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I've heard it said before and am not rejecting the idea. I simply do not know what it means and therefore do not understand.
 

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Just passing thru
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Did you ever ride a bicycle up an incline in too high of a gear? It puts tremendous strain on your legs and if you downshift it's much easier for you to make it up. It's less strain on your legs. Think of the pistons as upside down legs.
 

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its rusting
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good information. i'm guilty of doing this to my truck: i try to go uphill alot in overdrive gear with the rpms below 2500
 

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Official Ass Tweaker
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Lugging the engine, as well as putting more mechanical strain on, also causes pinging, or detonation (pre-ignition), and does it when the oil pressure is at its lowest due to lack of revs - the worst possible combination.

If you look at a typical torque curve, you'll see on the left side the torque is relatively flat until revs increase and torque starts to improve. This flat area is where lugging occurs, as the engine is not getting enough fuel/air to make the power being demanded of it to accelerate the weight of the machine and rider.

It is not harmful to be in this area as such - for instance when decelerating, cruising downhill, or stopped at idle - it's wide throttle openings in the lugging zone that put demand on the engine to generate power which it is not getting fuel/air to be able to do.

Generally, it's best to be firmly on the rising torque area before applying heavy acceleration loads. You will likely get away with light acceleration on the flat or downhill, but it's bad practice anyway.

Personally, my bike is supposed to peak torque at around 3,000 rpm. I like to keep it in the 2,000 area to accelerate moderately, a bit more if I want to accelerate hard.
 

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Discussion Starter #7
Ok Mr. Logan, that expands my understanding, but due to my ignorance leaves me with another question: Is the lack of fuel simply because of lack of throttle being applied?
 

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Ok Mr. Logan, that expands my understanding, but due to my ignorance leaves me with another question: Is the lack of fuel simply because of lack of throttle being applied?
Too much throttle, not enough revs. On a carb, lack of revs = lack of vacuum, so you are effectively dumping a load of fuel in while not having enough vacuum to pull in sufficient air. You're not getting enough mix, but also you are getting too much fuel for the air you can pull in.

As the pistons are moving more slowly, the resulting rich (denser) mixture is compressed for longer, creating higher chamber pressures, which in turn creates more heat, which in turn causes the mixture to go bang when it shouldn't (detonation).

So with mild lugging, you just feel the bike bog down which is a signal to downshift.

If you persist on keeping the throttle wide open without downshifting, you get the more extreme symptoms like detonation which put a lot of extra stress on the engine.

EFI is supposed to compensate by not allowing excess fuel when it can't get enough air, regardless of the nominal throttle opening. Some systems are more successful at this than others, depending on how they monitor, measure and calculate.
 

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COB
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Lugging your engine is tough on the main bearings. The connecting rod rides on a thin layer of oil in your main bearings. You can damage the bearings by too much RPM or too low RPM under load. Low RPM under load can cause the film to break down and you will get metal-to-metal contact at the main bearings. This leads to the dreaded "rod knock". Sometimes known as the "death rattle".
 

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Official Ass Tweaker
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And load is combustion in the chamber?
Yeah - combustion leads to expansion which in the confined space of the chamber causes load which should be used to force the piston down, thus forcing the crankshaft to go round and round. The engine is timed to start applying that load just before the piston reaches the top of its travel, so that the full load comes in as the piston reaches the top and starts down again. That's why we time the ignition to start typically something like 5 degrees BTDC (before top dead center).

If you get detonation (too early combustion due to heat and higher pressures), then the load is applied to the piston while it is still too early in its climb towards top, which effectively applies a load which tries to drive the engine backwards, which it isn't designed to do.

To continue the bicycle analogy, if you have a solid drive (no freewheel), then you want to apply the driving force just as the pedal goes over the top of its travel. If you apply it too soon, you are effectively trying to stop the drive train, and applying forces in the opposite direction the machine was designed to take them.

CBM is quite right also. If all of these things are happening at the same time as the oil pressure is at its lowest due to lack of revs, so the oil pump is moving slowly and not delivering pressure, then you have the worst of all worlds, with unfriendly loads being applied at higher than design pressures, at precisely the time when the engine is worst equipped to deal with them.
 

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STAND AND FIGHT!
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All good advice in general. Generically. Especially on a real hot day, or with cheap or low octane gas. Or REALLY heavily loaded.

