K-Bike Buyer's Guide

By Don Eilenberger
November 2001

First off: You must do some homework, and read most all of the K-tech pages. Lots of reading, but worthwhile. This will give you a grounding in K bike tech.

Specifics to an '85 (and not RT specific):

  1. Heat-shield on exhaust will probably rattle
  2. Mileage on odometer is bogus unless supporting documents are available (like service records). The speedo *has* been repaired or replaced under warranty. Plan on doing the additional work on it outlined in the K-tech-pages.
  3. Throttle-cable: If the adjuster is about 8" down the cable from where it enters the twist-grip - it should be replaced (for free by BMW).
  4. Centerstand: If the triangular reinforcing piece on the centerstand is welded all the way around, eventually the stand WILL break, tossing the bike on it's side. If it is open at each end it has been replaced with the newer design already.
  5. Mid-year '85 update to the K100 (and retrofitted to most of them) involved new footpeg mounting plates which are SOLID mounted to the transmission. If the ones on it are rubber mounted, this update wasn't done. It helped lessen buzz in the left footpeg.
  6. Fuel lights probably don't work correctly. Common on '85 model. Cure is to remove them and replace the clock with a Fuel+ (see IBMWR links page and K-tech page for Fuel+ info)
  7. There are probably leaks in the clutch area. Bend down, look at the bottom of the clutch housing (bell-housing in my terms, secondary-housing in BMW talk). There is a hole in the bottom of it - you'll probably see oil around the hole. This means you will want to plan a replacement of the rear main seal and the clutch basket nut O-ring. One of our members just completed this and is writing it up. This is a good time to do the spline lubes outlined in the Tech-pages.
  8. Consider the possibility that the final drive input shaft and the driveshaft are worn. Not uncommon if they weren't lubed regularly. This can be checked fairly quickly (you DID find this in the tech pages right? Anton's way?) - but it requires disassembly of the swingarm/final drive to do so - most sellers won't allow this. Factor in about $450 to repair this.
  9. Figure the rear shock is garbage - allot $300-900 for a replacement (allotment based on how good a shock you want).
  10. Figure you WILL be replacing most of the rubber bits on the engine at one time or another. Figure your own labor if you intend to do it and $100 or so for parts.
  11. Check that the cooling fan turns. Using your right hand, reach in the gills on the right side of the fairing. Your fingertip should JUST about be able to reach a blade - if it turns fairly freely - the fan is OK. If it is very stiff or frozen - figure $100 for a new fan and about 4-6 hours labor to install it.
  12. Look at the brake reservoirs. If you can see the rear one without removing anything, it's the original and will be due for replacement. Is the fluid light-straw colored? If so: good. If darker: then figure the brakes have been neglected. Best case: just needs a flushing. Worst case: may need new master cylinders both front and rear (figure $300 or so in parts) since these seem most effected by neglect (failure to do an annual flushing).
  13. Look under the front of the engine. *Any* signs of oil or coolant dripping from the lump on the very front means the oil pump or coolant pump seals are kaput. On an '85 I'd recommend replacing the pump as a unit with the newer design. Figure $350 in parts and several hours in labor.

That's about it. The list above and reading the Tech-Pages should give you a good idea of what to look for and ammo in bargaining the price down depending on what you see.

The bike should start easily when cold or hot, and run like a cat with it's tail on fire... :-)

Don Eilenberger, Spring Lk Hts, NJ JMP#1 deilenberger@monmouth.com
NJ Shore BMW Riders web page: http://www.njsbmwr.org/
Moderator BMW E39 Enthusiast Group: http://groups.yahoo.com/group/bmwe39