Engine Swap or not

[dlgarr]

I have a 88 4winns with a 3.0 OMC cobra. It is pretty tired and only does about 32mph. I found a 4.3 l OMC for $400 on craigslist. My debate is to rebuild the 3.0 or swap it out. I don't know what all is involved in swapping it out.
I'm not afraid of anything, I had never touched a transmission before and 2yrs ago using you tube I rebuilt the transmission in my 04 Yukon Denali. Spent $500 including tools instead of the $3500-$5500 to have a shop do it. Two years later still going fine.
Anyway can anyone tell me just how much is involved? I'm wondering things such as motor mounts, would I have to change them out, shifter cables, I'm assuming not, etc. That would help me decide between rebuild vs new engine with more power, Thanks

 

[HT32BSX115]

I have a 88 4winns with a 3.0 OMC cobra. It is pretty tired and only does about 32mph. I found a 4.3 l OMC for $400 on craigslist. My debate is to rebuild the 3.0 or swap it out. I don't know what all is involved in swapping it out.
I'm not afraid of anything, I had never touched a transmission before and 2yrs ago using you tube I rebuilt the transmission in my 04 Yukon Denali. Spent $500 including tools instead of the $3500-$5500 to have a shop do it. Two years later still going fine.
Anyway can anyone tell me just how much is involved? I'm wondering things such as motor mounts, would I have to change them out, shifter cables, I'm assuming not, etc. That would help me decide between rebuild vs new engine with more power, Thanks

Howdy,

Welcome aboard!

Well, it wouldn't be all that hard to change engines. You would of course need to install side engine mounts for the V-6 and the drive would be slightly wrong due to the wrong ratio.......but changing the prop would probably compensate adequately
(I.E. if you're running a 17p prop now, you might need to go to a 19 or a 21p prop) The 2 drive ratios are fairly close.....

The cables wouldn't need to be changed........although you would need to interface the throttle cable to the different carburetor and the shift plate would mount to the engine differently. If the 4.3L engine is an OMC marine engine already and has all the marine stuff with it..... it make the change MUCH easier. If it isn't, you'd need to find a whole bunch of marine "stuff" for the engine like flywheel housing, coupler, Y-pipe, alternator + brackets, carb, starter, manifolds/risers etc etc.......You may still need to scrounge a Y-pipe if the engine doesn't come with one.....

It's doable but it's MUCH easier if you're getting the engine from a "donor" boat. That way you have all the bits needed. If you don't have a donor (or that engine doesn't have the additional stuff) you have to get familiar with eBay and Craigslist for the missing "stuff".

There is definately an advantage going to the 4.3L engine. The boat will perform MUCH better and there's FAR more 4.3L engines out there (over the 3.0L) when it comes time to replace it.

Regards,


Rick

 

[dlgarr]

Thanks Rick! It is an OMC engine, so presumably it has all the marine bolt-ons, unless someone went the cheap route on a replacement part.
I think the side engine mounts would be a killer, the boat was not sold with the 4.3 I don't believe so it is not set up for the mounts. Come to think of it, the engine cover would have to go too. Great points to noodle over

 

[HT32BSX115]

Thanks Rick! It is an OMC engine, so presumably it has all the marine bolt-ons, unless someone went the cheap route on a replacement part.
I think the side engine mounts would be a killer, the boat was not sold with the 4.3 I don't believe so it is not set up for the mounts. Come to think of it, the engine cover would have to go too. Great points to noodle over

Yeah, you could probably easily make a new cover and adding the side mounts would require a bit of fiberglass work. You would just make a "jig" to locate where you'd want the mounts to go, then just use some hardwood to make the mounts. Then seal it all in using regular cloth fiberglass glass and standard marine resin etc. It's done all the time.

The 3.0L engine is one of the best engines ever used in a boat but they are a little anemic on HP.

The 4.3L V-6 is another really great marine engine too. (5.7 V-8 minus 2 cyl!) The upside is your 3.0L engine is worth a significant amount even as a "core" because it's the only replacement for any other 3.0L marine engine that might have been cracked due to freezing..........because with the 3.0L there is no automotive equivalent....OTOH, with a 4.3L V-6, you can use a pick-up engine as a suitable replacement.......

I would probably do the V-6 just for the additional performance.

 

[Howard Sterndrive]

if your boat has a 30 gal or larger fuel tank, that's a plus.
I pulled a 120HP i/o out of my old Grew and put a V6. boat had a 15 gal tank. It went like a jet- 53mph. But waterskiing was brutal. You could do about 45 minutes and then think about heading back in. you're getting less than 1 mpg when the kids are learning to ski behind a V6... we paddled in a few times.

I also pulled the 3.0 out of my Bayliner and put a V6. It has a 30 gal tank - much better. we can cruise all day without panicking.

In both cases I changed drive ratios, but repropping should work if ratios are close. My Bayliner is a Merc Alpha so I wanted the V6 ratio to spin the water impeller a bit faster - not an issue on a Cobra because impeller in the upper turns engine speed anyway.

 

[lakenormangal]

I really like my 4.3 OMC Cobra. Its a 1990, rebuilt completely 3 years ago. When my friend rebuilt it, he stroked it out a little. I forget how much. My 18.5 ft Sunbird will do about 40-45 all day long. And at times I'll take it up to 50 or so. Its pulls a skier, wakerboard or tube just fine.
And it seems easy enough to work on ( we just changed the head gaskets this week and it was a few hours to remove the heads, then a few hours to reassmble after the heads came back from the machine shop. ) The reason the head gaskets needed replaced was that the boat overheated due to a problem with the cooling system.
Its decent on gas, a tank will last all day, and when my boat is out on the lake, most of the time, its moving. So it gets a good deal of hours each weekend. On a 2 day weekend, I'll go through a tank and a half or 2 tanks of gas. About $30 to fill the tank.
One thing I did do, was change the prop on my boat, I went to a prop with more torque. I lost some high end, but man that thing snaps up on plane real crisp! I might get another prop for times when I want more top end, but we like to tube and wakeboard. If I changed back to the high end prop, that boat will easily do 50 all day without trying, if the water is smooth.
Depending on what you want to do with the boat, get the prop that will work best for whatever it is.

 

[Howard Sterndrive]

I have a 88 4winns with a 3.0 OMC cobra. It is pretty tired and only does about 32mph.

did you do a compression test? the lack of power could be something real simple like timing not advancing (flyweights and springs gummed up in the distributor- common problem on old points type 3.0 distributors) or maybe it needs a tune up or exhaust gases leaking or maybe the flame arrester needs cleaning.
stretched throttle cable even. or valves need adjusted. don't rebuild the engine without diagnosing the power issue.

 

[dlgarr]

Thanks for all the feedback, some good stuff. I'm about to invest in a timing light and get a compression tester, maybe that will fix it, or at least tell me something. Thing sat for 2 years, so can't be too surprised it isn't running like a top yet.