A balanced and rotating mechanism of an internal combustion engine, which combines adjustable variable compression ratio with long power and exhaust strokes and short intake and compression strokes to obtain an internal combustion engine with variable air intake flow and maintain a constant pressure ignition. The mechanism includes a mirror-image planetary-gear assembly, a gear-pin assembly, and a piston-and-connecting rod assembly. The mirror-image planetary-gear assembly includes a first planetary-gear assembly and a second planetary-gear assembly; wherein each includes a sun gear, a primary planet gear, a plurality of secondary planet gears, and a ring gear. The first planetary-gear assembly and the second planetary-gear assembly are mounted along a main rotation axis, offset from each other and mirroring each other. The gear-pin assembly is eccentrically connected between the primary planet gears. Resultantly, rotating the sun gears alters the orientation of the gear-pin assembly, and thus changing the top dead center height.