There are too things I am looking for on a concave on a conventional combine. How thin are the wiresIJ If they are close to half worn off, I personally think it is high time for a new concave, if not earlier. Second: How much of a smile does the old concave haveIJ I have to take the feeder house of to check this. Then I open the concave all the way and with the help of a second person pull a string across the first bar. The string will lay flat on the bar on either side but will show a gap in the middle, because the concave wears a lot more in the middle due to the way the material comes in. If a person harvests hard threshing grain and needs to close the concave to zero, there will still be a considerable gap in the middle. If you would only harvest corn it wouldn't matter so much. So it depends on the kind of crop you are harvesting, how soon you want a new concave. The feeder house has to be pulled of to turn or replace the sprockets of the feeder top shaft. That is the time to closely inspect the concave. If you put a hardened concave in like St.John welding makes it and try to harvest high moisture corn right away, you can get in trouble. The edeges on a new concave and especially a hardened one are so sharp, that they break the rather soft kernels of high moisture corn and turn it into silage. After the feeder house is off, replacing the concave is not so bad. After all the bolts are out, I take a come along and pull the front of the concave up against the cab floor, rolling it around the cylinder and it comes out. I have a fork lift ready to catch it. Installing the concave works the same way. I hold the front up to get the rear under the cylinder (with all cylinder bars in, but no filler plates). When the concave is in a little ways, I hook a chain to the back side of the concave a little ways down and lay it over the top of the cylinder and tigh it to a cylinder bar. By turning the cylinder, the concave rolls around the cylinder back in its place. After installing the bolts the concave needs to be leveld to make sure it squares up with the cylinder.