Finally earlier this week, the seller got it off his trailer, and called so I could pick it up.
And today, 5 days later I got to tinker a bit and generate more questions.

There are some things that make me suspicious the engine has not been used much. The oil was a butterscotch color and the sump filled to the 'add' mark. Does this sound like the way they come when new? Not a spec of dirt in the fuel filter housing. After I changed the oil and worked the air out of the fuel system I managed to get it to run. It runs nice, and restarts nice now that the air is purged. Added some 50/50 mix to the hopper and no sign of cracks or coolant leaking or getting into the crankcase so I guess there's no freeze damage. PS the oil drain plug was finger tight.

Questions:
As I said the data tag is worn away and unreadable, but....On a small decal near the fuel cap, are these numbers
XK06-105  1220.  A serial number perhaps? Or model number?

Also, I've attached a pic, what is the function of these 2 doo-dads? One on left has a spring under the threaded cap, and a 2 screw mount flange. One on the right has a nut that seems to turn but not round & round and just one screw to hold it to the engine.  I don't have a manual for this engine, it's for a similar one. Not very informative.
TIA

Tomorrow, the ST head. Perhaps I can measure the brush length, and if someone can tell me the length of new brushes, we might all get an idea as to the hours of run time this setup has endured.

Thanks, I'll check that out. The PDF you linked is generally helpful enough. The engine seems to run fine as demonstrated by the seller. As far as $250 goes, if someone can actually buy something similar to this for that price, I hope they post their score on this forum, it will be a treat to see.

Another thought, Masters Farm Supply based in Florida bought out all of Hardy Diesels parts stock of the Changfa / Chang-Chai type engines. They might be able to help you with a manual, and parts.

https://www.microcogen.info/index.php?topic=3355.0

It ain't pretty...
Found this, seller was asking $600 said he'd take $550. I saw it run, started right up with the electric starter.
He knows nothing about the ST head, wires are disconnected. Data tag is unreadable except for 2000 which may
be the year built. Is there a stamped model/ serial number someplace?

Worth the money?

Built one of those once out of curiosity, then gave it to a friend for his pole barn. Worked well. Been wanting my own every winter since, but hasn't happened yet. The 'electric free' aspect could be worth a lot in an extended power outage.

Brad, your post is comforting if not enabling...lol  I have yet to run any of my 3 project engines I've acquired in the last 3 years. First and 3rd ones are all apart. I was feeling quite guilty until I read your 15 year number....then I was just scared. I need and will get back to my project this summer! Thanks for the inspiration!

Anything for Youtube views I guess.....

https://www.youtube.com/watch?v=zwnMSgrusAY

Who says you only need one motor? I missed that rule. I'll just tell the wife the other motor was getting lonely....

Agree completely. I'm up to 3 at this point. And my GF even went on the trips to get them, and helped with loading.

38ac, The picture of the piston reminded me of the story of the old clock repairman. Customer brings in their non-working coo coo clock. The old feller takes the back off and shakes out a dead fly....He says "There's yer problem, the Operator's dead".

When all you have is a hammer, everything looks like a Listeroid

Indians may not have much to work with, but they are resourceful.