The semi-automatic clutch was not disengaging during shifts. Upon disassembly, I discovered that the posts were frozen to the basket. The clutch was still able to disengage at idle since there are different mechanisms used. These semi-automatic clutches pack an impressive amount of engineering into such a small package. The metal clutch plates were heavily rusted and after cleaning they were still very pitted. One of the teeth which holds the damping springs to the housing was sheared off as well. I opted to order all new parts for the clutch from eBay and DrATV – OEM housing, plates, disks, bearing, and screws along with EBC Heavy Duty Springs. After putting everything back together, the clutch now operates as expected.
This bike also is unique in that the clutch housing acts as a centrifugal oil filter. Oil passes through the front of the clutch from a passage in the side cover. In the small chamber underneath the clutch release bearing any contaminants in the oil are spun to the outside and trapped there. Oil then continues through the center of the clutch and down a hole drilled in the middle of the crankshaft to lubricate the rod bearing. Routing maintenance of the CM91 includes occasionally removing the bearing from the clutch and cleaning the debris out of the chamber.
