ours we have to pull all the way out for corn because it has the long stationary knifes and the lowest setting the knifes still stick out a ways but if you have the short ones you can just lower them all the way down and be fine. dont know about the engine ?
We had trouble with the 4th exhaust valve (if memory serves). We had a 1440 and I was told at the time that it was a common problem for them, particularly when those engines were in the trucks. They just turned too fast. Cost us $4000 to put in an updated camshaft, lifters and all.
Haven't heard of that with the engine. But the chopper bar like stated previously can be taken out, make sure and go to slow speed, I'd also check the size of the pan under the chopper the first choppers the pans were shorter than the later ones and stuff could come off the pan and hit the back of the sieves real easily.