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Author Topic: On lugging a Detroit Diesel  (Read 4629 times)
coolbus
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« on: June 27, 2007, 08:22:50 PM »


On lugging a Detroit Diesel...

I am aware that lugging a Detroit is a no no, but I read in another post that lugging is defined as 'any time you are asking the bus to accelerate, but are not able to, or are actually losing speed' (paraphrased).

I always thought that lugging only occured when the engine RPM dropped below a certain point.

I probably lugged my 8v-71 quite a few times on my 2500 mile trip accross the US. (based on the info in the article)  The engine never did overheat - in fact, the temp guage barely even fluctuated when pulling the several long grades I came accross along the interstate. And I always watched for black smoke - none produced.

Is the only danger in lugging a Detroit an overheat situation?

thanks
Mark
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NJT 5573
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« Reply #1 on: June 27, 2007, 09:26:22 PM »

Hi Mark, that description sure takes up alot of space! I agree with your statement on lugging being below a certain point. If an engine is hot, my preference has always been to keep the water pump turning max rpm. I always thought black smoke was good if it was mine!
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tekebird
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« Reply #2 on: June 28, 2007, 03:53:24 PM »

Luggin is when you are asking your engine to pull a gear that it can't.  simply, if the bus won't accelerate in that gear it is to high a gear.

this is generally associated with lower RPM ranges.  If you are at the governor chances are you are not lugging.

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gus
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« Reply #3 on: June 28, 2007, 07:42:05 PM »

Lugging is overloading the engine no matter what the rpm, it means that the engine is not generating enough power for the situation.

If you runout of gears and still can't move the bus the ultimate lugging is stalling.

Normally, in a bus, it means that you are trying to pull a hill without shifting down to the next lower gear when, as said before, the bus will no longer accelerate and usually will be losing speed no matter how far you push in the fuel control.

Black smoke results because the engine is being fed more fuel than it can burn.

All this is my personal understanding and subject to correction by the experts!!
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PD4107-152
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DrivingMissLazy
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« Reply #4 on: June 28, 2007, 08:06:23 PM »

Luggin is when you are asking your engine to pull a gear that it can't.  simply, if the bus won't accelerate in that gear it is to high a gear.

this is generally associated with lower RPM ranges.  If you are at the governor chances are you are not lugging.


My opinion is that you could be at the governor and still be lugging the engine.

I do not think you should ever have the pedal to the metal. You should back off the pedal a little bit so that if you increase the pressure the engine speeds up. If it will not speed up then you are lugging the engine and should shift to a lower gear.
Richard
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« Reply #5 on: June 28, 2007, 09:05:27 PM »

I don't think you can overload/lug at max RPM or at the top end of the RPM range.

if your load is great enough that the sequence starts to where you will be lugging your RPM will be dropping.

keeping the bus in the higher gear at a lower speed, while providing max fuel flow is lugging

if your at MAx RPM your using max fuel, or close to it.

unless of course your going downhill and your bus has reached the max speed it can do with the given wind resistance and your still holding the throttle at max.

my 04 going down the Westbound grade into Vail would max out at 76mph....no throttle or full throttle, I suppose if I gave it full throttle in that situation it would be lugging

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buswarrior
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« Reply #6 on: June 28, 2007, 09:53:21 PM »

Check the torque curves of the detroit 2 strokes.

Won't stay at top RPM (against the governor) under a gross load, not enough torque up there.

Be happy, if it makes full RPM's, you aren't loading it enough to create a lugging condition.

The concept missing in all this is to match the throttle position to the work the engine is doing, and no more. The engine will reach that point during the climb, that it won't accelerate, but it is maintaining speed at an acceptable RPM. That is not lugging. The throttle pedal should be eased back to match that point, not be held mashed to the floor. A pyrometer in the exhaust is a great gauge for showing the results of getting it right or wrong.

Otherwise, I like what I've read here.

happy coaching!
buswarrior
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gecole
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« Reply #7 on: June 29, 2007, 12:15:22 AM »

Lugging a diesel engine is more of a concern with the low rpm/low oil pressure problem associated with older design engines. When the manufacturers came out with constant displacement oil delivery systems in 4 stroke engines ( I know next to nothing about 2 stoke engines) they quit worrying about lugging. I'm thinking if your oil pressure is acceptable you are not abusing the engine at any reasonable rpm at full throttle. I've owned trucks which operated at full throttle at 1300 rpm for hundreds of thousands  of miles between overhauls. That same block with the old style lube system would have lived a short life at that rpm.
« Last Edit: June 29, 2007, 12:16:56 AM by gecole » Logged
RJ
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« Reply #8 on: June 29, 2007, 12:33:16 AM »


 ( I know next to nothing about 2 stoke engines)


Thanks for qualifying your remarks with the above statement.

