Well the brochures said it was to save weight. They shifted from the beefier 5 bolt gearcase to the lighter smaller weaker design formerly used on the 7.5’s. It was most likely done to save weight and cost. Not sure what year that happened; might have been 1958.
The difference has been noticed by 10HP Owners. Maintenance is vital on the newer lighter gearcase; little tolerance for water intrusion or inadequate lower unit oil.
