Field Work: Adjusting and Operating a Combine

Reel. The best height for the reel varies with the kind of crop and the condition of the crop. Usually you will get good results by setting it so that the reel bats strike the grain well above the center of the stalk. If you do not want to save the straw, set the reel as high as possible without missing any heads. Under most conditions adjust it so that the reel bats do not leave the standing grain until after it is cut. Set the reel low to pick up tangled and fallen grain.

Keep the reel speed in proper relation to the forward speed of the combine. If the reel revolves too fast, grain may be shatteredfrom the heads; if it revolves too slowly, grain may fall on the cutter bar and be chopped, or it may fall ahead of the cutter bar and be lost. But with short grain, or tangled down grain, you may have to increase the reel speed to get the cut grain delivered to the feeding unit.

Changing the speed of power-driven reels is accomplished by changing the reel-driving sprockets; two or more sprockets are furnished for this purpose. Ground-driven reels usually maintain proper relation to the forward speed.

Height of Cut. Unless you want to save the straw, set the cutter bar (header) just low enough to get all the heads. Cutting too low may overload the combine, slow up your rate of work, and make separation difficult.

Feeding. Keep the tension of the upper and lower feeder canvases (Fig. 7) just tight enough to prevent slippage; if they are too tight, you will waste power and cause excessive wear. Be sure these canvases run squarely in their frames.

The platform auger used in some models is adjustable vertically; raise it for heavy crops and lower it for light crops. Prevent wrapping of viny crops – peas or beans – on the auger by moving forward the adjustable stripper plate provided at the rear of the auger. In some models the speed of the auger can be changed to suit varying crop conditions and thus insure even and uniform feeding.

Threshing. Correct cylinder speed and correct clearance between cylinder and concaves are probably your most important adjustments. You will not get good threshing unless these parts are accurately adjusted because all the threshing occurs here.

Different crops and conditions require a wide range of cylinder speed – from 350 to 1600 revolutions per minute. Your operator's manual recommends speeds for many crops. If you check your work carefully you can soon tell whether the cylinder speed and clearance are correct.

If the speed is too fast and the clearance too close, you will be "overthreshing"; kernels of grain will be cracked and the straw broken and chopped up. This overloads the straw rack and sieves, and grain may be blown out with the straw. If the cylinder speed is too slow, or the clearance too great, the grain may not be threshed well.

You may have to change the cylinder speed frequently. At noon the straw may be dry and brittle, and then you can use a fairly slow speed; but in early morning, or late in the day, the straw may be damp and tough. Then you need a higher cylinder speed for good threshing.

Regulate the cylinder speed accurately. A V-belt drive and a variable V-belt pulley (sheave) may be used. Always use a speed indicator to check your adjustment.

Adjust the clearance between the cylinder and concaves. In several designs a single lever enables you to make this adjustment. The controls for making this adjustment are usually located near the driver's seat. In some designs you can make this adjustment "on the go."

Separating. Most of the grain is separated at the concaves and by the action of the cylinder beater (Fig. 7, G) with the finger grate beneath it. The straw rack should save the grain that is mixed with straw.

Be sure the rack runs at the proper speed. Check the adjustment of the belt driving it. In some models, the speed of the rack vibration is adjustable.

Set the deflectors (retarders) as low as you can without clogging the straw rack; raise them if heavy straw must be passed through.

To prevent overthreshing at the cylinder, do not cut too wide a swath.

Cleaning. Set the openings in the chaffer wide enough so that threshed grain falls through to the shoe sieve beneath it. But unthreshed heads should not fall through the chaffer openings: they should be carried back to the chaffer extension together with weeds and chaff.

Set the chaffer extension openings large enough to permit unthreshed heads to fall through into the tailings auger but small enough to float off straw joints, weed stems, and coarse material.

Raise the tailboard at the end of the chaffer extension if necessary to prevent threshed grain from being blown out.

To tell whether you are losing grain, catch a sample of the discharge from the straw rack with a sack or blanket.

Adjust the angle and the size of the openings in the shoe sieve. A sieve lets the grain grass pass through it but chaff or straw passes over it; a screen lets refuse, such as small weed seeds pass through it but the grain passes over it. Openings should be large enough to let all the grain through readily.

The sieve is usually placed in the shoe with a slight angle downward, toward the grain auger. But under favorable conditions you can have it nearly level; if it is nearly level, less chaff will fall through the sieve. But when cleaning dirty grain you may want to lower the front, or raise the rear, of the shoe sieve and use a heavy blast of air.

Regulate the air blast as directed in your owner's manual. Keep the fan rightly secured to its shaft and make sure the fan belt does not slip.

The air blast should be strong enough to carry off the chaff but should not blow out kernels of grain. It should be equal on all parts of the shoe sieve. To get even air distribution, make the air openings on each side of the fan housing equal.

Speed of Each Unit. To become a skilled operator, you must know how to get and maintain the correct speed of each unit of your combine.

Most operator's manuals give the correct engine or PTO speed and also recommend the best cylinder speeds for various crops. Some manuals give the factory setting of the speed of other units of the combine. But you may have to vary these speeds for your different crops and crop conditions.

A definite order must be followed in making (speed) adjustments if losses are to be reduced to a minimum. Assuming that the machine is in good mechanical condition, the first thing to check is:

Machine speed (proper r.p.m.)

Refer to the combine instruction manual to find the recommended r.p.m. of the power take-off or the engine on engine-mounted (or self-propelled) combines. A wide open throttle setting on the engine or tractor usually does not give correct power take-off speed. Adjust the engine throttle so that the power take-off is 15 to 20 r.p.m. above the correct speed when the combine is running empty.

After the power take-off or engine speed is set correctly, take the speed (r.p.m.) of the straw rack, cylinder, fan and beaters and adjust them to speeds given in the instruction manual. Use a speed counter to measure all power take-off and rack speeds. Most tachometers are not accurate enough for low speeds.

Grain losses may be excessive if the correct r.p.m. of the various machine parts is not obtained. Most straw racks are quite sensitive to correct speeds.