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.

 

[Sanddog]

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.

WILL CHECK POSITION OF LEVER, I THINK AM PRETTY SURE IT WAS IN THE CENTER (NEUTRAL) POSITION AND THE THREE-POINT ARMS ARE DOWN. if I UNDERSTAND THE OPERATION OF THE SYSTEM, JUST NOW CHECKING THE MANUAL, IN THE NEUTRAL POSITION THE HYDRAULICS ARE TO HOLD THE CURRENT POSITION. I WOULD THINK IF THE THREE-POINT IS DOWN THAT WOULD HAVE THE PRESSURE OFF THE SYSTEM, BUT MAYBE IT IS SOMEHOW TRYING TO PUSH THE ARMS DOWN. I WILL WORK WITH THIS TO SEE IF I CAN IMPROVE THE SITUATION.

 

[Sanddog]

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

YES, HAVE REMOVED FUEL TANK AND CLEAN IT, REPLACED FUEL FILTER, AND ALL FUEL LINES. FUEL IS GETTING TO THE INJECTION PUMP AND SEEMS TO INJECTING WITHOUT PROBLEM. THE MOTOR IS DEFINITELY COMING UNDER SOME SORT OF RESISTANCE THAT IS CAUSING IT TO DIE.

 

[Eagleview]

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.

You only have 1.5 - 2 thou bearing clearance , it wouldn't take much for the bearings to swell that much and get tight on the crank . It also wouldn't take long for that heat to dissipate from the bearings and into the engine block as they are a tight fit in the block .

Take the timing cover off and get someone to crank the engine over , I will bet money oil squirts out of the end of the cam as that plug is obviously loose .

Kubota 71 camshaft oil plug fix - YouTube

 

[bigdeano]

If you take the engine apart be sure to check the piston to bore clearance. Different piston alloys require different clearances. Maybe the machine shop got it wrong. The time involved seems about right for the pistons to heat up and drag. I had this happen with a car engine.

 

[D2Cat]

In your very first paragraph you tell how you "correctly" set the timing and added shims. I believe therein is your problem. On that engine the timing is set by the shims at the IP. The gears you lined up the dots on have to rotate several times to get them to line up. It's not, line up the dots and go.

Did you purchase your head from Kubota or aftermarket? That extra thin shim that came with the head gasket is for heads that have been milled off, and that shim gets that back to original height.

 

[Sanddog]

If you take the engine apart be sure to check the piston to bore clearance. Different piston alloys require different clearances. Maybe the machine shop got it wrong. The time involved seems about right for the pistons to heat up and drag. I had this happen with a car engine.

I described what is happening to the guys at the machine shop and they agree it sounds like the motor is trying seize up as soon as some heat gets generated. They have asked me to bring it back and they will recheck all clearances. Which is nice, but now I have to take it all apart again, bummer!!

 

[Sanddog]

In your very first paragraph you tell how you "correctly" set the timing and added shims. I believe therein is your problem. On that engine the timing is set by the shims at the IP. The gears you lined up the dots on have to rotate several times to get them to line up. It's not, line up the dots and go.

Did you purchase your head from Kubota or aftermarket? That extra thin shim that came with the head gasket is for heads that have been milled off, and that shim gets that back to original height.

When I took the engine down, I rotated it what seemed like 10 to 15 times but the dotes on the the timing gears never did line up exactly. It seemed like the closest they ever got is what I show in the first post. You say is it not just "line up the dots and go." I tried to follow the manual, but did not read anything other than to line up the dots per the picture in the manual. HOW IS THIS DONE CORRECTLY??? EXACTLY WHAT DO YOU DO? IS THERE SOME OTHER MARK, POSITION OF PISTON, ETC. THAT IS ALSO USED TO SET IT UP CORRECTLY?? THANKS FOR ANY HELP ON THIS.

The head is an aftermarket head. The machine shop had to clean up the seats to get it to hold a vacuum but otherwise it seemed to be OK. After rechecking the ring gap, I did add the thin metal shim and gave the intake valves a little extra clearance but as you have pointed out, the gears are off. I set the valve clearance at TDC on the compression stoke as specified in the manual. I watched the values as I turned the motor over by hand and the intake values are opening before TCD on the intake stroke. So, back to how to correctly install and align the gears?????

 

[Sanddog]

UPDATE

took the motor back down and returned it to machine shop. Based on the fact that it appeared to be seizing up after running a short time the guys at the machine shop said it sounded like the pistons, but after rechecking all of the tolerances on pistons, crank, etc. neither they nor I could find anything to explain the motor apparently seizing. The guy at the machine shop said to look down the line to see if anything is causing back pressure on the engine.

Before taking the engine down, I did remove the lines from the hydraulic pump to see if that was the problem, but could not tell any difference. I guess the input shaft going to the HST trans could be causing problems but I did keep the clutch depressed. I do recall the engine slowing down a bit when I let out the clutch, but did not seem to be sufficient to cause seizing of motor.

I had mentioned earlier a concern over the oil pressure, but do not think that is a problem. Upon disassembly, I found all bearing surface wet with oil. When the machine shop could not find any problems I began checking all oil passages and found they had placed the missing oil galley plug back in the wrong hole. It was blocking the port for the oil pressure sensor, thus the reading of no oil pressure I had just before tearing this thing down.

DOES ANYONE HAVE ANY SUGGESTIONS AS TO THINGS TO CHECK BEFORE PUTTING IT BACK TOGETHER AGAIN???

 

[bigdeano]

Can you turn the hydraulic pump by hand? Doesn't seem likely it would be seizing up though.

Did they tell you how much clearance the pistons have? I wonder if the pistons are hypereutectic alloy or not.

This is like a murder mystery on tv. Probably no fun for you though.

 

[Sanddog]

Can you turn the hydraulic pump by hand? Doesn't seem likely it would be seizing up though.
YES AS I RECALL, THERE IS NO RESISTANCE WHEN LINE DISCONNECTED. NOT SURE WHAT IS HAPPENING WHEN EVERYTHING IS CONNECTED.

Did they tell you how much clearance the pistons have? I wonder if the pistons are hypereutectic alloy or not.

THE MANUAL CALLS FOR ABOUT 0.003 INCH AND THERE IS 0.003 TO 0.004 ON EACH CYLINDER. I HAVE NO IDEA WHAT EXACTLY THE PISTON ARE MADE OF AND I BOUGHT THE OVERHAUL KIT FROM KUMAR BROHERS ONLINE. THE PISTONS LOOK FINE AND FIT WELL IN THE CYLINDERS. I GUESS THEY COULD BE REALLY EXPANDING BUT THE MACHINE SHOP GUYS DID NOT THIS WAS THE PROBLEM AFTER EXAMINING THE PISTONS WITH ME HAVING RUN THE THING QUITE A FEW SHORT CYCLES UNTIL IT DIED. THERE IS NO OBVIOUS VISIBLE SIGN ON THE PISTONS AND ANY OF THE BEARING SURFACES THAT THE MOTOR WAS ACTUALLY SEIZING.

This is like a murder mystery on tv. Probably no fun for you though.

THE FUN HAS DEFINITELY GONE OUT OF THIS PROJECT!! HOWEVER, I AM VERY CURIOUS TO FIND OUT WHAT IS CAUSING THE PROBLEM, SO I AM NOT GIVING UP ON FIXING THIS THING.