I had bought a Jinma; the reasons were that they are simple and easy to work on, tough, and reliable. I had the opportunity to test that.
Hydraulics; poorly engineered, replaced 4 pumps. Totally re-engineered the pluming because the lines were too small, 1/4 in. in dia where they should have been 1/2 in. dia. All leading to overheated pump failure.
Cooling system; poorly engineered, overheating because hot exhaust air was recirculating to the radiator input. Fix air dam on top of the radiator.
Electrical system:
Poor start/no start; fix, install a relay to switch the current directly to the starter solenoid.
Battery charging only to 70%. Fix, add diode to regulator to boost voltage from 13.6 to 14.3 volts.
Bolts constantly loosening; install better flat washers.
These are some of the improvements, now the tractor in near perfect.