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Old 12-22-2004, 09:27 AM   #1
John E Davies OP
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Has anyone balanced their LC4 engine?

The reason I ask is that Jerome at his website:
http://www.fowb.co.uk/indexBike.htm (look under Bike/ Modifications/ Engine)
says this:

"Swampy at Marsh Performance recommended balancing the crank, conrod and piston. The reason for the wide variability in the smoothness of 640's is that KTM use one set of criteria for all 620, 640 and 660 engines."

I like what Jerome has done to his bike, but when I saw that he has installed a fuel line magnet I got a bit wary of the validity of his claim...

Has anyone internally balanced their engine? With what results? Can anyone comment on Swampy's statement?

Thanks.

John
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Old 12-22-2004, 09:34 AM   #2
darmahman
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My KTM mechanic his motor balanced on his Duke and said it didn't make one bit of difference.
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Old 12-22-2004, 09:41 AM   #3
ChrisC
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Maybe if he had his fuel line magnet balanced....

CC
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Old 12-22-2004, 10:28 AM   #4
meat popsicle
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what's wrong with a fuel line magnet?
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Old 12-22-2004, 11:05 AM   #5
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In a single cylinder engine, there are two factors at work... rotating and reciprocating mass.
Rotating mass is everything within the diameter of the flywheel circumfrence, i.e. crankpin, bearings and thrust washers if any and one half the con rod at it's point of balance. Reciprocating mass, as you can imagine, is the piston, rings, pin and clips, bearing and one half the con rod, again, at it's point of balance.
Rotating mass is always balanced at a factor of 100%. Reciprocating mass is a percentage based on RPM limits, usage and just plain old experimentaion.

A single, cannot be balanced to 100% of it's reciprocating mass, but is usually balanced using a percentage of total weight.

Example:

750 grams is 100% of rotating weight.
500 grams is 100% of reciprocating weight.

We will use a balance factor of 60%, or 300 grams of reciprocating weight and add this to the 750 grams of rotating weight for a total of 1050 grams.

If we are balancing each flywheel independantly using the "static method", we will attach 1/2 or 525 grams of weight to one flywheel, at the crankpin position.
The flywheel half is positioned on a precise and level balance, and weight is removed (or added) opposite (usually) the crankpin balance weight until the flywheel can be placed in any position without rolling to a "heavy" spot.

We can change the percentage factor, and change the "sweet spot" where the bike is smoothest. If a bike vibrates at 4500 to 5500 RPM and we would prefer it be smoother there, but are willing to accept more vibration below that RPM, we can lower the percentage of balance factor, which has the effect of rasing the RPM range at which an engine is in its "best balance".

All this is a very generic overview of the process, and based on a few decades of balancing Harley-Davidson competition engines.

The point I'm trying to make is that there is no free lunch. Competition bikes are balanced to be smooth at the RPM they are ridden... at or near redline. Street bikes are balanced to be smooth at the most common and frequently used speeds. If a bike vibrates at a particular speed you use often, it would be cheaper and easier to change gearing, that to rebalance the flywheel assembly.

Manufacturers do not use the method discribed above, in production they have a standardized value, based on prototype experimentation. This value, although on paper is an exact science, can vary in the realities of production and this (and other reasons) are why two bikes of the same year and model, even bikes sequential in serial number, can be different.

I'm exhausted with all this thinking shit.

Creep
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Old 12-22-2004, 11:06 AM   #6
Jasper
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I have heard this one several times over the years that I have had LC4's. Most often from people that I think should know.

I have not done it, but it sounds right to me. It would explain some of the wide range of reports on vibration levels.

The story is that KTM's have had in the past a wide specification for crank balancing. This may not be as big of an issue on the newest LC4's. If you have a "good one" the benefit of a balance job would be small, is the idea.

My '03 SXC seems quite smooth to me, so I am not interested in doing it to mine, but I ride mostly off highway.

Jasper screwed with this post 12-22-2004 at 11:07 AM Reason: PPS
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Old 12-22-2004, 11:14 AM   #7
meat popsicle
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Quote:
Originally Posted by creeper

I'm exhausted with all this thinking shit.

Creep
Nobody likes a know-it-all creeper...

but thanks for the skinny on balancing.
(not that I was considering for one instant "balancing" my silky-smooth '03 )
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Old 12-22-2004, 11:18 AM   #8
Jasper
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woa!


I was typing while Creeper was posting.

The Creeper or someone may know better than I do, but my understanding of the KTM crank balance story is that the KTM crank is not one piece but three (I think), and that during assembly one can expect a certain amount of assembly error. The idea is to take it back apart and assemble it perfectly.

It is like the crank pin is out of phase, or something.

Where The Creeper says: Rotating mass is always balanced at a factor of 100%.

The idea to the story that I have heard is that the KTM is not at 100% here, sometimes.

This is different or in addition to what The Creeper is describing.

Jasper screwed with this post 12-22-2004 at 11:24 AM
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Old 12-22-2004, 11:35 AM   #9
GoGriz
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Quote:
Originally Posted by creeper
In a single cylinder engine, there are two factors at work... rotating and reciprocating mass.
Rotating mass is everything within the diameter of the flywheel circumfrence, i.e. crankpin, bearings and thrust washers if any and one half the con rod at it's point of balance. Reciprocating mass, as you can imagine, is the piston, rings, pin and clips, bearing and one half the con rod, again, at it's point of balance.
Rotating mass is always balanced at a factor of 100%. Reciprocating mass is a percentage based on RPM limits, usage and just plain old experimentaion.

