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Old 06-24-2007, 03:53 PM   #1
Sylvia OP
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Hi Chris,
I have a question for you and anyone else who wants to throw your 0.02c worth in.
Motor is LC4 2005 SM running very well.
I did a valve adjustment today. All good and runs like a champion.

I have been playing with valve clearances in my anal way and have discovered the following. With the exhaust valves just over spec clearance (say a loose 007) the motor runs with a lot less vibration all over the rev range. When I adjust to a tight 006 it vibrates a lot more than when itís over spec.

I run it right in spec all the time just to let you know. I just was playing around and sort of fell on this characteristic where loose exhaust valves have the effect of reducing vibrations.

Any thoughts.
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Old 06-24-2007, 05:21 PM   #2
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Quote:
Originally Posted by Sylvia
Hi Chris,
I have a question for you and anyone else who wants to throw your 0.02c worth in.
Motor is LC4 2005 SM running very well.
I did a valve adjustment today. All good and runs like a champion.

I have been playing with valve clearances in my anal way and have discovered the following. With the exhaust valves just over spec clearance (say a loose 007) the motor runs with a lot less vibration all over the rev range. When I adjust to a tight 006 it vibrates a lot more than when itís over spec.

I run it right in spec all the time just to let you know. I just was playing around and sort of fell on this characteristic where loose exhaust valves have the effect of reducing vibrations.

Any thoughts.
Hi pookie,

When you change the valve lash to more or less than "spec" you are in effect "changing" cam timing.
Depending on the individual engines state of tune, even a small change in cam timing will alter vibration levels and powerband characteristics.
By increasing valve lash, you shorten the lift duration in degrees... the valve opens later and closes sooner. This would tend to shift the peak power lower in the RPM range... although the amount you're doing it would be negligible.
The change in vibration is mostly due to a slight change in reciprocating/rotating harmonics and to a lesser degree, combustion pressure curves.

You need to be careful when you "play" with lash... larger clearances mean greater impact loads on the valve train, although again, the small changes you're playing with would be negligible.

You sure it's not a perceived reduction in vibration... or another change you made that, although coincidental, might have more of an effect on vibration than you might first imagine?

Fun with feeler gauges...
C
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Old 06-24-2007, 06:23 PM   #3
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This takes me back to my Triumph TR3B days. Triumph actually published two clearance settings; one for standard use and one for performance. The performance settings were slightly wider, meaning that the cam cam timing was ever so slightly later, giving a little boost to the top end. Everything that's old is new again, including Mr. Hickson...
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Old 06-24-2007, 07:06 PM   #4
Sylvia OP
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Quote:
Originally Posted by creeper
Hi pookie,

When you change the valve lash to more or less than "spec" you are in effect "changing" cam timing.
Depending on the individual engines state of tune, even a small change in cam timing will alter vibration levels and powerband characteristics.
By increasing valve lash, you shorten the lift duration in degrees... the valve opens later and closes sooner. This would tend to shift the peak power lower in the RPM range... although the amount you're doing it would be negligible.
The change in vibration is mostly due to a slight change in reciprocating/rotating harmonics and to a lesser degree, combustion pressure curves.

You need to be careful when you "play" with lash... larger clearances mean greater impact loads on the valve train, although again, the small changes you're playing with would be negligible.

You sure it's not a perceived reduction in vibration... or another change you made that, although coincidental, might have more of an effect on vibration than you might first imagine?

Fun with feeler gauges...
C
Hi Chris,
Thanks for the reply, I knew you had an explanation that was going to make sense in as few a words as possible.

I should point out here that I am careful not to run it out of spec by much and only to see what it does. Itís never that out of spec that you can hear em banging around in there like Iíve heard other motors do. Just enough to be on the high side of loose.

It defiantly has an effect on vibes however, its not perceived as a hypothetical whim of theatrical nonsense, its real. More gap, less vibes. I have it set now right on the money and it runs like a clock, only quieter, but with more vibes throughout the rev range. It doesnít bother me at all, Iím quite used the 640 and actually am getting to like em

I just needed to hear it from you, master, as I new would give me a succinct, and to the point answer. I am just amazed at how such a small adjustment can make such a noticable difference.

