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 03-19-2003, 18:34 Post: 51478
LarryJ



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 BX Engines

I understand the new BX series tractors have an engine that runs at higher RPMs than the older B series tractors. What is the real difference in these engines? Does this have any effect on the life of the engine? Is this a concern I should have?






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 03-20-2003, 06:46 Post: 51497
TomG

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Maybe somebody can comment on specifics of the two engines. My impression is that they are the same basic engines. There may be tuning differences such as cam duration, injector timing, fuel metering, and manifold lengths that affect an engine's power curve.

I don't think there'd be enough difference in the performance of the engines to make much of an issue for most owners. Higher rpm engines may be a bit better for mowing and lower for draft operations, and there may be a bit more wear per hour operation. New oils have reduced wear, and few compact owners would ever wear out their engines even with the old oils. I don't think are enough of differences to make rpm into a major factor in choosing a tractor.






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 03-20-2003, 06:56 Post: 51499
Art White



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Larry I would not worry about it. I was building diesels that were turning 5000 rpm years ago. With todays tooling there is no reason for concern. The higher RPM broadens the torque curve giving you a wider range of good useable horsepower.






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 03-20-2003, 09:19 Post: 51513
buzst1



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Hi Larry,
Take a look at the following web site:

http://www.engine.kubota.ne.jp/english/index.html

and look up the current bx and b series engines,the D722,D905,D1005,and d1105. You will notice that when kubota rates the engines for resale they are rated at a maximum of 3600 rpm. What this means to me is that when you are running at the bx rated 3200 rpm you are using almost 90% of the engines rated capacity. If the same engine were running at the more standard 2600 rpm it is running at slightly over 70% capacity. To me that is a big difference that will impact longevity. Acutally, none of this should really make a difference as none of us normally run our machines much over 1800 rpm, but on the bx machines Kubota geared the pto to reach speed (540 rpm)at 3000 thus requiring the bx user to utilize higher rpms.
In the end the bx is still avery good machine and I doubt the orginal owner will have problems. My concern is for later owners and resale value.






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 03-21-2003, 11:52 Post: 51566
slowrev



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Some of the compact tractor engines reach their maximum torque at a higher engine RPM than the RPM's required for 540 PTO operation. That is poor design and wasted power.
I like the slower tractor engines, more low end torque=usable power.






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 03-21-2003, 13:47 Post: 51569
Art White



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Slowrev, I don't think any new metal or change of designs would ever change your mind. The International 1066 in the early 70's with the legendary RPM at the time of 2700 and 2800 at the time was unbelieveable to many people when they introduced it. After all, most diesels at that time only revved to about 2000. Those lower revving engines were all based on 50's technology and were made out of softer metals by far than the Melrose engines were. Crankshafts needed turning for nearly every rebuild, egg shaped, not like the newer ones where only if you starve the oil system will you need to turn it. Standard to us was to drop a 4500 rpm govoner spring into the pump and lets go pull! We turned them up more yet, and run like no tommorrow and never grenaded one!!! The wider RPM band allows to build an engine with less overall stress than a high torque, low rpm engine with less flexability of range.






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 03-22-2003, 05:30 Post: 51594
TomG

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Art: I don't this tractor-pulling side of you has ever come out in your comments before.

I'm thinking about Slowrev's comment about max torque placed above pto rpm and true enough I don't understand the design theory. However, designs are complex and I don't expect to grasp all the complexities.

In my terms I guess there are a couple ways of thinking about it. My first thought is that max torque placed below pto rpm would help support the hp if rpm decreased under excessive loads. Such a design might help a tractor pull through situations where otherwise draft would have to be reduced. However, another way of thinking about it is that if an engine lugs, the first reaction of many operators is to reduce draft. Max torque placed above pto rpm would provide some 'torque-kick' to get the engine back to pro rpm. A lugged engine does have to carry the load plus accelerate itself and the drive train back to speed.

Don't know. The real reasons for one design or the other are probably considerations that escape me. For persons who are unaware of the relationship between torque and HP, the basic idea is that torque = hp/rpm. Another version of the formula is torque x rpm = hp. The actual formula contain a constant.

Regarding the engine stress: I started out thinking that I could see why it might be better if an engine didn't sit banging away at it's max torque rpm all the time during pto work. But then I thought 'well, if power isn't needed fuel the governor reduces fuel delivery to maintain the rpm.' Reduced fuel delivery should also reduce stress. Again, the real reasons for designs probably escape me.






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 03-22-2003, 07:52 Post: 51601
Art White



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Tom, depending on the injection pump which makes a lot of difference as to the adjustability you can do a lot. To have a low rpm engine with high torque you could exert a higher stress load to the rotating mass than having a larger band of rpm developing the same horsepower. We have seen it in the engines and the parts that need to be rebuilt and when. Case was the industry leader years ago in cubic inches, they were a low rpm engine with a narrow high torque band. They used a softer crank that nearly always needed to be turned. Often found bent rods due to different problems, maybe a leaky head gasket. JD to had softer cranks, not quite as soft as Case but close,IH used a system that was extremely hard, rare to need a turn unless it was scored, nearly impossible to egg like the others and good for high rpm. I can go on and on here and this is about compact tractors not the big ones.






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 03-22-2003, 08:48 Post: 51604
Peters

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To me the width of the torque band is key and the balance of the engine. If JD and Case had low turning engines then even if the iron in the crank was equivalent then their cranks experienced greater stress due to dyanamic stress caused by the poor balance.
I like an engine that has a low initial torque and a high RPM. The volvo B and F series 4 cylinder engines had a curve the started around 1500 and a max RPM near 6-7K. The engines regularly got 300K miles when NA engines rarely got over 100K. Very fun to drive, but few here would know as they tied it to a slush box rated for the peak HP not the torque.
From what I have seen of the old IH, I think the engine was much the same. Low intial torque and high RPM.
The band on my Cummins is similar 4K max and 1.5 peak.
The a lot of current CUT diesels have little or no torque under 3K. This means that you are running the engine at near max RPM all the time.
I believe that this is done for operating efficiency reason the same as the fact that a lot of engines are limited to automatics for EPA reasons. Longevity is not a primary consideration.
Oh well every thing my change if we go to the small diesel electric hybrids. If you talk to the large equipment operators they have suprising torque for the size.






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 03-23-2003, 05:00 Post: 51660
TomG

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Art & Peters:

I must have been cooking these ideas over-night. Here I am this morning with some refined ideas--at least refined for me. The engine stress thing may have to do with how active the governor is. The governor on a narrow-band high-torque engine is likely to be more active than on a wide-band engine. An engine at its peak torque rpm that receives frequent full-throttle pulses seems like it would be absorbing more stress than an engine with a less active governor that's not running at it's peak torque.

I seem to be thinking my way to endorsing modern design, but along with Slowrev I do like the feeling of a low rev engine when it gets down to work.






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Discussion Boards > Active Subjects > Messages as Posted > Kubota Review Forum

Thread 51478 Filter by Poster:
Art White 9 | buzst1 6 | DRankin 4 | LarryJ 1 | Murf 1 | Peters 2 | slowrev 5 | TomG 6 | WillieH 2 |




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