B7100 HST Low power. Cause?

[998cc]

A little history. My dad loved gardening and used a TroyBilt roto-tiller until he just couldn't manage it anymore. He then bought a B7100HST package from a rental yard; it included a front loader, box scraper, FL850 rotary tiller and RCR48 mower attachment. The B7100HST had been neglected/abused during its rental life and needed a complete engine rebuild. Dad was a very competent mechanic and happily took it on. I was involved with the rebuild and know he installed new sleeves, pistons, rings bearings, etc. The machine work was done by Del's machine shop in Sacramento. He likely put about 200-300 hours on the tractor after the rebuild.

Fast forward. I inherited the 7100 and attachments in 2013 and have been using mostly for maintaining a road on my property. It seemed to be suffering from low power in both high and low range but was adequate for the road work and roto-tilling. This week, I decided to service the mowing attachment and put it to use; the mower is in pretty good mechanical condition only requiring a little work on the wheel adjusters and all around lube. Problem: The tractor can barely spin up the mower on high PTO speed; trying to move forward will slow it down considerably. It is usable on low PTO speed as long as the grass in no more than about 8 inches tall and using a very slow forward speed. I assume this is not normal. Otherwise, the engine starts easily and runs well, and the fuel is new. Any thoughts on a possible cause/solution?

Thanks folks.

 

[ptsg]

Does the engine bog down as well? Or the mower just slows down along with the drive speed?

If the engine bogs down, then it could be fuel related. If not, then it could be the clutch slipping. Even though it's an HST, it still has a dry clutch to engage and disengage the PTO, however, the input shaft that powers the PTO, also powers the HST, so if the clutch splits, it will affect both PTO and drive.

There is a Workshop manual of this site if you don't have one already. It may help you some. Here is the link: Index of Kubotabooks/Tractor Owners Manuals/

 

[rScotty]

About every one of those older Bs and compact tractors from that era need that cleanable trans/hydraulic screen cleaned in the transmission case, and also a new fuel filter.
Both of those filters need frequent replacement and both will cause it to slow down. The symptom will be that it will start and runs OK at low rpm, but when you try to get up and go - or use more power - or go uphill ..... it will just bog down.

I think that model had a cleanable filter in the transmission. Take a look at the service manual, and if so, be sure to take it out and clean the screen so that your HST doesn't starve for fluid. Taking out the screen will dump all the trans/hydraulic oil so when you do it, replace the spin-on filter as well if it has one... and I think it does. Since the oil is lost, replace that as well with new good quality trans/hydraulic oil yes, that oil is expensive. so be prepared.

BTW, good trans/hydraulic oil is clear. If yours is looking murky or milky it has water contamination - very common in that model. If so, that's another reason to clean the screen filter.

And while you are doing filters, do the fuel filter as well. It's the other thing that will cause your tractorto start and run ok at low rpm as I said....but bog when you advance the throttle.
good luck,
rScotty

 

[998cc]

About every one of those older Bs and compact tractors from that era need that cleanable trans/hydraulic screen cleaned in the transmission case, and also a new fuel filter.
Both of those filters need frequent replacement and both will cause it to slow down. The symptom will be that it will start and runs OK at low rpm, but when you try to get up and go - or use more power - or go uphill ..... it will just bog down.

I think that model had a cleanable filter in the transmission. Take a look at the service manual, and if so, be sure to take it out and clean the screen so that your HST doesn't starve for fluid. Taking out the screen will dump all the trans/hydraulic oil so when you do it, replace the spin-on filter as well if it has one... and I think it does. Since the oil is lost, replace that as well with new good quality trans/hydraulic oil yes, that oil is expensive. so be prepared.

BTW, good trans/hydraulic oil is clear. If yours is looking murky or milky it has water contamination - very common in that model. If so, that's another reason to clean the screen filter.

And while you are doing filters, do the fuel filter as well. It's the other thing that will cause your tractorto start and run ok at low rpm as I said....but bog when you advance the throttle.
good luck,
rScotty

rScotty. That describes the problem pretty well. Bogging down when going uphill is a symptom. I do have the manual for the tractor and will look into it tonight.
Best regards.

