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Changing a omc 3.0 to a omc 4.3

R

rhays

Member
Hi, Please bear with me as I try to give as much info as I can,,,,I have an 18 ft 88 bayliner with an Omc 3.0 engine and outdrive. It runs fine, shifts fine and has no problems, but as you know, it lacks power. It was ok when the kids liked to be pulled around in tubes, but now that they want to ski, and it needs more power. Selling and buying a more powerful boat is hopefully a last resort as I really like this bayliner, and it is now in good shape. Two years ago (with much help and advice of this forum), I replaced the entire floor and stringers, and fixed or replaced almost everything that it needed and now everything works well. Now I need your help again. I have obtained 18' sunbird with a good running omc 4.3 (2 bbl carb) and with a good 4.3 lower unit that was practically given to me. The 4.3 boat runs fine, but the floors, stringers and upholstry are shot, so I don't think it's worth the money to fix and sell. (plus my wife doesn't want any more boats. So I thought I would try to put that combo in the bayliner. Pulling my 3.0 is easy, as well as removing the outdrive and changing the lower unit over, I understand I have to swap everything over and can handle the electrical, gas lines, etc but I have some questions I have not heard anyone talk about before. Does the gimball assembly need to be changed? they look the same but I am not sure about the inner plate that attaches the rear of the motor mounts because I don't have the boats side by side yet, Also, how do you align the engine with the side mounts on the stringers instead of the front mount as in the 3.0. The 4.3 has power steering, do I have to use that? or can I just keep it simple and manual how it is? Any advice will be greatly appreciated. I read this forum daily and think it's advise is worth its weight in gold.... I am planning to do this over the winter when I have lots of time,,,,,
thank you again for your advice...
 
I have stringers that run down both sides of the 3.0 that look as wide as the other boat with the 4.3. The 88 bayliner is a capri that had the option of coming with a 5.0 in '88 and I appears that it will easily fit. Although it will be much tighter than the 3.0 that is in there now... The manifolds on the 4.3 are the batwing style that are close to the engine and go up. The other boat just has the engine mounts bolted into the stringers on the side of it... Should there be a plate that goes in first, then the engine mounts attach to it? that makes more sense in that it will be stronger... Thank you again for your help...
 
My Capri appeared to have solid stringers for the engine mounts, but they were out too wide for where the mounts sit, and...get this:
they are HOLLOW!!!

So, I made an T shaped bracket out of heavy angle iron that sits on top of the stringer box with lag bolts, and also is lag bolted into the side of the box. My engine mounts sit on, and bolt through, the inner tee part. In my 3rd pic, you can see part of the plate with a lag bolt in it.

It is important to get the front mounts in the right place for alignment.

I hung the engine on the crane and got the alignment bar in. Then I made the brackets and installed them -never removing the alignment bar the whole time.

It was the first job for my new mig welder!
 
they are HOLLOW!!!

The strength of the stringers comes from their box beam shape. Wood core is merely a convenient form to wrap with glass as it it cheap and easy to shape. Cheap boats you often see the wood form either just tabbed to the hull or not completely encapsulated with thick roving.

Rhays:
The hull should be ready to accept all engines that were available options, which presumably included a V8 or V6. The stringers should be V6 ready.

>>The manifolds on the 4.3 are the batwing style

"Center riser"
 
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I like the idea of the L brackets that wrap the stringer for strength. I don't have a mig, but should be able to find a place easy enough that will weld one for me for a few bucks or a case of beer... (collision shop) nearby,,, and hanging the engine with the alignment bar in it while placing and adjusting the mounts sounds do-able, I dont have a crane, but I do have a home made A frame that goes on each side of the boat with a beam over it and a chain hoist that works well. another question I have not seen before, Is the wire harness pin connector the same for the two boats as they are both OMC,, or are they all different,, again, I don't have the two boats side by side yet, If not I was planning on just cutting one off and ensuring that the correct wire goes to the right home...(very time consuming) thanks again for all your help and suggestions...
 
Now thats what i'm talking about. I'm getting itchy, need a project.

How about this Moppie...
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or this F32
img_4890.jpg


Or even this Silverton:
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All are in NJ, and cheeeeep.
 
I thought the 4.3 went on the Cobra 800 outdrives. The outdrive for the 3.0L will only take the 2.3L as well (Cobra 400). I think you will eat up your gears in a hurrry.
 
Biffidum is correct.
A 4.3 Cobra drive would be required for 2 reasons:
1. bigger bearings to handle the power
2. correct gear ratio in the upper

I would recommend the SEI conversion to put a Mercruiser 1.81 drive behind the 4.3
 
Re read the original post. He is putting a 4.3 AND drive on his boat. His question was more about alignment and installation, which, by the way, should be absolutely no problem and a straight swap.
 
about the wires, just remove all the wires and mark them from the motor. Don't even unplug the barrel.

Your doing this the right way having the donor boar right next to the boat you working on.

I'm wondering about your 3.0 what you gonna do with it? And the drive .
 
Hi, Thank you again for all the help..
I do have the 4.3 outdrive to go with the engine, all looks go so far, I have a brother in law who is already claiming the 3.0 engine, (Bummer, that means I get a case of beer for it),, but I hope I can get something for the outdrive. (Imangine that,,, actually getting a few bucks back for the first time in my boating history) The outdrive is a good one, a 3.0 with the stronger bottom ( a 15 spline prop shaft instead of the smaller 13 spline.) I bought it used two years ago off of a guy with boat that only had miminal hours on it, had it checked out, and had new seals put in it. It has worked flawlessly. As soon as the weather starts to turn here in NC, I will start the swap. Chief, I like the idea of just unhooking, labeling, and wiring it back on. Looking at the two engines, both appear to have almost identical wiring, alternator, shift assist, coil, ect,,, Hystat, I did check out a link for the change with the SEI conversion. I had no idea that one could put a merc on a cobra transom assembly. this sounds like a fun swap. Has anybody done this with good results? I have had very good luck so far with the OMC drive. I followed the links that you guys have posted on how to adjust it, and it has shifted very smoothly for two seasons....
thank you again and please don't ever get frustrated or give up helping us diy'ers ,, your knowledge and advice is priceless to all of us dedicated people who follow this forum.
 
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