Frank: didn't SAAB's use a movable head somehow?
rkcarguy: no image, but a pretty good description from the
GCC article:
Quote:
The piston structure has an inner and an outer piston. The outer piston sits atop the inner piston, and constitutes the combustion chamber against a cylinder head; the inner piston has the function of a piston skirt, a lifter mechanism, and a lock mechanism....
Honda installed a small pump separate from that of engine lubricating oil pump. Oil passage was constructed from the external pump through the crankshaft and connecting rod to the piston.
To switch from low to high, the hydraulic pressure is turned on. This acts on the pin of a lock plate, freeing the outer piston. The outer piston rises the 3.5 mm by the resultant force of the piston inertia force and the cylinder pressure force. To go from high to low, the hydraulic pressure is turned off, the lifter plate rotates out, and the out piston lowers over the inner piston by the resultant force.
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