A chain saw guide blade includes a pair of side plates between which an axle is fixedly supported and a sprocket is rotatably supported with respect to the axle. The sprocket is rotatable about the axle with roller bearings therebetween for guiding a cutter chain for movement around the edge of the guide blade. A pair of annular seals are respectively disposed between the sprocket and one of the side plates and between the sprocket and the other side plate. Each of the seals includes an annular lip projecting obliquely into resilient contact with a surface of the sprocket or of one of the side plates. A grease-supply aperture in each side plate is normally closed off by a flap on the annular seal or resilient valve placed in a central hole of the axle. When under the pressure of forced grease through the aperture, the flap or valve is resiliently yieldable to allow the grease to be introduced for the lubrication of the roller bearings.
A power transmission mechanism includes a gear member and an annular and eccentric floating member having internal gear teeth meshed with external gear teeth of the gear member. A pair of guide plates provided on both outer sides of either the gear member or floating member prevent lateral disengagement of the floating member from the gear member. A pair of seal rings arranged between the inner sides of the guide plates and the outer sides of either the floating member or gear member prevent entry of dust or the like foreign material into a substantially closed space between the teeth of the gear member and the floating member, to thereby improve the durability of the mechanism.
A nose sprocket for a chain saw guide bar, where the bottom part of the teeth or the outermost part of the central region or both have indentations with softly inclined trailing edges, acting as hydrodynamical bearings to keep the sprocket centered between the side plates of the guide bar.
