Jinma 304 tractor was running with low pressure at idle. Now no pressure at all.

[quicksandfarmer]

Part II:
Disconnect everything on the left side of the tractor. FEL bracket, fuel lines, throttle, kill switch, electrical, steering hoses.

FEL Bracket. Yours may be different, I have the Koyker. The bracket attaches in three spots: two bolts in the front, two in the back, a bunch in the middle. Take all the bolts off and set the bracket aside. Careful, it's heavy.

Fuel Lines: The fuel tank will go with the back of the tractor. There are two lines coming out of it that need to be disconnected. At the sediment bowl there is a shutoff valve, turn it 90 degrees to shut off the fuel. There is a hose coming out of that valve that goes into the fuel pump with a banjo fitting. Have a cup ready to catch any fuel that spills, and remove the banjo bolt. Take the hose with the banjo fitting and put it into your fuel can. Open the shutoff valve and drain your fuel tank. Once the tank is empty you can disconnect the second hose, the fuel return hose, at the fuel tank. It loosens with a 10mm wrench. Good mechanic's practice would be to wrap both lines with a shop towel and a rubber band to keep crud out.

I like to put about a quarter cup of fuel in a bucket for cleaning parts.

Throttle: there is a linkage that comes from the hand lever and foot pedal across the transmission. It connects with a cotter pin. Remove the cotter pin and disconnect the linkage.

Kill switch: disconnect the cable and the housing at the fuel pump. With the cable removed the engine can start, so for safety jam something into the kill lever to hold it in the off position. I use a screwdriver handle.

Electrical: take a picture and write notes before disconnecting any wires. The tachometer and fuse box are just connectors that snap apart. The oil pressure sender has two wires held by bolts, 7mm I think. They are not interchangeable so make sure you note which is which. There is a ground wire under the fuse box held by a bolt. The glow plug wire has to come off, it is held by a thumbscrew.

Steering hoses: you want to disconnect them where the hard lines go into the hoses, near the front axle. You want to disconnect the hard line. This is where you need the 27mm box wrench. I actually used a plumbers's crescent wrench. Put a container under the fitting, you'll lose about a cup of fluid. Wrap the hoses in shop towels and rubber bands.

The steering lines will hang there, long and unsupported. I thought they looked vulnerable so I taped them to a 5 gallon bucket so they wouldn't bend under their own weight.

Now you can move on to the right side.

 

[quicksandfarmer]

Part III -- Disconnect everything on the right side of the tractor: hydraulic pump, FEL mount, electrical, hydraulics.

Hydraulic pump: On my tractor, it is necessary to remove the hydraulic pump to remove the FEL mount. It is not necessary to disconnect the hydraulic hoses. To get at the hydraulic pump you have to move the alternator out of the way. Loosen, but do not remove, the two bolts on each end of the alternator bracket (13mm) and the alternator pivot bolt (16mm). Push the alternator as far toward the engine as it goes. The bottom alternator bracket bolt, and a similar 13mm bolt are the two bolts that hold the hydraulic pump on. Remove those two bolts and the pump is free.

FEL Bracket: similar to the other side, two bolts in the front, two in the back, a bunch in the middle. It's heavy.

Electrical: take a picture of the alternator wiring. Write down the color and positions of the wires. Make sure the battery is disconnected, and disconnect the wires. Disconnect the wire going to the temperature sensor with a philips head screwdriver.

Hydraulic: Remove the bolts holding the steering priority valve to the engine block. Just like on the other side, you now have long hard pipes hanging free. Tape the priority valve to the hydraulic pump and tape them to a bucket to support them.

Now it's time to split the tractor.

 

[quicksandfarmer]

Part IV -- splitting the tractor: support the engine, support the transmission, remove bolts, separate.

Support the engine: You're going to split the tractor so that the back wheels and the transmission roll away, and the front wheels and the engine stay in place. You need to support the engine so it can't move. Put a piece of 2x4 in front of and behind each front tire. Make a crib out of your 4x4's and 2x4's that will hold the weight of the engine. At this point I attached my engine hoist as well as insurance. The front axle pivots so you need to jam block into it to keep it in place. Your safety depends on the engine not falling off of these supports.

