Top end

In engine terms, the top end means the parts above the crankcase: piston, piston rings, cylinder, cylinder head and, on four-strokes, the valves and camshafts. The bottom end is the crankshaft, connecting rod, bearings and, usually, the gearbox.

A top-end rebuild means replacing the piston and rings, checking the cylinder bore and, on four-strokes, servicing the valves. On racing two-stroke and four-stroke motocross and enduro bikes this is a regular service measured in engine hours, as given in the owner's manual.

Riders also use the term for engine performance at high revs ('lots of top end') or for a bike's maximum speed.