if this is difficult to answer, just ignore me..

[Zampano]

if it is possible, how would you describe the vibration when alternator "monkey nuts" need replacement. My bike is most smooth around 4000 and 40 mph. At all other speeds above that it is not bad, but I would no say silky smooth by any stretch. It's felt in the handgrips and footpegs. I had her up to mach I (80 mph) and with the clutch in most or all of it went away. Clutch in and revved up to 6K rpm there was some of it but not as much as with tranny engaged. So that is somewhat vague, as it could be from engine or drivetrain or combo. My plan is to do nothing unless the cause is fairly certain. The previous owners replaced the clutch and I am thinking that could be a source. The dealer told me they weren't totally confident in my tranny (whatever that means) and I'm sure that could be another source. If it was the alternator bushings that would be best case scenario. I was just curious if there were any "that's from bad monkey nuts" revelations out there. I wonder how many times some doctor in africa has said that.

[Motorhobo]

At 5500 rpms the engine is working. At 3000 rpms it's dozing and bored and it sounds that way. When it's working, you hear and feel it. You have to get used to the high rpms. Once you've done longer stretches at +90mph you start to realize that that's where the engine is happiest.

Having said that -- if you're not getting that impression maybe something's not as it should be -- but try not to compare it with a newer Yamaha or Honda that will go 130mph in 4th.

When monkey nuts fail, the drive dog fins aren't insulated against the fins in the cup, so the fins whack up against each other and make a clacking noise. In my experience its more pronounced at lower rpms and idle, maybe because it's partially drowned out by engine noise at high rpms, maybe because the faster it spins the more the drive dogs and cup are matched inertially so the force of the whacking becomes insignificant. That's my interpretation -- if it's incorrect I'm sure someone will correct me.

At any rate, pulling in the clutch and throttling down at 80mph will drop the rpms ergo the alternator will spin down, but even with full throttle at freeway speed any alternator noise will likely be covered by road noise. So maybe your best bet is to get yourself a stethoscope and listen to the alternator while throttling up on the center stand in neutral. That's how I was able to locate the cause of then clacking when my alternator was installed improperly -- the nutz had shifted during install and were not seated with the fin between them, which was allowing the drive dog fins and cup fins to contact each other. Stethoscope will help locate internal noises...but i still think your best bet is find an experienced motobricker to ride your brick at 80mph on the highway and give you the qualified skinny. Doesn't sound like your mind will be at ease until you get that frame of reference to work from.

My $0.02...
Van

[K75RT Keith]

Tell us again what year and model. 

If you've got a K100 variant, they all seem to have some buzz at higher RPM's.  Early K100's had foot peg mounts that seem to transfer more vibration than the replacement / upgraded part they used on later models.

Replacing the alternator drive bushings is a very simple project that shouldn't take but an hour. 

If you're finding metal bits on the magnetic plug for the transmission or when changing the transmission oil find the used lubricant to feel gritty, you may have a transmission issue.  If not, it isn't the trans. 

Plate alignment to the balance marks on the clutch assembly is imperative to smooth performance.  If the p.o. didn't do the job properly, it could be the cause.   

[Motorhobo]

I think he's got an 80s k75c. Zampano, how bout adding your bike to your profile?

[K75RT Keith]

Does the vibration occur when on the center stand and run up in neutral to the RPM's where the vibration starts? 

Try checking the exhaust mounting bolts for tightness and double check the exhaust bolts to to the engine also.

BTW di you add the Guard Dog to the trans yet?  I remember you had some really ugly lube that came out with some metal bits.  It is possible that the bearings and spacer bushings on the shafts have worn which will cause some buzziness at higher RPM's.  Don't ask how I know.  (I should have spent a couple hundred for another trans rather than emptying my bank account on the rebuild)

[Zampano]

thanks for the replies.

It's a '92 K75S

Lately it's actually been running pretty well, so i'm not overly concerned. My guess is the minimal vibration is just "buzz". It's a 20+ year old machine and any "less than brand new" feel could be from many sources. Don't get me wrong, it's not bothering me much. I'm a masochist and if someone gave me a new ferrari 458 I'd find something to straighten out on it. It's sort of a game to me to see how close you can get old machines feeling like they did when they came off the line. Like chess opposite kasparov.

Haven't added the guard dog to the transmission fluid yet but it's on the list. For $15 or whatever it costs that is a cheap/easy thing to do. I was hoping to find it somewhere and avoid the shipping (equivalent to one life-changing san diego burrito).

[K75RT Keith]

Bite the burrito and order it.  Put it in the trans and FD then go for a nice long ride and let it do its' thing

[Zampano]

Bite the burrito and order it.  Put it in the trans and FD then go for a nice long ride and let it do its' thing

that's the plan. Since my tranny oil was gnarly looking I thought I would put 500+ miles on after the change and then change it out again. I'll add the guard dog at that change.
Figures the additive for synthetics is a full burrito and bean tostada more expensive

I had cleaned the belly pan to the point you could eat off it when I had it off. Seemed after the engine/tran oil change there was a week of drips which have somehow slowed/stopped. I was too lazy to diagnose exactly where they may be coming from. Appeared more toward the right rear of the pan but I also noticed a drop right in midline where housing mounts to the engine. Which I believe means rear main seal. Or could it be that boot that's around the clutch lever (?). My delusion is that the leaks are from things like the oil pan seal or some transmission seal. If not for the risk of being stranded from a slipping clutch I would not give them a second thought. Who knows. As long I make it to Sun Tacos and back I'm happy. I tried to get a good pic but have not had the energy to take the belly pan off again. The lazy theme is prevalent.



I'm still curious about the monkey nuts. When I get out of this funk I'll pull the alternator and change those.

[Motorhobo]

Just curious -- when you took off the oil pan did you use sealant and if so what? There's no gasket for that so you have to seal it with something otherwise it'll drip. I'm taking mine off today and was planning on using black RTV unless someone tells me otherwise.

[Zampano]

Just curious -- when you took off the oil pan did you use sealant and if so what? There's no gasket for that so you have to seal it with something otherwise it'll drip. I'm taking mine off today and was planning on using black RTV unless someone tells me otherwise.

I actually didn't take the pan off. The previous owner did though. I just changed the oil/filter and trans oil. I thought about it but didn't have any sealant. I'm also curious what sealant is the gold standard to use.

[Motorhobo]

i was confusing oil pan and belly pan -- mine has not fairing, so no belly pan.