to imbalance. If a chopper knife comes off, the imbalance can create a vibration severe enough to rattle the operator’s dental fillings. Depending on the design of the chopper and amount of wear on the remaining knives, it is usually recommended to replace two or three opposing knives on the rotor, along with the missing knife, to return the chopper rotor to balance.

Meticulous operators can sometimes detect early signs of bearing failure via routine visual inspection or by monitoring bearing operating temperature with an infrared heat-sensing gun. However, the biggest, most expensive bearings found on cylinder drives, rotor drives and other major components often give subtle audible warning before they catastrophically fail.

Low-pitched howling noises or odd growling or moaning sounds can often be traced to large bearings. Their size and location on large shafts or components often amplifies vibrations into audible warnings of their pending demise. The bearings might look good but exhibit excess free play or unusual heat during operation that justifies a closer look and eventual replacement.

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