Lugging, what is really lugging the motor?
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Outstanding HDF Member
Joined: Feb 2007
Posts: 2,976
Likes: 49
From: Northern California
There sure are some great answers to the question posted here and thanks to all who did.
Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
Likes: 402
From: Phoenix '53, '88, '09 Big Twins
The Twin Cam motor does not have much of a flywheel to store rotational motion.
- this makes for a faster revving motor- which customers like.
but what it can do is allow the rotation of the motor to not be smooth, each stroke can cause surges in motion which a larger, heavier flywheel would smooth out....same for the piston trying to move up on the compression stroke and overcome the building pressure of the compressing mixture
these surges can cause motion which should be rotational, instead shock the bearings.
points of shock would be the piston/ connecting rod, the con rod/flywheel ( or crank), and the flywheel/case.
over time the tolerances in these locations will grow, and more slop will be allowed.
until the bearings break down.
attempting to run the motor at lowest rpm for fuel efficiency fails to take in other factors.
there is a peak volumetric efficiency for each motor- this is determined by flow design, cams and other factors
( for instance on my 1974 Kawasaki the owners manual gives best speed for MPG as about 72 MPH, which would be about 4600 RPMs)
The peak design efficiency is not published by H-D, AFAIK.
I suggest that revs be kept up above 2800 rpms.
In addition to keeping the rotation going, this has good oiling.
Oil pressure and volume are dependent on rpm, oil not only lubricates but is also part of the cooling system, removing heat from the hottest parts on the motor. ( this is whay idle speed is about 1000 rpms)
This also allows the rider to decrease speed by throttle control, rather than using the brakes. This can be pretty important in canyon riding.
what we call the "power band" where speed is instantly increased or decreased with the throttle
While the Twin Cam looks alot like the earlier H-D V twin motors, it is a completely different animal, and cannot idle at 600 rpms.
It does provide much better power and longer life.
explained as best I can.
mike
- this makes for a faster revving motor- which customers like.
but what it can do is allow the rotation of the motor to not be smooth, each stroke can cause surges in motion which a larger, heavier flywheel would smooth out....same for the piston trying to move up on the compression stroke and overcome the building pressure of the compressing mixture
these surges can cause motion which should be rotational, instead shock the bearings.
points of shock would be the piston/ connecting rod, the con rod/flywheel ( or crank), and the flywheel/case.
over time the tolerances in these locations will grow, and more slop will be allowed.
until the bearings break down.
attempting to run the motor at lowest rpm for fuel efficiency fails to take in other factors.
there is a peak volumetric efficiency for each motor- this is determined by flow design, cams and other factors
( for instance on my 1974 Kawasaki the owners manual gives best speed for MPG as about 72 MPH, which would be about 4600 RPMs)
The peak design efficiency is not published by H-D, AFAIK.
I suggest that revs be kept up above 2800 rpms.
In addition to keeping the rotation going, this has good oiling.
Oil pressure and volume are dependent on rpm, oil not only lubricates but is also part of the cooling system, removing heat from the hottest parts on the motor. ( this is whay idle speed is about 1000 rpms)
This also allows the rider to decrease speed by throttle control, rather than using the brakes. This can be pretty important in canyon riding.
what we call the "power band" where speed is instantly increased or decreased with the throttle
While the Twin Cam looks alot like the earlier H-D V twin motors, it is a completely different animal, and cannot idle at 600 rpms.
It does provide much better power and longer life.
explained as best I can.
mike
Last edited by mkguitar; Mar 11, 2014 at 02:57 PM.
Club Member
Joined: Jun 2007
Posts: 45,429
Likes: 2,898
From: Bedford UK
Between us we have just about covered the subject! Lugging is over-loading the engine. That can occur in a range of circumstances, as already mentioned, especially using a high gear at too low an engine speed. I suspect the latest fly-by-wire bikes have some sort of protection against it, but for those of us with a throttle cable, make good use of the trans!
Road Captain
Joined: Sep 2010
Posts: 722
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From: Deep south in a bunker
Outstanding HDF Member
Joined: Jan 2010
Posts: 2,916
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From: earth
I like to use the term "putting the motor in a strain". From whatever point in a ride, if you accelerate and the bike pulls weakly, I call that lugging. But in the in the next 1/10 of a second I have acknowledged it and down shifted, nothing lost. Hey there it is, if you feel like you need to down shift, do it. Keeping the engine in a strain for long duration is lugging
Last edited by fabrik8r; Mar 11, 2014 at 01:42 PM.
Thread Starter
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Outstanding HDF Member
Joined: Feb 2007
Posts: 2,976
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From: Northern California
Look at all these great descriptions of lugging the motor. I bet there are many who learned something by reading this. I did.
Thank you all who replied. This forum is great.
Thank you all who replied. This forum is great.
Outstanding HDF Member
Joined: Nov 2006
Posts: 2,144
Likes: 10
From: Mass
...that WAS CRAZY!...what was that guy trying to do?..looked like he was shifting every 1 m.p.h. increase, ...sheesh...
.."Lugging"...trying to ride a 10-speed bicycle up-hill,..in tenth gear...hows your legs?(connecting rods)...
.."Lugging"...trying to ride a 10-speed bicycle up-hill,..in tenth gear...hows your legs?(connecting rods)...
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Intermediate
Joined: Aug 2012
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From: Golden, CO
Harley engines are designed for low end torque. That's why we all like them so much. It's also easy to downshift to get in the sweet spot of the power band. Running a standard transmission in a car has the same issue. If you have no power response you are lugging the engine. Doesn't hurt anything, you just need to downshift to get the performance you want for the situation.
Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
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From: Phoenix '53, '88, '09 Big Twins
you might want to re-think that...
especially if you want to keep your "Hawgs 4 evah"
mike
especially if you want to keep your "Hawgs 4 evah"
mike
Last edited by mkguitar; Mar 11, 2014 at 04:41 PM.