Sets of apparatus for translating motion from a rotating non-circular loop to linear motion and in possible cases vice versa. Such mechanisms are used in muffler cap spinning technology and engine crankshaft with uneven strokes; but not restricted to said applications. The mechanisms include a non-circular cam, a linear sliding arm or piston and parts to connect them. Disclosure also includes an adjustable closure for a sliding arm which could be utilized for said muffler cap spinning mechanisms or other applications.