Bearing

A bearing supports a rotating or pivoting part and reduces friction between it and the part around it. A motorcycle has dozens: in the wheels, steering head, swingarm and suspension linkage, gearbox, crankshaft and water pump.

• Ball bearings – wheels, gearbox shafts.
• Tapered roller bearings – often in steering heads.
• Needle bearings – swingarm and linkage pivots.
• Plain bearings (shells or bushes) – crankshaft and connecting rod in many four-strokes.

Worn bearings show as play, notchy steering, a grinding noise or a wheel that rocks on its axle. Off-road bikes and ATVs need frequent linkage and steering bearing greasing, as pressure washing and water crossings wash grease out. Replace bearings in pairs and use a press or suitable drift, not a hammer on the outer race.