 

[998cc]

Does the engine bog down as well? Or the mower just slows down along with the drive speed?

If the engine bogs down, then it could be fuel related. If not, then it could be the clutch slipping. Even though it's an HST, it still has a dry clutch to engage and disengage the PTO, however, the input shaft that powers the PTO, also powers the HST, so if the clutch splits, it will affect both PTO and drive.

There is a Workshop manual of this site if you don't have one already. It may help you some. Here is the link: Index of Kubotabooks/Tractor Owners Manuals/

I agree that fuel may be an issue. Replacing the fuel filter this week. Clutch is not slipping as far as I can tell. It just bogs down (speed and mower jointly). I do have the manual for it.
Best regards.

 

[rScotty]

rScotty. That describes the problem pretty well. Bogging down when going uphill is a symptom. I do have the manual for the tractor and will look into it tonight.
Best regards.

I checked at the online parts using Messick's excellent website:
Messicks | Your home for New Holland, Case IH, Kubota & More.... I order all my parts from them.

Yes, the B7100 HST has both a cleanable screen (below) and a spin on disposable can type filter for the oil in the common sump used by the tractor's hydraulics and HST transmission. Replacing the spin on and cleaning the other will involve new oil there. (UDT or SUDT type)

You also have a replaceable fuel filter. Replacing that will require bleeding the fuel system - which can be frustrating the first time you do it and is simple the second time around. But messy both times.

Those are most likely to be the cause of your problems. But even if they are not, any mechanic is going to require replacing them before looking deeper.
rScotty

 

[998cc]

I checked at the online parts using Messick's excellent website:
Messicks | Your home for New Holland, Case IH, Kubota & More.... I order all my parts from them.

Yes, the B7100 HST has both a cleanable screen (below) and a spin on disposable can type filter for the oil in the common sump used by the tractor's hydraulics and HST transmission. Replacing the spin on and cleaning the other will involve new oil there. (UDT or SUDT type)

You also have a replaceable fuel filter. Replacing that will require bleeding the fuel system - which can be frustrating the first time you do it and is simple the second time around. But messy both times.

Those are most likely to be the cause of your problems. But even if they are not, any mechanic is going to require replacing them before looking deeper.
rScotty

View attachment 737374

I never knew there was a replaceable filter under that cover! Messicks was very helpful. I ordered all of the filters, o-rings and 4 gals of genuine Kubota Super UDT oil. If the problem is in the filter/screens, this should fix it. No worries bleeding the fuel system; between my old Ford 4000 diesel tractor and this Kubota, I have done it many times since the 1970's. 998cc

 

[998cc]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

 

[Jerry/MT]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

Check your fuel flow at the outlet from the fuel filter. Or better yet at the inlet to the injector pump (IP). It should gush out. If it dribbles or is intermittent, there are other areas that can restrict the fuel flow rather than just the fuel filter. The tank outlet, the line from the tank to the filter, the filter head passages, line to the IP. Line could be pinched, etc. If this is an older tractor then I would suspect the tank has crud in it. Some of these tanks have a screen at the outlet that can be clogged.

 

[SDT]

First off, thank you all for your advice.

I cleaned the screens and reinstalled with new O-rings. (The large screen was coated with gunk while the smaller one was fairly clean.) Installed a new Kubota Hydraulic oil filter and a Kubota fuel filter then new Super UDT2 oil. The old oil was murky and needed to be changed. After a few short runs and topping off the hydraulic oil in between runs, the oil level is now normal. No leaks.

The test:
The tractor has a little more pep than before; however, it still lacks enough power use the mower on high PTO. The mower is a little better on low PTO than before.
I was hoping for a better outcome but do have a higher comfort level in the tractor knowing the work has been done. It was well worth doing.

Thanks.
998cc

Assuming that you have serviced/replaced the air filter, sounds like a compression test is in order.

SDT

 

[LouNY]

I'm wondering if you may be expecting a bit much from that tractor;
16 engine hp, 13 hp on the pto.

