Home › Forum › Ask A Member › Converting OMC 5.5/7.5hp gearcase to ’58 10hp Gearcase › Re: Converting OMC 5.5/7.5hp gearcase to ’58 10hp Gearcase
No the 18hp gearcase is much larger, and a 5 bolt unit.
The 10hp OMC used a 5 bolt gearcase up to the end of 1957. Then in 1958, they started using the smaller 4 bolt gearcase from the 5.5 and 7.5hp models. It made it lighter, and a little quicker, but more prone to damage.
You need a few more parts than I had first thought would be needed to convert a 5.5/7.5 gearcase to make it work on the 4 bolt 10hp motors.
I was originally hoping the drive shaft from the 5.5/7.5 would work, and I would leave the shock absorber in. Im now starting to realize I need to swap out the drive shaft completely, and bearing plate under the water pump.
Might have to start digging through parts boxes! I