changing gear ratios in outboard engines

[rasorinc]

I have never owned an outboard engine and need to know if changing gear ratios in a used 4 stroke engine is a big deal or not. And is it an expensive proposition? Want to buy a 60-75 hp. and have a 2.33/1 gear ratio. Thanks.

[thudpucker]

Ras, I think you change that with the Prop.

[Submarine Tom]

I suggest you contact the manufacturer of the engine. That will give you an answer pretty darn quick. What ratios, cost, availability, shipping time, complexity, side effects, complications, detriments, etc, etc, etc...

-Tom

[powerabout]

plenty of 60-70 have that ratio
what model do you want to change?
4 stokes generally have low ratios as they are gutless

[rasorinc]

Yamaha Hi Thrust and Honda Power Thrust engines have this gearing and compared to their regular 50,60hp, models all other specifications are the same. So they want more money just for a different gear setting. I'm sure the props are different but engines are quoted W/O props. I want high thrust so if I buy used it appears if I install 2.33 to 1 gearing, I will hava a less expensive high thrust engine--with the right prop of course

[thudpucker]

Good thought Ras!
Remember not to load the engine down, or you'll burn up a Rod Bearing. Keep it singing hi "C" and it'll last longer.

PS: That Locust Tree is still standing, but if it ever suffers any wind damage, your first on the list!

[rasorinc]

Thanks, Stan

[powerabout]

are they just a gear ratio change or are they using the gearbox from a larger engine?
Do they take different diameter props?

[Jimboat]

Originally Posted by rasorinc

I have never owned an outboard engine and need to know if changing gear ratios in a used 4 stroke engine is a big deal or not. And is it an expensive proposition? Want to buy a 60-75 hp. and have a 2.33/1 gear ratio. Thanks.

Mercury, Tohatsu, Suzuki, Yamaha 70hp motors all have ratio 2.3:1. As interest, what is reason for specific gear ratio requirement? Torque/RPM is usually optimized by effective propeller selection? Also, remember that OEM designs their engine for particular gear ratio and propeller matches, so changes will also change performance of engine.

[powerabout]

you get a bonus if they install a larger gear case on a smaller engine so can get bigger diameter props
and also a bit of longevity as the case is designed for a larger horsepower engines
typical back in the day of OMC commercial engines

[Jimboat]

Originally Posted by powerabout

you get a bonus if they install a larger gear case on a smaller engine so can get bigger diameter props and also a bit of longevity as the case is designed for a larger horsepower engines typical back in the day of OMC commercial engines

Can't really imagine why we'd want a larger gearcase than OEM spec. If using larger props than the engine is designed for, then engine RPM will be reduced and gearcase under less load, so longevity not likely to be an issue.

[powerabout]

Jim
they only make sense at displacement speeds
As I remember OMC put V6 cases on V4 and the 3 cyl large case on the 2 cylinder engines etc
regards
Powerabout