A burger and fries is a great meal once in a while, but you wouldn’t want to make a steady diet of it. BMW riders in the late 1970s were getting tired of the same old menu—air-cooled boxer twin, modest power, dowdy looks—at about the same time as Japanese manufacturers were offering up some pretty tasty in-line fours that were smoother, faster and cheaper than anything from BMW. So the chefs in Bavaria gathered in the kitchen and whipped up a real treat—a liquid-cooled four, laid on its side and clothed in swoopy bodywork—that still tastes good today, and borders on becoming a modern classic as well.
The K100RS threw BMW orthodoxy out the window with its liquid-cooled 987cc four, but toed the company line with a longitudinal crankshaft that aligned with the driveshaft to reduce the power losses typical in drivetrain layouts with several 90-degree changes of direction. With the head on the left and the crankcase on the right, routine maintenance like adjusting the valves was simplified.
The “brick” engine was fed by Bosch LE-Jetronic fuel injection in place of the carburetors that had fueled generations of boxers, and two valves per cylinder were deemed appropriate to the bike’s sport-touring mission; in all, about 90 horsepower were available at a full twist of the throttle. The shaft drive got a new moniker, too––Compact Drive System.
It took a while for roundel fans to embrace the K100RS. The bike felt top-heavy despite the low engine layout, and vibration plagued early models, as did engine heat; while good at letting cooling air into the radiator, the bike was less efficient at channeling it out of the engine bay, and the rider paid the price. The styling, too, was a bit too avant-garde for those who preferred the less flamboyant boxer. The heat issues were resolved on later models, and the K100RS model’s solid sport-touring performance, optional hard cases and sporty seating position soon won over not just the doubtful BMW faithful but others who found nothing as attractive in other brands’ lineups.
Contrary to what you might think, the best used K100RS is one that’s been ridden a lot. Examples that have sat idly for years get grumpy when they’re awakened, and develop issues that need immediate, and often expensive, attention. Check the weep hole under the front of the engine for signs of oil or coolant, and the one in the rear of the engine case for oil that indicates the rear main seal or forward transmission seal has died in its sleep. Watch out for lateral movement of the rear wheel, notchy steering-head bearings and poor fueling, and ask if the splines in the drivetrain were lubed on schedule.
Prices are still reasonable—between $2,500 and $3,500—and don’t shy away from high-mileage bikes if they come with complete service records. The K100RS is one of the best budget-sport tourers out there, and a good bet to appreciate over the years.
1985-1992 BMW K100RS
A landmark sport tourer with a healthy dash of style and the potential to become a practical classic.
Vibration and heat plague early models. Awesome power and acceleration were not on the options list.
Final drive: Shaft
Wet Weight: 536 pounds
Fuel Capacity: 5.8 gallons
Seat Height: 32 inches