Looking for help researching noise/vibration problem

[bmwcyclist]

Bike: 1995 (1994 07/1994 mfg date) K75RT, 50K miles, not well maintained by the previous owner but things might be getting better.

Symptoms: Idle fine. Rev in neutral fine. I engage gear, release clutch and I get a vibration and noise that goes away in just a few seconds.

Other possibly relevant information

Clutch adjustment has been checked and rechecked.

Had a leak at clutch/gearbox boot, replaced boot.

Alternator and monkey nutz recently replaced.


I was wondering if the problem might be related to the clutch throw-out rod/bearing system but I did not have success finding a thread on that topic.


Thank you.

[The Mighty Gryphon]

Is the noise kind of a metallic clank that comes from around the alternator between 1200 and 2000rpm?   My K75RT does that and it is caused by a sloppy fit in the drive between the output shaft and the balance shaft that allows for the balance shaft to bang around when coming off an idle under load.


DSCN1758.JPG (46.82 kB . 768x576 - viewed 583 times)

I have torn my engine down to to fix it, and it appears to be intentional, and after nearly 70,000 miles there is no signs of any wear or damage.  It sort of sucks that such a nice bike has that thing going on, but I have just chalked it up to being part of the charm of my bike.

Have you checked the valve clearances and balanced the throttle bodies?  That will help to smooth out the running of the engine.

[bmwcyclist]

Thank you very much for your reply!

Because the noise only happens right after engagement of the clutch and for a few seconds after drive-away, I am making the assumption that it is not related to the alternator unless you think my thinking is misplaced.

Have you checked the valve clearances and balanced the throttle bodies?

Yes. Thank you for asking. Any other ideas?

[Laitch]

Because the noise only happens right after engagement of the clutch and for a few seconds after drive-away,

Is this noise a knock, rattle, squeal, screech, rumble or howl? Is engagement of the clutch smooth or hesitant? Does this noise happen with every engagement of the clutch after every shift, or just in first gear from a stop?

Can you record the noise, post it on YouTube and send us a link to the recording?

[bmwcyclist]

Is this noise a.....rattle,

Yes

Is engagement of the clutch smooth or hesitant?

smooth

Does this noise happen with every engagement of the clutch after every shift, or just in first gear from a stop?

Just in first gear from a stop, or just checking I found also from second from a stop.

Can you record the noise, post it on YouTube and send us a link to the recording?

Yes, I will attempt to do so.


Thank you.

[johnny]

greetings...

does it sound like this...



j o

[Laitch]

Is this noise a . . . rattle . . .?

Yes

I don't want to disappoint you and make this seem less serious than you might like it to be, but there is a chance that you aren't giving it enough throttle at takeoff and aren't running up to high enough revs before you shift to second gear. Bricks like revs. Maybe your other 75 is just different.

Take heart though. It could be something serious after all.     We're all eager for the recording.

[Laitch]

. . .  just checking I found also from second from a stop.

Takeoff from second gear needs high revs and careful clutch release. I wasn't recommending that as part of diagnosis.

[Bon Jon Bovi]

He mentioned a vibration in his first post and not too well-maintained by the PO, makes me think of a dirty/ oily friction disc. Oc other possibilities would need to be eliminated before diving that deep.

New bricker here so if that's total bollocks, apologies.

[bmwcyclist]

Ok, did some riding got some audio/video.

This one is after the bike warmed up and it had the vibration/noise BOTH in 1st and 2ond gear, only time I observed this.



This one is initial start out cold. Case is blocking video but you can hear well.

TWO starts with the sound disappearing during roll out at 5 seconds and on the second run 18 seconds.

[Laitch]

Ok, did some riding got some audio/video.

Thanks for the video.  More throttle from the get-go. That tach shouldn't be climbing then plunging. The rattle seems to be happening when acceleration is recovering. I call that lugging. You can call me hopeful.

How does your other Brick perform in first and second gear?

[Laitch]

. . . if that's total bollocks, apologies.

We don't have bollocks in Vermont so I don't recognize it if it is. Is it like fajitas?

[Filmcamera]

more  like huevos...

[The Mighty Gryphon]

Between my abnormal hearing loss and the crap speakers in my laptop I have no idea what your noise sounds like. 

Question: Do you hear the noise at a specific engine speed?  On my bike I get the clanking at 1500 rpm regardless of whether the bike is in gear, the clutch is in or out, or if it's moving or standing still. 

I get the clank on my bike starting from a stop in first gear, but after that, the engine doesn't drop the rpm's enough when shifting to set it off. 