 

[rScotty]

Check your fuel flow at the outlet from the fuel filter. Or better yet at the inlet to the injector pump (IP). It should gush out. If it dribbles or is intermittent, there are other areas that can restrict the fuel flow rather than just the fuel filter. The tank outlet, the line from the tank to the filter, the filter head passages, line to the IP. Line could be pinched, etc. If this is an older tractor then I would suspect the tank has crud in it. Some of these tanks have a screen at the outlet that can be clogged.

I would agree with that. Just replacing the filter isn't enough. Just as you say, what is needed is a steady flow to the inlet of the injector pump. It's surprising how many times there is an obstruction somewhere other than the filter. But if there is good steady flow at the injector pump then all is correct.

And it's an easy check to make. With any luck you can loosen that connection at the pump, check that the flow is strong, and then remake the connection all without needing to purge air from the lines again.

About all that I can add is to check the valve clearance. You know how to do that, and the clearance amount isn't critical as long as itis close and as long as there is some clearance there.

And if that is the case, then comes the decision.... do I use it as is? It won't hurt to do so. Or do I go another step deeper? The next step is also not too difficult and is non-invasive. It is to remove the injectors and check that they are spraying properly. While they are out, you can also do a compression test. Then you can bolt it back up and use it....but at least knowing that all the diagnostics are in place.
rScotty

 

[998cc]

I would agree with that. Just replacing the filter isn't enough. Just as you say, what is needed is a steady flow to the inlet of the injector pump. It's surprising how many times there is an obstruction somewhere other than the filter. But if there is good steady flow at the injector pump then all is correct.

And it's an easy check to make. With any luck you can loosen that connection at the pump, check that the flow is strong, and then remake the connection all without needing to purge air from the lines again.

About all that I can add is to check the valve clearance. You know how to do that, and the clearance amount isn't critical as long as itis close and as long as there is some clearance there.

And if that is the case, then comes the decision.... do I use it as is? It won't hurt to do so. Or do I go another step deeper? The next step is also not too difficult and is non-invasive. It is to remove the injectors and check that they are spraying properly. While they are out, you can also do a compression test. Then you can bolt it back up and use it....but at least knowing that all the diagnostics are in place.
rScotty

rScotty.
I did replace the air filter prior to testing and will check valve clearances and do compression tests. Will check fuel flow at the injector pump. It also struck me that my dad could have erred in setting the valve timing--a tooth off? Is it possible to set the injector pump slightly out of time? The engine revs up slowly like an engine with a large flywheel; is this normal? I suppose the engine could be theoretically too small to spin up the mower deck.

Edit: The fuel tank became brittle and cracked a few years back. It has been replaced with a 1-1/2 gallon aluminum fuel cell. The fuel lines are fairly large.

Thanks.
998cc

 

[rScotty]

rScotty.
I did replace the air filter prior to testing and will check valve clearances and do compression tests. Will check fuel flow at the injector pump. It also struck me that my dad could have erred in setting the valve timing--a tooth off? Is it possible to set the injector pump slightly out of time? The engine revs up slowly like an engine with a large flywheel; is this normal? I suppose the engine could be theoretically too small to spin up the mower deck.

Edit: The fuel tank became brittle and cracked a few years back. It has been replaced with a 1-1/2 gallon aluminum fuel cell. The fuel lines are fairly large.

Thanks.
998cc

I think you meant fuel - not air - filter. Check the fuel flow first. It's easy. Yes, all that is possible, but I'm assuming that a mechanic as good as he seems to have been would get the basics correct. And he sounds like he was very knowledgeable about it. And if he had made a mistake, it would have been easier for him to figure out and remedy long before he put severl hundred hours on it.
But he might have. Or he might have known what he did wrong and just decided that being old he would just use it in low gear & fix it "sometime". Of those possibilities the fuel pump is the most common to mess up and is also the easiest to take off. Plus there is a guy here on TBN who rebuilds them. It takes specific tools and a master's touch so we can always do that. Lets keep that in the back of our mind while doing all the simple things first.

BTW, the accessories seem sized correctly. In fact, they are made for that very tractor. An RCR48 mower is 48" Perfect.

