Knocking sound -electrical problem? - BMW Luxury Touring Community
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post #1 of 5 Old Mar 29th, 2008, 11:11 pm Thread Starter
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Knocking sound -electrical problem?

Hi Gang,
I own, and love, an '05 LT. I have one issue I can't resolve. When the engine is hot (and especially when it's hot) and I have the bike in neutral and apply the brakes, i get a knocking sound. I get the same sound when I put the bike up on the electric center stand. It seems that any electrical load, at certain temperatures and idle rpm, will cause a knocking sound. I've asked the dealer to check this out and they say they don't hear it or "it's fine, don't worry about it" or "it's all that tupper wear". I also get a similar sound when I hold the brakes and let the clutch out enough to slightly strain the engine and lower the rpm's. the bike has just over 16K miles and otherwise runs like a top.

Any answers,

'05 Dark Graphite
Greensboro, NC
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post #2 of 5 Old Mar 30th, 2008, 5:43 am
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Re: Knocking sound -electrical problem? -> lose drivetrain?

Just a shot in the dark: how about if it is related more to rpm's than electrical load (judging by your clutch experiment).

Maybe at lowered rpm's (due to alternator or clutch loading) you can hear the valve train or crank bearings more? Normally, I'd say you hear the clutch basket more (our favorite basket of rocks...) - but I don't think that you'd hear it as much with the clutch applied.

At this point, my uneducated guess would be that it should not cause any worries - probably normal loosening up - if it is the drivetrain, it will get worse gradually .

Sounds like my LT's, although I cannot confirm: bike still under wraps. But, I finally got the GS out for a post-winter shakedown yesterday. Spring's here!

Robert in Northern NJ

'09 R12GS, '08 R12RT, '03 R1150RT, '01 F650GS - time to thin the herd?

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post #3 of 5 Old Mar 30th, 2008, 8:27 am
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Re: Knocking sound -electrical problem?

It could be the drive gears for the alternator. They are supposed to be set up at the factory for a specific amount of clearance. There are three different sized gears available to set this. It is a BIG job to tear down the rear of the engine to measure this, and more work to replace the intermediate shaft with one of a different size.

There is another possible cause, which I had. Broken exhaust header pipes where they are welded into the flanges that bolt into the head. Mine had a pronounced rattle at low RPM, and it took me a long time to narrow it down and find the problem. Welded them back and no more rattle.

There have also been several breaks in the welding between the catalytic converter and muffler section of the exhaust. I also had this happen, again re-welded.

I don't want to achieve immortality through my work...I want to achieve it through not dying.

David Shealey
Dandridge, TN
EX: '01 Black LT, BAT BYKE (Totaled at 110,000 miles)
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post #4 of 5 Old Mar 30th, 2008, 8:38 am
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Re: Knocking sound -electrical problem?

Sound's like altenator noise. As you stated when you apply brakes or use center stand the noise increases, both increase electrical load which leads me to believe it's the altenator. It maybe slightly loose, I believe you can see the bolts on the righthand side just in front of the battery. Check those out and tighten if neccesary. If not loose then it's the altenator gears or the exhaust as David said.

Pat Rourke
White Lake,MI.
2002 K1200 LTC, Champange

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post #5 of 5 Old Mar 30th, 2008, 11:56 am
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Re: Knocking sound -electrical problem?

Might just be the tupperware. My 05 rattles the tupperware at idle and it changes with even the slightest RPM change. Hitting the brakes runs the boost pump and that slows the idle RPM a bit and it starts rattling. It can sound like engine knock when it hits just the right resonant frequency.


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