Re-build KB7100

[Bill_in_MI]

I have a Kubota B7100 (gear) of the 1980's vintage. I would like to do a refurb of the whole tractor...tear down all sheet metal and repaint, new fittings and fasterners as needed, any new parts needed, etc. I am uncertain about what to do regarding the engine, however. It has a little under 2000 hours, and seems to run ok, but I am starting to see quite a bit of black smoke on start-up and under heavy load. Additionally, I am accumulating a lot of oil/crud on the engine surface that seems to "come back" soon even after cleaning.

I am reasonably good a mechanical stuff. Should I consider new seals and perhaps rings as part of a mini-refurb for the engine? I loaned it to a neighbor a couple of years ago and he brought it back with NO water in the radiator...said he couldn't keep it running for some reason. I found the radiator hose blown. Don't know what kind of damage that may of done, or if it is related to the issues described above. I have plenty of time and willingness to buy any special tools or parts to do the job myself. Suggestions welcome!

 

[jinman]

My guess is that black smoke under load is just the burning out of carbon deposits. You said that the engine has an accumulation of "<font color=blue>oil/crud</font color=blue>" that seems to accumulate. What is your oil use? For example, do you use a quart every 20 hr of operation? 100 hr? 200 hr? I'm a firm believer in not fixing something that isn't broke. If the tractor just needed cosmetic attention, that's all I'd give it. ...my two cents.

 

[Thomas]

Bill by the sounds you have a winter project.I'm not sure if you have a service manaul but it might be good idea,also once you have your list made make sure your dealer can indeed get the parts to keep you going.Depends how much you play on rebuilding the engine..more than be on the damage,for old parts against new parts can cost you extra time and money.I've done some complete tear downs on older tractor,and once you start the inventory list of goodies can really get long..know your cut of point or go all the way.Can you send photos of the start..middle..finish of your project,for it would be most interesting.

 

[HR_Mutt]

Bill
Sounds like fun! And you got a Great new barn to do it in/w3tcompact/icons/smile.gif
regards
Mutt

 

[Bill_in_MI]

Jim,
I hear you on the "if it aint broke" advice. I use the B7100 so little now that it is hard for me to measure the oil consumption, but it's not alot. But I sure would like to find the source of what's making the engine look so filthy. It never used to get "black" like it is. I guess I just like to keep the thing looking decent inside and out. I'll probably start with the extrior metal and easily replaceable stuff and see how much staying power I have for the project. Thanks.

 

[Bill_in_MI]

Thomas,
Good advice. Don't think I could start without the right manuals...shop and parts. And you are probably right about the list (and price) tending to run away from you. I'll keep a photo record of the project when (and if) I get started. Thanks!

 

[BobinCols]

Your neighbor didn't do you any favors when he used it. The motor may need no internal attention. I would clean the exterior of the engine thoroughly, make sure fluids were full, and then run engine to find exact source of your leak. Once you know exactly where the leak is coming from you can decide on course of repair. I would hate to fix the tractor up cosmetically and then have the leak continue. It might not be too hard to repair when the sheet meat is off.

 

[Kelvin]

Bill,
I pretty much have the same vintage B7100 tractor. And my 2nd tractor, a B2150 w/FEL, is almost as nice as your 2nd tractor.

I assume that the black smoke is coming out of the exhaust pipe and not the valve cover vent hose. My B7100 had obviously been overheated before I purchased it (due to lack of knowledge of its unique thermo-siphon cooling system) and I had oily smoke (blow-by) coming out of the vent tube. This smoke got worse and eventually started having oil drops come out; then pour out. After an engine breakdown, I discovered that the cylinder closest to the radiator had a compression ring that had gone bad; the other two cylinder's rings and the rest of the engine were in excellent shape.

Summary: Based upon my experience with an overheated B7100 engine, you may have blow-by that may be the source of your recurring oil/crud on the engine.

Kelvin

 

[jinman]

Bill, I don't mean to discourage you if your tractor needs repair, but it takes so darn little oil to spread around the engine and collect dirt that it might be a tiny leak that air from the engine fan is spreading outside your engine and making things look a lot worse than they are. I have to admit that I shuddered when I read that your neighbor had brought your tractor back with no coolant. That's not a good sign. I'd recommend that you look at the crankcase breather tube and around the oil filler for evidence of blow-by escaping out of the engine. Also, look closely at your valve cover gasket. Even if you are going to overhaul the engine, you might get a compression test done (or do it yourself) just so you can have a reference for compression. You will have your shop next year too, so take the time now to make sure your tractor needs the engine overhaul before starting. I say this because I have an old gasoline Ford Jubilee that has used a quart of oil every 10 hours since I bought it over 8 years ago. I put anti-foul adapters on the spark plugs and it runs great. I have to clean the blow-by residue off around the oil filler cover several times per year, but it is still a great old tractor and good for rotary cutting. I may rebuild it next year, but only because I have to break it apart to rebuild the clutch and transmission (recently started making noise).

If you do decide to tear you engine down, I know it will be an interesting project./w3tcompact/icons/cool.gif

 

[Egon]

Bill:
Have the injectors ever been cleaned or have you ever added a cleaner to your fuel ?

Egon