Physics of engine "lugging"

lastcowboy32

Well-known Member
Just a question to ruminate on, not necessarily on restoring an engine, but more to the effect of what wears on an engine to need restoration in the first place.

So....lugging.

Just by the sound of an engine, I learned from my brother (who was 14 years older) to shift a tractor to keep the engine in a very narrow RPM band. If the engine lugs, shift down. If the engine revs, shift up.

I always assumed that this was the best thing for an engine, and I have passed this same method onto our three daughters, who can all drive standard cars. For instance, if they're driving uphill with our Kia; I tell them to pick a gear to keep the RPMs between 2500 and 4000.

People from other families and with other experiences do differently. For instance, my father-in-law. When he pulls out onto the road with a tractor and haywagon, he'll shift directly into road gear and dump the clutch. The tractor will start out almost puking...then sloooooooooooooooooooowly work its way up from about 400RPM to the 1500 or 1800 RPM that his throttle setting would dictate.

During the sometimes thirty or so seconds that it takes for the tractor to get up to speed, he'll just sit back, look straight ahead and drive as if everything is just fine. I'll be riding and thinking...shift down...shift down...shift down.

Am I just being compulsive about this? Or are there actual physics that would say that an engine is being worn down during these extended lugging periods???

PS...I'm not going to get on my father-in-law about this, no matter what. He's my "Pops", and I'm glad for his help on the farm. If it means a few more repairs here and there...no biggie. I am just wondering if there is actual fact behind what I learned by feel as a kid.
 
(quoted from post at 11:10:46 08/14/15) Just a question to ruminate on, not necessarily on restoring an engine, but more to the effect of what wears on an engine to need restoration in the first place.

So....lugging.

Just by the sound of an engine, I learned from my brother (who was 14 years older) to shift a tractor to keep the engine in a very narrow RPM band. If the engine lugs, shift down. If the engine revs, shift up.

I always assumed that this was the best thing for an engine, and I have passed this same method onto our three daughters, who can all drive standard cars. For instance, if they're driving uphill with our Kia; I tell them to pick a gear to keep the RPMs between 2500 and 4000.

People from other families and with other experiences do differently. For instance, my father-in-law. When he pulls out onto the road with a tractor and haywagon, he'll shift directly into road gear and dump the clutch. The tractor will start out almost puking...then sloooooooooooooooooooowly work its way up from about 400RPM to the 1500 or 1800 RPM that his throttle setting would dictate.

During the sometimes thirty or so seconds that it takes for the tractor to get up to speed, he'll just sit back, look straight ahead and drive as if everything is just fine. I'll be riding and thinking...shift down...shift down...shift down.

Am I just being compulsive about this? Or are there actual physics that would say that an engine is being worn down during these extended lugging periods???

PS...I'm not going to get on my father-in-law about this, no matter what. He's my "Pops", and I'm glad for his help on the farm. If it means a few more repairs here and there...no biggie. I am just wondering if there is actual fact behind what I learned by feel as a kid.
nlikely to get any "facts", but you will get a lot of "opinions".
 
Ah but how many tractor as made to be shifted on the fly??? Most are not and doing so can/will cause major problems. Yes a car or truck you shift on the fly a tractor most of them NO
 
I think any real low idling or lugging of the engine in gear is just pounding the lower end bearings and is to be avoided.
 
"Ah but how many tractor as made to be shifted on the fly???"

There's lots of TA's, quad ranges, ampli-torques and powershifts out there, old!
 
(quoted from post at 08:58:57 08/14/15) Ah but how many tractor as made to be shifted on the fly??? Most are not and doing so can/will cause major problems. Yes a car or truck you shift on the fly a tractor most of them NO


I understand, but growing up (mostly with Farmall 60, 06 and 56 series tractors). I would be more inclined to start out in a lower gear to get the load moving. (or with the TA back, as has been suggested) and then either put the TA forward, or clutch and sweep the throttle handle down. As the RPMs dropped, I would move the shift lever and usually be able to upshift without grinding by feeling for when the engine/transmission meshed.

The other side of that, especially with the 06, 56, 66... series of Farmalls, if you selected too high of a gear to start out with and stalled the engine...you have about half a second to shift into neutral and throw the park lever down.

Otherwise, you're free-wheeling; because the brakes are hydraulic and no engine means no hydraulics...means no brakes...and no steering.

We have never had to rebuild the tranny in any of those old 60, 06 and 56 tractors and they've all been through a few engine rebuilds, as dad ran 120 dairy cows meaning 30,000 small squares, two silos full of silage...with just three of those old tractors. The 706 and 856 probably have 20,000 hours on them without ever needing a tranny rebuild.

So, I would say that starting out in a proper gear and upshifting at a proper time can be done without killing the tranny.

edit...the TA has needed repair on all of the old Farmalls, but show me a Farmall with 20,000 hours and an original TA, and I'll show you a TA lever that's never been used...
 
(quoted from post at 10:07:32 08/14/15) "Ah but how many tractor as made to be shifted on the fly???"

There's lots of TA's, quad ranges, ampli-torques and powershifts out there, old!

Right, but TA's and such can wear too.

If the wear from lugging were bad enough, and the damage from shifting on the fly, even with a TA were bad enough...then instead of starting out in road gear and lugging, I would:

-Pick a lower gear and leave it there.