Support the transmission: I found it easiest to put the jack on the transmission, tighten the strap as tight as I could, and then extend the jack to the floor.

Remove the bolts: With everything supported you can remove the bolts holding the transmission to the engine. There are ten 16mm bolts: three studs with nuts on the bottom and one on the top, and three bolts on each side. The single stud on the top requires a swivel adapter on a socket to get off without removing the steering. I found that the threads on the studs were rough enough that the studs came out instead of the nuts coming off, on reassembly I had to clean them up.

Separate: Stand behind the tractor and pull the rear wheels toward you. It should come apart pretty easily, if not probably something is stuck, walk around and look for a hose or wire that is catching. Take the back end several feet back so you have room to work.

 

[quicksandfarmer]

Part V: Remove clutch, flywheel and oil pan.

Clutch: Once the tractor is split, the clutch is exposed. It is held to the flywheel with six bolts. Remove them. The clutch weighs about 40 lbs and is several pieces, so carefully remove it and set it aside.

Flywheel: The flywheel is held on with six bolts. Remove them. The flywheel is heavy, remove it carefully and set aside.

Oil pan: behind the flywheel are four bolts, two 13mm and two 16mm, that hold the oil pan to the transmission housing. Remove them. There are 20 13mm bolts that hold the oil pan to the engine block, eight on each side and four in the front. Remove them. There are two brackets that connect the front wheels to the engine, each has bolts that go into the engine block and into the oil pan. Remove the bracket on one side. On the other side, just remove the bolts going into the oil pan, leave the engine block attached to the front wheels so it is supported.

Lift your engine using your hoist so there is daylight between the bottom of the oil pan and your support. Using the cold chisel and your hammer, gently but firmly try to crack the gasket on the oil pan. Once it cracks it should come off pretty easily.

It should be about lunch time, wash your hands and go have lunch, you need to keep your strength up.

 

[quicksandfarmer]

Part VI -- replace oil pump.

For this part, you need to work under the engine. Safety first! You need to support the engine with your hoist, and remove the blocking and oil pan from below. Reconfigure your blocking so that if the hoist fails you don't get crushed.

When working inside the engine it's important to keep dirt out as much as you can. I wear rubber gloves because I feel it's easier to keep the crud off of my hands.

Disconnect the oil pump outlet pipe from the engine block, it's held by two 13mm bolts. The oil pump is held by a single 13mm bolt. Once the pipe and the bolt are off it just slides down. Remove the two 13mm bolts that hold the outlet pipe to the pump.

Ordering a new pump: there are three versions of this engine, the Y385, Y395 and Y485. There are three versions of the oil pump. See this site for a description of the differences: Complete Oil Pump Assembly-200
This says it all: "See the pictures for measurements as the number doesn't always correspond with the engine."

Reassembly, as they say in the manuals, is the reverse of assembly. Just kidding.

For reassembly, use a torque wrench on every bolt. I used this chart as a guide, every bolt has a grade marking on the head:
US & Metric Bolt Torque by Grade

Note that the bolt size is not the wrench size. The most common wrench sizes are 13mm (8mm) 16mm (10mm) and 19mm (12mm). Note that those little 8mm bolts with the 13mm heads take 17 ft-lbs, which is not very much. I snapped one off on reassembly and it ruined my day.

I found the most time-consuming part of the whole project was cleaning the old gasket off of the oil pan. It's thick, hard and firmly attached. I broke several razor blade scrapers before I settled on a sharp, broad wood chisel. Cleaning the gasket off of engine block was particularly challenging because you have to lie on your back and work above. The little pieces of gasket get everywhere and you have to be vigilant to keep them out of the engine.

Put the outlet pipe back on the oil pump, put the oil pump back in, and attach the retaining bolt and the two bolts for the outlet pipe. You'll need new gaskets for both ends of the outlet pipe.

Make sure you have the right oil pan gasket. There are at least three versions for this engine. The way I was able to get one, after several tries, was to send Tommy at Affordable a picture and he found one that looked like it in the gasket room.

Put the oil pan gasket on the oil pan and put it into place. I put a coating of grease on one side to hold it in place. The oil pan is heavy so it's challenging to hold it up while you get the bolts started. This is where i use the floor jack, a helper is handy here too. Once you get two bolts in it's much easier. Replace all 20 bolts, and the four bolts that hold the pan to the transmission. Once they're all in go round and gradually bring them all up to torque.

