Hi t78j
Sorry only just seen your message - as I had given up waiting for a solution - however I have finally sorted the problem out. It looks like it is all down to the play in the bill hook beak, ie the little tooth that has a rolling ball on one end, this tooth opens as it turns,captures the twine and then close right at the end of the cycle as the roller ball falls off the main frame cliff (cant think of a better word than cliff) at the point where the end of the cam has done its job basically. My problem was that because of a slight play in the tooth/beak it wobbled which meant that it is not forced to close by slipping off the cliff.
After speaking to someone they advised that a quick fix is to file the cliff a couple of millimeters so that it compensates for the play in the beak, this is irreversible and will creat problems if you get a new or better bill hook. So I waited and eventually by luck managed to buy a nearly new whole bill hook. After fighting to position the cam in the right place to knock out the pin I got the new one in. After adjusting the knife position to make sure that the twine was not cut too early it seems to work almost perfectly - sadly the day I tested it in a stationary position it has rained every day since!! But I am confident that this was the only problem. It took a lot of playing around to work out what was wrong but after it seems so obvious, the ball on e end of the bill hook has too much side to side play - its like a having a wonky loose tooth as a kid. If you can do a make shift job perfect but I would try and source a bill hook with no play in it first, seek and thee shall find, took me 2 years and a lot of luck in the end.
I am happy to post some pictures for those that would like some description on the problem. Just to mention my bill hook that was loose was the outside one? The one away from the hay being drawn up into the baker, it may be that this one always has the wear issue first, something to think about if stripping an old baler for spares.
Greenboy