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Vibration Fixes

Curing Early K100 Vibration Problems

by Don Eilenberger

As a new owner of an 85 K100RS, what did you do to cure the vibes?

Lots – I’ll list them more or less in descending order of effectiveness:

  1. Bashed heat shield on muffler so it doesn’t pinch between exhaust and left foot peg mount. Result – no (NO!) vibrations noticeable in left foot peg.
  2. Refitted right side crash bar so it doesn’t rub against the fairing … a few washers under one of the mounts did it. MAJOR reduction in fairing noise and vibration. This one I blame on the dealer since they installed the bars.
  3. Retimed bike to 30 degrees full advance (had been set at 24) … major reduction overall in vibration. See IBMWR tech pages for how-to-do (Lentini method – which I slightly modified – measure ANGLE instead of circumference … you’ll understand when you read it).
  4. Use premium gas – some better than others – generally best on Sunoco Ultra, OK on Mobil premium … this can be noticed right away. Later models may be able to use regular gas – the ’85 cannot and stay happy. I can frequently feel an immediate difference when changing brands of Premium gasoline. Experiment and find which one your K likes.
  5. Went through RT fairing adding rubber wherever I saw rubbing occurring … it’s pretty obvious where it occurs ’cause the paint between parts is worn, or you’ll see shiny spots. Requires disassembly, but basically easy to do.
  6. Replaced the O rings on the bar-end weights – these wear out and dry up. Install the weights so the ends don’t quite touch the end of the bars (they have to be free to vibrate – which absorbs bar vibes …) Helped a bit – not a major factor.
  7. Retorqued all engine mounts – had been done by a butcher (air-wrench prolly) – to specs shown in book for 1985 – which are done in a diff sequence than later models. We’re starting to get to where things are subtle – but still noticeable. Also – check to see if any shims are missing – loosen one mount at a time – if the frame moves away from the engine – you need a shim there. I made several from some thin flat stock. Made some difference at some peak vibration periods – but again, not a MAJOR difference (we are working our way in descending order of effectiveness).
  8. Replaced rubber mounts for handlebars – minor effect.
  9. Foam grips (not so good if you have heated grips) … minor improvement, if any, but I like the larger grip.
  10. Get ridda the stock seat. Like sitting on a cinderblock. Get a Russell made. If you need a seat to borrow while Russell makes your seat – lemme know. I have a loaner (and 1985 is different than other years).
  11. Played around with some rubber under the tank … was able to reduce vibration in the tank where my knees touched it – also added the rubber pads to the sides of the tank – good for vibes plus insulates your knees from the heat from the tank (and it DO get hot in the summer).

And lots of little things … chase any source of vibration – like anything that CAN vibrate and damp it (I have self-adhesive thin rubber foam tape – about 2″ wide – works great for this)..

Make certain the BMW upgrades were performed on your bike. At Fontana, I actually saw an ’85 K100 which still had the original footpeg mounts.

Plus it prolly helped when I:

  1. Rebuilt the intake – replaced all the rubber – (throttles to air-box, throttles to head) – had leaks – causes rough running – causes vibrations.
  2. Replaced the rear-main seal, which didn’t really NEED it, but the O-ring in front of it did – on retorquing the nut on the clutch basket (you first tighten it to XXX FT/LBS, loosen it, then retighten to somewhat less FT/LBS) much of the engine rattle on de-cel (common on K’s) went away … suspect it took up some play in the secondary shaft that had developed from wear.

The two above – you can PLAN to do … your bike is old enough, and both are caused by the aging and drying up of rubber parts..

The results of all this are – it has less vibration in it than later models of the K100 that I’ve ridden – and about the same or less than the K11 … also – if you still have a remnant of vibes in the bars … some people have suggested putting lead shot into them – I bought gel palmed gloves (Olympia Model 400) – with these on – there is NO vibration reaching my hands AT ALL … they work great.

Also – a FWIW. I added a throttle-lock-screw (standard BMW issue). Before installing the screw I found I got real pain in my right hand and wrist. I suspect the pain was caused by gripping the throttle grip tightly enough to keep it open all the time. Adding the screw, and adjusting it to a neutral adjustment (throttle stays where it is set, but is easily returnable to closed) cured this pain instantly. Have not had any wrist pain or numbness – even after 12 hours of riding.

I also like the throttle lock because it helps me ride the bike smoothly. The throttle on a K is very sensitive to on/off transitions. Loaned one to a fellow club member who has a K100RS – haven’t been able to get it back yet!


Muffler Vibration Fixes

By Peter Cooke
August 2001

My K1100LT (60,000 km) has a vibration at ~3000 rpm. Initially I retorqued the engine mounts to spec (~40 N-m) as directed by the Clymer manual. The 2 front rubber mounted ones were in fact quite loose, the rear 3 were tight. The vibration was a little bit reduced.

My bike shop found that the faring support bracket was sheared at the lower end and needed welding (probably caused by dirt road riding). A lot of the vibration stopped (but not all).

Another local BMW shop said that the main source of vibration in K1100’s is a cracked header pipe where it joins to the muffler. Sure enough there is a crack in the header (I haven’t fixed this yet – next week).

However I replaced the rubber mount between the muffler and the bracket attached to the centre stand mount (the original was actually bent). The vibes at ~3000 rpm immediately vanished.

I am hoping that the remaining lower level vibration will disappear after the header has been welded. I thought that this might be useful info on your web page since it is not that obvious to check the exhaust system as a source of vibration (not to me anyway).

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