Symptom:  Three point arms fall on their own requiring the operator to continually move control lever to bring the arms back up. Suspected Cause:  Overloading system with weight, and or running the hyd. oil too hot long periods. This tends to weaken O-Ring material causing leak by. Prevention:  Do not overload, or bounce the design load past limits.  Remember that a 500 lb implement can momentarily weigh 2000 lb or more on a big bounce. A "transmission style" oil cooler mounted in front of the radiator will help to keep oil temp down. We will cover this later.

No advanced or technical knowledge is necessary but basic hand tools are required - air tools will speed the process.  You will most likely spill some oil, have something on hand to soak it up.  This service was performed on a  JM-184.  It should be accurate and helpful for any Jinma. Particularly the 28 hp or smaller.  You can make your own gaskets or use "High Temp   Silicone" available at any auto parts store for the two gaskets.  Before starting, we recommend having on hand a complete set of the O-rings necessary.  Plus at least one extra of each required size in case you damage one installing it. If you don't use them this time then keep them on hand. Your book "Parts List With Ill" has numbered parts that are listed as "Ser. No."   We reference them here as "item #."  This book is supplied with all new Jinma Tractors.  If you do not have one, we sell them for $9.00 + shipping - when available.

The Hyd. Power Lift is housed inside of the "case box" that sits directly under the seat. (see Fig. 32 on page 111) Note:  Although we did not do it, it may be possible to replace the O-rings without removal of the entire Power Lift Case but clearances would require that the Drive Gearbox Cover come off. (see page 48, fig. 13). Not having done it this way we cannot tell you if it would be easier or not.

Study and become familiar with all components necessary.  We recommend you power wash the entire area before beginning. Drive the front wheels up on blocks and drain the oil. Capture and re-use the oil if you wish. We do not.

Item #55 is the Case Box, #16 is the cylinder, #14 is the Cylinder Cap, and #18 is the piston.  This #55 case sits directly
on top of the rear 1/2 of the Drive Gearbox. (page 39, fig. 12).  The front 1/2 of the Drive Gearbox is covered by the Drive Gearbox Cover. (page 48, Fig. 13).

Remove the seat and the brackets shown on page 73,  Remove the hollow bolt on the left side that fastens the low pressure return line to the case.  Removal of the C-Clamp forward of the line will help. Take note of the washer on each side of the banjo fitting.  Remove the delivery pipe (see page 94, fig. 12) from the connector #13 on top of the case.   On the right side of the case is the valve (not shown above) that controls the lift and fall of the 3 point arms.  Coming up to the bottom of that valve is another banjo fitting.  This next step can be done in one of two ways. 1) Remove the banjo fitting from the bottom of the control valve and leave the valve affixed to the case or 2) Only loosen the banjo fitting and then remove the three bolts (not shown in the picture on page 118) that hold the valve to the case and remove the valve. There are two O-rings on the back side of this valve.  Don't loose them!  Tip - a bit of axle grease will help hold an O-ring in place.

Remove the 4 bolts that hold the Cylinder cap #14 onto the case.  The cylinder should come out with the cap. The Piston #18 is inside the cylinder and may try to slide out on it's own, so be careful not to drop it.  Take note of O-ring shown in Pic.003.  Separate #14 cap and #16 cylinder as these are two different items. Do not be tempted to hold the cylinder in a vise.  Hand hold it vertical and tap round and round the "face side" of #14 till it separates from #16. O-ring #15 seals these two together. Remove and replace O-rings.  #9,  #15, and 2 of the additional O-rings shown in Pic.024. Grease the O-rings and reinstall with steady pressure #16 cyl. back inside of #14 cap.
 
 

Pic.007 shows the piston complete with two white wipers and the rubber O-ring between the two.  These two # 19 "white teflon split ring" wipers may not have been damaged but if you have replacements then use them now. These wipers are split just like rings on a standard piston cylinder and are removed and replaced in a similar manner. Final positioning of the splits after reassemble should be 180 degrees opposite from each other. Finally put #18 piston back inside of #16 cylinder.  You are now ready to reinstall the completed piston/cylinder/cap assembly back into the case.

Double check your assembly and then you are ready to put the completed case back on the tractor, make sure the ball of #27 Piston Rod is inserted into the cup shaped area on the end of the piston before and during the re-installation of the Rear Cover. This is easily done by just reaching in through the access and positioning it by hand before putting the cover on. Reverse previous procedures and reinstall all other parts and lines (except driver seat). Get the tractor down off the blocks, fill with oil to mark on dipstick using basic "Tractor Hyd. Fluid " available at most auto parts stores  Start tractor and check for leaks and performance. If all is OK then reinstall seat.

Symptom: Broken bearing in the swivel seat mechanism. Cause:  Leaving pin out and sitting on the seat.  Factory design
does not allow for human nature.  Everyone does not always put the pin in each and every time.
REMEMBER THAT LEAVING OUT THE PIN WILL NOT KEEP THE SEAT IN PLACE DURING A ROLL OR TIP OVER ACCIDENT. ALWAYS REPLACE YOUR PIN!
 

Procedure:
Remove the 4 bolts that hold the swivel mechanism to the tractor. Remove the 4 bolts that hold the swivel mechanism to the seat.

When replacing the bearing you need to get both rings of the old bearing off.  The replacement bearing is a Jinma part number
184.21S.050  (also used in the clutch)  The bearing itself has a brand name of ZXY  part # 630111 embossed in the rubber seal.  So far we have not been able to find a cross reference number to any other brand. Dimensions seem to be: ID 2.164 OD  3.546
Width of  0.683  Most Jinma dealers and Jinma parts suppliers should have this bearing in stock.

The plate that bolts to the seat has the female pipe.  We will call this plate "S".  (We used a drill press, but this can be done
with a hand drill.)  Tilt the assembly slightly up on on an angle and drill 4 holes from the interior of the "pipe side" out though the
plate.  Tilting the plate insured the drill bit stayed right at the inside edge of the pipe.  These holes allow access to insert a rod
(punch) to tap the old exterior bearing half out of the large pipe it is seated into.

On the plate with the male pipe (the part that fastens to the tractor)  Call this plate "T".  Drill 3 holes from the back (flat side) just a bit out from the center hole. (Some bearing pullers might work - try it first if you have one)  This allows the punch rod to reach through to push the inner ring of the old bearing off. Move the punch from hole to hole to slowly drive it off.

Put the new bearing into its female surface.  Lay a board across the face and gently tap it down flush. Reinstall plate "S" on the seat.  Reinstall the plate "T' to the tractor.

Remember the warning:  Caution:  With pin removed the seat is free floating and will fall out if the tractor turns on its side or turns over. The seat belts are fastened to the seat.  If the swivel assembly is not fastened with the lock pin then the seat can and will separate from the tractor. And the operator will not be protected inside the roll bar in the event of a tip over.