The R100S’s growth from a 600 has not been entirely without problems, most of which seem to have been recognized and solved.

One particular difficulty came from the very compactness of crankcase that provides the engine its strong foundation. Due to the opposed motions of the BMW twin’s pistons and its high crankcase compression ratio there always has been in it a tendency to huff, puff, and blow its oil out on the ground.

In the R100/S’s immediate relatives this huffing was controlled with a simple spring-loaded flapper disc, which kept the engine from inhaling a volume of air equal to its own displacement with each 180-degree rotation of its crank and then exhaling much the same volume of oil mist when the pistons returned to bottom center.

The flapper disc permitted only the exhale, which didn’t amount to much when not preceded by an inhale–in the smaller-displacement BMWs.

Unfortunately, there proved to be so much huff-and-puff in the 900 that the simple flapper arrangement began to lose control of the situation when some rider took his R90/S on a long, fast run. Under those conditions a lot of oil droplets would escape past the flapper valve, sneak down the short hose leading to the air filter/chamber, and find themselves being eaten by the engine they were supposed to lubricate.

BMW realized that if this could be a problem at the 900cc displacement level it would be one with the engine stretched to l000cc. They fixed it before it happened by casting a small baffle chamber in the crankcase–which holds the case fumes long enough, before they go out the flapper, to let oil droplets collect in the chamber’s floor and drain (via small holes) back to the sump.

The 900 had also demonstrated that a BMW clutch could be brutalized into slipping, and that, too, could have been a more serious problem in the R100/S. The new clutch has been strengthened, without added weight, by thinning the flywheel and adding thickness to the pressure plate.

This particular example from the 10th of June 1980 and dispatched to the Netherlands. With 3 owners since 1980, showing a mere original 36,917 km on the odometer, this "R110S" has been well looked after and maintained.