B7100 engine rebuild question.

[Jonas Smith]

I just bought a '82 B7100. My first Kubota.

I knew it had a broken connecting rod cap when I bought it. The PO stated that he had the engine scoped, and that it looked like just the rod was damaged and nothing else. Anyway i bought it and pulled the front end off so I could drop the pan, pull the head and install a new piston and rod.
Well, things are not so rosey. After getting the piston out, the crank seemed like it had some play in it. Actually it has a lot of play in it. If I grab the front of it I can move it up and down and hear it click. there is no back and forth movement though.

I talked to the Kubota dealer in town and they said undersize bearings are only available up to .04mm for this engine (D750-A) and if I can feel it knocking around, I am probably out of rebuild limits. A new crank is $1700!

Should I just scrap the engine and start looking for a good runner? Are there other size engines that will fit in its place? (D902? I see one on CL.) What should I be looking for? or is it worth it just to rebuild? Also, my injection pump has a hydraulic pump on the side for the hydrostat I believe. Do I need to find a engine with this pump, or can I mount my pump on a non-hst injection pump?

Thanks for any help.

 

[Apogee]

Hey Jonas,

I knew I recognized you from the Power Wagon forum! Welcome to the world of orange tractors!!!

Yeah, as you've already found out, the parts are gold plated.

I'd pull the crank and have it mic'd at the machine shop. You can always have the journals welded up and it re-ground to stock.

The other option would be to start watching for another 750, 850 or 950 for sale. The problem with going with the bigger engines is dumping the heat they develop. Short of that, they will all bolt right up.

Also, for reference, the cranks are the same between the three models listed above.

Stick with it, gold plated or not, you will really like the little beast once it's fixed.

Kind regards,

Steve Majerick (in Tacoma)

 

[birddogger]

Definitely mic it out. It is 0.4mm or about 0.015 inch for the undersized bearings. You can feel movement at about 0.002, clicking will start around 0.008. It might not be as bad as all that.

 

[Jonas Smith]

Will the crank out of a D902 or 905 interchange with the D750-A?

 

[Apogee]

Jonas,

I believe the cranks are the same between the 750, 850 and 950. Unfortunately, not sure about any other models. Best thing to do is to compare crank part numbers and see if they happen to match.

Good luck!

Steve

 

[hodge]

Welcome to OTT, Jonas. How is the condition of the rest of the tractor? If it is in good shape, I would say it is worth fixing. These are tough tractors, and serve a valuable purpose. If your time is flexible, hunt for the parts used, instead of paying the high prices. There has also been a running post on here about repowering with a larger engine- it is definitely doable.

 

[Rob]

hi , I had a similar descision to make with my B7100, the D750 fitted to it was starting to show its age and was in need of a major rebuild, i had a few quotes to rebuild it, also just the cost of parts to do myself, it was not cheap.
I decided to go down the donor engine route with a D850 egine, very low hours and a good clean runner.
had a few tech problem but overcame them, it was the best option for me, a bit more output and a good runner now, i'd do it again anyday.
cost wise, all in, it cost me approx a 3rd of the rebuild/recon method.

Choice is yours myfriend.

 

[Jonas Smith]

Well, It's OK. The hood is in poor condition with rust out. The tires have good tread, but are cracked and checked. It did come with a installed front end loader, a rototiller and a brush hog. I paid $2600 for it. Looking around it seems like the implements alone may be worth what I paid or close to it. What I am nervous about now is the rest of the drive train on the tractor.
Kubotas have a reputation of being tough and reliable. But this has only 1200 hrs on it and the engine is worn out. It reminds of my '01 Dodge with the cummins that blew the injection pump at 88k miles. $3000 and no help from cummins or dodge. That ended my affair with diesel pickup trucks.

This has a hydrostatic transmission and to be honest, I don't want to have to pull that apart if there's problems. I do not work on automatics beyond filters and fluid just because there seems to be some magic going on in there that I don't understand.

There are a couple of nice looking running B7100's around for $3500. Honestly, I'm contemplating buying one and transfewrring the implements over to it, and keeping this sick one around for a parts tractor.

 

[Rob]

I have both versions a mid production B7100 DP and a mid prod HST ,i prefer the manual version anyday.
Be very carefull about swapping parts between the hst and manual versions, their are a heck of a lot of parts that are differnt and wont fit if swapping either way, trust me i have been their and found out at my cost.

The hst is longer and has a wider tranmisson tunnel to start with, so lots of manual parts wont fit straight off, and lots of other parts .

maybe just sell the hst ,keep the implements and get a nice manual version , thats what i'd do..

rob

 

[Jonas Smith]

I hear you. One of the 7100's is a HST, the other is a manual. I am leaning toward the HST because it has under 1000 hours on it, and is a couple hundred miles closer, and I have a parts tractor.
It would be cheaper to rebuild this engine, but it would really suck to spend the money, bolt it up and have the hydrostat be junk.

I wonder though, if the subframe for the loader on the junk 7100HST '82 vintage, will fit on the 7100HST of '96 vintage? Something tells me with my luck, they would be different.

 

[Rob]

just been looking at the chassis spec on the HST's, you'd be ok if you were fitting the FEL subframe etc between hst's the chassis has not changed much as far as loader fitment is concerned, it must be your lucky day.. probably one of the few areas that are the same, well between HST's that is.

 

[Jonas Smith]

Funny Rob, I also own a Ducati. A 900SS/CR. Absolutely love the bike! I am in a strange place when going on group rides though. The Ducati folks tend to look down their nose at me because well... carbs (GASP!) and the other riders think I'm just another Ducati snob.

 

[RS16017]

Will a Kubota 902 engine bolt into a B7100 with the 750 engine?