The 336 were good balers, we owned one back in the early 80's. When working on the knotters you can also clean out the bale chamber, then reach down between the divider and pull the twine up through hole.
Pull enough through so that you can get a good grip. Hold some back pressure against the twine and have someone turn the flywheel over by hand (trip the lever to engage the knotters). This helps if you are working on it in the shop or don't what to mess with feeding hay into it, this also helps to slow down the process which sometimes helps to find the problem.
You can do both knotters, but most of the time I will cut the twine on the working one and just do the problem one.