Now that's interesting about the revving.. No, in neutral they don't rev like a dirt bike - or even like a car - but they are not slow to respond as you are describing unless spinning a load on the PTO. Without a load on the PTO the engine itself revs quite quickly in fact. Hmmm. I am surprised that plastic tank failed. One of the reasons for the plastic tank is that some sorts of metal - and aluminum is one - can react with the water condensate in diesel fuel and grow a kind of metal and bacterial goo that plugs things up. I wish he had used steel or gotten a replacement plastic tank. They are usually very good.

It still sounds like fuel starvation to me. I think that is where we will find it. Not only does fuel starvation fit all the problems, but it is something that is so common when a tractor sits unused for a few years. Add an aluminum tank and some high humidity and the problem could be anywhere from the fuel tank to the shape of the spray that the injectors actually spit into the cylinder. Injectors do get fouled and it could be that as well.

I still agree with your dad - that model is a classic. An inspired design from a age known for such. Well worth the effort to get it back to right. He did all the hard work.

So check the flow is good into the pump. It should flow freely from the tank. And maybe loosen the connections at each injector and see if you can make a fine mess of things there with pulsating diesel dripping all over the place. That would be a good sign. Pulling the injectors would be next. You can try with hand tools but don't force them. It is worth while to rent or purchase an inexpensive injector puller.

And give some thought to that tank and fittings.

Good luck beats good planning,

It's about time to put the battey back into the family Commando & see if it still wants to snort.
rScotty

 

[rScotty]

I was reading through the PARTS/REPAIR forum today and saw the companion thread:

"1710 engine stalls, I really need your assistance"

Yep, you guess it. Fuel starvation.
Same problem I had last year on our JD. But luckily I recognized the first symptom.... which is it wouldn't get up to anywhere close to normal speed in high gear when going up a slight incline. From there it just got worse. It still started and ran fine in lower gears if I didn't ask for more than half throttle.

 

[998cc]

I think you meant fuel - not air - filter. Check the fuel flow first. It's easy. Yes, all that is possible, but I'm assuming that a mechanic as good as he seems to have been would get the basics correct. And he sounds like he was very knowledgeable about it. And if he had made a mistake, it would have been easier for him to figure out and remedy long before he put severl hundred hours on it.
But he might have. Or he might have known what he did wrong and just decided that being old he would just use it in low gear & fix it "sometime". Of those possibilities the fuel pump is the most common to mess up and is also the easiest to take off. Plus there is a guy here on TBN who rebuilds them. It takes specific tools and a master's touch so we can always do that. Lets keep that in the back of our mind while doing all the simple things first.

BTW, the accessories seem sized correctly. In fact, they are made for that very tractor. An RCR48 mower is 48" Perfect.

Now that's interesting about the revving.. No, in neutral they don't rev like a dirt bike - or even like a car - but they are not slow to respond as you are describing unless spinning a load on the PTO. Without a load on the PTO the engine itself revs quite quickly in fact. Hmmm. I am surprised that plastic tank failed. One of the reasons for the plastic tank is that some sorts of metal - and aluminum is one - can react with the water condensate in diesel fuel and grow a kind of metal and bacterial goo that plugs things up. I wish he had used steel or gotten a replacement plastic tank. They are usually very good.

It still sounds like fuel starvation to me. I think that is where we will find it. Not only does fuel starvation fit all the problems, but it is something that is so common when a tractor sits unused for a few years. Add an aluminum tank and some high humidity and the problem could be anywhere from the fuel tank to the shape of the spray that the injectors actually spit into the cylinder. Injectors do get fouled and it could be that as well.

I still agree with your dad - that model is a classic. An inspired design from a age known for such. Well worth the effort to get it back to right. He did all the hard work.

So check the flow is good into the pump. It should flow freely from the tank. And maybe loosen the connections at each injector and see if you can make a fine mess of things there with pulsating diesel dripping all over the place. That would be a good sign. Pulling the injectors would be next. You can try with hand tools but don't force them. It is worth while to rent or purchase an inexpensive injector puller.

And give some thought to that tank and fittings.

