By: Dave Mowitz
Adjusting a combine is like balancing a tire. True, running a combine is far more complicated than just adding a weight to ensure smooth tire rotation. Keeping a harvester at peak capacity — so it gleans all the grain from residue and produces a clean sample free of broken kernels — requires some fine tuning. Harvest speed must be in sync with the operation of the header or platform, threshing area, separator, and cleaning shoe.
Still, the tire analogy applies, because adjusting a combine is a true balancing act. Making a change in one area of the combine operation can throw another area out of kilter.
For example, a poorly set head can cause an uneven flow of crop into the cylinder or rotors. This, in turn, causes part of the crop to be underthreshed, resulting in cobs with kernels still attached riding out over the separator into the cleaning shoe.
“If you see the cobs and kernels in the cleaning shoe or on the ground, you mistakenly increase threshing speed to remove those kernels,” says combine expert Graeme Quick. “Instead of making the needed adjustment at the head, now you are overthreshing the entire crop. This results in broken cobs with kernels still attached as well as damaged grain coming off the chaffer sieve.”
To make matters more complicated, combine adjustment is challenged by advances in crop breeding, which are turning those tried-and-true homespun adjustments that served you well in the past on their head.
Today’s hybrids feature corn shanks that rarely drop ears in the field. Tenacious shanks can make it harder for a header’s deck plates to strip ears from stalks, resulting in more butt shelling, for example. Green soybean syndrome delivers a mixture of both dry and green pods, which challenges threshing adjustments.
To guide you with the balancing act of combine performance, Successful Farming magazine’s Combine Doctors, Earl Knuth of Barker Equipment (a John Deere dealership based in Indianola, Iowa) and Graeme Quick (a retired Iowa State University engineer and one of the leading authorities on combine operation in the world), present this short course on key adjustments that will keep you speeding across fields this fall.
Finding the sweet spot
While there is no single path to discovering the operating sweet spot in a combine, there are some absolute rules you must follow to fine-tune a harvester for peak performance, advise Quick and Knuth. The first of these binding rules is to live with your operator’s manual. “It should be worn from use,” says Knuth. “The manual reveals the crucial first baseline adjustments and gives a wide variety of tips on fine-tuning settings.”
Besides employing the manual, other key commandments in Quick and Knuth’s harvesting bible include:
- Make only one adjustment at a time.
- Know why you are making an adjustment before making it.
- Double-check the result of the last adjustment before making another change.
- Operate the combine at its full capacity as you adjust speed and operation “to handle a full flow of crop in order to keep the harvester as full as possible,” Quick explains. “The result will be more grain-on-grain threshing, less grain damage, and higher field efficiency.”
- Check operation frequently and especially whenever crop conditions change.
- Perform a kill-stop examination of your combine from time to time. This involves stalling the combine in operation while it is fully loaded. “This freezes the action to reveal what is actually happening in the concaves or cleaning shoe, for example,” Quick explains. “Make doubly sure that a kill-stop is allowed in the operator’s manual. Otherwise, you may harm the combine.”
Following are 7 key areas where you can make adjustments to your combine.
- The crop
Beyond the obvious effects of weather, a key component in establishing a baseline to adjustments is to size up the crop. This can only be done by getting out of the cab and walking fields. “Break cobs in half and check their composition,” says Knuth. “Cobs that have soft, white centers are going to be harder to thresh than those that are firm and pink.”
If the soybean crop is delivering up a high amount of green beans, your only option is to hold off on harvesting. Don’t wait too long, though. Soybeans that reach 13% moisture content should be harvested as soon as possible. Again, the combine’s operating manual will offer initial settings to accommodate particular crop conditions. Set according to that guide and adjust as needed.
For beans, check pod height off the ground to adjust platform height. For corn, look at stalk diameter since that can affect the deck plate setting.
