K75 doesn't seem as smooth as it should be

[F14CRAZY]

Today I took the longest trip yet on my K75, which was about 68 miles (each way) at about 75 mph. The speedo shows 80 but with how cars are still passing me sometimes I think it displays a bit fast.

I don't have experience with any other K75, let alone any other motorcycle, but it seems like it isn't as smooth as those RPM's as it should be. At "80 mph" and in 5th it was turning 5k rpm and my hands were getting numb from the vibration. From running it around town and slowly running the throttle up to 5k rpm in neutral and stationary it seems the vibes noticeably get bad at 4k on up.

Is this normal? I've read and heard of how the K75 is often considered the smoothest motorcycle engine ever. Mine isn't "turbine-like smooth" as someone else has put it.

I'm confident my bike has been well maintained (it was Drake's for a while after all) and is pretty up to date but I've been busy (and kind of broke) so I haven't checked the spark plugs, valves, or throttle bodies. Would any of these cause this? It starts up quick and is responsive (again my experience is limited but I've opened it up a few times and it feel crazy fast). I was wondering if it was a driveline issue (I greased the driveshaft and clutch splines before putting it on the road) but with it feeling the same way in neutral and stationary  as it does at 75-80 mph it seems like it's just engine related.

What do you guys think? Thanks in advance

[Chaos]

not normal, shouldn't get handlebar buzz even at 80mph.  Something's out of whack, plug misfiring, valve tight, dirty injector(s)

[johnny]

check your sparkplug tightness and sparkplug wire tightness... id go to oreilys and getts the 20oz 2 for 1 techron... 1/2 bottle to full tank... run 4 consecutive tanks with 1/2 bottle in there...  then install a new 3032 filter... if still buzzy id do a throttle body sync...

i say 1/2 bottle to full tank cause i dont wanna tell anybody to use too much... butts i use a whole 20oz bottle to full tank and run 2  consecutive full tanks... just did it today by the way...

and run no corn ethyl when you can get it...

j o

[TimTyler]

... if still buzzy id do a throttle body sync...

Do a TB sync anyway, yo. :riding:

[Zipster]

Download the Road Pilot App and it will give you your GPS speed which is more accurate than your speedo!

[F14CRAZY]

heh I do have a speedometer app for Android but I don't have a mount for my phone yet and don't feel like risking holding onto it

A DIY throttle body sync thang seems easy enough to construct so I suppose I can get on that pretty soon

I've got some Sea Foam that would likely work as well as Techron (but I know Techron is good stuff). I'll run some through the system soon.

I'll check the plugs and wires too.

Thanks for the help so far

[Motorhobo]

Maybe you could find someone with a k75 who will let you ride theirs... Hard to make any assessment without a frame of reference.

Or find someone with a frame of reference who will ride yours.

[TX brick]

I had the same experience with my 91 75RT. Even after tuning it, it would put my hands to sleep at 4000 rpm or greater. The troubleshooting section of my Haynes manual said to check all mounting bolts. I found the muffler bolts very loose and I noticed improvement even at low rpm. Once at speed the engine was very smooth. I found that the nuts would loosen with time, so I double-nutted them and they stay tight.

Your speedometer is way off. 5200 rpm gives me 70 mph.

[F14CRAZY]

I checked out the plugs and wires this morning...gap's were good, color was good, electrodes were good, and wires visually looked good. I started it with the spark plug cover off and didn't see any arc-ing.

I'll check over the hardware though, exhaust included. I took a like 2-3 mile test ride when I bought the bike in February, and I don't think I took it over 55 mph. I did the spline lube job before riding it again so it's possible that I left something loose.

Weird that my speedo is thaaat far off. I'll check with with a GPS soon though

[F14CRAZY]

I did a quick check over the hardware on the bike and it seems that the screws holding the right side side case mount to the footpeg bracket (if that's the right terminology) won't tighten any further but the side case mount is still a bit loose. I've been riding with the cases on but will try riding without them tomorrow and see if the vibration goes away.

[TX brick]

Those screws on the left side also hold the muffler isolation mount. Tighten these and find out why the ones on the right side won't tighten.

[F14CRAZY]

I did try riding without the side cases but that didn't change the vibration.

But, I have a feeling its in the rubber alternator drive bushing things, as they weren't in the best shape when I took the alternator off when I greased the splines. I ordered some from the dealer and will report back after replacement

[F14CRAZY]

I think I fixed it.

The alternator drive bushings arrived yesterday and I got to installing them today. While the existing bushings seemed decent the nut that holds the cup to the alternator shaft was off  :yow I cranked that down the best I could and added some locktite I had in my tool bag and threw it back together with the new bushings. I went for a spin, hitting 5-6k and its definitely smoother.

