I put Calmer crushers on my 893 JD head last fall. I shelled 3 gearboxes in 900 acres. Had 2 gearboxes go out the last week of November, cost me 2 days that ended up being pretty valuable. Didn't finish the last 50 acres until March. One of the rolls on the broken gearbox broke apart, probably after the gears shelled, I was sort of hoping Calmer would stand behind it to some degree but they won't return my phone calls. I bought over $10,000 in parts from them.  I'm wishing I had gone a different route despite the fact that they do a nice job if you don't go to fast. One other problem I have had with them is the rolls grab and pull the stalk so aggressively that I have a lot of ears bouncing around. If I slow the head down to under 600 RPM is is better but then the stalks don't get crushed up as well.