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ENGINE REVIEW: O.S. 56 FS-A

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PHOTOS BY PETE HALL Has 4-stroke technology taken a new turn? Left: the small hole in the head casting just under the right valve spring acts as a jet to bring atomized oil up from the lower crankcase to aid lubrication without a crankcase breather tube. TOTALLY BRILLIANTóAND A LESS OILY FUSELAGE IS MERELY A FRINGE BENEFIT I'VE WATCHED O.S. introduce their .60 FS and .75 FS, which had rear-drive valve systems with exposed pushrods...

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