- The cutting platform
Fine-tuning adjustments are crucial for the cutting platform as they account for 80% of total harvest losses in soybeans. Soybeans can be a challenge to cut, due to green stems and low-hanging pods. To cut losses, Knuth gives these adjustment tips.
- Use a reel speed 10% to 25% faster than ground speed (up to 50% faster if crop is lodged).
- Keep the reel axle 6 to 12 inches ahead of the cutter bar and as low as possible.
- Notice if the reel bars leave soybeans just as they are cut. The reel depth should be set low enough to control the beans.
- Check the movement of cutter bar, suspension springs, and support runners on cutting platforms.
- Drop the cutter bar as low as possible if more pods are close to the ground. The front drum of the feeder should be low enough so the chain just clears the floor of the feeder house. If plants are shorter, smaller clearances may be needed between the reel, cutter bar, auger, and the feed conveyor chain, to make sure stalks are feeding through the platform.
- Set reel position and speed (if operating a draper header and these have grown in popularity on wide platforms) so the reel lightly flicks the crop onto the drapers without impeding crop flow across the header. This typically works out to a reel speed about 10% faster than ground speed. Also, draper speed (which is not dependent on ground speed) should be set to provide a consistent windrow formation entering the combine.
- Complete the harvest as quickly as possible after beans reach 13% moisture content.
- The head
Automatically adjusting deck plates have certainly simplified tweaking heads. Adjustable plates are prone to spacing problems, however. “Over time, one or another of the plates across a head can seize and become inoperable,” Quick warns. “You won’t realize this unless you get out and measure the spacing at each row.”
Since deck plates detach ears from stalks, their openings should be narrow enough to keep ears from butt-shelling but not be so wide that small ears can fall through. Too-narrow plate spacings will result in excessive trash coming into the head. Also, plate openings should be tapered from front to back. Generally, the bottom gap would be set 1/8 inch wider than the top opening.
Other key corn head adjustments include:
- Check to see that the gap between snapping rolls is the same as the deck plates.
- Match snapping roll speed to the forward operating speed; this speed ought to snap ears off about one half to two thirds of the way up the deck plates.
- Set trash knives close to the rolls to prevent weeds and stalks from wrapping.
- Match the gathering chains’ movement to the forward speed of the combine. If chain speed is too fast, stalks may be pulled out of the ground and broken, which results in ear losses. If the combine is traveling too fast for the chains, stalks will be pushed forward, and ears will be stripped off and thrown to the ground.
- Set the flighting clearance on the head’s auger from the stripper bar so that crop or stringy material is not carried over and around the auger. For heavy crop-residue conditions, clearance can be brought up and forward for greater capacity and less carryover by the auger. Typical cross auger-to-pan clearance for corn should be 1 inch.
- Inspect the entire header height control system (if your head is so equipped) for sluggish and inconsistent height-control reaction, because that’s what will result if this system is incorrectly adjusted.
- The feeder house
Often overlooked, the feeder house serves a crucial role in presenting the crop to the threshing cylinder rotor. “Whatever comes in and the way that it comes in is also the way that it will go through the entire machine,” Knuth notes. “In other words, if the crop comes in bunches as a result of a faulty feeder house adjustment, then it is going to be threshed in bunches, and it’s going to go out the back of the machine in bunches, resulting in losses.”
Check to see that the feeder house runs smoothly by setting its slats 1 inch above the floor in front of the feeder house.
- The threshing and separation units
Like an 800-pound gorilla walking a tightrope, the threshing mechanism works best when the cylinder or rotor(s) speeds are balanced with concave clearance. “The relationship of speed and clearance is key not only to threshing but also to doing a good job in properly loading the cleaning shoe,” says Knuth.
Begin the process with those settings listed in the operator’s manual, he recommends. After that, adjust to fit field conditions. For example, concave clearance should be changed in steps. Start with the widest setting and narrow the spacing until it is close enough to just thresh out the grain without causing seed damage.