Thanks again.
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Old 06-24-2007, 08:53 PM   #5
creeper
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Quote:
Originally Posted by Sylvia
I am just amazed at how such a small adjustment can make such a noticable difference.

Thanks again.
I'm pretty amazed myself... wouldn't think it would, but in this instance with this motor, that small a change apparently does have an effect.

C
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Old 06-24-2007, 09:51 PM   #6
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Hmmn. I should try this, as I'm on an never ending quest to deal with my 04 SXCs vibes.

By the way, I stumbled upon this today, not that I want to loose the magic button, but interesting. Older pre hi-flow head motor.

http://www.altmann.haan.de/ktm_lc4_flywheel/
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Old 06-24-2007, 11:47 PM   #7
Sylvia OP
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Quote:
Originally Posted by creeper
I'm pretty amazed myself... wouldn't think it would, but in this instance with this motor, that small a change apparently does have an effect.

C
Yep, no more surprised than me, thatís why I had to ask, I thought I was dreaming as well. I guess you get to know your motor pretty well after a while, its noises and little things it does that make it just that little bit different from others. Thatís one of the things I like about KTM, their bikes have soul that you can't always get out of some, here to be nameless, brands.

I spent about 6 hours yesterday farting around with valve tolerances. All within specification in a loose sort of fashion, so to speak and the bottom line is: loose exhaust values have a smooth effect on my motor, inlets does not seem to have any effect at all. Performance wise I think it is crisper right on the money, but more vibes everywhere in the rev range.

Anyway I read your long winded diatribe that you have now removed. I got a fuzzy feeling and had to bail out, it was too much for the left frontal lobe to digest.


Thanks for your time and explainations Chris.
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Old 06-25-2007, 06:15 AM   #8
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Quote:
Originally Posted by crazybrit
Hmmn. I should try this, as I'm on an never ending quest to deal with my 04 SXCs vibes.

By the way, I stumbled upon this today, not that I want to loose the magic button, but interesting. Older pre hi-flow head motor.

http://www.altmann.haan.de/ktm_lc4_flywheel/
waidaminnit... was i the only person who noticed this? this doode's a nutter!
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Old 06-25-2007, 07:16 AM   #9
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Wow! 5.3 pounds of flywheel weight may be a new record. I'm guessing it would be quite smooth, just like my old hit and miss engine. You could prolly set the idle down to 200rpm or so. I should suggest one of these to a buddy of mine who can't deal with the hit of his CR125 except it might topple off the side stand.
John....


/hate to hijack Sylvia's thread but a five pound flywheel weight is absurd.
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Old 06-25-2007, 07:24 AM   #10
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Quote:
Originally Posted by creeper


The change in vibration is mostly due to a slight change in reciprocating/rotating harmonics and to a lesser degree, combustion pressure curves.

I'm going to memorize that sentence.
I don't think I've seen anything quite ike it here.
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Old 06-25-2007, 08:13 AM   #11
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Quote:
Originally Posted by Sylvia
Anyway I read your long winded diatribe that you have now removed. I got a fuzzy feeling and had to bail out, it was too much for the left frontal lobe to digest.

Thanks for your time and explainations Chris.
After I looked at it for awhile I thought... nobody wants to know that stuff, and it really just scratches the surface of how cams work, so why muddy up the waters with techno-babble.

When someone asks a question such as your's, it opens a door in my memory closet and sometimes the only way to close that door (so I can get some sleep) is to write stuff... to empty the contents so to speak.
Doesn't mean it's worth knowing or has a bearing on reality.

You do have to give the flywheel guy... AKA "nutter" an 'A' for effort. Put enough flywheel mass on an engine and it's bound to soak up a bit of something... including throttle response.

Hi Colie...

Hey Sycamore... you'd probably do well to forget it. Chances are I'll never repeat it again.
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Old 06-25-2007, 08:15 AM   #12
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Quote:
Originally Posted by Loadedagain
waidaminnit... was i the only person who noticed this? this doode's a nutter!
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Old 06-25-2007, 08:16 AM   #13
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Look who's talking... King Nutter of Southern Woooooshington.
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Old 06-25-2007, 08:20 AM   #14
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Look who's talking... King Nutter of Southern Woooooshington.



















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Old 06-25-2007, 11:43 AM   #15
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But I still love ya'.
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