Replace 2.3L OMC with 3.0 Mercruiser?

Keyboardman

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Sep 10, 2015
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Hi all. I have a locked up 2.3l OMC and have come across a good running 3.0 Mercruiser and outdrive in a junked out boat. How much trouble making the swap? Am I going to have to do a lot of transom work to retrofit it? Thanks.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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A bit of fiberglass work, relocate the motor mounts drill two extra holes in the transom.

Easier than dealing with the omc 2.3

Get the merc controls if you can
 

Speak

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Jul 29, 2012
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Hi all. I have a locked up 2.3l OMC and have come across a good running 3.0 Mercruiser and outdrive in a junked out boat. How much trouble making the swap? Am I going to have to do a lot of transom work to retrofit it? Thanks.
Go with a 4.3 if u can find. Easier install in my opinion. No glass work needed
 

Keyboardman

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Thanks for the advice guys. Maybe I'll look for a 4.3 rather than do a bunch of transom work.
 

Speak

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Speak, How is a 4.3 easier?
I removed my 2.3 and installed the 4.3 - no glass work as I used the existing motor mounts. Other may disagree I'm sure. But I found the overall experience pretty good.
 

Scott Danforth

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Thanks for the advice guys. Maybe I'll look for a 4.3 rather than do a bunch of transom work.

your transom is fine, the fiberglass work is to do the motor mounts because the 2.3 mounts in different locations than either the 3.0 or 4.3. you just need to drill 2 holes in the transom no mater what mercruiser you get
 

Speak

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your transom is fine, the fiberglass work is to do the motor mounts because the 2.3 mounts in different locations than either the 3.0 or 4.3. you just need to drill 2 holes in the transom no mater what mercruiser you get


I did not have to fill any holes in the transom. Everything just bolted up for me. see my 2.3 to 4.3 thread. the only holes I had to fill were on the motor mounts because i found the 4.3 stat ahead by around 1 inch. other than that was really straight forward. huge increase in spead and so much quieter when just cruising...Im glad i did it.
 

Maclin

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I went through your swap thread Speak, pretty neat.

Regarding this... "I did not have to fill any holes in the transom" I believe there would be no holes to fill in the transom, but 2 needed to be drilled in the transom. I looked for where you did that in your thread but missed it I guess.

It will be interesting to see if the OP's boat has the V6 mount pads ready if it was an option for that model :) Yours sure worked out well!
 

Lou C

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Nov 10, 2002
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I agree with the idea of swapping in a full Merc 4.3 replacement, but first make sure you have enough room for the added width of the engine vs the 4 cyl. If you have the style of boat with the engine dog house and the jump seats on both sides, make sure it is wide enough for the 4.3 including the exhaust manifolds. Keep in mind it is just as wide as a 305/350 but shorter, like 3.5" shorter than the V8s and shorter than the 4 cyl. You need to check if you have the engine mounting pads on either side of the block are in the right place for the 4.3.
 

HT32BSX115

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Dec 8, 2005
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Hi all. I have a locked up 2.3l OMC and have come across a good running 3.0 Mercruiser and outdrive in a junked out boat. How much trouble making the swap? Am I going to have to do a lot of transom work to retrofit it? Thanks.

Howdy,

I had to read this thread twice to see what model 2.3L engine and drive you have. Maybe you didn't say. I am assuming that you know it's a 2.3 (not a 2.5L) and it is in fact a Cobra

It it's REALLY a 2.3 ......That is, it is really a dog-clutch Cobra, then you will have no problems putting any 4/6/8cyl modern Mercruiser in the boat. You'll only need to consider moving the engine mounts and whether the engine cover will fit over whatever engine you decide to use.

I had to drill 2 additional holes in my transom going from the 460 King Kobra to the Bravo. Alpha GEN-II is the same. Don't know about PRE GEN-II and I don't think early Mercruiser (Merc-1, 2, 3) has the same bolt pattern

I also had to fill the engine mount pad holes, re-glass and drill new side-mount holes because the engine mounts were not in exactly the same place for the 454 vs the 460.......

In addition, I replaced the throttle and shift cables, and used the complete boat wiring harness from the donor (1998 Bayliner) boat. I kept my original steering wheel/cable though. I also replaced the old shift quadrant with a new Teleflex model.

Other than that, it was basically a "Drop-in" replacement.

If this is NOT a Cobra, forget it. Not worth the trouble.

Cheers,

Rick
 

Lightwin 3

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May 18, 2010
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I also believe you can go Volvo (SX) drive if you find one of those.

I liked the last Volvo I had because of the smoother shifting and the raw water (impeller) pump being inside the boat.
 
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