Two-strokes are different than four-strokes, and what works for a four doesn't necessarily work for a two, and vice-versa.

"I'm from the government - I'm here to help" killed the OTR two-stroke, not the engine's design.

Not too many engines originating in the 1930s survived as long as the two-stroke Detroit. . .

As good as the Series-60 is, it's future is dim, again, thanks to government intervention trying to save us from ourselves.

FWIW & HTH. . .

 Wink
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RJ Long
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TomC
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« Reply #9 on: June 29, 2007, 06:33:08 AM »

The original way that the 2 strokers were tuned (71 series using 60 injectors, 92 series using 80 injectors) were aimed at the fact that the bus drivers drove the bus more like if they had an on/off switch rather than a variable position gas pedal.  Even increasing the injectors to factory settings (71 series using 65 injectors, 92 series using 90 injectors), the engines were still tuned to be operated for short periods of time (15 minutes per hour) at full throttle without damage to the engine.  Do you think truck drivers back in the 70's with non turbo 8V-71's were babying their engines?  Most owner/operators then increased their injectors to 70's, changed the timing, and many times revved them to 2800rpm with actually good results.  With my past truck with the 8V-92TA mechanical (435hp) I always had my foot in it climbing hills, but watched radiator temp like a hawk (still do) and got an almost unheard of 500,000 miles out of the engine before overhaul. 
If you have a 4 or 5 speed manual-shifting is simple-accelerate up to governor limit then shift.  Simply notice the speed that you up shift at and then downshift back down at the same speed for that gear.  If you have an automatic, you can't lug the engine-but you can overheat the transmission when climbing a steep grade in converter mode (that's a whole different story).
Final thoughts-most of the engines in our buses are under powered making running down the road without your foot on the floor almost impossible.  Drive the bus as described and the engine most likely will out last your usage of the bus.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
belfert
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« Reply #10 on: June 29, 2007, 09:45:49 AM »

As good as the Series-60 is, it's future is dim, again, thanks to government intervention trying to save us from ourselves.

The Series 60 could possibly be modified to meet 2010 emissions standards, but Detroit has choosen to go with just one engine for 2010 and beyond.  They have the MBE 4000 and Series 60 now and the MBE 4000 or a successor will be the only choice starting in 2010.
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lostagain
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« Reply #11 on: June 29, 2007, 10:55:03 AM »

I agree with Tom C. If I didn't have my foot to the floor the whole time, I wouldn't get anywhere. Those 2 stroke engines are underpowered, but they were made tough. They are meant to be used. Down $#!% when it obviously won't stay in a gear without slowing down or heating up. Enjoy the "screamming" from back there. When the engine is done, which will a long time, rebuild it and drive it for another life time. If you want to baby it, do it with proper maintenance.
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JC
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« Reply #12 on: June 29, 2007, 11:10:47 AM »

Belfert, i have been hearing that the 60s were going away for 4 years and they out sell any engine on the market like they out sell the mbe 4000 by 5 to 1 the Germans are not dumb they bought DD just to get the DDEC because they could not make a electronic system to work
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Busted Knuckle
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« Reply #13 on: June 29, 2007, 12:19:11 PM »

The Series 60 could possibly be modified to meet 2010 emissions standards, but Detroit has choosen to go with just one engine for 2010 and beyond.  They have the MBE 4000 and Series 60 now and the MBE 4000 or a successor will be the only choice starting in 2010.

Brian MBE 4000 (Mercedes Benz Engine) Detroit Diesel, Setra, etc. = DAIMLER CHYRSLER! HMMM!
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Buffalo SpaceShip
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« Reply #14 on: June 29, 2007, 01:02:57 PM »

my 04 going down the Westbound grade into Vail would max out at 76mph....no throttle or full throttle, I suppose if I gave it full throttle in that situation it would be lugging

I sure hope you're not behind me (or anyone else) in a twelve ton vehicle coming down a 6% grade in top gear at top speed. Wow!  Shocked Your brakes are not sufficient to stop the coach at that grade/ speed, or even slow it down that much. There is a runaway ramp after the first bend coming down into Vail that might help.  Wink

BTW, a 8 to 10% downgrade on my old '06 was enough to overwhelm the governor and overspeed the engine, requiring me to use the brakes to moderate... but that was in first or second gear, not fourth. I now have Jakes on the '08 and swear by 'em for mountain driving.

The old adage, "go down the grade in the gear you climbed up it" is golden. Even with Jakes.

Brian B.
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Brian Brown
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Longmont, CO
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