OMC Identification and Outdrive Swap

[MXrider164]

Ok so heres the deal, I was out on my 1988 Galaxie Works boat its has a 4.3l GM motor with a OMC Cobra outdrive, I noticed a milky white gear oil in the bilge and had a very distinct burning smell coming from the drive. I immediately pulled it out of the water to get home and drain the upper and lower unit oil to find chunks of metal shards and water coming from the outdrive. Assuming its completely toast. I wanna just find another outdrive on craigslist and swap it out because I do not have nor wanna spend 2k to either fix it or buy a conversion kit and throw a mercruiser on it. So I am confused about what can fit my boat. My model number is a 983842, could a 985268 work? or possibly one from a 5.0l? I am just very confused. Please help. I will attach a pic of what it currently has.

 

[HT32BSX115]

Re: OMC Identification and Outdrive Swap

I wanna just find another outdrive on craigslist and swap it out because I do not have nor wanna spend 2k to either fix it or buy a conversion kit and throw a mercruiser on it. So I am confused about what can fit my boat. My model number is a 983842, could a 985268 work? or possibly one from a 5.0l? I am just very confused. Please help. I will attach a pic of what it currently has.

Howdy,


You really need to find another drive that is the same ratio as what you have. You may be able to go with a ratio that is slightly higher or lower but that will require you to use a different pitch prop (if the drive is close)

I think a 985268 is for a 3.0L engine........it might be a little low (ratio) for a 4.3L engine.....

The problem with just buying another (used) drive is that you might get one that is in as bad a shape (or worse) than what you currently have. (Previous owners don't always tell the truth)

This is probably why most people will suggest getting your drive rebuilt or replacing with an SEI etc is usually a better course of action.

Good luck,


Rick

 

[MXrider164]

Re: OMC Identification and Outdrive Swap

Rick, Thank You for a response, well how crucial is matching up the ratio? I mean if it says it is from a 5.0 or possibly a 3.0 will it still match up size wise? I can practically buy it, replace the seals, bellows, oil and maybe the prop and should be good to go?

 

[HT32BSX115]

Re: OMC Identification and Outdrive Swap

Rick, Thank You for a response, well how crucial is matching up the ratio? I mean if it says it is from a 5.0 or possibly a 3.0 will it still match up size wise? I can practically buy it, replace the seals, bellows, oil and maybe the prop and should be good to go?

Well, it WILL bolt on and operate. The problem is that if it's to "tall" (high ratio) you may not be able to make rated WOT RPM..

It's possible (permissible) to use the "wrong" ratio sometimes and just re-pitch the prop to make up the difference. You cannot go very far (pitch wise) and stay efficient though.....most standard boat props are efficient in a small range of RPM. Get out of the range and you lose efficiency from either excessive drag or cavitation etc..

You need to know what your current ratio is (and if it's correct) and/or what the ratio of the drive you plan to replace it with.

You can use a prop-slip calculator to experiment too....

http://www.go-fast.com/Prop_Slip_Calculator.htm

Regards,


Rick