2012 Bennche Bighorn 700x - Advice needed

[Robert Ross]

I recently bought a 2012 Bennche Bighorn 700x (Hisun 700 motor). It was worth the money, & was a "little rough around the edges," but I've been getting it fixed up (winch, tires, cv boots, etc). It ran fine, until recently on a trip with the family..... probably 15mph on a logging road, and it simply died. In diagnosing; it's getting fuel and spark, & I don't have a compression tester, yet. I removed the two round covers (timing chain/mark access) and rotate the motor by hand, which seems extremely easy.  When rotating the motor, the cam/timing chain does not move.

Broken timing chain, or could it be a key sheared off on the gear on the crank?

Since I expect this to be a relatively major teardown; what else would you recommend replacing while it's torn apart? Cylinder? Piston/rings?

Thanks in advance for any/all advice!