3.0 OMC Outdrive Change from 21/21 to 21/18

[carhopper]

I'm only doing this because my upper unit is toast and I found a 21/18 in good condition cheap. What kind of negative affect will this have on my 3.0 OMC. This is a 1.16 gear ratio vs my 1:1 so I'll probably be over propped now right. Will this hurt anything?

 

[Don S]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

At least say what model and year drive it is. Not all OMC drives are the same.

 

[carhopper]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

Sorry, it's a 1993 Caravelle 17.5' runabout. I don't know the actual model of the drive and I don't have the boat to check right now. The drive I'm putting on is from a 1989 2.3L Sunbird.

 

[Don S]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

Get the right drive. The 2.3L lower unit was a lot lighter built than even the 3.0L you now have.
Trust me, the drive manufactureres wouldn't use different drive gear ratios if just changing a prop was such a good idea.
It's all about keeping the prop slippage in the "Usable" range.

 

[carhopper]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

Thanks for the feedback, I value your opinion. I find it hard to believe that people haven't done this since it's a direct bolt on. Are there any actual cases out there on the forum where someone has done something similar?

 

[carhopper]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

The seller just emailed me back and it is indeed a 21/21 so I'm getting the right one. Thanks anyway.

 

[Don S]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

He took it apart and counted the teeth on the gears? Why do I doubt this???

I find it hard to believe that people haven't done this since it's a direct bolt on. Are there any actual cases out there on the forum where someone has done something similar?

Sure, it's probably been done, people half azz things together all the time and say how great it is. They also normally sell it right after the change to someone with even less knowledge.

 

[carhopper]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

He took it apart and counted the teeth on the gears? Why do I doubt this???

I didn't say that. This guy on ebay has over 400 transactions with 100% feedback selling OMC parts so he obviously knows his stuff. That's the beauty of ebay, If it isn't as advertised, I send it back. Heck of a deal for a decent unit for $230 and free shipping I think. Thanks for your comments Don, this thread is dead.

 

[Don S]

Re: 3.0 OMC Outdrive Change from 21/21 to 21/18

This guy on ebay has over 400 transactions with 100% feedback selling OMC parts

You never said who you was buying it from, it could have been someone selling a drive that he had laying around his garage for 10 years and just trying to get rid of it. We have no way of knowing, thus my questions and comments.
People buy supposedly good stuff off ebay everyday that turns out to be pure junk.