B7100 with a slight mechanical issue.

B7100 D950 swap with alternator upgrade and partial restoration.

Hello everyone, I'm new to the forum. I have recently purchased a very well used and mechanically abused B7100 4WD with a front end loader. Before I start asking a ton of questions about the issues this tractor has I thought it would be a good idea to introduce myself and what I have learned about the B7100 since l acquired it on Saturday 10/18/2014 and brought it home.

My name is Steve and I live in Estill Springs Tn. I spend most of my free time tinkering around with old cars here and there. My mechanical skills are above shade tree but below professional status. I built my first house in early 2007 and of course that's when I bought my very first Kubota. The first Kubota I bought and still have is a G6200HST. This machine is hands down the absolute best lawn mower I have ever owned. It had 843 hours when I bought it and currently has just over 1300 hours now and still runs as good as it did the day I got it.

So, on with the new toy.
I've had the B7100 for about 6 days now and this is what i know about it.

It has the d750 3 cylinder and it has the flu. I bought the tractor knowing first hand that the engine would most likely need a complete rebuild but now I'm not so certain a rebuild is needed. The engine fires right up cold or at normal operating temp. However the problem I have is heavy white smoke when the engine is cold but after running for 15 minutes or more the smoke is less but not gone and its making a knocking sound that it shouldn't be doing.

The knocking sound is from the top end so i removed the valve cover to inspect. All valves are moving freely and the rockers feel fine but I'll check with a feeler guage anyway, nothing binding up there that I can see for now.

The middle injector is leaking, not too bad but bad enough to make me believe that all 3 injectors need to be rebuilt and are most likely causing the heavy smoke and i am currently working on getting them removed.

There's hardly any blow-by and I mean very minimal. I did turn the engine over with the valve cover off kind of expecting smoke to come up through the valves or crankcase but to my surprise there was none, nothing at all.

When I get the injectors out I will do a compression test on all 3 cylinders to rule out worn rings and of course a cracked head/head gasket.

Am I kind of heading in the right direction thinking that the injectors are my problem?

The hour meter reads 804 and it does work as I have run it long enough to check out the front end loader, gears, 4WD and rear hydraulics and everything works fine.

kubotasam said:

That looks like a nice tractor. I have two just like it. You will be impressed how much work they will do. Yes. I would definitely have the injectors tested. A defective injector can cause the knocking sound you are describing.

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Thanks, out of the 6 B series I've looked at in the past month only this one had straight sheet metal all the way around. Only 5 small dime size dents were all I could find. Aside from a lot of scratches, torn up seat, faded paint and some minor surface rust all over i think it has survived the elements well over the years. The overall condition plus having a front loader was the main reason I chose this one over the ones I looked at that were beat to crap.

North Idaho Wolfman said:

Second the injectors being the issue!

Go to Kubotabooks.com and download the service manual (three parts), great info in there.

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Thanks for the link. I'll check that out this evening. I did order a service manual and even found a manual for the front loader, should have them by the end of the week.

I am soaking the injectors with PB blaster for the time being. They are really stuck in there and I don't want to mess anything up.

ShaunRH said:

IF that hobbs meter isn't broken and you really have 804 hours on it, it's still a baby and I would seriously doubt compression problems unless it's been completely ignored mechanically.

Put this way, if it were a car it would only have around 30,000 miles on it.

I would verify meter operation, check common wear points against what should be expected at around 804 hours and if they line up, I'd trust the meter. Then you'd know to start looking at 'lack of run time' issues with the vehicle.

White smoke is usually unburned fuel so I agree with the injector (or injector line) diagnosis. It could be water getting into the chamber as well but you can check that with run time and a water level test. It might also be contamination in the fuel so make sure that is not happening.

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Thanks, I do know for certain that the hour meter is working as it now reads 807. Is it the original hour meter ? Who knows I sure couldn't positively say it is or isn't but the overall condition of the unit is very good and I would hope the meter is original to the tractor.

The diesel fuel in the tank did smell kind of odd now that you mentioned it. I will drain the tank, clean it and put new fuel in before I run it again. I use off road diesel in my G6200 and have for years so the B7100 will get the same.

First I'd like to say thanks to those who have replied.

I really had high hopes of my issue being a bad injector. I did a compression test and the results are not good at all. I'll start with the injectors because I know for sure the #2 injector is sticking/leaking because that cylinder had a lot of wet fuel sitting around the glow plug. Cylinder #3 was the same way only not as bad. Cylinder #1 was bone dry.

All 3 injectors were filthy with #2 being the absolute worst one. Now onto the compression test results.

#1) 240
#2) 210
#3) 200

After a valve adjustment.

#1) 290
#2) 220
#3) 240

I don't see how this thing is even running at all and it even fires right up. I bought the B7100 knowing that it could possibly need a rebuild but I sure had my fingers crossed that it would be the injectors.

I am going to drop off the injectors tomorrow and see if they can be rebuilt.

Just a quick update and a sigh of relief. The compression test I did last night was incorrect and it was completely my fault. Its kind of embarrassing to mention what I did but I'm going to anyway.

I dropped off the injectors at our local diesel shop. The guy will call me when he finds out the condition of the injectors. I told him if they are rebuildable to go ahead and do the job and I left.

While at work today I called a Kubota dealer and ordered a new head gasket and shim, new valve cover gasket, 12 copper crush washers and a new cable for the decompression control. Parts should be here mid next week.

Now back to the compression test results. Its kind of hard to get accurate readings with the intake completely blocked off wouldn't you think?.

Well as I was preparing to clean up around the engine so I could pull the head off this evening there it was hiding in the intake manifold, a rag that I had stuffed in the intake and taped up to prevent any debris from getting in there while I removed the side panel that was full of junk.

So I thought I'd do one more compression test just to see if the numbers would change after I removed the rag i had stuffed in there. And here are the results,

#1) 400
#2) 390
#3). 395

Going to cover the engine, wait for my injectors to be rebuilt and just clean up the tractor in the mean time. Old fuel is drained and the tank looks clean so I'm not going to take it off.

I had a bad feeling something was wrong internally and its not good. I installed the rebuilt injectors this afternoon, bled the lines and fired up the engine. It was running about the same as before and the knock or light tapping I could hear was still present.

So long story short I pulled everything apart again and removed the cylinder head. What I found was not good but I kind of expected something was amiss in there.

# 1 cylinder is OK.
# 3 cylinder is OK.

Cylinder head looks very good, kind of dirty but I can't find any traces of cracks between valves on any cylinder. Push rods are perfect, no sticky valves and none seem to be bent and they operate smoothly.

Now # 2 cylinder is where I believe the problem is. I think this is called piston slap. The piston is actually hitting the cylinder head. This would be the tap I hear and not an injector as I hoped it would be.

While I was cleaning up the piston top on cylinder # 2 it moved down, not by much but enough for me to notice though. The oil pan is coming off and there's no way around it.

No, crank did not move, only the piston moved down.

Pistons are tight in the cylinders so its got to be the rod bearing.

Its going to take some time to get the oil pan off as I need to remove the front axle assembly in order to drop the oil pan, this should be interesting.

The tractor is up on jack stands for now. I think the oil pan can be removed without taking the front loader and sub frame off. My service manual is not here yet and I don't know if there are hidden pan bolts at the front of the engine.

Even if I did remove the front loader it wouldn't help getting at the front pan bolts as they are hidden by a steel plate surrounding the engine.

I hope the engine does NOT need to be removed to get the oil pan off or is that why the front loader needs to be removed so the front sub frame can be removed as well?

Oh I need my service manual.............................