JD 7720nSet the combine

magpiene

Member
Do or have any of you guys set a 7720 for beans. I have set everything to the book. I am having trouble with splits, and complete beans out the back. The beans are dry, but have some weed issues. The concave is at about .75 inch the separator has been from 650 to 900 RPM, the chaffer and sieve are set to the book. WHERE DO I GO NEXT?
 
Whoa Whoa. Slow that cylinder down. Where did you find your specs? In the greenest bneans and even weed areas I never went over 550 rpm. What are your concave settings? My guess you are to wide and trying to overcome with cylinder speed. Are you keeping the cylinder full? Split beans are usually a sign of to much speed. Unthrashed beans is normally to wide of concave. Double check for your concave to be level and condition of cylinder bars
 
Well your WAY too wide on the concave and WAY too fast on the cylinder.

Clean your rock trap out. Then start your combine. Engage the cylinder, leave the combine engine at idle speed. Close the concave all of the way. (it will close easier with the cylinder running) Stop the cylinder. Check the concave wheel to see that it is against the close stop. (Forget what the adjustable indicator is saying) If your closed all of the way open the cylinder 8 to 10 full turns. This is a good place to start out. Now start your combine again and engage the cylinder again. Run the engine up to high idle (operating speed) Slowly turn the cylinder speed down to 400 RPM. This is a good starting point.

Now go cut a strip of beans 50-100 feet long. Shut the combine down. Look on the ground and see if your getting any whole pods. If you are then close the cylinder down. When you getting few whole pod then look at your clean grain sample. If you have many splits than slow the cylinder down. If your having trouble getting all the beans out of the pods then speed the cylinder up some. When adjusting the cylinder speed do it 50 RPM at a time, up or down. Then check your results.

For setting your chaffer and sieve. The front half of the chaffer (top screen) should be at 3/8 and the rear at 1/2 inch. The lower sieve should be a little tighter then 3/8 maybe 5/16.

Start with your fan speed at wide open. If you find beans blow over then slow it down some. Usually in good test weight beans you will blow few over wide open.

PS soybeans are real dry this year so far. I was cutting at 350 cylinder RPM and still splitting some beans.
 
Another thing , the concave has to be straight, and if it is worn in the middle, you are going to have trouble doing a good job. A 100% of the grain touches the concaave and only 60 % touch the rasp bars, If is worn in the middle, you can take it out and have it machined smooth this winter, or a new one.
 
Also jd combines you are going to need to tweak the sieves every time you move to a different field. They will be that sensitive to the bean size. Also are you running full throttle - only throttle position where readouts are accurate. When they went to 9400/9500 there was no throttle lever anymore just a slow and fast switch.
 
JD has given you some good starting points. Your cylinder/concave spacing is way too wide and the cylinder speed is too fast. You want the beans to go through the cylinder and be threshed in one pass. With the concave set like you have it the cylinder bars are "pawing" at the beans and making repeated beatings on them. The fast cylinder speed just exacerbates the problem. When your threshing is right the bean plants on the walkers will be nearly whole unless the bean plants are tremendously dry. Ideally, the rear of the concave should be open about the size of the beans themselves or slightly tighter. The front will automatically be twice that on these combines. As for setting the chaffer and sieve for each field that is rubbish. With plenty of air and the width settings JD gave you you should not have to bother much with the screen settings at all. You will want to run your fan speed no lower than about 850 and more likely in excess of 900 to fully utilize your cleaning system. To confirm if your fan and screens are set right look how the chaff is coming off the chaffer. If it is falling off turn the air UP. If the chaff is floating and the grain is going through the screens the air is right. Use as much air as necessary to clean the grain. If excess grain is going through the return either open up your bottom screen or back off the air somewhat (usually the former). Set the bottom screen so the beans just fall through and then slightly wider. (I usually use my little finger as a gauge.) There should be some material going through the return but not much. With these settings you should be able to save all the grain and sterilize what you get. Mike
 
MANY Thanks to all who replied. With this information I was able to cut beans today. This machine is new to me. I really appreciate the knowledge on this site.
 

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