Where is your lack of capacity? Are you throwing over on the rotor or shoe? Is it in all cereals or just wheat? I'm guessing it's not a lack of power, being it's a 9870. If your shoe is being overloaded with chaff, you might be beating it up too much in the rotor. What concaves are you running?
An adjustable precleaner will help but I don't think thats your major problem.
A adjustable precleaner WON'T be of any use to you because they changed the design of the cleaning shoe. All of the grain that does go through the precleaner will have to go through the chaffer before it can get to the sieves. On the 60 series, the grain that made it through the precleaner went directly to the sieves, this is why the adjustable precleaner was an improvement in the 60 series. There is an extra plate that Deere put in that redirects the grain in the 70's in which also makes the first 12 inches of the sieves useless because no grain can get to it but it keeps grain from getting into the cleaning fan, but that's another topic altogether!
Garry I believe that an ajustable precleaner will help . The fixed precleaner opening is just to wide for some small grains. I had trouble last fall with short pieces of canola stocks plugging the precleaner and also when I went into Flax there was to much of a mat of chaff dropping through the precleaner overloading the front of the chaffer. The Brains in our industry always have the same answer (Crank The Wind ). Everyone alway forgets that you have to create the proper air blast through the sieves not only across the top .I have been looking into different precleaners all winter and I was told Friday Jan.30/09 ( Lowen Manufacturing or A&I )is working on one .
We have been running a helicial concave in the front & two narrow wire jds in the middle& rear. Concave set at 8-12 rotor at about 950 chaffer13 seive7 fan 750-800. Problem is i think is that the helical concave is letting to much through on the left hand side thus overloading the seives and repeat.9870s seam to run alot of repeat.Going to try making a strap to go on the left hand side to even up the load.Also thought an adjustable precleaner may get more chaff aloft before it hits the seives instead of going through. This year was a difficult year down our way small droughted grain which was hard to keep in the machine. Any thoughts greatly appreciated.
i have never seen a helical concave, but if the framework of the concave is the same as the deere's, deere has a new filler plate where you can remove sections from the band, thus opening up the left or right side