Mercruiser 3.0 to OMC 4.3L - doable ?

donberry

Petty Officer 3rd Class
Joined
Dec 27, 2010
Messages
94
I know, I know - why would you switch from a Mercruiser to an OMC ?
I currently own a 1988 Dynasty 190 Fish & Ski with a 4.3L OMC Cobra engine/outdrive. Runs great, zero problems with it. Cosmetically it is a definite fixer upper and also needs new stringers. I am using it as is but am(was) planning on starting on the resto here pretty soon. Been waiting for my garage to get done as it is being remodeled.
Besides the stringers, floor is fine but also planned on new flooring (probably seadek) and all the upholstery needs redone.
I ran across another 19' fish & ski that the boat itself is in much better condition. Upholstery etc are in nice shape and have not physically checked the stringers yet, am guessing they will be fine - or at the worst still much better than my current boat. My boat has obviously been one of those left outside, not covered for a decade or 2 (I will never understand why people do that - buy a $35 tarp at least).
Anyway, the other boat has a 3.0 Mercruiser in it. Runs okay but was thinking I would like to either swap it out with my 4.3l or more likely (depending on how fast the boat goes with the 3.0) just keep my OMC engine/drive as a spare. I have the room to store it, covered, so if I ever had any problems with the mercruiser I was thinking i could just drop in the OMC instead of having the 3.0 rebuilt or having the drive replaced if it went out.
Pretty verbose way (sorry) of basically just asking if it is a pretty straight froward swap or would I get into some things that would make it a real pain. Figured since I had the outdrive, as long as the hole in the transom was not bigger, could basically just drop in the OMC engine and drive if needed and not have any real down time.
Big job ? Pretty straight forward swap ? Any info appreciated.
Figured it would cost me at least half of what the other boat costs to fix mine ande sure would be easier than re-doing my stringers, all the upholstery etc. Headache saved would be worth the other half - plus basically zero down time as I live in Tennessee and we can pretty much use a boat year round.
 

cr2k

Captain
Joined
Mar 19, 2009
Messages
3,730
Re: Mercruiser 3.0 to OMC 4.3L - doable ?

You would need to at least re-gear it to the proper ratio (higher for the 4.3) or change the outdrive to the right one. You are gonna have to fab some side mounts for 4.3 also at the correct position and height. It's do able but will require some work and parts.
 

donberry

Petty Officer 3rd Class
Joined
Dec 27, 2010
Messages
94
Re: Mercruiser 3.0 to OMC 4.3L - doable ?

I was thinking i would also be using the drive off of my current boat. Pull the 3.0 and outdrive, swap in my 4.3l and outdrive - so was thinking (hoping) the only real concerns would be
1. the size of the hole in the transom. If the outdrive on the 3.0 was bigger, too big a job for me and would be a no go. If it was smaller, no big deal as I could make it bigger. Guessing a good chance it would be the same size.
2. the motor mounts. But on my Dynasty, the mounts are just bolted to the stringers with 2 big lag screws per side. Was thinking the spacing for those was pretty standard even from different boat manufacturers so as long as the OMC was the same measurement width wise, probably just have to drill new holes in the stringers for the lag bolts ? This is the only boat I have ever really owned so don't really know if they all mount the same or what.

I obviously have no clue, but my thoughts were the things I may run into the biggest "problems" or headaches would be maybe the steering and linkages for the throttle. While not difficult if you pay attention to what you are doing, apparently the OMC was known to be not very forgiving when it came to adjusting the linkages and apparently would eat up the gears pretty quickly if not done correctly. Is the only one I have ever done, so not knowing any better it did not seem difficult to me. Thought maybe worst case was I would have to also use the cables from my boat if I did the swap to insure they are the exact same length ? Was wondering tho that since they are both 19' boats, should not really be that big a problem ?
 

Struc

Chief Petty Officer
Joined
Jul 27, 2011
Messages
409
Re: Mercruiser 3.0 to OMC 4.3L - doable ?

A 4.3l is a 4.3l. Find the correct Merc bell housing, coupler, the exhaust y-pipe, and a few other things, and keep it all Mercruiser. I would think it would be a LOT easier than swapping everything to OMC. Gear ratios may be messed up, but you could probably compensate with a prop rather than getting a whole new outdrive or changing the ratios.
 

donberry

Petty Officer 3rd Class
Joined
Dec 27, 2010
Messages
94
Re: Mercruiser 3.0 to OMC 4.3L - doable ?

biggest reason I was thinking about swapping both the drive and the engine was cost. Just off the top of my head, was thinking swapping out bellhousing, coupler etc would run me $400-$600 ?
I know the OMC Cobra is not highly regarded, but since it is all I really know (only one I have ever owned), I don't notice if it is harder to adjust etc. From what I have researched, as long as you do the adjustments right, it really isn't that bad as far as eating gears etc ? I pulled it when i first got the boat (and the engine) and did all of the adjustments when I put it back on, have used the heck out of it but for only 1 year, but runs great right now.
Maybe, just thinking out loud as I obviously know nothing about this stuff - use the OMC outdrive but keep the Merc and if the OMC fails, then do the swap ?
While I am not poor by any means and sure I am way ahead of many, many people, I am on a fixed income (disabled vet) so any cost savings I can come up with is a big plus.
Only reason i am even considering doing this is the boat with the merc on it is for sale for $1500.00 and in much better cosmetic shape. I am thinking by the time I do my stringers, replace the carpet (seadek hopefully) and redo the upholstery, while I won't have $1500 in it, i would have a fair amount plus a whole bunch of time (and down time - I use the boat year round) - saving me a whole bunch of work.

So just kicking around the idea of buying it........tho I guess I need to be careful what i want. While mine does need painted (I can do that myself, have painted a bunch of cars - tho I would just use auto base/clear with a marine clear. Figured would easily last me until I did get a newer boat. I am hoping to keep this for another 3-4 years and my house will be paid off so can get a newer boat) and the other work, it does run great. I go to the lake, hit the key and go. I would hate to end up "trading" in for a prettier boat but then end up having mechanical problems. I will take mechanically sound over pretty any day.
Anyway - I am not trying to be disagreeable, I sincerely appreciate ALL responses. Only trying to see all sides before I make up my mind.
Thanks
 
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