From the Inside Out

August 27, 2008 12:24 PM
In the limelight at a field day, with competitors' machines running alongside and skeptical farmers watching their every move, how do equipment manufacturers prime their combines for optimum performance in only one or two passes?
They get dirty. They abandon the air conditioning and surround-sound comfort of the combine cab and tempo-rarily ignore the video-game-quality digital displays and screens.
"You can't set a combine from the operator's seat,” says Jeff Gray, senior product specialist, Claas Lexion. "Sure, on the new machines you can make all the adjustments from the seat, but you won't know what adjustments to make if you don't get out of the cab. To really understand what the machine is doing and set it for optimum performance, you've got to get a little dirty.”
The best way to determine exactly what a combine is doing is to stop it dead in its tracks when it's running at full capacity and full of crop. Each manufacturer has a recommendation on how to carry out "kill-stalls” or "power shutdowns,” but Dan Renaud, a Case IH combine specialist, suggests moving the engine speed control to low idle with one hand while using the other hand to push the multifunction handle to the fastest forward position. At the same time, apply full brakes (with the brake pedals locked together) until the combine stalls.
Once all motion is stopped, restart only the engine. Allow it to cool down, and then shut it off. Exit the cab, remove the side shields and open the access doors to see what's going on inside the machine.
"Don't be afraid of using a kill-stall,” Renaud says. "A kill-stall is a controlled condition, not like a plug from overfeeding. A kill-stall is the most effective way to analyze total machine performance and how all of the different systems are performing in relation to each other.”
Maximize machinery muscle. Renaud emphasizes that optimum combine performance comes from smooth crop flow through the machine. He uses an analogy that will make you grin.
"Improper machine adjustments, which slow crop flow—anywhere from the header all the way back to the chopper—constipate the machine,” he says. "If you've got crop hesitating at the front of the feederhouse and it feeds into the rotor in bunches, or if you've got poor material mat traction in the rotor area that allows the crop to go round and round, rather than processing it to the rear, you're constipating the machine. Those bunches are hard to thresh efficiently and can result in crop damage, higher horsepower consumption and possible rotor loss.”
Renaud wants the concave and rotor to do all of the threshing and, for the most part, separate the grain from the residue.
"In our combines we want 100% of the threshing and 90% of the separation to occur in the concave area,” he says. "We strive for 65% plus of that separation to occur in the first pass of the rotor. When I ‘tickle' the belly of the concave with my finger after a kill-stall, I want to see a large amount of threshed grain [fall from the] front of the concave and lesser amounts as I move rearward.
"If the crop isn't threshed by the time it reaches the rear of the concave section, it's probably going out the back of the machine because the rear of the rotor is designed to separate grain from crop residue, not thresh.”
Renaud notes that straw choppers "hide the uglies.”
"Visible grain loss goes down when you run a straw chopper,” he says. "It's hard to see the powdered grain on the ground behind a combine with a straw chopper. That's why you really need to perform a kill-stall to see what's happening inside the machine.”
Richard Bunton, John Deere marketing sales and service represen-tative, diagnoses concave/rotor or concave/cylinder problems by looking at the shoe augers under the concave after a power shutdown (John Deere's term for a kill-stall).
"If [crop material] is overloaded to one side of the shoe auger pan under the concave, it's going to move through the rest of the machine overloaded the same way,” Bunton says. "When that overload hits the sieves, air from the cleaning fan will take the path of least resistance and blow more air through the part of the sieves where the material is thinner and less air where the material is thicker. That causes all sorts of problems with keeping the crop mat floating so grain can separate from the MOG [material other than grain].”
Float on air. Bunton and other manufacturers' representatives emphasize the importance of keeping the crop mat "floating” on air as it passes over the sieves. Inadequate or uneven air from the cleaning fan makes the crop mass move across the sieves as a tangled mat, with grain trapped inside and unable to fall through the sieves.
When they see excess trash in the grain tank or free grain going out the back of the combine, farmers often open the top sieve to save the grain and close the lower sieve to clean it.
"It's very common for operators to use the lower sieve to try and correct problems elsewhere in the machine,” says Case IH's Renaud. "That lower sieve really shouldn't do anything except a final cleaning, putting very little material back into the return elevator. If you do a kill-stall and see a lot of material on the lower sieve or in the return elevator, you need to reset your concave, rotor or fan speeds so the lower sieve isn't doing so much work.”
Another point to consider when using a kill-stall to diagnose combine performance is to pay attention as soon as your feet hit the ground at the bottom of the cab ladder.
 Many losses blamed on the combine's separator actually occur at the header. Adjusting concaves and sieves can't cure problems with grain that's on the ground due to reel shattering in beans or butt shelling in corn. (See sidebars on tips to adjust headers for optimum performance.)
Once a combine operator has spent time after a kill-stall getting dirty and analyzing machine performance, the next step is to optimize those efforts by properly operating the combine.
Factory representatives recommend that operators monitor engine revolutions per minute (rpm) in concert with miles per hour while harvesting.
"If operators push the machine until the rotor or cylinder speed alarms go off, they've really killed combine performance,” says John Deere's Bunton. "The slower separator speeds have probably created a wad that's going to move through the machine with increased losses, all the way out the back, until they get the engine back up to rated engine rpm. Maximum performance comes from keeping the engine at or just above rated full load rpm.”
That's why at field days the ground speeds of the demonstration combines vary across the field. Their operators know that ground speed is a function of feed rate and use ground speed to keep the engine slightly above rated full load speed.
The other factor the company reps know that many of the onlooking farmers are unaware of is that most of the settings were pre-set before the demonstration started.

"All the field men from all the companies spend time getting in and out of the combines before the actual field demonstrations, getting things set,” says Case IH's Renaud. "During the demonstrations, they only have to fine-tune it for the exact conditions on that day. With a man on the ground relaying results, [the operator] can generally [make those final adjustments] from the cab.
"To initially set a combine for a field day—or when a farmer switches fields or varieties in a field—you've got to stop, get out and check what it's doing,” Renaud says. "You can't do a good job adjusting a combine from a sitting position.”


You can e-mail Dan Anderson at

Read more of Dan's work on his "In the Shop" blog.


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