Have short sieve 1680. Put 28"IJ shaft and extended bearing supports install third bearing. Make removable for sieve removal. Turned bats on side. Raised chaff pan over axle to get under spreaders. Did not increase speed. Have chopper. Worked extremely well for the cost,(2 bearings some shaft and flat iron) neighbour shopbuilt. Possible experimentation required for proper length as chaff now not sliding off chaff pan in very tough conditions (30 degree late night) Also need to place deflector over spreaders as most straw comes off right side and stream is not caught soon enough by spreader allowing it to make slight windrow off 10' to right. Or lay bats flat thereIJ Hope this helps. We harvest wheat barley canola peas.
