2000 LT (engine) rattles when hot @ ~3K rpm - BMW Luxury Touring Community
 
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post #1 of 11 Old Aug 7th, 2007, 2:06 pm Thread Starter
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2000 LT (engine) rattles when hot @ ~3K rpm

Just purchased used 2000LT with 25,000 miles last week. I was out last night and heard rattling from the engine area after the bike warmed up when revved around 2500-3500 rpm. If I slowly increased RPM in neutral, the noise would start like individual "bangs" and then get worse until the rpm was around 4K and there was too much other noise to pick out the rattling. Dropping the revs by letting loose of the throttle and you definitely hear it as the tach passes through ~ 3000.

Could be a resonance of loose stuff. But my first thought of was valves / timing chains or whatever ($$$). Pretty scary, I checked oil level (OK), couldn't locate the source by ear, it sounded like it was coming from the engine itself when I moved my head around. No loss of power when riding, just the added noise.
Sounded like the "box of rocks" described elsewhere on this forum that was resolved through welding cracked exhaust headers or tightening same. However, I don't recall reading that the onset of the noise with increasing tempertature. I started the bike this morning and rode to work in 77 degree (as opposed to 85 degrees last night) ambient temperature - no box of rocks. I did take a rubber mallet and bang around on the headers (what I could do with the tupperware on), muffler & guards, and there were no weird resonances.

I took it to Lonestar BMW at lunch today and of course it didn't rock-on. The service manager said these beasts are fairly indestructable, but that I might want to check the header tightness despite the fact the noise typically happens cold, not hot.

Any ideas O' great body of LT knowledge?

Thanks,
Wayne

Last edited by waynelt; Aug 7th, 2007 at 2:12 pm.
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post #2 of 11 Old Aug 7th, 2007, 2:15 pm
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Sure it aint a tupperware rattle ? Mine had the same symptoms, and I thought it was engine noise, then I found this forum. Problem sovled.

2000 K1200LT
1981 Honda CBX ( kind of for sale)
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post #3 of 11 Old Aug 7th, 2007, 2:20 pm
 
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I was told it was the injectors knocking when hot...i have noticed my Vic makes the same noise when its hot...
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post #4 of 11 Old Aug 7th, 2007, 2:21 pm
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One of the other rattles I seem to remember was from the catalytic converter which is located inside the exhaust system, seems I remember a few where it had developed a crack and had an annoying rattle, you should be able to isolate that type of rattle to the area near your left foot (that is where the converter is located).
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post #5 of 11 Old Aug 7th, 2007, 10:14 pm Thread Starter
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Made a recording for you to hear

Thanks for the replies, at least nobody has predicted a dire situation so far. The noise does sound like something's resonating, but for the life of me the source location sure sounds like the engine itself rather than tupperware or muffler. The frequency content doesn't have a lot of "highs" to it, which might mean plastic rattling. I'm still pretty concerned since if there is a major issue the longer from sale to calling the seller the less likely he'll be responsive.

If you have a moment, click on the link below (or paste it in your browser) and listen to the stereo recording (windows wma file) that I made and see if it sounds familiar. The onset (tonight) begins when I slowly raise the revs to 1800, the noise rate is slow, then gets more frequent as the rpm increases. Not obvious in the recording, but when the throttle is closed and rpm decreases, the rattle is fairly prominent. When I shut off the key from idle, there's a couple quick pulses of the noise as the engine stops.