A single, cannot be balanced to 100% of it's reciprocating mass, but is usually balanced using a percentage of total weight.

Example:

750 grams is 100% of rotating weight.
500 grams is 100% of reciprocating weight.

We will use a balance factor of 60%, or 300 grams of reciprocating weight and add this to the 750 grams of rotating weight for a total of 1050 grams.

If we are balancing each flywheel independantly using the "static method", we will attach 1/2 or 525 grams of weight to one flywheel, at the crankpin position.
The flywheel half is positioned on a precise and level balance, and weight is removed (or added) opposite (usually) the crankpin balance weight until the flywheel can be placed in any position without rolling to a "heavy" spot.

We can change the percentage factor, and change the "sweet spot" where the bike is smoothest. If a bike vibrates at 4500 to 5500 RPM and we would prefer it be smoother there, but are willing to accept more vibration below that RPM, we can lower the percentage of balance factor, which has the effect of rasing the RPM range at which an engine is in its "best balance".

All this is a very generic overview of the process, and based on a few decades of balancing Harley-Davidson competition engines.

The point I'm trying to make is that there is no free lunch. Competition bikes are balanced to be smooth at the RPM they are ridden... at or near redline. Street bikes are balanced to be smooth at the most common and frequently used speeds. If a bike vibrates at a particular speed you use often, it would be cheaper and easier to change gearing, that to rebalance the flywheel assembly.

Manufacturers do not use the method discribed above, in production they have a standardized value, based on prototype experimentation. This value, although on paper is an exact science, can vary in the realities of production and this (and other reasons) are why two bikes of the same year and model, even bikes sequential in serial number, can be different.

I'm exhausted with all this thinking shit.

Creep
BOW DOWN!!
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Old 12-22-2004, 11:52 AM   #10
meat popsicle
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Quote:
Originally Posted by GoGriz
BOW DOWN!!
Now that's gotta make a feller feel like he's worth sumpin'

When is this expertise going into the biz creep? I know you won't touch my 7-port RD heads but hey I think there is a world out there that needs ya using that knowledge for more than just chrome haulers
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Old 12-22-2004, 11:54 AM   #11
ktmnate
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Damn Creeper! you must have been a teacher because I actually understood that.
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Old 12-22-2004, 12:12 PM   #12
creeper
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Quote:
Originally Posted by ktmnate
Damn Creeper! you must have been a teacher because I actually understood that.
Yea... I used to teach this kind of stuff for Harley-Davidson and MMI. Knowing stuff ain't that hard, learning to teach it to others can be the real trick.
I'm just an tricky idiot... but I'm very good at teaching others how to be tricky idiots as well.
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Old 12-22-2004, 07:00 PM   #13
creeper
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Quote:
Originally Posted by meat popsicle
Now that's gotta make a feller feel like he's worth sumpin'

When is this expertise going into the biz creep? I know you won't touch my 7-port RD heads but hey I think there is a world out there that needs ya using that knowledge for more than just chrome haulers
Maybe include balancing as part of the available services when I can aquire enough equipment to conduct complete engine rebuilds in house.


And how's yer' holidays goin' Meat?
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Old 12-22-2004, 07:10 PM   #14
dagwood
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Quote:
Originally Posted by creeper
In a single cylinder engine, there are two factors at work... rotating and reciprocating mass.
Rotating mass is everything within the diameter of the flywheel circumfrence, i.e. crankpin, bearings and thrust washers if any and one half the con rod at it's point of balance. Reciprocating mass, as you can imagine, is the piston, rings, pin and clips, bearing and one half the con rod, again, at it's point of balance.
Rotating mass is always balanced at a factor of 100%. Reciprocating mass is a percentage based on RPM limits, usage and just plain old experimentaion.

A single, cannot be balanced to 100% of it's reciprocating mass, but is usually balanced using a percentage of total weight.

Example:

750 grams is 100% of rotating weight.
500 grams is 100% of reciprocating weight.

We will use a balance factor of 60%, or 300 grams of reciprocating weight and add this to the 750 grams of rotating weight for a total of 1050 grams.

If we are balancing each flywheel independantly using the "static method", we will attach 1/2 or 525 grams of weight to one flywheel, at the crankpin position.
The flywheel half is positioned on a precise and level balance, and weight is removed (or added) opposite (usually) the crankpin balance weight until the flywheel can be placed in any position without rolling to a "heavy" spot.

We can change the percentage factor, and change the "sweet spot" where the bike is smoothest. If a bike vibrates at 4500 to 5500 RPM and we would prefer it be smoother there, but are willing to accept more vibration below that RPM, we can lower the percentage of balance factor, which has the effect of rasing the RPM range at which an engine is in its "best balance".

All this is a very generic overview of the process, and based on a few decades of balancing Harley-Davidson competition engines.

The point I'm trying to make is that there is no free lunch. Competition bikes are balanced to be smooth at the RPM they are ridden... at or near redline. Street bikes are balanced to be smooth at the most common and frequently used speeds. If a bike vibrates at a particular speed you use often, it would be cheaper and easier to change gearing, that to rebalance the flywheel assembly.

Manufacturers do not use the method discribed above, in production they have a standardized value, based on prototype experimentation. This value, although on paper is an exact science, can vary in the realities of production and this (and other reasons) are why two bikes of the same year and model, even bikes sequential in serial number, can be different.

I'm exhausted with all this thinking shit.

Creep

Ow my head hurts now... Danger Will Robinson Danger Danger . The evil Proffesor of BST has gone bottom end.





























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Old 12-22-2004, 07:15 PM   #15
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Quit it Dag... I know you have a fully functioning brain.
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