No, I haven't had any trouble with the drive clutchs. 

I've been through what your are describing with my NH baler and the obvious wasn't so. 

I had just started baling for the season this year (first bale...) and I broke a shear bolt on the flywheel during the tying cycle. Odd.. baler was working fine at end of last season. Replaced shear bolt, ran everything by hand and I found that I also broke the knotter drive clutch shear bolt. Replaced it, found the needle brake disc stuck, holding the needles up (rusty) so I got them freed up, everything appeared to be in &quot;time&quot; so we attempted to bale. Broke a shear pin on the flywheel at the next tying cycle. Headed back to the barn...

I checked timing a few more times, and looked good, but the safety stop was in the way. I looked at the bolts that hold the stop adjustment and they were not loose, the paint around the bolts wasn't disturbed and you could see that it had not moved. How or when it got out of adjustment is a mystery. I adjusted it and everything was fine after that. Sure seemed like timing to start with. Was odd that I was able to run the baler by hand through a tying cycle in the field and then bam.. couldn't. I figured my timing was off.

My 520 baler has given me nothing but trouble with the left knotter not tying. I went as far as replacing cam gear, the entire knife arm, bill hook, etc.. still trouble. What I finally determined the problem to be was not that it didn't tie, but that the knot was being broke. After the knot was swept from the billhook, the billhook managed to retain a hold of the &quot;tails&quot; of twine that are hanging out of the knot. Sometimes it would pull free, other times the knot would break. I checked, then rechecked the adjustments for the knife arm, twine disc, needle position, twine tension, and billhook tension. I started at the beginning of the operators manual and went through each step of the baler adjusting process (I need to get a spring scale to do it right) but this season I was able to do two dozen bales (we baled up the leftover stuff in the field that we didn't get with the 68... the 520 wasn't ready and I needed to get the hay in) and it worked like a champ. 

Combination of problems may have contributed to the issue with the 520. I had certainly tried loosening the billhook tension before (prior to parts replacements and after replacement of the hook itself), but when I made my adjustments this time, I grabbed the billhook tongue and lifted it up, it felt tight, so I adjusted the tension until I could easily flip it. 

I also borrowed a trick from my NH baler... when the knotter clutch pawl is tight against the knotter stop, mark a line across both halves of the clutch assembly. (Make sure you have all the backlash out by pulling up on the needle yoke.) Keep these two lines together when your putting the chain on etc.. Complete the rest of the timing procedure. When you check timing after putting it all back together the two lines should come within 1/2&quot; or less. This may also tell you if something slips.