I dunno if I would call it "turbine-like" but again I don't really have any experience with K's or any other road bike for that matter. To me, something "turbine-like" smooth would be like hanging onto the steering wheel of my brother's Town Car. I haven't ridden it for a couple hours straight yet but I don't think it'll make me numb again.

[pauvil]

Are you sure it's an engine thing, I found the slightest little flat spot on one side of my front rims and I looked at this rim a thousand times and never noticed it before. After changing my rear shock and doing the fluid in the fronts I got a vibration and it was the front rim being a tad bit out of round. My speedo seems to be off as well, around town in a 30mph zone I'm showing around 40 and people are riding right up on me, I thought they were just tailgating but my wife followed with the car and sure enough around 8 to 10 mph off, don't know why yet, the tires are stock size.

[mystic red]

My speedo seems to be off as well, around town in a 30mph zone I'm showing around 40 and people are riding right up on me, I thought they were just tailgating but my wife followed with the car and sure enough around 8 to 10 mph off, don't know why yet, the tiors are stock size.

Almost all of them are off...

[F14CRAZY]

I checked my speedometer against an Android satellite based GPS app. I used Drake's adjustment procedure but turned it too far last weekend so instead of being 5 fast its 5 mph slow...will have to try that again.

The bike was smooth when I pull the clutch at 75 mph and it did it when revved in neutral on the center stand so I'm certain it was from the engine, not wheels or driveline.

I'm certain it's fixed after putting the alternator nut back on though

[F14CRAZY]

Go to ride the bike on an hour long trip and about 45 minutes into it my hands and feet were numb again. I pulled the alternator and the nut was not off like I found recently. Quick test shows the vibration is still present with the alternator removed.

What else could it be? The bike is smooth at 70 mph with the clutch pulled and engine idling. Could something be up with the clutch, flywheel, or something inside the trans?

I swear that at idle, with the clutch out, there seems to be a rattling sound coming from the trans. It goes away with the clutch pulled. Also, I don't really hear it when the engine is cold, just when the engine is warm

Or again, did I screw up something when I did the driveshaft and clutch spline lube?

Bike runs and shifts fine, maybe even great.

But you know, I still haven't checked the ignition timing or synced the throttle bodies. Could this really be it?

Any other idea guys?

[Motorhobo]

I swear that at idle, with the clutch out, there seems to be a rattling sound coming from the trans. It goes away with the clutch pulled. Also, I don't really hear it when the engine is cold, just when the engine is warm

I had exactly that symptom. For me, As it turned out the alternator mounted incorrectly. The drive dogs have to sit directly in between the sets if monkey nutz. If even one of them shifts during install and doesnt properly insulate  the drive dog, the drive dog will slap against the separator walls within the cup at low rpms. At higher rpms the slapping sound goes away. I tried the install a couple times and got the sound before finally using a very small amt of silicone sealant to keep the monkey nutz in place during install. Made sure the guide marks were lined up properly and on the third try the clacking went away....

That's probably the simplest possible cause...other things would be a much greater PITA to diagnose and fix.

The clutch assembly is supposed to be balanced, meaning you're supposed to mark the clutch parts and reassemble exactly as installed. Also, there is a clutch centering tool for installing the clutch and ensuring that the friction disk is  properly centered on install. If it wasn't properly centered, that could cause vibration at high rpm's, I would think. Lots of people don't have the clutch alignment tool and use all kinds of kooky BS to get the clutch pack in without it. In a pinch, a screwdriver with duct tape wrapped around it would work...but not sure how well. So it is possible that an improperly installed clutch could cause excess vibration.

Having said that, every bike vibrates. Wearing summer gloves I feel it too at +5000 rpms. If you don't have a frame of reference it's hard to determine what's normal. Best thing to do IMO would be to find another motobricker to ride it and tell you how normal it is.

[F14CRAZY]

I swear that at idle, with the clutch out, there seems to be a rattling sound coming from the trans. It goes away with the clutch pulled. Also, I don't really hear it when the engine is cold, just when the engine is warm

I had exactly that symptom. For me, As it turned out the alternator mounted incorrectly. The drive dogs have to sit directly in between the sets if monkey nutz. If even one of them shifts during install and doesnt properly insulate  the drive dog, the drive dog will slap against the separator walls within the cup at low rpms. At higher rpms the slapping sound goes away. I tried the install a couple times and got the sound before finally using a very small amt of silicone sealant to keep the monkey nutz in place during install. Made sure the guide marks were lined up properly and on the third try the clacking went away....

That's probably the simplest possible cause...other things would be a much greater PITA to diagnose and fix.

