I have had my 1994 K75RT for a little over three months now and have almost 5,000 miles on her, mostly interstate at 65mph+ as I commute 110 miles per day to and from work.  Bike was well cared for by previous owners and does not look it's age. 

Bike had lots of rattles and engine noises which I have been hunting down.  Found bad bearings in the alternator, replaced the alternator and rubbers, but a tapping/clanking noise, while reduced, is still there, coming from somewhere between the alternator and the starter. 

The engine ran a bit rough when I got it, but running Seafoam in the gas has smoothed things out a lot.  Also did an idle vacuum balance on the throttle bodies which has helped.  Engine idles well, but a little fast(1050rpm) and has nice throttle response.

Had noise coming from the front of the engine that I thought might be timing chain slap.  Bike has 59,000 miles so I decided to replace the chain and the tensioner/guides.  All of the old parts still looked like new when I replaced them.  As I expected from the old parts condition, there was no significant impact from the change.

The problem I am after now is that when riding, I get a lot of clatter from around the intake valve on cylinder #1 at idle that goes away at 2000rpm.  When I changed the timing chain I checked valve clearances and all were at the bottom of the spec, .006-.007" on intakes and .010-.011" on the exhaust.  Low, but in spec.

The engine runs like a sewing machine from 2000 to about 5000rpm, but above that begins to clatter again, the exhaust note get a lot louder and changes to more of a moaning snarl, and the engine develops a mild vibration that is barely perceptible in the grips.  While it is making all this commotion there is no discernible loss of power or throttle response.  

What should I be looking for, or is this normal for this bike?  I think she shouldn't be behaving like this.  The clatter at idle and low rpms is annoying while the clatter at high speed makes it hard to relax and enjoy the ride.

As to the low rpm rattle do some research on the output shaft, esp. the rivets and the tension spring assembly. Here's a resto write up that's great. Go about halfway down the page: http://hrsbstaff.ednet.ns.ca/bvogel/K100/K100.htm 

As for the high rpm do an inspection of the exhaust/muffler/muffler cover mounts. Vibes can fatigue the mounting points and back out fasteners, as well. Mine did this and when in the upper revs it sounded like all hell breaking loose. 

Not the definitive remedies, but a start.

good suggestions kyle


many noises are harmonically related

I find even at certain revs with the rt fairing, lots of things start rattling ....

I found a quiet solution one time ...but then I pulled it down again ..the noises returned a little ...ill get round to it again soon

No need to check the rivets...........75's doesn't have them.

Is the output shaft problem common to the 75 or just the k100?  Looking at the link, I wonder if the alternator drive gear bearing is bad.  It looks like a bear to change, have to take most of the drive train apart to get to it.

Exhaust system should be tight, I just replaced the studs, nuts and tightened everything only two weeks ago.  Good suggestion to check for loose stuff, though.  A cursory inspection reveals nothing obviously loose.  A closer inspection will be done shortly.

Just wondering, is it the nature of the RT fairing to direct and amplify engine noise to the rider?  Am thinking of making a few runs with the lowers removed.  Might help with the high rpm noise, but the low speed noise is coming from that area around cylinder #1 which is outside of the fairing.

The fairing can resonate engine noise but not to the point of annoyance. Wouldn't be a bad idea to do a go-around and check that all the fasteners are snug and all washers are present and accounted for. Remember, with all bikes vibes cause all kinds of havoc if not addressed. 
 
Removing the lower will mostly help w/cooling, which is no small thing these days. In fact, I just noticed I took my avatar pic when I had them off.

Point-Seven-five wrote:Is the output shaft problem common to the 75 or just the k100?

It's mainly a K100 problem.

Inge K. wrote:

Point-Seven-five wrote:Is the output shaft problem common to the 75 or just the k100?

It's mainly a K100 problem.

And it's usually the tension spring, not the rivets.

Kyle10 wrote:

Inge K. wrote:

Point-Seven-five wrote:Is the output shaft problem common to the 75 or just the k100?

It's mainly a K100 problem.

And it's usually the tension spring, not the rivets.

Correct, the tension spring on the very early K100 models.

About the noise in the area of #1 inlet......it might be a idea to check the cam
follower......I think Charlie did have a noisy one a ~ couple of weeks back.

Inge K. wrote:About the noise in the area of #1 inlet......it might be a idea to check the cam
follower......I think Charlie did have a noisy one a ~ couple of weeks back.

Any idea of what I should look for?  Could I have a sticky valve or weak spring?  How would I test?

Can't pinpoint what you should look for...but guessing a bad cam follower.

Charlie went offline before seeing this......but I think he described the sound
in his "Show Bike Thread" in the renovation section.

Also check the tip of the cam lobe for wear. I had a worn no 4 inlet cam lobe on my K100RT and it caused the engine to vibrate.

