Kubota B7100 Overhauled now will not run

[Hooked_on_HP]

Did you check the ring end gap before you installed the pistons. I am thinking you don't have enough end gap and the engine is trying to sieze. After the engine dies try turning it over by hand and see how hard it turns while hot. If its is tight I would tear it back apart to see what is wrong before you tear it up
Bill

 

[TomNOh]

Has oil pressure been checked? Connecting rod caps mismatched? The rod caps MUST be put back on the rod that they came off of & MUST be put back on in the correct orientation. i.e. cannot be flipped the wrong way.

 

[Sanddog]

Is the lower radiator getting hot also. Your description gives thoughts on circulation restriction. Running a water hose in either direction on the bottom hose should indicate if all is clear. Any head gaskets that could stop/interfere with circulation? Remember it is thermo syphon and there is no water pump.

The radiator is hot at top if I only run one time and you can feel the heat slowly spread after running the motor the short run it makes before dieing. If I run several short runs, then the entire radiator gets hot, so I think the water is moving.

 

[Sanddog]

Did you check the ring end gap before you installed the pistons. I am thinking you don't have enough end gap and the engine is trying to sieze. After the engine dies try turning it over by hand and see how hard it turns while hot. If its is tight I would tear it back apart to see what is wrong before you tear it up
Bill

I do not recall checking the end gap? We bored the block and went back with the oversized pistons. I bought the oversized overhaul kit that included piston, rings, all bearings etc. Should those rings not have been sized correctly without having to be filed down???

 

[Sanddog]

Has oil pressure been checked? Connecting rod caps mismatched? The rod caps MUST be put back on the rod that they came off of & MUST be put back on in the correct orientation. i.e. cannot be flipped the wrong way.

I do not have an oil pressure gauge, but the oil pressure light comes on when ignition is turned on and the goes out after it starts. I did install a new oil pump and I know it is pumping oil, as I had an oil leak when I first tried to start it (shop left plug out of oil galley at back of block and has now be replaced). The rod caps were not mismatched and end caps put back in same orientation (was very careful about that). Now wondering about ring end gaps though!#!#!

 

[murphy1244]

Ring end gaps should at least be checked. We would put them in a cylinder or 2 end use a feeler gage to check.

 

[truckdiagnostics]

I wonder if you have head issues, getting hot and compression is getting into the water passages causing the poor water circulation and lack of power. When it is running you seeing bubbles in the radiator? Or with radiator pressure tester installed is the pressure rising?

 

[Hooked_on_HP]

I do not recall checking the end gap? We bored the block and went back with the oversized pistons. I bought the oversized overhaul kit that included piston, rings, all bearings etc. Should those rings not have been sized correctly without having to be filed down???

I always check all clearances. Mistakes happen. I have seen the wrong size rings in kits. Even 1 wrong piston out of 6.
Bill

 

[Hooked_on_HP]

Do you have a hydraulic pump on the tractor that could be building too much pressure and bogging the motor.
Bill

 

[Sanddog]

Do you have a hydraulic pump on the tractor that could be building too much pressure and bogging the motor.
Bill

There is the factory hydraulic pump that runs off the end of the short "cam" shaft that actuates the injection pump. I had wondered if somehow it was building up enough pressure to bog things down.

I did the overhaul back over the Christmas holiday and it has been long enough now that I just cannot remember for sure checking the ring gap. As I said earlier, I know I did not file anything down or I would have remembered that. So, I am going to (next weekend??) pull the motor back off and pull the pistons to make sure the ring gap is not an issue. The motor seems to me to be trying to cease up and I had better pay attention to what I am observing. It will at least give peace of mind that nothing is off internally and I am not doing damage trying to start it to check other possibilities.

Thanks for pointing this out, as I may never had though to go back and check.

 

[Sanddog]

I wonder if you have head issues, getting hot and compression is getting into the water passages causing the poor water circulation and lack of power. When it is running you seeing bubbles in the radiator? Or with radiator pressure tester installed is the pressure rising?

I don't think there is a head issue. There are no bubbles, no water in oil, etc. I put on a new head, as the former was cracked. Apparently, the last owner did overheat the engine.

The radiator appears to be OK,it although maybe some passage are partially blocked??? I have just flushed it out with a garden hose and water runs through it freely; not certain if that means water is getting through all passages. And, I did clean out all trash from the fins.

 

[Sanddog]

looks like Hooked_on _HP (Bill) was on to something with the piston ring gap. Tore the engine down yesterday and sure enough the oil rings were too tight. One of them would hardly go in the cylinder; cannot believe I totally forgot to check this. Anyway, I of course broke the last oil ring putting it back on the piston so it will be next weekend before I find out for sure but it definitely looks to have been the problem.

The pistons had a slight outline of the exhaust valves, so I am glad I took it back down. The overhaul kit came with an thin extra head gasket and I plan to add it on reassembly. Hopefully that and a new oil ring will put an end to this saga.

Thanks for all the help and will update once it is back together. If someone thinks the addition of the "extra" head gasket is the wrong way to go then, the please speak up.

 

[Billrog]

I don't think a double head gasket is the way to go.

 

[truckdiagnostics]

I don't think a double head gasket is the way to go.

agree

 

[Egon]

Sounds like Bill made a good call:thumbsup::thumbsup:

No on the double gasket.

 

[Eagleview]

The valves should be NOWHERE near the pistons . Either the head gasket is too thin , the valve timing is wrong or the rockers are set too tight .

These things DON'T have a water pump , WTH ?

 

[Sanddog]

I know the timing is set correctly in regards to the gear set as shown by Eagleview. The repair manual discusses using a plastigage to check spacing between piston and valves with min. allowance of 0.6mm and says the gap may be increased by using a shim gasket. I don't particularly like the idea of stacking head gaskets but the overhaul kit did include a regular head gasket, which I used, and then a second thinner metal?? head gasket. The thinner gasket is I assume the shim gasket referred to in the manual. I thought I would also increase the valve gap to max end of the range to possibly provide a little more clearance.

What other recommendations do you guys have??? If you go back to the very first page you will see a picture of the alignment of the timing gears with the dots not lined up as shown in the manual. This is what I found when I took it down, the dots were not perfectly aligned as shown in the manual. When going back, I lined up the dots as shown in the manual.

 

[Leejohn]

Where was your piston at when you took the pictures on the 1st page?

 

[Sanddog]

Where was your piston at when you took the pictures on the 1st page?

I cannot recall now, as I took the pictures back in December. I checked back through the pictures I have left and none show the position of the pistons. I do recall spinning it around and around that was the closest they ever came to lining up with each other.

If I were to pull the timing gear cover off to recheck, where should the piston (assume we are talking about front piston #1) be when these timing marks are aligned?

 

[Eagleview]

Check the two fuel return lines to the tank . If either are chaffed or cracked , they will suck air as they loose their prime (for the want of a better term) and aerated fuel would return to the filter housing . This would stall the engine out .

I would also back the rockers off a little to give you some more lash as there is something going on with piston to valve clearance .

I would also buy an electric inline water pump when you do get it going , I dont like that Thermo system one bit . I would bet it is the cause of all the cracked heads people speak of . Thermo siphon does work , but what happens when you are in a bit of steep country and you get an air lock in the head ? You get a hot dry spot with no circulation to force it out and a cracked head would be a surety .