How about Marvin's helical concavesIJ They are on my list for 05 improvements for my 1688 matching the circular pattern of the rotor bars, it seems like they would be the ideal answer to hard to thresh damp conditions
We had a set of St John concaves in a 1460 a few years ago...Terry gives good service and takes time to answer your questions on the phone...The bar is higher than the wires than original concaves if I remember right...They would thresh with much more clearance but I ran them closer to keep green stems from clogging the concaves...I just needed to be told how to run them. I am thinking about Marvin's helical concaves for my 1688 at next replacement time, probably 2005...The curvature matches the rotor bars and should help in green stem and damp conditions...A lot of small improvements seem to add up to a much better machine to harvest n1 grade product.
The helical concaves look good on paper, but I never hear much about them on here. I've considered them several times, and kind of wished I had tried them last year when the wheat threshed so hard. My main concern with them is how much they would slow down the material flowIJ It seems like when the rotor bars are trying to auger the grain backwards and the concaves are trying to move it forwards, the operator has less control with the vane adjustments. I have noticed that to some extent with the Gorden bars. I decided to go with the St. John rasp bars, which are straight, and the normal (non-helical) concaves so that I can independently adjust the material flow with the vanes. Hopefully they will stay near the middle position to conserve HP.
For 20 acres I would not change unless they are for seed maybe. You may have some whitecaps. If you can get JD on here to answer I think he made some cover plates or awning plates to go with his round bar concave to combine wheat with. You may want to do something like that. Ilnewholland
My opinion depends on which crop your harvesting. A well worn concave will shell corn, but wheat or tough threshing beans need a square edge on the concave. I just replaced mine and have only ran wheat, I could run the rotor slower and get a better sample than last year. If you get a lot of pods in your soybean sample while cracking others is a good sign it needs replaced. Wolffman
I farm in England but we now run 2 wide wire on a 1680 long shoe sieve, with Gorden bars for Wheat, Barley, and have cut beans like this too. Have cut canola with 1 wide wire ok. Jimmy Clark in Scotland runs helical concaves with no wires at all. You could do as Jimmy said to me and pull some wires out of narrow wire concaves. I would certainly get at least 1 wide wire concave and perhaps one narrow, then maybe another narrow and pull some wires, you can always put them back in. It all depends on how much material is going through the machine. I don't know anything about flax.
You might want to get both. That's what we use. Wide wire in malt barley and peas, narrow in wheat canola and flax. Or you could do like my dad did in his 1680 and use 2 narrows at the front with 1 wide at the back. Works OK, but not as good as having the proper ones in for the crop. Another option could be wide concaves all the time, but with cover plates installed for the small seeded crops. I have no experience with this tho... Good luck!
I kept my old concaves, pulled every second wire and use them for peas or anything else that needs wide wire, put new narrow wire concaves in for all other crops. I grow wheat, durum, mustard, canola, lentils, canaryseed and flax.