[motorcyclistonline] - 1985–1992 BMW K100RS | SMART MONEY

[Ninjette Newsbot]

In the late 1970s, BMW’s trademark Boxer was on the ropes. In addition to tightening emissions regulations threatening the old slugger, a horsepower free-for-all had just broken out among the Japanese, and without a four-cylinder contender BMW was relegated to the undercard. The Bavarian propeller-heads had to come up with something newer, cleaner, and faster. The result, an inline, water-cooled four, hit flat-twin traditionalists like a haymaker between the eyes and launched BMW into a new era of multi-cylinder powerplants. One of the first fours from BMW, the K100RS, remains one of the company’s sleekest and sexiest bikes ever.


Not content with merely breaking the Boxer mold with a four, BMW laid the 987cc engine on its side, with the head on the left and the crankcase on the right, positioned longitudinally in the frame for less power loss from crankshaft to driveshaft. The layout kept the weight low—though many riders still complained the bike felt top-heavy—and simplified maintenance. Bosch LE-Jetronic fuel injection replaced the carburetors that had been standard equipment on Boxers. BMW boffins preferred two valves per cylinder rather than four, and yet the brick engine put out 90 hp, transferred to the road through the Compact Drive System that debuted on the K series.

Initial impressions of the bike were favorable if not wildly enthusiastic. The riding public took to the new design slowly but eventually warmed to it, though the subsequent introduction of a three-cylinder engine in the K75 threw a spotlight on the K100 series’ vibration. The K100 engine might not have run hot, but the same couldn’t be said for some riders whose thighs were roasted by the blazing heat pouring off the engine. This issue was resolved eventually, and the K100RS took its place as BMW’s sport-touring flagship, gaining a reputation as a solid performer and an able accomplice with a dash of style, a sporty seating position, and optional hard bags.

Those in the know say if you’re looking for a used K100RS you should go after one that’s been ridden regularly and comes with complete service records; seldom-used models with spotty paperwork seem to develop problems that all come out when the bike returns to service. There’s a weep hole under the front of the engine; if oil or coolant appears to be leaking, the oil pump and/or water pump are suspect. Another weep hole in the back of the engine case warns of a bad rear main seal or forward transmission seal.

Lateral movement in the rear wheel means possible final drive problems. Check to be sure the drivetrain splines have been lubed regularly. Front wheel bearings and steering head bearings should also be inspected for clicks or notchiness. Cracked exhaust pipes can make the bike run hot. High mileage shouldn’t stop you from considering well-cared-for examples. Used prices are on the low side even for good ones, and even though some Boxer purists still turn up their noses at its brick engine, the K100RS is a proven sport-tourer that threatens to emerge as a bargain classic in coming years.

Cheers

Great looks, solid performance, attractive buy-in price.

Jeers

Vibey engine, excess heat, modest power, leisurely acceleration.

Watch For

Fluid leaks, little or no regular maintenance.

Verdict

BMW’s breakout hit of the 1980s still draws crowds today.

Value

1985 / $2,550
1986 / $2,650
1987 / $2,760
1988 / $2,845
1989 / $3,220
1991 / $3,360
1992 / $3,475

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