Crankshaft bearings for JOG 50 3KJ — two 6204 bearings (manufacturer TATA). They hold the crankshaft in the crankcase and carry the main load while the engine runs.
Replace them if the engine hums and vibrates. The job requires splitting the crankcase; during the repair, replace both bearings and the crankshaft oil seals. When buying, compare the markings on the old bearing: they define the size unambiguously.