-Pick a lower gear and shift from a dead stop somewhere on a downhill or more level slope which wouldn't cause lugging.

Even in my scenario above in involving upshifting on the fly, I would usually wait until going downhill or on the level somewhere that would allow momentum to let the tractor coast a little, which allows a rolling shift to be done under less pressure.
 
As an off topic aside, that little issue with Farmalls and hydraulic brakes/steering going dead with the engine is also why, for my own farm, I keep things small and only allow my wife and children to drive simpler tractors with mechanical brakes/steering, if possible. I know that old Ford 2Ns and such don't have live PTO...but they always have live steering and brakes. I can replace shear pins. Can't replace my wife or kids.
 
When I was a kid in our area several older farmers traded work. Mainly in harvest time but two or sometimes three would be together with their tractors. Dad and Grandpa always shifted up to road gear. Others did not. We are talking in the late 40's and I am sure that the ones that didn't could not get the hang of it. Those old tractors had to have the engine speed matching the gear speed and when missed on a hill was a problem. Old habits are hard to break or new habits are hard to learn.
 
I dunno...drove lots of old tractors over the years and with practice, I could shift most through the gears to high without stopping---except for those with a hand clutch---then you need three hands to shift, double clutch and throttle up/down.

Ben
 
Ya some like the H or M farmall you had to pretty much do that from 4th the 5th but most your lucky if you can shift them and most people that try end up wit ha bad transmission. I have only owned maybe 50 plus tractor if not more. Plus drove many many more
 
Well I am talking OLD tractor as in 1960 and older and MOST of those you shift on the fly and things tend to come apart other then the Ford SOS
 
Lugging is hard on main bearings and is defined as an increase in throttle opening without a corresponding increase in engine speed.
 
I spent many years as a european auto tech.
When Mercedes-Benz introduced the automotive diesels to the USA, it was know as a " high speed" diesel, meaning the operator was supposed to keep it revved up. Typical American drivers were used to lugging along with large gas engines, and this habit would damage the little engines. They quicky realized the improbability of drivers changing their habits, and went from 3 main bearings to 4 mains to prevent broken crankshafts.
All engines have a preferred cruise speed, and a sweet spot where torque and rpms meet for optimum power and effeciency. Unfortunately most makes do not publish that info.
 
Lugging it up on the road won't do much damage. Lugging it down below rated speed and holding it there in the field will do more damage.
 
If you lose brakes and steering when you kill the engine you have a problem with your tractor since they are designed to have manual brakes and steering if the hydraulics fail. It will take quite a bit more effort but they will continue to work. Having the brake pedals locked together makes a big difference in the amount of pedal travel needed to apply the brakes manually. That is why the operators manuals say to lock the pedals together when traveling on the road.
 

I'd agree, but it's not my experience. My brother's 706, with good brakes, with both pedals locked together will not hold once the engine has failed. You have about a second or two to get them applied and hold while there is residual hydraulic pressure. During that time, if you want to live, you need to get the park lever thrown down.

Otherwise, if you let up on the pedal, when you go to put them down, there is no amount of pressure that a human can put on them that will stop that tractor.
 
(quoted from post at 20:20:18 08/16/15) Lugging it up on the road won't do much damage. Lugging it down below rated speed and holding it there in the field will do more damage.

I think that this is probably the truest statement of all.

That's similar to what I was teaching our daughters about driving a standard car up a very long hill. If you're in such a high gear that the engine is never getting up to its rated speed for a very long time; then I believe it's better to shift down.

Running an implement or working a tractor in the field in such a high gear that it never gets to the point where the governor is satisfied for long, long periods of time, to me, would be a condition that would really lug down an engine and wear on it.
 
I learned to shift on the go with a John Deere B. I can still go up or down through all six gears on the go. It can be done. Mike
 
(quoted from post at 12:30:28 08/17/15)
I'd agree, but it's not my experience. During that time, if you want to live, you need to get the park lever thrown down.

Otherwise, if you let up on the pedal, when you go to put them down, there is no amount of pressure that a human can put on them that will stop that tractor.

This is a fact of this series. Our farm in North Dakota was very hilly, and I didn't know that the tractor (806 Diesel Wheatland) was going to do this at age 13. Talk about panic. I never knew about the parking brake working that way - but I did bail off safely and the tractor rolled to a place where it stopped moving without incident.... but BOY - is that a heart-chest-pounding experience as the tractor picks up speed headed downhill and you don't know what you should do! Since the tractor was going backwards, I had to bail forward - and while trying to NOT land under the front wheels, I crawled up onto the hood to bail off the front!
 
Unless the main bearings are under-designed for tractor use, or if oil pressure is low, bearing wear should not be a problem with short periods of lugging. It is the rings, sleeves, and valves that are hurt the most by lugging. Heads and head gaskets can suffer too if an engine is allowed to lug for extended periods. This latter issue is especially true in diesels. That being said, some non-power shift tractors will easily tolerate power shifting and some just won't. There are no gear synchronizers in older tractor transmissions, so you must double clutch and speed match the gears when you shift. With some designs, a certain amount of prayer is also required. On these later designs, the only options are to briefly lug the engine, to do a abundant amount of clutch slipping, or to continue attempting to power shift until the transmission is "wonked out" enough to shift easier.
 

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