To swap the shredder hammers, I took the top off (6 bolts, I think). This provides suficient access to the guts. Then I punched out the roll pin on the end of the 4 main bars that hold the hammers.
There is a small round hole (perhaps 2.5 inches) that's covered by a removable metal disk which allows the main bars to be pulled out through the housing as you rotate the shredder bars to aligh with the hole.
Once you realize that the top comes off fairly easily and you find the hole the bars slide out through, the reset should be obvious by inspection. I sent e-mail to Mackissic in PA to ask them about this, and they called me back to explain it to me.
On a different note, I had some carbide saw blades sharpened and decided to get the
chipper blade reground and shaprened professionally while I was at it. They did it for $5, and it came out very nice. I like to get these things reground once in a while to get the exact angle back, remove and nicks, and to remove the areas softened by repeated heating and cooling. I can do this myself, but it's a lot of effort, and I can't do flat ground very effectively --
chipper blades should not be hollow ground on a round wheel. The blade didn't really need the regrinding yet, but I happened to be taking the other baldes in, and I wanted to see how good a job they did. It should be good for several years on hand sharpening now.
Cliff