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I have a 1953 Big Twin and a 1954 Big Twin Electric (got tired of rope starting the ’53) and a 1972 Johnson 25R all of which push a 1952 Feathercraft Deluxe Runabout. The high and low speed needle bearings are brass on the 1950’s motors but aren’t moving parts. I didn’t have to tear either down much to get either running though the ’54 had a mouse nest in the exhaust but the cylinders were clean. They both run well on 24:1 and I’m not worried about saving money. By the mid-late 1960’s all OMC engines were running 50:1 and typically at 5000 to 5500 RPM where as the old Big Twins are only 4000 RPM. OMC quit recommending automotive 30 weight oil and recommended 2 stroke oil exclusively. The Johnson runs 5000 RPM, is a smaller block so one would think it’d need more oil but 50:1 is recommended. So the question for me is why? I don’t know if there is much difference in their construction which would make sense if there was. I had assumed it was automotive oil vs. dedicated 2 stroke oil which likely has superior lubricating properties. Especially since two different mechanics (both of whom work on vintage motors) both felt the motors could be run on 40:1 and that seemed arbitrary so thought I’d ask. I appreciate the replies.
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