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Kubota B7800 HST correct operating RPM speed

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bhaxel
Join Date: Nov 2010
Posts: 17 Lovingston, VA
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2010-11-19          175242


I recently got a B7800 which has a hydrostatic transmission and I am wondering about something the previous owner told me. He said that running the engine slowly when going slow causes a lot of wear and to always have the engine speed above 2000 RPM. I've never opererated one of these before and I'd like to hear what some of you more experienced folks know on this subject. I thought it would be covered in the owner's manual, but it really isn't. The only clues are that the specification for "rated" engine speed is 2600 RPM and that to get the standard 540 PTO RPM the engine needs to be at 2600. Do I need to be running the engine at 2600 RPM regardless of ground speed? Thanks in advance...

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AbbasChild
Join Date: Aug 2009
Posts: 72 Western Pennsylvania
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2010-11-19          175245


I own a NH T2210 (31hp) with HST transmission. My experience is limited only to the 120 hours I have on the machine. Although as I spend more time doing things, I find that I am usually operating it around 2000-2200 rpms. That is only just listening to the engine to hear if it strains or bogs down as I climb a hill with a load of manure. Brush hogging I will push it to the recommended rpms for the 540@ the PTO. Using the FEL to move gravel and sand usually the same thing--in low gear range. I have 3-gear ranges--Low, Middle and High--I am really, if ever in the high range--too many hills!

Hope this helps. I am interested in what others would have to add, too. ....

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AbbasChild
Join Date: Aug 2009
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2010-11-19          175246


Oh yeah, if I am just heading back to the shop-garage for the day's end, and I am on the flatter spots I will drop the engine speed down to around 1700rpms.
....

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kthompson
Join Date: Oct 2005
Posts: 5242 South Carolina
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2010-11-19          175250


No expect here but have about same size with HST also. My use has been in about same range as AbbasChild. Then mine idles about a 1,000 RPM it seems and it would never enter my mind to drive it at that engine range other than just to creep up or back for hooking up.

OK Art, Murf looking for your comments. ....

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Murf
Join Date: Dec 1999
Posts: 7199 Toronto Area, Ontario, Canada
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2010-11-19          175251


First off, welcome aboard!!

The concept is, that lugging a hydro-static drive is a bad thing.

Not the engine, but the drive itself.

In order to know the 'why', you have to have a bit of understanding of the 'how' first.

A typical HST (Hydro-Static Transmission) uses a pump of a variety called a "swash-plate" pump. The engine drives a plate which has the ability to tilt away from the typical 90 from the drive-line. Think of it as a flywheel that is not fixed rigidly to the flywheel, but rather can pivot at that connection. That movable plate is what pushes the pistons.

The big advantage of this setup is that the same single pump has the ability to produce large volumes at lower pressure, or lower volumes at very high pressures, or anywhere in between.

This is what allows you to have 100% power at a creep, or moderate power at 'roading' speeds.

Now, the problem is that when you over-work the pump at the 'high volume, low pressure' setting it creates tremendous heat & wear. This is easily fixed by increasing the RPM's if possible, otherwise backing off on the pedal some.

However, working at proportional settings, that is load matched to power supply, is no problem at all. For just moving a machine say around a yard, 1,200 - 1,400 rpm at walking speed for example, isn't an issue generally.

Basically it will take a bit of time for you to get used to matching power provided, to the demand you've created. Say 1,400 rpm for walking speed, 1,700 rpm for jogging speed, 2,000 rpm for running speed when empty. Increase that proportional to added work, i.e. load on the FEL, pulling a trailer, etc., etc.

I usually tell people to set the throttle such that the engine is neither lugging, nor racing. If it doesn't sound right, it likely isn't right.

Best of luck. ....

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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2010-11-19          175252


The manual for my Grasshopper diesel zero-turn (hydraulic drive system) says to always work at full RPMs. ....

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2010-11-19          175254


Both my blue and yellow (New Hollands) mauals say "run at or near full throttle which is 2600-2800 RPM".

Murf knows (but forgot to mention) these modern diesels need top speed for good combustion.