[johnny]

greetings...

the moar the motobricker wears earpluggs the moar they stop freaking and getts some yeeeehaaaa motobricking...

try it...

j o

[Laitch]

On my bike I get the clanking at 1500 rpm regardless of whether the bike is in gear, the clutch is in or out, or if it's moving or standing still. 

It isn't clanking on his. That might be Marley's ghost you're hearing. Does it happen more around Christmas?

[The Mighty Gryphon]

Haven't noticed it at Christmas.  I suspect all the snow muffles the sound.

[volador]

Huevos rancheros, fajitas... any one around for Taco Tuesday?

Ok, did some riding got some audio/video.

This one is after the bike warmed up and it had the vibration/noise BOTH in 1st and 2ond gear, only time I observed this.

https://youtube/kxt3oC62rkE

This one is initial start out cold. Case is blocking video but you can hear well.

TWO starts with the sound disappearing during roll out at 5 seconds and on the second run 18 seconds.

https://youtube/kxt3oC62rkE

Yo, BC a total of 12 seconds of bullocks, bugger

[bmwcyclist]

Here is the correct link for the second video/audio

Quality is not great but you can really hear when the rattle stops during roll out at 5 seconds and on the second run 18 seconds.

[The Mighty Gryphon]

I just listened with my headphones.  Sounds like the balance shaft in my K75RT.  My theory is that the slightest imbalance between the cylinders will cause that tang to rattle around in the slot.  Once the engine speed gets to a certain point the shaft is spinning too fast to let things rattle enough to hear.  There does seem to be a second, maybe resonant rattle at about 3000rpm on my bike.  It's hardly noticeable because it's a lot quieter and doesn't really happen until the bike has a lot of miles and needs a tune up.

Have you done a compression test to see how balanced all the cylinders are?  Checked that all the valve clearances are correct and reasonably matched?  A good throttle body balance and new spark plugs won't hurt.  The throttle body balance is important to get all the cylinders working as close to the same as possible.

Like I said earlier, I consider that rattle just off idle to be part of the charm of my bike.   3M Skull Skrews ear plugs help a lot too.

[bmwcyclist]

I just listened with my headphones.  Sounds like the balance shaft in my K75RT.  My theory is that the slightest imbalance between the cylinders will cause that tang to rattle around in the slot.  Once the engine speed gets to a certain point the shaft is spinning too fast to let things rattle enough to hear.  There does seem to be a second, maybe resonant rattle at about 3000rpm on my bike.  It's hardly noticeable because it's a lot quieter and doesn't really happen until the bike has a lot of miles and needs a tune up.

Have you done a compression test to see how balanced all the cylinders are?  Checked that all the valve clearances are correct and reasonably matched?  A good throttle body balance and new spark plugs won't hurt.  The throttle body balance is important to get all the cylinders working as close to the same as possible.

Like I said earlier, I consider that rattle just off idle to be part of the charm of my bike.   3M Skull Skrews ear plugs help a lot too.

I did sync the throttle bodies BUT one was significantly out compared to the others. I did a spray test for air leaks and found nothing. I just ordered a set of new injectors, perhaps that will all them to be in closer adjustment and lead to smoother running. I checked the valves, they were good.  I also replaced the Z-hose and renewed the vacuum caps.


.
 

[bmwcyclist]

Note, I have a 1990 K75 (factory low) that does not produce this sound or anything like it. It has less than 10k miles.

I also have two close friends with K75RT bikes that I ride with (one has 2 1990 K75RTs and 1 has a 1991 K75RT) they also do not produce this sound/vibration.

[Laitch]

Note, I have a 1990 K75 (factory low) that does not produce this sound . . .
I also have two close friends . . . they also do not produce this sound/vibration.

Your last submission is the way to do a mobile sound recording! 

Have you inspected, cleaned and appropriately lubricated all driveline components all the way up to the intermediate housing?

While waiting for your new injectors to arrive, I suggest you perform a compression test with wide-open throttle on this neglected moto. Based on its results being good, and if you hadn't done so already, remove the throttle body air adjustment screws, clean them, clean their ports, replace their o-rings, reinstall them then redo the TB balance.

I don't hear much that concerns me. Your 1990 is barely broken-in so I am reluctant to use its noise level for comparison. In your last recording, your throttle input seems better. If you discover in your research something that achieves your goal of lowering the level of noise type that concerns you, please post it here. Other than that, I have only one fallback position.

Wear earplugs.

[johnny]

greetings...

i thinks its the exhaust mount...

j o

[bmwcyclist]

Thank you.

I will check back in after:

Compression test
Injector install
Port clean and 0-ring replacement
Exhaust mount check

Thanks!