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  1. #1
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    Default Lugging a diesel engine?

    I cut and pasted this info below from another thread regarding lugging a diesel engine and would like to get more feedback about it. We are very careful about "lugging" an engine and we all know what serious lugging is and sounds like. However, could some of us be lugging an engine and not know it? Are there degrees of lugging? Any more thoughts on this?


    "......There is one firm rule that every equipment operator and truck driver memorizes on their first day: NEVER LUG A DIESEL ENGINE! With the throttle wide open under load, keep the RPMs above 80% of the maximum RPMs. For example, if your maximum engine RPM is 2600, never let it lug below 2000. When you get below that you will drop off the power curve anyway, and lugging a diesel will hammer the rod bearings right out of the engine....."
    ******

    May I be the kind of person my dogs think I am,

  2. #2
    Epic Contributor Soundguy's Avatar
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    Default Re: Lugging a diesel engine?

    if the engine is laboring at a certain load and throttle.. increase the throttle till it is smooth. If you get to a point that increasing the throttle does not increase rpm.. you are lugging it.

    soundguy

  3. #3
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    Default Re: Lugging a diesel engine?

    I would also like more info...I thought I understood but maybe not.
    B2920 TLB, turfs and loaded ags, thumb, 60 & 50" QA buckets, Kubota QA forks, toothbar, BX42 chipper, 60" front hydro blade and hitch, Herd M96 spreader, turf vent 48" 3pt aerator, Woods LRC 60" rake and Woods 48" estate BB, County Line 60" rear blade, rear spacers, pats easy change. Polaris 800 w/60" Blizzard plow & John Deere 717a ZTR

  4. #4
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    Default Re: Lugging a diesel engine?

    Quote Originally Posted by sixdogs View Post
    I cut and pasted this info below from another thread regarding lugging a diesel engine and would like to get more feedback about it. We are very careful about "lugging" an engine and we all know what serious lugging is and sounds like. However, could some of us be lugging an engine and not know it? Are there degrees of lugging? Any more thoughts on this?


    "......There is one firm rule that every equipment operator and truck driver memorizes on their first day: NEVER LUG A DIESEL ENGINE! With the throttle wide open under load, keep the RPMs above 80% of the maximum RPMs. For example, if your maximum engine RPM is 2600, never let it lug below 2000. When you get below that you will drop off the power curve anyway, and lugging a diesel will hammer the rod bearings right out of the engine....."
    I let my diesel truck engines drop below 2000 RPM all the time. Lugging creates excessive EGT's and is not good for your engine. You'll know when you're doing it. Engine gets loud, rough, might see black smoke, no throttle response. Drop a gear and see if it clears-up.

  5. #5
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    Default Re: Lugging a diesel engine?

    90% of the time my JD4300 is running between 1500-2000rpm and not under "load". Just carrying a bucket of something or dragging logs. About the only time it see's 2600 rpm is when I'm road running, mowing or snow blowing. (well, maybe to climb a steep hill as well)
    If the rpm starts to drop, I'll either lift the "go-petal" or increase the throttle till I crest the hill.
    Its worked for me for the past 4000hrs...

  6. #6
    Elite Member Chilly807's Avatar
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    Default Re: Lugging a diesel engine?

    "Lugging" any engine is not good for it, however I don't buy into the 80 % rule. Provided the engine is providing smooth power delivery and isn't on the verge of stalling you're not doing any damage.

    Case in point: Some of the stuff I work on is multi-cylinder, high horsepower, medium speed engines. The best example is a 20 cylinder engine fitted in a frigate as "economical" cruise alternative to gas turbines. It develops about 10,000 horsepower at 1050 rpm maximum. Because of the gearbox configuration it runs under load anywhere from 400 to 1050 rpm depending on the speed demand. Most of the ones we have are between 12,000 and 24,000 hours into their life cycles, so I'd say things are ok in general.

    If you drop below idle speed under load, that's not good. As I said before, if it's running smoothly and not labouring, you're not hurting it. As Soundguy said, if pressing the accelerator doesn't produce an increase in speed you're either at the top end of the governed speed range or you're on the verge of being overloaded. Drop a gear or otherwise reduce the load.

    A diesel doesn't require an increase in "throttle" setting to deal with an increased load, the governor deals with that. There is no "throttle" as such, just a governor that tries to maintain a given engine speed within the power limits of the engine. In fact, there are no throttle plates at all, the engine has full air supply at all times, only the amount of fuel being delivered varies.

    Sean

  7. #7
    Gold Member First one's Avatar
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    Default Re: Lugging a diesel engine?

    While de-rocking my blueberry field, my tractor's RPM's would die back while trying to get out big rocks ,the bucket wouldn't even move, I'd let off and the RPM's would come back up .I have the L 40 series with load sensing, so does this prevent any damage to it because the engine won't stall? or should I not be forceing it that hard?

  8. #8
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    Default Re: Lugging a diesel engine?