Here's the link where I've uploaded the file:

www.3dr.com/lt/rattle.wma



Thanks for your help.
Wayne
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post #6 of 11 Old Aug 8th, 2007, 1:32 am Thread Starter
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Found a thread that might explain it

I found a thread on a similar rattle (although at idle) where CharlieVT suggests letting the clutch slip to load the engine to see if it goes away. It appears to do just that. The engine was cool and the rattle wasn't as pronounced, but it did dissapear. Whew. Here's CharileVT's post:

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.
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post #7 of 11 Old Aug 8th, 2007, 4:33 am
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Great idea, the recording that is, my 99 had that same rattle though maybe not as pronounced but the same, and the same circumstances surrounded it. I never did anything to eliminate it and it never created a problem for me.
It strikes me that if a lubricated part is the cause of this rattle that you should see an effect on it by changing the oil viscosity which may contribute to the change you are experiencing with temperature. Depending on what type of oil is in it you might try changing to 20-50 synthetic or even a heavier grade if available to see what effect that has on the sound. It seems likely that if subjected to normal service intervals and types it probably contains a 10-30 or 15-40 oil so a change to a heavier viscosity may reveal a change in the sound thus confirming the diagnosis with regard to the shaft movement
.
I make the assumption that you understand that good synthetics hold their viscosity much better than "dino" oils and that the natural thinning that is related to temperature is less pronounced. A word of caution here (which may not be needed) should you try a viscosity heavier than 20-50 it would be wise to allow the engine to warm up a little before actually driving anywhere.

Good luck
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post #8 of 11 Old Aug 8th, 2007, 8:10 am
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That does not sound like alternator drive rattle. Alternator gear train rattle is also not affected by slipping the clutch, as that does nothing to load the drive. You have to increase the load on the alternator by turning on high load items, like high beam headlight etc. to load down the alternator so the gear backlash is taken up.

There are a couple common problems with exhaust components that can cause heavy rattles like you are hearing, the most likely is broken header flanges where the exhaust bolts into the head. Remove the lower engine fairing, loosen all the exhaust flange nuts, then try to rotate the flanges slightly. If any move, they are broken where the pipe is welded inside them. These can be re-welded by removing the exhaust system.

Next to check is the joint between the catalytic converter and muffler. These have cracked nearly all the way around, and will rattle, also leak exhaust gasses. Also can be re-welded easily.

I had both issues, re-welded them.

Another possibility is the exhaust hanger bolted to the centerstand bracket. Check the heavy wire spring loop between the mount and exhaust. These have broken on some bikes.

I am almost positive it is NOT in the valve train at all. There have been almost NO problems in the valve train on any of these bikes.

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post #9 of 11 Old Aug 8th, 2007, 9:37 am
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You can take the post by dshealy to the bank. He's a guru here.

Excellent description, by the way, and MOST excellent recording. While the rattle does increase and decrease with rpm, it did not sound to me that it did so linearly, another reason why it is not likely to be in the valve train.

If you have gone thru the exhaust system possibilities (and as a long shot, I would check the tightness of the exhaust heat shield bolts, although when the heat sheild rattles it sounds more "tinny" to me) and have not found the source of the rattle, check for a loose fairing or loose front fender. My fender vibration caused a similar rattle that increased in frequency with rpm, although it was less "sharp" than your recording. A mechanic's stethescope or a cardboard tube held to one ear while blocking the other ear can often help isolate the position of the source of the rattle. Good luck.

Bill
Guilford, CT
'99 Canyon Red K1200 LT - Buddah Bike
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post #10 of 11 Old Aug 8th, 2007, 11:12 am
 
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Agree with all the above pointers. Also note that the fans come on when hot and will draw alternator power and mine sometimes rattles then.
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post #11 of 11 Old Aug 8th, 2007, 9:48 pm Thread Starter
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Thanks for all the suggestions on here, and to CharlieVT who authored the drive line lash theory above and PM'd me today.

I pulled the lower left plastic off, removed the header nuts and checked the flanges. All looks good there, and no cracks in the muffler joints. Using a wooden dowel to listen to the engine, I'm pretty that the source is inside. CharlieVT PM'd that the loudest area on his LT was at the right rear, which matches mine. Since it goes away with drivetrain load (slip clutch with a blocked wheel), I suspect it's the drive train lash CharileVT wrote about.

I guess time will tell whether this is the case. Now to go out into the mosquito infested yard and see if I can match screws with the appropriate tupperware holes.

Wayne
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