The "needle guards" aka plunger stops are doing their job. The primary causes of your problem are wet hay plugs, too fast a feed rate, dull plunger knives,and pto rpm too low.
I blew thru 2 shear bolts myself yesterday. I had double raked all windrows and there were a few wet globs that stalled the plunger. When I stop the tractor to reduce the feed rate, sometimes I push in the clutch too far and this removes power to the baler as well as the tractor. Oops. In very dry hay, I sometimes run a higher gear and this can choke the plunger throat area. I'm lousy at raking and turn around areas of my windrows get too big. Dull plunger knives and poor knive spacing loads up the plunger cycle excesively. And finally, balers are designed to run at rated rpm 540/1000 rpm. I see so many users who run at 1/2 speed because the tractor moves too fast, they think they are saving fuel, or the ride is too rough. Pick a gear set that gives the pto rpm and ground speed that your machine was designed for. If you are moving faster than a brisk walk with your equipment, its probably too much.