The clutch assembly is supposed to be balanced, meaning you're supposed to mark the clutch parts and reassemble exactly as installed. Also, there is a clutch centering tool for installing the clutch and ensuring that the friction disk is  properly centered on install. If it wasn't properly centered, that could cause vibration at high rpm's, I would think. Lots of people don't have the clutch alignment tool and use all kinds of kooky BS to get the clutch pack in without it. In a pinch, a screwdriver with duct tape wrapped around it would work...but not sure how well. So it is possible that an improperly installed clutch could cause excess vibration.

Having said that, every bike vibrates. Wearing summer gloves I feel it too at +5000 rpms. If you don't have a frame of reference it's hard to determine what's normal. Best thing to do IMO would be to find another motobricker to ride it and tell you how normal it is.

With the alternator...

The original nuts vibrated, though they weren't in bad shape. Kinda struggled to get it together.

Then put in the new "nuts" recently, kinda struggled, no change.

Today when I put the "nuts" back in I used vaseline and the alternator slipped on really easily. But it's still vibrating.

I'm gonna try taking the alternator off and going for a good ride, then evaluating the situation again and putting it back together, again. The cup the nuts go in looks to be in good shape along with the piece that drives it. It seems like any error in alternator mounting would have been not-done again but if it took you that many tries I'm willing to keep trying.

I've read about how the clutch assembly has tick marks that are supposed to be staggered. I didn't take note of any marks but then again I didn't touch the disk, pressure plate, etc when I took the trans off to clean and grease the splines.

I agree that it would help to try riding another K, or having another K rider try mine, but I've read in many places that these are often said to be some of the smoothest motorcycle engines ever. With BMW's having a reputation for being great on long distance trips it doesn't seem like my body parts should be going numb in less than an hour at cruising speeds  :falldown:

[mjydrafter]

Or again, did I screw up something when I did the driveshaft and clutch spline lube?

Bike runs and shifts fine, maybe even great.

I think you did fine then, most of the symptoms of the clutch splines are shifting related.

But you know, I still haven't checked the ignition timing or synced the throttle bodies. Could this really be it?

I would definitely check the throttle body sync, that can cause some vibes.  Plus it's pretty easy on the K75

[Motorhobo]

Today when I put the "nuts" back in I used vaseline and the alternator slipped on really easily. But it's still vibrating.

Just vibrating or also still making a clacking noise at low rpms? If you're not getting a symptomatic noise then the alternator is probably in properly.

Not wanting to belabor the point, but the alternator will go on just as easily with the nutz improperly seated as it will with them properly seated. For me, the issue was at they were shifting within the cup when I tilted the alternator up to vertical to push it into place. Unless they have some kind of adhesion to the cup its easy for them to get knocked out of place or just to fall out of place due to gravity during installation. I ended up following a BMWMOA post that suggested using a bit of silicone adhesive on the nutz and letting it dry before installing.

I didn't take note of any marks but then again I didn't touch the disk, pressure plate, etc when I took the trans off to clean and grease the splines.

It's common practice to take out the clutch pack inspect and measure the friction disk whenever you have the transmission off especially if its a recently acquired brick. It gives you the opportunity to check the installation and make sure it's in right and make sure there's no oil behind the clutch housing. I think the only way to make absolutely sure the clutch is installed properly is to do it yourself.

But like mjydrafter said, if the clutch disk weren't centered right, it probably wouldn't shift so well. I've never had the clutch installed wrong, I.e. unbalanced, so I don't know how that would manifest itself wrt vibration but sadly the only way to check that is to disassmble and reassemble so at this point seems you'd want to explore all other options before pulling the tranny agan.

[K75RT Keith]

Are you getting this vibration when the bike is on the center stand and run up to highway rpm in neutral?

If you are, you're going to have to pull the trans and check the alignment marks on each piece of the clutch, pressure plate assembly.  If they're not aligned to the marks the balance is off and will, over time, do some serious damage. 

[F14CRAZY]

I'll get on a throttle body sync and check the clutch component alignment this weekend...I wish I would have known or thought to do that when I had the trans off to lube the splines but oh well. I'll report back with my findings

[johnny]

id change my fork oil and take a close look at the wheels tiors suspension...

j o

[F14CRAZY]

Wellp, I spent 6-7 hours today getting to the clutch:



Someone previously made their own marks on the parts which seemed to be contrary to the factory marks. I found an orange dot on what I would call the "flywheel," a white dot on the back of the "pressure plate," and a white line on the outside thing. I set these to be more or less 120 degrees clockwise from each other.

I went for a 45 minute ride, keeping it at 75-80 mph (around 5400 rpm) and it seems that I fixed the problem . No more numbness in my hands and feet! Again my experience is limited and I wouldn't call it "turbine like" or "electric" but it sure is smoother than it used to be.