Engine vibration between 3K and 4K rpm

[Andy FitzGibbon]

Hi guys, finally have got my '85 K100RS roadworthy enough to take some 50-100 mile loop rides.  There is a noticeable vibration/buzz, which seems to emanate from the engine, and which starts around 3K RPM and goes away above 4K RPM. 


Where should I look first?  Timing chain? The bike seems to run just fine, though it should be noted that it's my first K bike, so I don't have a feel for how it "should" feel or sound.  I am used to single cylinder thumpers.


Thanks,
Andy

[Laitch]

Where should I look first?

Look at this thread and then look at this.

[know_fear]

My '85 K100RS has always ( I've had it since new) vibrated from 3500 to 4000 RPM. It was an RT originally so it has a lower ratio final drive on it than the one for RS's. This puts my RPM at legal cruising speed to just over the rough zone.
You should be able to reduce the buzz but it may never go away completely, just the nature of the beast I'm afraid. Ride faster in the smooth RPM range, I'm sure the cops will understand once you explain it to them.
 :dunno

[jakgieger]

Andy, doesn't this pale in comparison to the R75/5????  I ran an R60/5.  By comparison the K is a sewing machine !

[Andy FitzGibbon]

Thanks, guys. Good to know that it's normal. I suspect it will improve some when I get around to balancing the throttle bodies and adjusting the valves. It will likely improve more when I ride the bike enough to just get used to it...

Andy, doesn't this pale in comparison to the R75/5????  I ran an R60/5.  By comparison the K is a sewing machine !

True that. Coming from the DR650 and various single cylinder off road bikes, either of the BMWs is a smooth machine. Part of the problem here is that I'm really just not used to motorcycles that want to rev over about 3K :)


Andy

[jakgieger]

Part of the problem here is that I'm really just not used to motorcycles that want to rev over about 3K :)

In a nutshell, that is the issue.  On the K, the fun starts at 4K.  I had to retrain myself to "drive it like I stole it"!.  JO has it right...the engines are made to RUN, not idle along.  My vibration has went away since I am seldom in the 3-4K range :hehehe .  The R /5's had a bad vibe range as well.  I remember that in top gear @70 mph it went away, so that was where I ran!  At 80 to 90 mph it was SMOOTH...

[johnny]

greetings...

where should i look 1st... at the tach above 5k with a case of techron through there...

you are warned... you may exceed maximun yeeehaaaa...

j o