Remember that the primary duty of concave clearance is to regulate the amount of material that flows through the threshing unit. Running a concave too wide will result in grain not being removed from cobs or pods. Running the clearance too tight, however, can crack seeds and break up cobs.
Regarding cobs, a general rule to their condition is if the cobs are split lengthwise, the clearance is too tight. Cobs that are snapped in half mean the clearance is too loose. After clearance is set, the most frequent adjustment needed for the rest of the season will be cylinder or rotor(s) speed. This happens to be the most misadjusted setting on combines, Quick says.
A too-fast speed damages grain, breaks cobs, and results in excessive tailings, he explains. A too-slow speed results in grain not separating from cobs or pods, which, in turn, causes crop to build up in the concave. Also, a too-slow threshing speed can overload the separator and cleaning shoe.
The place to start setting speed is at the top of the rpm recommended in the operating manual, Knuth notes. Next, take a run across the field and check for grain damage. If some exists, back down the speed until damage disappears.
The only exception to this rule is when harvesting hard-to-thresh corn like high-moisture or frost-damaged crops. In this case, Quick recommends trying to reduce the clearance slightly to see if that improves threshing. If that doesn’t do the trick, then you will have no other choice but to turn up speed to get the grain off the crop, even if it damages some kernels in the process.
- The cleaning shoe
As long as grain isn’t blowing out the back of your combine and tank samples are clean, usually you don’t mess with cleaning shoe adjustments. However, Quick warns that only adjusting cleaning shoes once a season per crop can have a huge impact on combine capacity.
A combine set to allow free as well as unthreshed grain to return to the threshing mechanism loads the cylinder or rotor with additional material and impedes efficiency. “Threshing grain more than once is never a good idea, as this increases both breakage and stress cracks in corn,” Quick says.
How do you establish a cleaning shoe’s sweet spot? “There is no ideal setting that works the entire season, so keep on double-checking adjustments by chaffer and sieve openings and fan speed as often as crop conditions (variety, grain moisture, etc.) change,” he adds.
With the owner’s manual in hand, make initial cleaning shoe adjustments after threshing and separation settings have been established.
With the chaffer and sieve openings at their maximum recommended openings, begin to fine-tune adjustments by setting fan speed to its lowest recommended level. Gradually increase fan blast until kernels begin to be blown out of the combine or into the tailings return. Then reduce fan speed a small amount, Knuth says. This process establishes the maximum acceptable fan speed.
Next, close the chaffer and sieve openings slightly until just a small amount of foreign material is being carried back to the tank. “As a rule, grain should fall through the first two thirds of the chaffer,” Knuth notes. “If there is a mat of material on the shoe, grain cannot fall through, and it’s prone to be carried over the ear of the combine.”
Knuth warns that chaffer and sieve opening affect air velocity and direction. They should be adjusted together, he says, adding that “once initial settings are made, it’s a fine-tuning balancing act for the rest of the season.”
- Chopper settings
The residue management system, or the chopper, was once an afterthought. In this era of super-wide heads and platforms and high yields producing greater amounts of material other than grain, that has changed. Now, the chopper’s operation is key in determining how residue will impact next year’s crop. “That chopper consumes a lot of horsepower,” says Knuth. “If it is improperly set, you’ll definitely feel a power drain on the rest of the combine.”
Here are three key tips to chopper adjustment.
- Make sure chopper and chaff spreader speed is set to the crop as recommended by the manufacturer. Making sure that the chopper is operating at the necessary velocity to compensate for residue volume and density not only improves distribution but also minimizes components’ wear and tear.
- Stationary knives should be positioned into the cut for soybeans and out of the cut for corn. Stationary knives influence how well residue is cut, particularly in crops with high volumes of material other than crop. The better the cut, the more efficient tailboard vanes are at distributing residue across the back of the combine.
- Tailboard vanes’ settings (when adjustable) should be dialed in according to residue volume and the velocity needed to inject it uniformly