A number 17 is a great spreader, you just have to understand what it is capable of. I still have a #12 that does a great job. It can be filled to the point that no more will fit on it, and it does a great job.
Let's talk generalities about these units. If being loaded with an FEL, you need to break the stuff up some first. Digging large piles of straw and wet cow manure, makes it very hard on the unit. The leaver on the right that controlls the drag chain has numerous settings as to how fast the chain moves. If you are running really wet stuff, only set it in the middle. The betters only have one setting, on or off. I have never had one jump that chain off the sprocket. The sprockets vary a lot from 12-12A-17-206, each is different. Same operational idea, but different axles etc. Does the chain come off during spreading, or when you are stopping? If you stop too fast after the load is gone, I could see it jumping off then.
In your driving this spreader, how fast are you driving? They were only ever ment for a ground speed of about 3to 4 MPH. You may be able to push 5 if you are lucky and loaded with dry stuff.
The ratchet drive for the drag chain, probably just needs cleaned up and lubricated, or maybe the spring for it is gone or week. Some had springs, some did not. If those ratchet teeth are warn out and the beater sprocket is worn out (never seen this happen, seen them break, but not worn out) time to get another spreader.
The beater sprocket is cast, and none of the castings are available new any where. Used parts are the only thing you will find,and they are getting harder to find any more. I used to rebuilt these for the horse people in the area, but the supply of spreaders and parts just got too small.