Also, the charge pump which keeps the pistons pressed against the swash plate needs the proper engine speed to make pressure.

One way of "feeling" if you're lugging the system (not the engine) is the backpressure feel or resistance through the "go pedal"---a high resistance tells you wrong range (too high). However, a very soft or no resistance pedal is not a concern but can indicate that a higher range may work too.

FWIW, very rarely will an engine stall when running in too high a range; usually the system's relief valve will kick in---BUT that causes the oil to get hotter and create air bubbles in the oil which leads to heat and wear. ....

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Kubota B7800 HST correct operating RPM speed

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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2010-11-20          175256


Bhaxel,


Before engaging the PTO, or engaging any power-driven implement, be sure to reduce your engine rpms. Engage the mower deck, tiller, or snowblower (for example) only when your engine is at low rpms. Once the implement is under power, you can then let out the clutch (slowly) and then begin to throttle up.

It's always best to use your PTO driven implements at full rpm and under full engine power. Just be careful when engaging them. It's never good to let the clutch out when the engine is making full power. (Very hard on clutches, PTO u-joints, mower deck belts, etc.)

When using your loader for delicate work, such as when near the foundation of the house, it's best to run your engine at lower rpms. This will give you very fine control of your loader operations and tractor ground speed.

All pulling operations should be performed under full engine power, such as when tilling, cultivating, mowing, plowing, etc.

Hope that helps.

Joel ....

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earthwrks
Join Date: Dec 2003
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2010-11-21          175291


Quote:
Originally Posted by candoarms | view 175256
When using your loader for delicate work, such as when near the foundation of the house, it's best to run your engine at lower rpms.This will give you very fine control of your loader operations and tractor ground speed.


Joel I beg to differ. Doing as you precribed has no affect on the situation as locomotion is a function of the "go-pedal" as I call it. Lugging the engine in the interest of fine control is counterproductive and unnecessary. Precise and delicate work is where HST shines! ....

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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2010-11-21          175295


Earthwrks,

Loader operations are greatly affected by engine rpms. Higher engine rpms cause the loader and bucket movements to become more rapid and a bit more difficult to control when performing delicate work.

I find that when using the forks to load a pallet in the pickup, I have much more control over the loader movements when the engine is running at about 1/2 to 3/4 throttle.

Joel
....

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Art White
Join Date: Jan 2000
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2010-11-22          175298


Murf did a great job of explaining the need of engine RPM's under load to keep the hydro from cavitating. To low of engine speed will not allow the pumps to supply enough oil supply ingesting air and causing the metal parts to become dry and ruining the surfaces of the hydro drive. ....

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bhaxel
Join Date: Nov 2010
Posts: 17 Lovingston, VA
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2010-11-22          175308


Wow! Great thread. Thanks everyone for your input. ....

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AbbasChild
Join Date: Aug 2009
Posts: 72 Western Pennsylvania
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2010-11-23          175311


As I mentioned, my experience is limited, and I am always afraid of doing un-repairable damage as I learn--so let me go the next step after Art's post--if (or after) the pumps "ingest air", does that air ever escape if run at appropriate engine speeds? And over what period of time are the metal parts ruined?

Thanks--this has been educational! ....

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2010-11-23          175313


The system doesn't run dry nor ingest air as Art states. It doesn't get enough lubrication which leads to rapid wear. And more importantly since the pump DID have fluid originally, it still has residual lubrication it it.

(Important distinction: The so-called ingestion can happen and related to having too low fluid level and therby sucks in air through the suction line in the tank---which doesn't apply here.) Cavitation can happen not unlike a boat propellor in water.

As far as how long one can do this is really a function of many things: oil type, oil temp, if aerated, RPM, etc. I've run a few hydros out of oil with no lasting effects. However, a gear pump can be wiped out in a matter of a minute or so. ....

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earthwrks
Join Date: Dec 2003
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2010-11-23          175317


I think you're dealing with a pressure-compensating pump system---a sort of "governor" if you will. My manlift has the same system--the pump swash plate returns to neutral when no demand is present. As soon demand is called for, the pump then adjusts volume as needed. It makes for a smooth running system and quiet noise levels. ....

