Kubota B7100 Overhauled now will not run

[Sanddog]

Hi All:

I recently completed an overhaul of my B7100. The tractor was not running when I bought it, so I knew there was some work ahead. I recently completed a full rebuild. When dismantling the engine, I noted the timing gears were off a bit (see pictures) and decided to line them up "correctly" according to the repair manual. I anticipated this may throw the timing off but tried to start the engine after completing the rebuild without checking timing just to see how it acted. It produced a lot of white smoke and tried to start, but that was it. I added some shims and now appear to have the timing set correctly. The tractor will now start but only runs about 3 to 5 seconds and then dies. It still produces a fair amount of smoke. I did install new Kubota fuel injectors just to make sure everything was good after the major overhaul.

Does anyone have any suggestions as to the problem? I am thinking possibly fuel pump??? I checked the diaphragm and it looks OK? Injection pump??? How can I diagnose these areas with my limited tools, expertise??

After the short run session, I noticed oil leaking from the back left (exhaust) side of the block where the steel plate mates up. (see picture) It only leaks when trying to start the tractor, no leak just sitting. I did have the block bored out and I noticed there is a plug in the side of the block near the leak, but it is not the source. Maybe there is a similar plug on the back side of the block?? It is not coming from above at the oil pressure sensor - I wish that was it. Looks like I will have to split the tractor again to get to the source but just wanted to know if anyone has any ideas based on the area of the leak??

Thanks for any help!!!

 

[Sanddog]

UPDATE

I found the oil leak. There is a missing plug in the back of the block, adjacent to the one I could see on the side at back left side. Apparently, the machine shop left this out after the completed boring the block and cleaning it up. It the same diameter as the holes used to bolt on the rear flange and I did not notice it missing either AAUUUUGGG!! Problem solved with a lot of extra work, assuming I can get a replacement from Kubota - it does not show in my parts diagram???

Back to the engine not starting. Before splitting the tractor I tried several more times to start it thinking maybe there was still air in the lines. And, I think maybe there was because it did finally start and would run for maybe 10 to 20 seconds before dying again. I did not try to many times as I wanted to figure out the oil leak first, but I did notice an interesting thing. If, after the tractor dies, I hold the glow plugs for a good 20 seconds and then try to start, the tractor roars to life and seems to run strong for may 10 to 15 seconds. If I immediately try to restart, then it may or may not start but only runs for a few seconds before dying again. If, I wait and hold the glow plug, then strong start and run???

It seem as though it needs the extra heat to no only start but to run, at least for a short time period. Is the head helping the fuel to ignite even though maybe I have poor atomization??? Could this be a week fuel injection pump??

Picture of missing oil plug, second hole up from bottom left.

 

[KYErik]

If you can test compression and that checks out good, I would assume the injector pump needs a rebuild. If you loosen the fittings on the lines to the injectors, do they spray/leak fuel?

 

[truckdiagnostics]

If it is has what I think it has, that style injection pump is bullet proof. Needing the heat from the glow plugs to run.... makes me think you might have a timing issue with the pump. My thought there is the fuel is getting injected to early in the compression stroke or way late in the power stroke when there is not heat to ignite the fuel without the heat of the glow plugs. Before I got carried away I would make sure I was not getting air in the fuel. Splice in a clear line after the lift pump so you can see it. I want to say on engines with a pre-combustion chamber poorly atomized fuel might just act this way, air getting in the lines may cause this. It has been a while but I think the Kubota in our Bobcat acted this way when we sucked in air.

 

[Sanddog]

Great, thanks for the suggestions. As soon as I get the oil plug and put this thing back together I will check for pressure on the injection lines and to see if possibly it is sucking air. I did replace the fuel line from the tank to the lift pump, but the line from the lift pump to the injection pump is still original and could be allow some air in the line. I also recall when starting to dismantle the engine I tried to remove the fuel line from the lift pump and the brass male fitting, which the hose slippers over, actually pulled out of the lift pump block. I shoved it back in, but I guess this could be allowing some air at this point. I will replace the old line with new clear line and see what that shows.

I checked the timing again this morning and it appeared to be right on the money - 25 degrees BTDC. I turned the engine over slowy by hand and the front injector port on top of the injection pump showed an indicatation of fuel rising right at the 25 degrees BTDC. Before I retimed the injection pump (after alining the timing marks on the gears), it would not start, just acted like it was out of time and blowed a lot of white smoke while spinning over.

Thanks again for the help. Hope to get back on it next weekend.

 

[Egon]

Starts and runs for a bit when using glow plugs.

Mine used to require the glow plugs to start unless the engine was fully warmed up.

Is the fuel flow to the injection pump consistent? No blockages or restrictions?

 

[truckdiagnostics]

Sanddog, air is only going to come in on the suction side By putting the clear line after the lift pump you should see if any is getting in on the suction side. Also, if yours is the same as mine there is a screw on the top of the pump, where the return line comes in from the nozzles. There is something about opening and closing that that helps with bleeding. I wonder why the timing was off to begin with? Did they do that to try and compensate for something else wrong?

 

[4570Man]

If you don't mind me asking, what did the rebuild cost? I have a similar sized Kubota diesel out of a lawn tractor. It needs a rebuild, but when I checked about 20 years ago the parts alone were going to cost 1100 dollars. The motor would work great on wood splitter or something, but it isn't worth nearly that much.

 

[Sanddog]

I am not sure how much I have in the rebuild but think I could have got a new rebuild for what I have spent. I think around 600 for overhaul kit plus another 600 for machine work and new head another 400. The machine shop missed the cracked head or I would have gone a different direction.

 

[Sanddog]

Ok, got the missing oil plug replaced and the tractor all back together. I had previously replaced the fuel line from the tank to the filter and replaced the filter. I now replaced the fuel line from the filter to the lift pump and put a clear line from the lift pump to the injection pump. I also replaced the O-rings on top of the injection pump (I don't think this had anything to do with short run time), which were seeping. After opening the fuel valve on the filter and opening the bleed plug on the injection pump, diesel flowed through the filter and lift pump and came part way up the clean line to the injection pump, where it appeared to balance with the fuel level in the tank, more or less. I spun the engine over and it pump diesel up to the bleed port. It was a little slow it seem like to me, but not sure how fast it should pump. After most of the air was out of the line, I closed the bleed port at the injection pump.

Held glow plug for a good 30 seconds it did not spin over too long before starting. As before, it ran for maybe 10 seconds and died. I held the glow plug again and this time it fired up and ran for probably 30 seconds or maybe longer. Smoke cleared up and it sounded pretty good. I did not see any bubbles in the fuel line other than a very small bubble at top of line where it enters injection pump. It continues to start fairly easily, but then wants to die after maybe 10 - 15 seconds. On one run, it seems like I was able to keep it running longer by working the throttle back and forth. It does seem to accelearate strongly and eventually all of the bubble was purged from the line. I did not see any more indication of a lack of fuel from the lift pump, but it continues to die after a short time.

It has me stumped. It seems like if the injection pump had problems that it would behave the same right after it starts and not suddenly change after 10 to 30 seconds? It certainly seems like a fuel delivery problem???? There are small pieces of rusty metal blowing out of the exhaust, as the old muffler is pretty rusty. I did install a new air filter, but just left if off today when starting to eliminate one more possibility. I took the radiator cap off afterwards, and there was just slight pressure, but signs of bubbles or anything else odd>

Any suggestions???

Thanks!