Pfaff 346-H2 won't pick up bobbin thread.

[GPD]

A new to me Pfaff double needle 346-H2.  Won't pick up the bobbin thread.  Ya, I've tried moving the rotary hook closer to the needle scarf.  Used the needle bar clamp and gauge.  (1.8mm).  finally called in a repair guy from the local sewing machine shop that serviced industrial machines.  No joy, couldn't "fix" it.  There has got to be something I'm missing here.  The repairer say the hooks are probably worn out?  No, it has never sewn for me.  Just now starting to get it recommissioned after picking it up a couple years ago. .  

SOOOO...  what am I missing?

OR, anyone know of a replacement part for these rotary hooks?  I can't find any info on interchangeable parts/modern made.  Are any Pfaff single needle machine parts interchangeable?  I found a resource that suggests that the 335 machine shares many parts with the 346, such as rotary hooks.  Can someone confirm this?

[friquant]

Double needle...nice!

You can pull the cover off the backside near the hook, and put one of these endoscopes down there and see what's happening:

https://www.amazon.com/dp/B0CKQH4VZY

Then with a brand new needle in the machine (scarf on the hook side), and the machine threaded, put a piece of fabric or leather under the foot and turn the machine over slowly with the handwheel while you watch the (cell-phone screen of the) boroscope. Ideally, the needle goes down and stops. Then it starts to come up and forms a loop. And the hook comes by at about the middle of the scarf and grabs the loop and takes it around the bobbin. Watching it zoomed in like that will show you what's happening. .

It may also help to draw a black mark at about the middle of the scarf as a reference point for where the hook will come by. Maybe the hook is arriving at the wrong time. Maybe the hook is too far away from the needle. Maybe no loop is being formed. Maybe the hook point is very dull

If the hook bushings are worn, you may need to adjust the hook closer to the needle to make sure it all but contacts the needle when you actually sew. If the hook point is worn to where it is no longer sharp, you can inspect this and possibly re-sharpen if it's not too bad.