I was working on a 40-year-old combine today and had to dig into the archives to get some specifications. One thing I noticed in the yellowed pages of the tech manual was a bold-faced, capitalized warning to operators of that combine:
"Allow separator to run for 30 seconds after shutting off the header, to allow the clean grain elevator system to empty. Stopping the separator with the clean grain system full of grain can cause severe damage when the separator is restarted."
That's still important advice today, especially with 12-row corn heads stuffing 200 bushel corn into grain tanks with extensions that threaten every power line they pass under.
Stopping the separator with the clean grain system full of grain is a double whammy on that system. First, there's the sheer load of all that grain in the lower clean grain auger, the vertical clean grain elevator, and in the grain tank loading auger. Second, a lot of the grain that's in the clean grain elevator will cascade past the paddles to the bottom of the elevator when the elevator stops moving, putting a humongous load on that elevator chain (and its drive belt) when things are turned back on.
Another consideration is when the grain tank is full, mounded over the end of the grain tank loading auger, and the operator has to shut off the separator while waiting for a truck or grain cart. Even if the operator allows the clean grain system to "clean out" before shutting off the separator, grain mounded over the end of the loading auger will leak past the flighting and fill the lower auger housing and sump. Again, that's a big load for the drive belt, gearbox and associated components to break lose once the separator is reengaged.