well, I guess we're both in the *censored* with these GJ stokers.
I'm about to rip the thing out and throw a different stoker - even a different anthracite stoker in the boiler.
Update: I tried bit coal (sized much the same as buck anthracite) and it powdered it instantly - couldn't even START the fire, nevermind getting it going. Apparently, the guy I bought it from didn't use the auger extension for this reason - he couldn't burn buck anthracite in it with the extension, explains why the auger extension is basically in new condition. So he just put the pot auger directly into a drum against the boiler. It would burn rice anthracite ok through the auger extension, but he wanted to burn buck, so he ditched the extension. I do not know if this is the OEM joint design or not - I am not very familiar with the various anthracite coal boilers and their auger designs.
I ran the stoker with the coupling open (once I stopped the tube from twisting) and the coal appears to be more or less intact arriving at the coupling. I did this with bit pea coal (which ground up worse than the anthracite buck). I thought these things were designed for buck anthracite, hence the large auger tube diameter?
Since it appears that I agree with bksaun, that it is the coupling, how do other mfg'rs with small auger shaft diameters have their extensions coupled? is the coupling itself flighted? no bolts? Are there any other flexible coupling designs that work better in this application?