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Self-propelled forage harvester adjustment for better quality

Josh Harkenrider for Progressive Dairyman Published on 05 August 2016
Self-=propelled forage harvester

Nowadays, everyone wants to know what to adjust on a self-propelled forage harvester to maximize forage quality and minimize fuel consumption.

A lot of manufacturers have been able to design machines to make it simpler for the owner to get these results. Most manufacturers have designed their machines so that some adjustments can be made from the cab of the machine, but there are still some important parts of the machine that need to be checked or adjusted.



Among the parts that need checked and adjusted, probably the most important ones are the knives and shearbar. They are the “scissors” of the machine. They take the incoming crop and cut it to the desired theoretical length of cut (TLOC).

Remember, there is a difference between the length of cut setting (or TLOC) and the actual size of the particles of chopped material. The settings are called “theoretical” because what is displayed on the machine’s monitor or display might not actually be precisely the size of what is being cut.

When chopping whole-plant corn silage, the TLOC is usually quite close to the actual particle size. That’s because the crop is being fed uniformly into the cutterhead. But when chopping haylage, the average size of the particles is often longer than the TLOC because of the way the crop enters the cutterhead. That’s because haylage tends to enter the cutterhead in a more random manner.

Just like scissors, if the knives or the shearbar are dull, or if there’s improper alignment of the knives and the shearbar, you’ll need more power to do the job, and the cut will become ragged and uneven. The knives need to be sharp so that when they come down to the shearbar, they take as little power as possible to cut the crop.

Sharp knives also reduce shearbar wear. The shearbar plays a part in this, too. If it has a nice, square edge on it, then the knives will be able to cut through the crop more easily.


Knives and shearbars can come in different designs and be made of different materials, so it’s important to make sure you have the correct combination in your machine to do the job. To fine-tune chopping performance, you can equip your cutterhead with grass or corn knives and matching shearbar to customize it to the crop and field conditions.

Grass (universal) components are great for use in a wide variety of crops. They offer high-abrasion resistance and won’t easily chip if a small stone is mixed with the crop. Corn knives have a different, thinner profile, with a steeper chopping angle to cut more efficiently.

Like the corn shearbar, they are made of a harder material that will take a sharper edge and stay that way longer with high crop volumes going through the chopper.

The next important part to adjust is the plate on the bottom of the cutter drum. Most manufacturers provide you with a measurement of how close the knives need to be to this plate. The adjustment can be different for each type of crop you are chopping.

When chopping grass or hay, the plate tends to do a better job when adjusted closer to the knives to help move material through when the crop gets sticky or gummy. On the other hand, when chopping corn, the plate doesn’t need to be as close to the knives, which could give you a little more power to do the work.

The recommendations for each manufacturer are different, so be sure to refer to the operator’s manual of your machine for this adjustment specification.


The third thing to check and adjust is the crop processor, which is usually only used when you are harvesting corn. The processor consists of a set of two rolls with saw teeth. Wider rolls allow more crop to fit through the small gap for maximum capacity.

Most farmers would like their corn crop processed so that their animals can get every last bit of nutritional value out of the end product. Of course, a lot of this depends on what you want or what your nutritionist recommends. Having the proper roll gap stops set in such a way that you can close down the gap if needed is essential in today’s market.

When the roll gap is set properly for corn silage, the cobs and stems are sheared, and the kernels of corn are cracked and crushed. The result is better fermentation and more effective fiber, which increase the energy potential of the feed. The kernel processor cracks the corn kernels by passing the chopped crop through a pair of rolls.

If the roll gap is set too wide, kernels will pass through without being cracked. If you set the rolls too tight, you’ll reduce the capacity of your forage harvester.

Some self-propelled forage harvesters have a heavy-duty processor as an option. With the heavy-duty processors, the roll gap can be larger for higher throughput and still provide complete kernel processing for maximum feed efficiency.

Forage harvesting is a time-sensitive task. Good crop flow through the machine is important to keep the chopper and support vehicles moving and the harvest coming in. The last adjustment that is important on a self-propelled forage harvester is the rear door of the accelerator/blower.

This is the part that the chopped material rides against when it gets its kick from the accelerator/blower. Proper adjustments here will help ensure efficient crop transfer from processor to trailer.

The ideal clearance between the accelerator/blower paddle and the rear door is dependent on the crop you are chopping. For the most part, when you’re chopping hay, you usually want it closer because of the way that material “rides,” but when chopping corn, it really doesn’t need to be as close.

One thing to keep in mind is that having the rear door adjusted too close to the accelerator/blower can cause damage to the machine. So again, be sure to refer to the manufacturer for their suggested clearance.

Although adjustments will be different for different crops, it’s very important to remember that not every adjustment will be the same for every owner. Contact your dealer if you have specific questions about certain conditions that apply in your situation.

Maintaining a self-propelled forage harvester adjusted for maximum performance in every crop is not only essential for producing a top-quality forage product, but will make a measurable difference in fuel consumption during chopping. That’s a win-win situation – a higher-quality end product at a lower production cost.  PD

PHOTO: Knives, shearbars, kernel processors and even blower adjustments make a difference during harvest to run efficiently and lower fuel consumption. Photo courtesy of Josh Harkenrider.

Josh Harkenrider is a self-propelled forage harvester sales specialist with New Holland