    Quote Originally Posted by Chilly807 View Post
    "Lugging" any engine is not good for it, however I don't buy into the 80 % rule. Provided the engine is providing smooth power delivery and isn't on the verge of stalling you're not doing any damage.
    If you drop below idle speed under load, that's not good. As I said before, if it's running smoothly and not labouring, you're not hurting it. As Soundguy said, if pressing the accelerator doesn't produce an increase in speed you're either at the top end of the governed speed range [or you're on the verge of being overloaded]. Drop a gear or otherwise reduce the load.
    Sean
    While I agree with most of what youve said one cannot generalize to term loss of rpm at full throttle to be lugging. Lugging is rpm and throttle related. When running at full rpm setting and load causes rpm to fall below that where maximum torque occurs then it is time for a downshift ... soon if load is not being reduced. Altho, as you said, the engine is not lugging until rpm falls well below that.
    larry
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  9. #9
    Elite Member Chilly807's Avatar
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    Default Re: Lugging a diesel engine?

    I'm going to go a little deeper into this one, I hope it'll clarify things. Diesels and governor operation are different enough from gas engines typically found in cars or trucks that I think it's worth digging deeper.

    There are several different types of governor available to the engine manufacturers. Cost and accuracy are directly related, as is the degree of complexity.

    Electronic and hydraulic governors have a very high degree of accuracy, usually within 1 to 2 rpm speed variance under all load conditions within the capacity of the engine. They are normally only seen in power generation units where that kind of accuracy is needed, or in the case of the hydraulic controls where more output force is needed to control the fuel rack (as in the case of the frigate engine I mentioned earlier, which is electronic control over a hydraulic actuator.)

    In our world of tractor and automotive type diesels, we don't need that kind of accuracy in speed control. PTO speed isn't that critical even when running a PTO generator, unless you want to run co-generation with the electric utility, which is highly unlikely.

    So, we typically have a mechanical flyweight type governor. For anything a tractor was intended to do they are perfectly suitable, and far more cost-effective.

    They do have one inherent characteristic that impacts on this discussion, in that they will reduce the speed setting as load on the engine increases. This isn't a design goal, it's a limitation of that particular governor type.

    So for example, imagine you are running a brush hog at a steady 2300 rpm engine speed, over a sparsely grown field. Near the edge of the field is a heavily weeded, densely grown area. As the tractor and brush hog moves into this area, the rpm drops slightly as the load on the engine increases.

    I'm not talking about an initial drop than recovery back to 2300 rpm, I mean it drops down to maybe 2100-2200 and stays there until you come back into the lightly grown areas and the load on the engine decreases. The governor still has control over engine speed, and the engine isn't overloaded.

    It's hard to see unless you're using the throttle lever and not a foot pedal, our natural reaction from years of operating cars or trucks is to press harder on the pedal to bring the speed back up.

    This doesn't mean the engine is "lugging" or overloaded, just that the governor is doing it's job as best it can within it's mechanical limitations. With a hydraulic or electronic governor (set for "0" speed droop) you would see no drop in rpm, just a deepening of the engine exhaust note as more fuel was added to compensate for the increase in load. Exhaust temperature, turbo speed, and cylinder pressure also rises.

    Lugging occurs when the ignited fuel mixture has no where to go, the piston is moving too slowly to allow the combustion gases to expand at their normal rate. You typically get jerky power delivery, a loud fuel knock from the engine, and very high forces on the con rods and bearings. To make matters worse, the engine is turning slowly and has a harder time maintaining an effective oil wedge in the bearings to carry the load.

    Sean

  10. #10
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    Default Re: Lugging a diesel engine?

    Quote Originally Posted by Chilly807 View Post
    I'm going to go a little deeper into this one, I hope it'll clarify things.

    [SNIP]

    Lugging occurs when the ignited fuel mixture has no where to go, the piston is moving too slowly to allow the combustion gases to expand at their normal rate. You typically get jerky power delivery, a loud fuel knock from the engine, and very high forces on the con rods and bearings. To make matters worse, the engine is turning slowly and has a harder time maintaining an effective oil wedge in the bearings to carry the load.

    Sean
    A very good treatment of the subject. Thank you!

    Our L2550 has a hyper active governor that acts close to the zero droop you describe ... esp when the engine is set to full speed. That speed is held quite close throughout large load changes. Could it have to do with a good fueling curve .. good governor mechanics .. both.. ? I wish all my tractors had so good a torque / power response characteristic.
    larry
    This side of 40
    JD2010, Kubota L3450/FEL w SK QC, L2550 w FEL
    Mahindra 7520 [Pinky] /FEL w Skid Steer QC/w Tilt Tatch & BH, BX1500 [Mighty Mouse]
    IH37 Baler, CCM165 Drum Mower, JD Rake
    JD 127 bushog, Flail, SK Tilt Tatch , KK tiller, Rhino rear blade, Post driver, post auger, chipper, pallet fork, Grapple/Loader Buddy, Homemade Splitter/DC Welder

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