Kubota B7100 Overhauled now will not run

[Leejohn]

It should be at TDC on the compression stroke. Look in your manual and see if they are setting the timing on #1 and see what one front or back is #1. I do know if the valve timing is just a little off the valves well hit. After you get it all set turn it over by hand while holding you hand on the rocker arm. If any are hitting you can fell it. The crank mark and idler mark should be dead nuts on. Make sure they do not move while lining the others.

 

[Sanddog]

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 .

This little tractor has one return fuel line that comes off the back of the injectors. There is a metal line that connects across the top of all three injectors and then a rubber vent lint back to the top of the fuel tank. When I took this line off to remove the head, I did notice a small volume of fuel in the line, but did not know if this was correct or not. I do not recall any cracks in that line but will check closer.

I will back off the rockers a bit to help with the clearance.

Yes, the electric water pump does sound like a good idea. I plan to mount a small backhoe on this tractor so it will be operated stationary; probably not the best for getting air through the radiator.

 

[Sanddog]

It should be at TDC on the compression stroke. Look in your manual and see if they are setting the timing on #1 and see what one front or back is #1. I do know if the valve timing is just a little off the valves well hit. After you get it all set turn it over by hand while holding you hand on the rocker arm. If any are hitting you can fell it. The crank mark and idler mark should be dead nuts on. Make sure they do not move while lining the others.

Thanks, I may take the timing cover back off to check this again. I know both the crank/cam and crank/injection pump marks were dead on when I put it back together. I cannot now recall when the piston was at that point but I did slow turn it over by hand and made sure that all valves were opening and closing in time with the pistons on their compression/exhaust stroke. Everything seem to work just as expected and I am surprised by how close the piston and exhaust value are running. Looking back to my first post and pictures, it looks like it was set up so that the valves and injection timing were both slight ahead of the pistons???

The attached pictures shows that the clearance is not the same on all three and hopefully some valve adjusting will ease the situation. hat

 

[Leejohn]

I got to correct myself, the piston should be just BTDC to TDC.

 

[Sanddog]

STILL WILL NOT KEEP RUNNING

I set the gap on all rings, two oil rings were too tight. Put it all back together, with a little extra gap on the intake values to help keep them off the pistons. It took several attempts but after getting all of the air out of the fuel system, it started and ran probably one minute before slowing down while putting out a little black smoke and then dying. It started again, ran a shorter time before dying again, same as before I checked the ring gap.

It seems as though it will run a few times until it gets hot and begins to seize up. After about the third time, if you try immediately to start again, then the starter has a hard timing turning it over. If you wait about 20 seconds, holding the glow plug, then it will turn over without any apparent resistance.

It looks like something is seizing or building up pressure after about one minute of running and then after several short runs, has enough resistance to prevent the starter from turning it over. Then within 20 seconds the seizing or back pressure reduces such that the starter can spin it over.

It still think it is the motor but how can I best check to eliminate any back pressure on the hydraulic pump, keeping mind the short run time.

Oh, forgot to mention on the last run today the oil light did not go out after it started. This is the firs time I noticed this and I am pretty sure it was pumping oil; I did install a new oil pump. And, it was pumping oil out of of the missing oil galley plug right after I first tried to start it a few weeks ago. I noticed this and got a new plug, as it was left out at the machine shop. Also, when turning the motor over by hand to set the valve clearance I noticed oil begin to drip from beneath the motor before I put on the oil pan.

 

[Eagleview]

These engines are notorious for having low oil pressure due to the aluminium oil gallery plug coming out of the camshaft . People put a piece of steel in the hole and weld it in and they regain their oil pressure . Judging by the grind marks on your plug and the ones on the cam not lining up , someone has done this and now your plug is likely loose . The Red arrow is pointing to what appears to be a gap where your oil pressure could be escaping from . Probably where the weld tore out and the plug has turned a little .

It takes 7psi to put out an oil light , an engine needs 10psi of INITIAL oil pressure and 10psi for every 1000 revs after that . An engine doing 3000 rpm needs at least 40psi for example . If you have only got 6 0r 7 , it is likely your Mains/Big Ends and cam bearings are swelling with the heat and acting as brake on your cam and crank .

What did the bearings look like when you pulled the pistons to fix the ring gap ?



I have no idea what holding the Glow plugs on is doing to help unless it is just the 20 seconds that it takes you to do it is allowing the crank and bearings to cool , just as they do when you said you can leave it for a few seconds and it will wind over .

 

[Leejohn]

Without reading all thru the thread. Make sure the hyd oil pump is not building up pressure and stopping the engine. Make sure the 3pt lever is all the way down.

 

[rrrkkk]

Reading this post is very interesting I will follow, hopefully you will find a conclusion

 

[aczlan]

Jumping in here late, but you have checked the fuel flow going into the injection pump right? Those symptoms sound like the ones seen when you have a piece of crud blocking the outlet of the tank.

Aaron Z

 

[Sanddog]

These engines are notorious for having low oil pressure due to the aluminium oil gallery plug coming out of the camshaft . People put a piece of steel in the hole and weld it in and they regain their oil pressure . Judging by the grind marks on your plug and the ones on the cam not lining up , someone has done this and now your plug is likely loose . The Red arrow is pointing to what appears to be a gap where your oil pressure could be escaping from . Probably where the weld tore out and the plug has turned a little .

It takes 7psi to put out an oil light , an engine needs 10psi of INITIAL oil pressure and 10psi for every 1000 revs after that . An engine doing 3000 rpm needs at least 40psi for example . If you have only got 6 0r 7 , it is likely your Mains/Big Ends and cam bearings are swelling with the heat and acting as brake on your cam and crank .

What did the bearings look like when you pulled the pistons to fix the ring gap ?

YES, I HAD READ ABOUT THE PLUG IN TH END OF THE CAM COMING OUT AND IT APPEARS THAT HAS ALREADY BEEN FIXED. IT LOOKS LIKE A STEEL PLUG THAT HAS A SMALL "SPOT" WELD HOLDING IT IN. I CHECK THE PLUG CLOSELY BEFORE AND IT LOOKED TO BE GOOD AND TIGHT. THE PICTURE I TOOK IS NOT THE BEST, BUT I WAS AWARE OF THIS BEING A POTENTIAL PROBLEM AND DID CHECK IT TO MAKE SURE THERE WERE NO SIGNS OF IMPENDING FAILURE.

THINK I WILL RUN DOWN THE FITTINGS NECESSARY TO REPLACE THE IDIOT LIGHT WITH AN ACTUAL GUAGE SO I CAN SEE EXACTLY WHAT IS UP WITH THE OIL PRESSURE. THIS IS SOMETHING I HAD THOUGHT ABOUT DOING IN THE FUTURE ANYWAY AND NOW APPEARS TO BE THE TIME TO DO IT.

The rod bearings looks good, very little indication of any wear and no discoloration to suggest any problems with those. I did not pull crank, so did not get a look at main bearings.

View attachment 465975

I have no idea what holding the Glow plugs on is doing to help unless it is just the 20 seconds that it takes you to do it is allowing the crank and bearings to cool , just as they do when you said you can leave it for a few seconds and it will wind over .

YES, I DO NOT THINK IT HAS ANYTHING TO DO WITH THE GLOW PLUGS, BUT RATHER THE TIME DELAY. IT IS VERY INTERESTING THAT THE MAIN BEARINGS, WHICH CERTAINLY COULD BE THE PROBLEM IF NO HYDRAULIC ISSUES, WOULD COOL DOWN THAT FAST AFTER GETTING HOT ENOUGH TO SEIZE THE MOTOR.