After taking a look at the chart that oldemtr provided, a few things became apparent.
This chart is from 1963 or later. The OMC 7.5 Hp had stopped production in 1958. The other models continued to be produced through 1963, and improvements were being made. Taking a look at the section titled “Crankshaft Bearings – Diameter Clearance” the 7.5 Hp looks to have relatively larger bearing clearance numbers, when compared the 3 and 5.5 Hp. The 5.5 is listed as having “Roller Bearings”, so that may explain why it’s oil recommendation went from 16:1 up to 24:1. I don’t what the justification was for the 3 Hp change from 16:1 up to 24:1.
As Einstein famously wrote “Don’t forget CD and AD use 16:1” (but maybe not for the 1963 CD)?
Improvise-Adapt-Overcome
