low RPM

[ametcalf]

I am new to my BX23 but not to diesel engines. My FIL who was a potato farmer and owned lots of tractors and trucks taught me never to lug a diesel engine. I think that is why truckers use so many gears. As an indicator if I am lugging the engine or not I increase the throttle a little, if the rpm picks up the engine wasn't lugging, if the rpm doesn't pick up then the engine was lugging and I should downshift, mow less wide, raise the mower or do something else to lessen the strain on the tractor. At the other end of the scale, it is bad to overspeed an engine of any kind. When I was training to be a flight mechanic on C-54s (DC4s) in the Navy I learned about the dangers of a propeller going into flat pitch and overspeeding an engine. One of the things that can happen to an engine that has some time on it is that a ridge develops in the cylinder at the top of the piston travel. In an engine that is overspeeding the top rings hit that ridge and they can break. I told the guy that was training me that at least in my little Aeronica Chief with a 65 hp engine and fixed pitch prop I wouldn't have to worry about overspeeding the engine. He pointed out to me that if I put the plane in a dive with the throttle wide open the engine would almost certainly overspeed. Several years ago we loaned our 5040 Allis to a couple of guys to pull a little planter that needed to go slow but required no power to pull it. I happened on them in the field and they were running the engine wide open in 1st gear. I told them not to do it and they told me diesel engines were made to run wide open. That may be true but not when they have no load on them. It cost me $1,700 to overhaul the engine after their little stunt. The one place that I see that it would be easy to overspeed my 5040 is when I am on the road going down a long hill, I back the throttle off some. I am careful not to lug or overspeed the engine and it has 3600 hrs on it since that overhaul and is still running strong and uses no oil. I am not sure about overspeeding the little Kubota engine with the HST and hydraulic pump in my BX23. Maybe those two items give enough resistance to prevent an overspeed. I just don't know at this time.

 

[RoyJackson]

Low RPM can result in "pounding" the main bearings. Remember, these are shell bearings that do not rotate and depend on a very thin film of oil. Low RPM also results in lower oil pressure.
"Pounding" would be equivalent to hammering on one spot continously...picture that.
On a shell bearing, it can ultimately result in wear at one point of the bearing...that turns into low oil pressure and premature bearing failure or scoring of a crank journal.

Even when I'm idling the tractor with no load, I keep the RPM at 1500.

Of course, how low is "Low RPM"?
Depends on the engine. Shipboard diesel turn very slow (300 RPM) but also have very thick bearings and a (relatively) easy method of replacing them. Some tractor diesels max out at 2000RPM.
But for our CUTs with engine displacements of 100 ci and maximum RPM limits at around 3000, I suggest keeping a no load idle at 1200-1500,

 

[Jay4200]

Even when I'm idling the tractor with no load, I keep the RPM at 1500.

FWIW, my Kubota manual specifies running the motor at PTO speed for everything, from sitting and warming up after a cold start, to all forms of operation.

I do let the machine warm up at close to idle, but do push up the RPMs to maybe 25% into the operating range. I do run wide open (at or just past PTO) when operating my backhoe or snowblower, but usually run about 80% of PTO speed for driving around or most other operations.

JayC

 

[Denwa]

FWIW, my Kubota manual specifies running the motor at PTO speed for everything, from sitting and warming up after a cold start, to all forms of operation.
....... I do run wide open (at or just past PTO) when operating my backhoe or snowblower, but usually run about 80% of PTO speed for driving around or most other operations.

JayC

I stopped by my dealer and inquired as to why my backhoe operations seemed
to be on the jerky lurchy side. He suggested that keeping the RPM up would help smooth things out by providing more available power and therefore less control travel to achieve same result. Or something along those lines.

More power would also help overcome any stiction issues with a particular system.

Dennis

 

[Soundguy]

more power? HMM... more flow.. but pressure it develops should be the same at idle vs throttle... at least if it is a positive displacement pump..

soundguy

 

[jtheise4]

FWIW, my Kubota manual specifies running the motor at PTO speed for everything, from sitting and warming up after a cold start, to all forms of operation.

I do let the machine warm up at close to idle, but do push up the RPMs to maybe 25% into the operating range. I do run wide open (at or just past PTO) when operating my backhoe or snowblower, but usually run about 80% of PTO speed for driving around or most other operations.

JayC

My MF owners manual states the same thing. States to run the engine at full throttle once warmed up.

 

[2LMAKER]

Does RPM matter with HST tractors? I was under the impression with HST you were supposed to run tractor at certain RPM and control speed with trans.

 

[nybirdman]

Yes RPM's matter on HST tractors....for all the reasons stated above.Get it up to operateing range.I don't run mine below 1500,when working 2,000+.Pto speeds at 2400-2500.

 

[dodge man]

I've seen people operate equipment that are running to low of a RPM. I think people think they are going to "save" the motor by spinnin it slower. My in laws were running a tractor and doing loader work at very low RPM's. It was lugging the engine so bad I was about ready to say something. On the other hand, for a lot of tasks, why run the thing wide open if you can throttle back a little bit. I own a Kubota BX and the only thing I do at full throttle is mow. If I run full throttle for loader work, it seems to jerky. There seems to be a sweet spot for most tractors to run at, the trick is to learn what that RPM is and use it. For my BX it seems to be around 2500 rpms for most things except mowing, which I run flat out just to get the blade speed as high as possible.

I don't think it is possible to overspeed the engine on my BX, it has a govenor that seems to work well.

 

[xtn]

I don't think it is possible to overspeed the engine on my BX, it has a govenor that seems to work well.

It might not be possible to overspeed it with the throttle, but a gear driven machine can be mechanically over revved by going too fast down a hill.