Combine Adjustments

Originally written February 1, 2006 | Last updated October 18, 2018

Combine settings and operation are critical to minimize harvesting losses. The combine is a complex machine that gathers, threshes, and cleans the grain. Poor combine adjustment can result in not only lost yield, but reduced grain quality as well. When set properly, most combines, both cylinder and rotor types, can do a good job of preserving yield while separating kernels from the non-grain portion of the crop.

  1. Be sure the crop is ready to harvest. Test for grain moisture percentage

  2. Growers are advised to set the combine to manufacturer-recommended settings as a starting point, and then adjust to the condition of the crop. The combine must be correctly adjusted and equipped for the crop to be harvested. Inspect rasp bars for chips, bends, or cracks. Replace as necessary. Start with initial settings for the crop from the operator's manual.ecessary. Start with initial settings for the crop from the operator's manual. Frequent checking and readjusting can then keep the combine set appropriately to reduce both harvest losses and kernel damage. When crop conditions change during the day, small adjustments may be necessary.

  3. The goal of proper combine settings is to achieve a smooth, even flow of crop material moving through the machine. The combine should run nearly full to minimize impact on the grain. A near-empty machine, on the other hand, leads to multiple contacts of the machine and the grain, which increases breakage.

  4. To get the maximum efficiency without grain loss, the header must be operated efficiently. Use the proper size header for the machine and know the adjustments needed to achieve best results. Read the header operator's manual for specific adjustments.

  5. Operate at full throttle. All drives of the combine are based at governed engine speed.

  6. Gathering snouts: Adjust snouts so that they just touch the ground under normal conditions. If plants are lodged, let snouts float on the ground and reduce ground speed a needed.

  7. Snapping roll and stripper plate spacing: Set snapping roll spacing according to stalk thickness. Set the stripper plates (aka, desk plates or snapping bars) as wide as possible without losing ears or shelling corn off the ear (this reduces amount stover taken into the machine). Plates should be set slightly narrower (1/8 to 3/16 inches) in front than in back to prevent wedging. If ears are small in diameter due to drought, narrow the stripper plates accordingly so ears are not pulled through and lost.

  8. Ground and snapping roll speed: The ground speed depends on the condition of the crop, but should generally be as fast as possible without plugging the head of threshing mechanism. Snapping rolls should be set relative to ground speed. When set too fast, snapping rolls increase the impact of the ear on stripper plates. This causes kernels to be shelled ad lost, increase breakage of ear butt kernels and results in ear bounce. Keep an even, uniform flow of material moving through the combine. When the combine is running near empty or taking in bunches of crop material, increased grain losses and grain damage are likely. Select a ground speed that will not overload the combine or overrun the header's ability to do its job. Observe the engine overload monitor. When engine speed is reduced, cleaning system speed is reduced also.

  9. Cylinder/rotor and concave: The cylinder or rotor is designed to thresh corn from the cob. It is no surprise then, that cylinder/rotor speed is the leading cause of grain damage by the combine. In one study, increasing the cylinder speed from 300 to 600 rpm increased kernel damage from below 5% to over 30%. However, if threshing is too gentle, unshelled kernels can be lost with the cobs. Growers should use the lowest possible cylinder/rotor speed that will shell the grain within acceptable loss levels (less than 1% in good-standing fields). Excessive cylinder speed is the leading cause of grain damage - always use the lowest possible setting to achieve the best total threshing. To reduce unthreshed losses without increasing grain damage, try decreasing the concave clearance before increasing cylinder/rotor speed. If this does not achieve satisfactory threshing, then begin to increase cylinder/rotor speed as required. Always try to eliminate unthreshed losses by adjusting concave clearance first rather than cylinder speed.

  10. Concave clearance should be set so as to avoid breaking the cobs excessively, which can lead to kernels left on cob fragments. Cobs should only be broken into 3 or 4 pieces for best threshing results and minimal threshing losses.

  11. Separation and cleaning: After threshing, the grain is separated from non-grain crop material by the chaffer and shoe sieves and the cleaning fan. Lighter chaff is blown out the combine, while heavier unthreshed cob segments are returned to the thresher by the tailings system. Screens allow fine grain particle and foreign mater to be removed in the cleaning process. The sieves must be open far enough to let all grain through. The chaffer sieve should allow all grain and unthreshed cobs/pods/heads through. The shoe sieve below should let only threshed grain through, so that the unthreshed portion goes to tailings and is returned to the rotor cage to be re-threshed. If the chaffer setting is too open, it overloads the shoe. If the shoe sieve is too tight, tailings will increase; if it is too open, the grain in the tank will be dirty. Set sieve to widest recommended setting and work back if required.  Wind blast through the sieves should be strong enough to remove all particles lighter than grain. Too little air from the fan causes shoe overload, high tailings and sloughing of the crop. Set fan to highest speed recommended and work down if required.

  12. Check all augers for wear because grain handling can increase seed damage also check grain cart). Proper rotor speed , concave clearance, fan setting and sieve adjustment will reduce the amount of tailings. Tailings should include only unthreshed particles. Above all else, perform only one adjustment at a time to minimize your time spent adjusting to optimum performance.

The goal of separation and cleaning is to achieve a clean, high-quality end product while minimizing grain losses. To accomplish this, sieve and fan settings are critical. If the fan speed is too high, kernels will be lost. If too low, excess foreign material is retained in the grain. Begin with manufacturer suggested settings and check and adjust frequently. Crop conditions, including non-grain crop moisture, can change rapidly during autumn days. Monitor losses behind the combine and grain quality in the grain tank throughout the day.  

Read you operators manual thoroughly for detailed settings for you specific combine model. Attend combine clinics to learn fine-tuning methods from other combine operators. With proper adjustment, a quality crop can be harvested.

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