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  Topic Review (Newest First)
May 15th, 2007 6:30 pm
CharlieVT
K bike rattle

Main point here is for Skip, the rattle you're are hearing is probably normal. It goes way when you increase RPMs, when you let out the clutch, and when you turn on your Hella lights.

Quote:
Originally Posted by CARNEYM
Alternator, I know this because when I turn on and off my Hella lights, the rattle changes.
What was that proverb about the blind men and the elephant? They guy holding the tail says an elephant is like a rope, and the guy feeling the leg says an elephant is like a tree.
Any alternator that is rattling probably isn't long for this world. Two bearings, stator, rotor, field coils, diodes... none of that should rattle. However the drive train that powers the alternator could make noise. Hmmm, power is coming from the engine drive train, so increased load on the alternator (e.g. Hella lights) puts more load on the engine drive train and quiets the rattle. The rattle occurs at low engine RPMs and under no load conditons. So that's why people think the alternator rattles; the rattle ceases when the alternator is loaded. Actually what you are quieting is drive train noise.

That's my theory, and I'm still sticking too it.

And it is an annoying rattle, my bike sound like a shaking metal pail full of rocks when idling.
May 15th, 2007 6:26 pm
jzeiler
Quote:
Originally Posted by CARNEYM
Alternator, I know this because when I turn on and off my Hella lights, the rattle changes.
That is because you change the loading on the helical cut gears by changing the load on the alternator. CharlieVT hit the nail on the head on this one.
May 15th, 2007 9:03 am
CARNEYM Alternator, I know this because when I turn on and off my Hella lights, the rattle changes.
May 15th, 2007 8:07 am
CharlieVT
K bike rattle

Quote:
Originally Posted by SkipI
I recently purchased a 2005 K1200LT with 7800 miles and was just wondering if the bikes normally have a rumble noise when at idle. It sorta sounds like there is a box of rocks rumbling around in there. Raise the rpms a couple hundred and the noise is gone. Wanna get any problems resolved before the warranty expires!

Thanks!
People have attributed this rattle to the clutch or the alternator (assuming it is not fairing plastic or a exhaust manifold stud loose or broken.

I looked into this extensively when I first got my 2000. (Note that this rattle varies from bike to bike, some very noticeable, others don't seem to rattle at all.

I listened around with a mechanic's stethoscope with the plastic off, discussed the issue with an experienced BMW service tech and studied the engine design.

Another test for this rattle is to slip the clutch out a little while hold the brakes; this will load the drive line. Helical cut gears at the crankshaft and intermediate shaft result in axial movement of the shafts back and forth when the drive line is unloaded resulting in the "rocks in a can" rattle. By loading the drive line, the axial oscillation of the shafts stops and the rattle goes away. Shims are installed to limit axial movement of the shaft and depending on how much end place there is in any particular bike determines how much rattle you have. Assuming the engine was assembled with endplay within specified limits, those engines with end play at the larger limit of specified end play will rattle more than those shimmed to the minimal limit of end play.

That's my theory and I'm sticking to it

The rattle is normal, characteristic of the engine, and not to be worried about.
May 15th, 2007 7:49 am
Ekim Good idea Jer. (one of those "why didnt I think of that" moments)

I have some door isulating foam with a sticky back that will probably fit in there nicely. I will give that a try.
May 15th, 2007 7:45 am
jers99lt
Foam to quiet

Quote:
Originally Posted by Ekim
My 2005 rattles at idle too. Some of my noise comes from the lower fairing just in front of the radiator. While its idling I'm able to grab the lower portion of the fairing and the rattle goes away or rev the motor and it goes away. Havent found a way to keep it from rattling, but I gotten used to it and probably would think something was wrong if it didnt make noise
I "wedged" a strip of foam rubber about this thick [ ] and long about a half inch deep where the two plastic pieces meet. That's where I found a rattle.

Jer
May 15th, 2007 6:17 am
Ekim
Normal

My 2005 rattles at idle too. Some of my noise comes from the lower fairing just in front of the radiator. While its idling I'm able to grab the lower portion of the fairing and the rattle goes away or rev the motor and it goes away. Havent found a way to keep it from rattling, but I gotten used to it and probably would think something was wrong if it didnt make noise
May 15th, 2007 5:42 am
GSinNC
Quote:
Originally Posted by SkipI
I recently purchased a 2005 K1200LT with 7800 miles and was just wondering if the bikes normally have a rumble noise when at idle. It sorta sounds like there is a box of rocks rumbling around in there. Raise the rpms a couple hundred and the noise is gone. Wanna get any problems resolved before the warranty expires!

Thanks!
When I bought my '05 LT about 18 months ago I asked the same question .... response I got was yes that is the normal sound.
May 15th, 2007 12:49 am
Ted Shred
Quote:
Originally Posted by SkipI
I recently purchased a 2005 K1200LT with 7800 miles and was just wondering if the bikes normally have a rumble noise when at idle. It sorta sounds like there is a box of rocks rumbling around in there. Raise the rpms a couple hundred and the noise is gone. Wanna get any problems resolved before the warranty expires!

Thanks!
The bike has a single plate dry clutch. It's normal noise. Pull in the clutch lever and it goes away...
May 15th, 2007 12:43 am
SkipI
Idle noise of LT

I recently purchased a 2005 K1200LT with 7800 miles and was just wondering if the bikes normally have a rumble noise when at idle. It sorta sounds like there is a box of rocks rumbling around in there. Raise the rpms a couple hundred and the noise is gone. Wanna get any problems resolved before the warranty expires!

Thanks!

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