The 75's have solid front engine mounts, checking they are torqued up nice will eliminate that sound, so will tweeking the fairing side panels and they're mounts, before you go pulling the bike apart.

Thanks for all the tips.   Looks like I will be busy with this for the next couple of weeks. 

Also, found this on You Tube last night.  It is exactly the noise I am hearing at low speed(from 1000 to 1900 rpm) on acceleration.  Don't know why it sounds like it's coming from both the rear and the front of the engine.  Looks like a loose bearing.  Anyone ever run into that???

https://www.youtube.com/watch?v=LdSNT4WPxBc

Update:  While oiling the cable connection to the clutch lever last night I noticed that releasing the clutch produced a clank from the vicinity of the rear of the engine.  Turns out that when the clutch is fully released the arm the cable attaches to hits the muffler and then just sits on it.  Running the engine makes it bounce and rattle adding another voice to the mechanical cacophony that seems to be inherent in the running of my K.  

In order to correct it, I had to reduce the length of the exposed cable from the 73mm spec by about 3-4mm and make the appropriate correction in the screw that pushes on the clutch rod.  Just took the bike out for a quick blast this morning and she is sounding really NICE!  Woo Hoo!!! 

There is still that ticking from ~1300 to 1800/2000rpm, which I am beginning to think is a bearing in the alternator drive, but as long as it doesn't get worse, it can wait for the winter tear down I am planning.  For now I am just going to ride the heck out of her.

My wife's K75 was doing that and rattling on the muffler, I had to take it back to 70mm before it stopped completely.

Not a unusal problem on the 75 I'll guess....see on a lot different forums that
owners have problems to adjust the cable to the correct length of the exposed
part as the arm rests on the silencer before it's achieved.

Point-Seven-five wrote:There is still that ticking from ~1300 to 1800/2000rpm, which I am beginning to think is a bearing in the alternator drive, but as long as it doesn't get worse, it can wait for the winter tear down I am planning.  For now I am just going to ride the heck out of her.

I have that noise in my K100RT but I'd describe it as a fast clunking. I was very worried at first but a retired BMW mechanic a mate introduced me to, he told me it was the anti-vibration device between the crankshaft and output shaft and not to worry about it. I only hear it as I take off in first gear when cold and it quickly goes away.
I've tried to find it on http://www.realoem.com but can't seem to locate it. Need a part number.
Cheers

Captain Holister wrote:a retired BMW mechanic a mate introduced me to, he told me it was the anti-vibration device between the crankshaft and output shaft

can't seem to locate it. Need a part number.

I would guess it's the anti-backlash spring that your mechanic did have in mind:  
11 21 1 461 532  SPRING

It's not really a clunking on my bike.  If anything it sounds like someone tapping very quickly on the intermediate case with a ball pein hammer.  It starts suddenly at about 1300 rpm and goes away abruptly at some point between 1800 and 2000 rpm.  I cannot recall it occurring at any engine speed above 2000 rpm.  Seems to do it cold or hot whenever I am pulling away from a stop in first gear(rpms don't go low enough to trigger the sound unless I fail to downshift for a turn and wind up lugging the engine in third gear).  I have checked with a stethoscope with the bike on the center stand in neutral and the sound appears to be strongest when I listen at the top of the intermediate case between the starter and the alternator. 

My question now is whether or not I can get to the alternator drive gears without completely dropping the engine from the frame which looks like a lot of work.   It looks like there is not enough room to pull the intermediate case back with the engine in the frame because of the frame member at the rear engine mount.

If I do have to drop the engine, is there an easy way to do it.  Looks like a lot of stuff to disassemble and disconnect.

You don't have to drop the engine and no there is not an easy way to do it.
You will need to remove everything up to and including the intermediate housing.  You need to prop the rear end of the bike up on a stand and prop the engine under the oil pan then go in from there.
I haven't read all this thread but I presume you have checked the alternator drive monkey nutz.
I once got the vanes between the monkey nutz in the wrong position so it was metal to metal and it stopped making a noise above 2000rpm because the alternator was getting a load and was pressing tight against the vanes.

RicK G wrote:
I haven't read all this thread but I presume you have checked the alternator drive monkey nutz.
I once got the vanes between the monkey nutz in the wrong position so it was metal to metal and it stopped making a noise above 2000rpm because the alternator was getting a load and was pressing tight against the vanes.

That is correct.  I have replaced the nutz(which looked exactly like the new ones) and the alternator which had a noisy bearing.

I am pretty sure I have the alternator clutch housing aligned correctly as I used the index marks on the outside as a guide when I installed it.  But... that is an excellent thing to check anyway as the noise is very much like I would expect those vanes to make if they were making contact.  I guess I should make a run with the alternator removed from the bike to make a positive diagnosis of the source of the noise.

So much to check and so little time available in the next couple weeks.  Darn!