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Kubota B7800 HST correct operating RPM speed

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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2010-11-23          175318


Dear Friends,

I thought I'd pass this along.

Kubota offers a variable trottle setting feature on their Grand Series tractors. It allows the tractor to operate and function at lower engine rpms, until a greater demand is placed on the system, at which time the engine rpms increase to meet the demand.

Kubota has a video explaining how their Auto Throttle Advance system works. It can be seen at the Kubota website under the L-40 Grand Series of tractors.

Click on the L-40 Grand tab, then click on the HST Plus video at the bottom of the page.

I hope this helps.

Joel ....

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hardwood
Join Date: Dec 2002
Posts: 3583 iowa
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2010-11-24          175327


Joel;
Your post about the automatic throttle advance reminds me of my BIL working for a neighboring farmer this fall.
It is a new tractor and I've lost track of the latest model numbers, but it is a 300 hp. front wheel assist John Deere pulling a chisel plow. He ran it for a couple weeks and his complaint was that there is nothing to do while driving it. It steers it's self automaticly knows from a satellite when to raise and lower the chisel at a waterway then on the ends the computer throttles the engine back downshifts the transmission raises the chisel plow, turns around on the end lowers the chisel on and on. If the engine senses too much load it dowenshifts then shifts back up. The man was bored stiff, all he did was ride along listening to the radio.
I guess the owner can keep track of the exact location, engine temp, oil pressures, engine load, fuel consumption, acres completed, plus lots more from his laptop any time or anywhere he may be a the time.
Things sure shot past me in a hurry, I still like to shift gears, control the throttle, decide when to raise the chisel plow, etc, but I'm just behind the times and that's OK with me.
Frank. ....

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Art White
Join Date: Jan 2000
Posts: 6898 Waterville New York
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2010-11-24          175329


I might have said it wrong! yes again!

The problem is that the system needs more oil then the pump is pumping do to low RPM and high demand. That leads to a dry situation. This will give you metal to metal contact in a system that is supposed to have oil sperating the metal parts.

Hardwood, these systems are even here in NY with the smaller chopped up fields. I've listened to the farmers tell of the reduced costs of field prep from fertilizer to seed as well as fuel! ....

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kthompson
Join Date: Oct 2005
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2010-12-13          175736


auerbach, does your manual tell you to run it at full speed for transporting or when mowing or all the time? I would guess they are mainly talking about cutting when tip speed is so important which means engine rpms must be up.

Frank, so why place an operator in the cab? No doubt would be required on the road. Can the operator override the computer quickly? ....

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hardwood
Join Date: Dec 2002
Posts: 3583 iowa
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2010-12-13          175737


KT;
Yes an operator is still required in the cab. I talked to the BIL a bit more about it the other day. It does everything I stated earlier except at the ends of the field the operator uses the steering wheel to get the tractor past 90% of a 180% turn on the ends, then lets go of the wheel. The GPS then finds where the tractor needs to go on the following pass and does all of the steering from then till the other end of the field.
Yes the operator can overide the system, and a driver is needed for road travel.
Even the garbage man is policed by a GPS on the roof of his truck. The fellow who stops at the farm to empty our dumpster is a friendly sort of guy and likes to visit a bit. If the GPS detects that his truck hasn't moved in a certian number of minutes the engine stops, his cell phone rings asking why he isn't moving. A couple years ago one day he was visiting with me when the engine stopped, his phone rang, a company lady asking why he wasn't moving. I'll leave out the profanity, but in a nutshell he told her if she wanted to drive that stinking blankety blank truck with rotten garbage dripping out of it, have at it, he'd walk home from here.
He is still driving, still visits, engine still stops, phone still rings, he just don't answer it a and leaves when he's done visiting.
Frank. ....

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candoarms
Join Date: Mar 2007
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2010-12-13          175738


Frank,

A young friend of mine farms about 1300 acres just east of me. He's got that system in his tractor. When I call him while he's in the tractor, he can tell me how many acres he's cultivated, the speed he's running at, the number of acres remaining on that plot, and the estimated time of completion.