Good luck beats good planning,

It's about time to put the battey back into the family Commando & see if it still wants to snort.
rScotty

rScotty. Good thoughts on all of this--thank you. I actually changed out all filters prior to testing. When I replaced the fuel tank, there were no original replacements or aftermarket substitutes to be had. The new tank is coated on the inside--perhaps powder coated? The cap is wide and all internal areas are easily viewable, so any internal problems will be easily noticed.

Busy with other things this week, so will wait a week or so to check into the fuel supply and check valve lash. Though I have bled the injectors a few times on the Kubota and on my old Ford many times, I've never tested injectors and don't know the procedure.

*** When you put the battery in the old Commando, there are two urgent upgrades that need to be done if it is to be ridden:
1. Replace the inner layshaft bearing in the transmission. The original bearing, made in Portugal, is prone to failure in the Norton box and can result in an accident or internal damage as you can imagine.
2. Install an aftermarket safety spring on the rear brake foot lever. These are cheap and can be installed in an hour or less. Without it, if the brake cable fails, the long brake lever will drop and dig into the roadway and likely cause an accident. In the 80's, a rider in our club was thrown from his bike as result of this scenario.
998cc

Full-size photo of my toys. I had a 750 Commando in the 90's and regrettably sold it. Found this 850 in 2018. I've had the Vincent for 43 years.

 

[rScotty]

rScotty. Good thoughts on all of this--thank you. I actually changed out all filters prior to testing. When I replaced the fuel tank, there were no original replacements or aftermarket substitutes to be had. The new tank is coated on the inside--perhaps powder coated? The cap is wide and all internal areas are easily viewable, so any internal problems will be easily noticed.

Busy with other things this week, so will wait a week or so to check into the fuel supply and check valve lash. Though I have bled the injectors a few times on the Kubota and on my old Ford many times, I've never tested injectors and don't know the procedure.

*** When you put the battery in the old Commando, there are two urgent upgrades that need to be done if it is to be ridden:
1. Replace the inner layshaft bearing in the transmission. The original bearing, made in Portugal, is prone to failure in the Norton box and can result in an accident or internal damage as you can imagine.
2. Install an aftermarket safety spring on the rear brake foot lever. These are cheap and can be installed in an hour or less. Without it, if the brake cable fails, the long brake lever will drop and dig into the roadway and likely cause an accident. In the 80's, a rider in our club was thrown from his bike as result of this scenario.
998cc

Full-size photo of my toys. I had a 750 Commando in the 90's and regrettably sold it. Found this 850 in 2018. I've had the Vincent for 43 years.View attachment 738793

Glad to hear that the tank is coated. That ought to do it. I've never tested injectors, but seen it done. Mounted to spray onto a piece of cardboard. You might as well do that if checking compression. Use safety first with high pressure fuel spray.
There just isn't any reason for it to be down on compression with a rebuild as you describe - but it couldn't hurt to check and it is bound to be interesting. That B7100 was the beginning of an era, what an interesting old tractor. And look where we are now.

Injectors are a lot like spark plugs, I think. They are the type of part that we used to tend to them annually - and now I have cars that have never had a plug change.

Good grief.... a Vincent. Astounding. From before my time, I'm afraid. I've never even seen but one. No, make that two. A friend stopped by a few years ago to show me his Vincent powered Indian. Maybe the cleanest conversion job I've ever seen.

I probably changed that layshaft bearing on the '76. I seem to recall doing so back in the early 1980s....or was it the ' 70s? Whenever the Norton Owners Club wrote an article about it I think. I've had the bike so long now I forget. Will definitely take a look at the rear brake. Thanks for the warning. Although mine being an 850 ES (electric start & kick start) with the reversed side shifter so may be different.
It is a a blessed bike. with 12K miles and just now finally a few little things needing attention - speedo cable & battery for instance..... But engine & transmission & electrics still as new. Actually everything is....dusty but original. Basically it gets ridden around the local area a few times a year for over 40 years now with only routine maintenance.

Unfortunately I haven't ridden in 2 years now. Getting older....it's time to move on.
rScotty