91 OMC Cobra Outdrive 4.3L 21:19 replace with a 21:18?

[gssieg]

Hello,

I have a 91 with a 4.3L and a Cobra Outdrive. The unit grenaded over the weekend. I started looking at repairing and woah it's costly. I've found a few complete outdrives used reasonably priced however they all seem to have come out of a 5.0L and have the 21:19 gear ratio. My question is could I replace with this and just reprop? Or would there be other problems and should I look for an outdrive that came off a 4.3L?

Thanks in advance!

 

[Maclin]

How big is your boat?

 

[gssieg]

It's an 18' Four Winn Horizon. I just received an update from the guy and he is saying he was incorrect and it truly is off a 4.3L It sounds like my easiest way to confirm is to spin the output shaft and see how many rotations the prop makes? My fear is will I see that much of a difference between a 21:19 and a 21:18 that I will know for sure?

 

[Maclin]

The overall ratio is the one you want to know, so spinning it and counting rotations will get you what you need to know. I think the 5.0 one would be within what a prop change could cover with your size of a boat. If it was a 20-21 footer then you would definitely need the proper 4.3 ratio drive. But definitely check it, easy enough to do. Hopefully he is right about being wrong! and it is for the 4.3

 

[gssieg]

Thanks, I'm waiting to hear back from him yet. When I checked mine last night it was basically a 5:3 it was more like 5:2.95 but close which came out to about a 1.70 ratio? I'll see what he comes up with.