Replace the bracket that holds the front wheels on, and the bolts on the other side.

Now you're ready to put the tractor back together.

 

[quicksandfarmer]

Part VII -- flywheel and clutch

The conventional wisdom is to replace the throwout bearing and clutch disks whenever you split the tractor because they are wear parts. I'm not convinced about the disks. Taking the clutch apart complicates things.

To remove the throwout bearing, remove the clutch fork. I just bashed the bearing off with a hammer and chisel, being careful not to damage the seat. Press the new bearing on and replace the fork.

Bolt the flywheel back onto the engine with six bolts. Note that there is a locator pin that needs to be positioned in a slot. A helper is handy here because the flywheel is heavy and hard to hold in position while you place the first bolt. Assemble the clutch pack around the clutch tool and put it against the flywheel and bolt it down. Again a helper is handy because it's heavy and hard to keep all the pieces together. I found the plastic clutch tool sagged a bit under the weight of the clutch pack, which made the clutch tool very hard to remove. I pulled it out with channel lock pliers. But it didn't seem to affect reassembly.

 

[quicksandfarmer]

Part VIII -- reassemble transmission to engine.

This is often considered the most difficult step, although I didn't find it particularly challenging. The idea is to get the engine and the transmission aligned and gently push them together while rotating either the engine or the transmission until the transmission shaft pops into the clutch.

First step is to clean up the four studs that hold them together. Get them as clean as you can, and then run the nuts up and down to get the threads moving freely. Use a doubled nut to crank them into the engine side of the housing. They will then stick out and you can use them as locator pins.

Next you need to put a new gasket on. I use a layer of grease to glue it to the engine side.

Push the back part of the tractor close to the front part. Use the transmission jack, the floor jack, the hoist, whatever it takes, to get the two pieces level and even in height. You should be able to get the studs into the transmission just by pushing and wiggling. To get the transmission shaft into the clutch you need to apply pressure while rotating. You can either rotate the engine by putting a 27 mm socket on the fan belt pulley and turning clockwise (make sure the fuel supply is off) or you can rotate the transmission by engaging the PTO and turning the PTO shaft. I've used three methods to apply pressure:
1. Push on one rear tire as hard as you can, and put a block under the tire. Repeat on the other side. This only works if the alignment is very good.
2. Put an extra-long 12mm bolt into one of the bolt holes on each side of the transmission, and slowly tighten.
3. Put a come-along on each side and gently pull.

You need to apply even pressure from two sides, and it has to be gentle, just enough to get the shaft to slip in. I've also heard that if you have 3-4 friends you can just have everybody push while one person turns.

What should happen is that as you turn the shaft suddenly slips into place. Once it's in you can put the ten bolts in and go around with a 19mm socket and tighten them all.

 

[quicksandfarmer]

Part IX -- final assembly.

From here it really is just a matter of putting everything back where it came off. There are two tricky parts:

For the hydraulic pump to go back on, the slot in the pump has to be aligned with a ridge on the drive shaft. What I do is hold the pump in my left hand while cranking a 27mm socket against the fan belt pulley. When the pump is aligned you'll feel it fall into place. Make sure the fuel supply is cut off while you do this. On my tractor the FEL bracket has to go on before the hydraulic pump.

The front driveshaft can be tricky to get back on. Clean the ends and balls thoroughly. If you put a dab of grease in each slot it will glue the ball in place while you work the shaft into position.

You probably should adjust the clutch while you have it open, but that's a different tutorial.

Don't forget to fill the crankcase oil and top up the hyraulic fluid.

Go have dinner and call it a day!

 

[erj]

quicksandfarmer,
Thank you so much for taking the time to put this together for our education!
RonJ

 

[dmgks]

When my oil pump failed the driveshaft sheared off

Quicksandfarmer: Was it the driveshaft to your oil pump that failed? I had my cam shear in half on my 354 (which basically had the same result -- no oil pressure).

When I immerse my oil pump and run it using a drill, it seems to pump oil well. I just don't want to put this thing all back together and have the same problem...