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9 things that cause a combine to break down

Successful Farming magazine’s Combine Doctor, Rodney Edgington, identifies often neglected components in this preseason preparation guide.

1. Feeder house, slats, chains

The feeder house has a big influence on threshing in the way it presents the crop, particularly a wet crop, in an even stream to the rotor or cylinder, Edgington explains. Yet, slats and chains are often passed over in preseason inspections. 

In that regard, check to see that all the slats are operating parallel to each other and are not worn. “A bent slat is an invitation to a breakdown since such a slat can become loose and jam, and possibly damage, the feeder house,” he warns.

While you are rotating the feeder house drive, inspect chains for wear and proper tension. If they have reached the full extension of their tensioning adjustment, then you will need to replace the chains. 

“A lot of operators miss inspecting the keepers on connecting links to make sure they are secure. Also examine the chain guides and replace if worn. While you’re at it, scan the top drive sprockets and the bearings of the front drum for wear.”  

2. Concave elements

Generally, you do a great job inspecting the rotor or cylinder. Where preseason inspections fail is in examining concave elements for rounded or bent bars, missing wires, foreign objects, or residue buildup. Edgington urges you to remove all the concave panels, thoroughly cleaning them before reinstalling. “Make sure the units are level when reinstalled,” he says. Finally, check to see that the seals on covers are intact so they don’t leak crop during threshing. Also, inspect the front beaters plates for wear. 

3. Chaffer, sieve elements

One of the dirtiest jobs in prepping a harvester for the season is removing the chaffer and sieves, so that task is often avoided. With the chaffer and sieves out, look for general wear, particularly in the center of the front half of the chaffer. This is where the highest amount of residue and grain flows in from the separator. Examine frames. Check their sides and corners for stress cracks and breaks. You can weld cracks, if necessary.

Next, check assembly bolts for looseness, then tighten them to the torque specified in the owner’s manual. “Only use the proper grade of bolt specified in the manual when replacing fasteners. Your overall aim is to have solid frames since you don’t want the chaffer or sieve operating loosely,” Edgington says.

During this inspection, look for bent or missing fingers. Notice where the chaffer and sieve rods (wires) operate in the frame and look for elongated holes in the frame. Then examine the deflector flaps and high-crop dividers to see if they are missing or damaged.

4. Cleaning Shoe Fan

The cleaning shoe fan is one of those components that seems indestructible. “Today’s fans turn at a high rate of speed. A piece of residue sucked into the fan can bend a vane, jeopardizing its operating balance, which will eventually destroy a fan,” Edgington warns. His advice is to remove the drive belt and spin the fan, watching for trueness in its operation while listening for any bearing noise. Pay particular attention to the belt on variable-speed fans, as these often become glazed and cracked with use.  

5. Elevators

Take the drive belts off both grain elevators so you can rotate the chain assembly. This allows you to find any worn or missing paddles and sagging chains. Next, check chain tension and adjust as needed. Recheck tension daily during harvest. A sure sign that tension is lacking reveals itself in paddles that sag backward in operation, which causes grain to cascade back down the elevator. 

“When turning the elevators, listen for bearing noise,” Edgington says.

6. Chopper

Worn knives not only do a poor job sizing (chopping) residue but also cause chopper operation to drag, consuming more horsepower. If new knives are needed, you must replace the entire set of knives. Otherwise, the chopper is thrown out of balance, which can cause the entire unit to self-destruct.

Take extra time to examine the entire residue management system assembly. Check tailboard vanes for cracking and wear since they are critical to evenly distributing chopped material.

Finish the inspection by scrutinizing the unit’s mounting hinge points (looking for stress cracks) and the rotor bearings (looking for smooth operation).  

7. Sprockets

Sprockets on combines provide incredibly long service. As such, you probably assume that unless their teeth are broken, sprockets are good to go. But cupped teeth with distinct hooks on their ends can greatly compromise the smooth operation of the drive chains they are powering. Chains tend to crawl on worn sprockets, as their hooked teeth won’t readily release from the sprocket teeth. By the way, hooked sprocket teeth are a good indication that the chain they’re powering is misadjusted.  

8. Belts

Unless belts are obviously frayed or showing signs of separation, they are often only given a cursory inspection. “Considering the job they must perform in transmitting a huge amount of power, the entire length of every belt should be inspected,” Edgington urges.

Examine belt covers for separation, chunks that are missing, burned streaks, and grooves in their sides. Discovering such issues requires the belt to be replaced. Such symptoms can also indicate a problem with misadjustment (of an idler or tensioning pulley) or an impending parts failure (such as a bearing going bad). Unlike typical V-belts, the belts powering the feeder house are of a special design for transferring a lot of power. Much of the work they do requires power to be transferred strictly on the sides of the belts, so closely examine the belts for burned spots and grooves in their sides. 

Finally, after inspecting a belt, adjust its tension according to the owner’s manual.  

9. Yield Monitor

A misadjusted or broken yield monitor won’t stop harvest, but it jeopardizes the collection of yield data you’ve come to depend on when mapping fields. Joe Luck, an Extension precision agriculture engineer with the University of Nebraska, has advice on yield monitors. “A critical element of yield monitor operation is calibration of the mass flow (impact plate) sensor or optical sensor in the clean grain elevator,” he explains.

The calibration procedure for the mass flow sensor is time-consuming but absolutely vital for accurate yield measurements. Since mass flow sensor readings may be affected by crop type, moisture content, and test weight, you should consider performing separate calibrations under these differing circumstances.

The mass flow sensor calibration process usually involves harvesting two to six small loads of grain (around 3,000 to 5,000 pounds depending on manufacturer specifications) and measuring the scale weight of each load. The reason for taking this number of loads is to compensate for varying yields expected across a field during harvest.

You can get more details on this procedure by going to

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