He can cultivate all night long, without fear of running into a fence, or driving into a drainage ditch. Each of those landmarks were entered into the GPS beforehand.

I always know when to put the coffee on, because that GPS system of his is pretty danged accurate (barring any mechanical failures, getting stuck, etc.)

Joel ....

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Art White
Join Date: Jan 2000
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2010-12-14          175767



With the newer GPS systems and being able to tie into computers it won't take this decade to see in some areas that the tractor operator won't be needed as they are today.

The ability is there to do it now! The first time I saw some form of it was in Illinois with IH in the late 70's and it has improved since then by huge amounts.. ....

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hardwood
Join Date: Dec 2002
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2010-12-14          175769


Art;

Last evening John deere had an hour long show on RFD TV with Max Armstrong hosting three Deere engeneers, perhaps you saw it.
The engeneers were explainmg to a call in segment of the show teling the latest changes on their new 2011 8R and RT series tractors. Most of the show was devoted to the latest in computer controls, tractors being able to self diagnose and send an instant alert to the service dept. of the dealer for instant analysis of a problem, etc, erc,. Much more than I could comprehend.
Frank. ....

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auerbach
Join Date: Sep 2007
Posts: 2168 West of Toronto
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2010-12-14          175770


"auerbach, does your manual tell you to run it at full speed for transporting or when mowing or all the time? I would guess they are mainly talking about cutting when tip speed is so important which means engine rpms must be up."

Ken, that's what I assumed, and it doesn't elaborate. Another poster suggested using low revs for engaging the PTO. I used to do that, and had to report to the dealer that it would stall. (In fact, I'd pull the engage control and instatntly push it back in a few times to break the blades' inertia, until I could leave it engaged without stalling or, as I assumed, straining the system by using high revs.) Dealer answer: "No! FULL throttle BEFORE engaging the PTO."

So that's what I do. Hard on the teeth, though -- from clenching them.

....

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AbbasChild
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2010-12-14          175771


I will have to check but I thought my OM for the NH T2210 states to engage the PTO at a much lower engine speed then push the RPMs to the target speed. I am operating a 5' Woods brushhog on the rear PTO right now and so far that has worked well for me--does seem to be much less strain on the system that popping the clutch at full throttle! IMHO. (and very limited experience!) I may drop the rpms down to around the 1700 or so to engage the cutter.
Mike ....

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kthompson
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2010-12-14          175772


Abbaschild, think you are using a foot clutch where as auerbach is using electric pto clutch. Think every body here would agree with your method on the foot clutch use. May be some variance on how low to drop the rpms and some of that does vary with the piece of equipment and the tractor itself. ....

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AbbasChild
Join Date: Aug 2009
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2010-12-14          175773


Ahhh! Thanks for the clarification!
Mike ....

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auerbach
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2010-12-14          175774


I should have clarified that it's not a rear PTO but a front one that I gather is some kind of electric and/or hydraulic control to engage the PTO to the front deck. No clutch pedal anywhere. ....

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hardwood
Join Date: Dec 2002
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2010-12-14          175775


Electric clutches like most lawnmowers us to engage the deck drive are similar to the clutch your car uses to operate the air conditioning compressor. I don't think it hurts the clutch to engage it at full throttle, but the drive belts that give the instant squeal are being stressed more than need be. I usually go to half throttle before snapping the switch, at half throttle you aren't likely to stall the engine, and your belt life will be extended.

The compact tractors I'm familiar with that have the standard 540 RPM rear PTO use a multi disc clutch that is activated by hydraulic pressure from the main hydraulic pump of the tractor. Some are modulated meaning the engagement and disengagement of the clutch is done on a gradual pressue increase or decrase to keep from the "Slam" effect of instant engagement. I stll feel lots better slowing the engine to half throttle to start something that has lots of heavy rotating mass like a bush hog type rotary mower.
Frank. ....

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Art White
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2010-12-20          175872



Frank, that kind of equipment is already to hit the streets! It's just that it is in the car your looking at to buy in a couple of years ....