However, on a big Harley, without two heavy riders and a ton of gear, or bad gas or hot weather, I'm not sure I'd worry about it one bit. Yeah, if you could maintain throttle at the very edge of stalling the engine I wouldn't. But if I feel like hearing the individual cylinders firing on a long grade, I'm quite comfortable, and I believe the engine is quite comfortable, chugging along like an old John Deer tractor.

One of the concerns expressed, heavy load when oil pressure is low...
In the first place, Harley's don't make or need much oil pressure, as I recall the last time I saw a pressure gauge on a Harley, it looked like there was never any pressure. I'm speaking from the engine knowledge I had 30 years ago, but I'd bet Harley's still use "roller bearings" Oil pressure and riding on an oil film are true facts on engines with fixed babbitt bearing and very close tolerances to hold the oil film under pressure, but roller bearings don't hold, or need pressure, they just need to be wet. Another note that doesn't make much sense to me, is the concept of high load at near stalling rpm. If the engine makes 30 X as much power at peak, how can lugging along at near stalling speed be high load?

I'm not trying to be argumentative, but I don't believe big long-stroke Harley motor riders need to worry much about keeping the rpms up. They are made to pull at low RPM.

For Lil, roller bearings vs babbitt bearings...
 

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Official Ass Tweaker
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In general, I agree with what Nathan says also.

The Harley engine relies on volume of oil rather than pressure. 12-15 lbs of pressure is normal, against say 60 in some car engines.

To successfully lug a Harley engine you have to point the thing up a serious incline, get the revs down under 1,000, crack the throttle wide open, and keep it there in spite of all the protesting noises from underneath :D

And that's on a carb. EFI should be better - ie: more difficult to lug.

All of that said, and not wishing to contradict anyone, I still ride in the torque band.

Looking at more or less any torque curve, max torque is between 3 and 4,000 rpms.

Under 2,000 and above 5,000 the torque is relatively flat.

Obviously, you can use rev ranges under 2,000 and not lug the engine. Like when slowing down. You can also rev the thing to the limit - computer controlled in some cases, controlled by fear in mine :D

But for general purposes, and when you want power on hand, riding in the 2,000 to 5,000 range will do just fine and will not run any undue risks of doing anything bad to the motor.

Says he with the broken bottom end :rofl::rofl::rofl:
 

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Discussion Starter #15
Yeah - combustion leads to expansion which in the confined space of the chamber causes load which should be used to force the piston down, thus forcing the crankshaft to go round and round. The engine is timed to start applying that load just before the piston reaches the top of its travel, so that the full load comes in as the piston reaches the top and starts down again. That's why we time the ignition to start typically something like 5 degrees BTDC (before top dead center).

If you get detonation (too early combustion due to heat and higher pressures), then the load is applied to the piston while it is still too early in its climb towards top, which effectively applies a load which tries to drive the engine backwards, which it isn't designed to do.

To continue the bicycle analogy, if you have a solid drive (no freewheel), then you want to apply the driving force just as the pedal goes over the top of its travel. If you apply it too soon, you are effectively trying to stop the drive train, and applying forces in the opposite direction the machine was designed to take them.

CBM is quite right also. If all of these things are happening at the same time as the oil pressure is at its lowest due to lack of revs, so the oil pump is moving slowly and not delivering pressure, then you have the worst of all worlds, with unfriendly loads being applied at higher than design pressures, at precisely the time when the engine is worst equipped to deal with them.
Please pardon my forgetting to say thank you.

Thanks Pete!
 

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Official Ass Tweaker
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Please pardon my forgetting to say thank you.
On the contrary, it is those of us with overweaning egos and a compulsive attraction to an audience who should thank anyone who is willing to listen to our silly wittering :rofl::rofl::rofl:

I thank you, I thank you, I thank you :D:D:D
 

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Too much throttle, not enough revs. On a carb, lack of revs = lack of vacuum, so you are effectively dumping a load of fuel in while not having enough vacuum to pull in sufficient air. You're not getting enough mix, but also you are getting too much fuel for the air you can pull in.
Curious how this works. With a carb being dependent on a vacuum to draw fuel into the intake path, how does it dump a load of fuel without enough vacuum to pull in sufficient air?
 

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STAND AND FIGHT!
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People get into the habit of thinking it is the fuel flow they control with the throttle, when it is only the air, except for carbs w/ an accelerator pump.
 

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Official Ass Tweaker
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Yep - I was being too focused on my own rig, which is an S&S Super 'E' with an accelerator pump that dumps a squirt of fuel in when you crack the throttle hard. It also has twin Dial-A-Jets, which complicates things.

Other carbs don't work this way.
 
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