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lencamp
Join Date: Oct 2006
Posts: 29 Trufant, Michigan
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2011-01-01          176120


Lets hope somebody learned something from the Toyota fiasco which was a media circus. How about brakes take precedence over throttle? Problem is I can imagine situations where that could cause an accident also. I really don't like drive by wire but it's unavoidable unless you want to maintain an antique. Next step is you won't get to drive at all and yes it's already here.

JD has been selling a fully autonomous Gator to the military for over a year now that requires no operator whatsoever. It also has manual and remote control modes.

For the tractor I try to run the engine to suit the job - you get a feel for it. I don't want to lug the engine but I don't like to run the crap out of it either. The tach goes up to 3000 RPM so I raerly go above 2500 unless really digging into hard banks with the snow blower. Also helps to match the gear range to what you're doing. I spend most of my time in 2nd (NH TC33D hydro). Sometimes I think I'm killing it with kindness - need to run harder.

I've noticed when back blading and trying to pull too much the smell of the exhaust changes and the engine temp drops a little. That's a sure clue for more throttle and/or lower gear. Problem is in low the tires just spin and in 2nd I don't have enough power - maybe I need a bigger tractor.

I'm not proud of this but I have managed to overload and stall the engine. Running the loader into a pile of dirt or back blading too long and too hard the engine just seems to run out of wind and die even at high throttle. Another clue to rethink what I'm doing - trying to exceed the tractor's capability. ....

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earthwrks
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2011-01-02          176137


Read your OM--it says run the engine at 2600-2800 RPM. If you're stalling it, you're in 3rd. I use mine commercially and have stalled maybe three times---all when brushhogging and got tree limbs caught in the mower. Twice I've pulled a fully loaded (at least) 18,000 lb gross wt dump trailer 2 miles and my 33D barely acted like it was pulling anything. That was in 2nd. If you're stalling it, most likely your hydro pedal had A LOT of resistance which is a precursor indicator you're abusing it which will have sent the drive pump into relief (not good) which causes the oil to get hot and aerates it too. ....

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lencamp
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2011-01-04          176192


I never paid much attention to go pedal resistance - guess I'd better start. Hardly do anything in 3rd except go to and from the barn. So here it is - if the tach goes up to 3000 RPM what does that really mean? Is that the max the engine is governed for so you can't overrev it?

Thanks for your comments ....

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Kubota B7800 HST correct operating RPM speed

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hemrich@att.net
Join Date: Feb 2002
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2011-01-18          176478


I own a B2700HST( basically the same tractor as your B7800) that I purchased new in 1999. The power curve of a diesel engine is much different than a gasoline engine. Best to operate the diesel at it's torque peak which is slightly below the rated speed. In general, whenever I engage an implement such as a mower or brushog, I do so at idle speed to avoid shock loading the equipment's driveline and abusing the tractor's clutch. Once the device is engaged I spin the engine up to the recommended 2500-2600 RPM and let the blades catch up before moving off. When working with the FEL I generally keep the RPM at about 2200 and use the M range in the transmission. For very heavy loads I might use L on the trans. Low RPM when using the loader is very hard on the engine and pump, you want to keep the hydraulic pressure up to the rams that lift and articulate the bucket so you have the maximum mechanical advantage over the load in the bucket. These B series Kubotas are as reliable as a hammer. Just change the oil and hydraulic fluid as recommended and grease the fittings regularly and the machine will outlast you. ....

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earthwrks
Join Date: Dec 2003
Posts: 3853 Home Office in Flat Rock, Michigan
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2011-01-20          176520


Quote:
Originally Posted by lencamp | view 176192
I never paid much attention to go pedal resistance - guess I'd better start. Hardly do anything in 3rd except go to and from the barn. So here it is - if the tach goes up to 3000 RPM what does that really mean? Is that the max the engine is governed for so you can't overrev it?Thanks for your comments


It may say 3000RPM, but that doesn't mean you can throttle up that much. My truck's speedometer shows 120 MPH, but I don't drive it that fast. ;) ....

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