Swap an OMC 5.8 with OMC 5.7

[Retired SFC]

I have a 1992 Four Winns 225 Sundowner with an OMC 5.8 & King Cobra outdrive. I just completed and transom replacement and now I’m moving to the engine. I was curious to know if an OMC 5.7 will bolt up to my existing setup. Any info would be greatly appreciated.

 

[Bondo]

I have a 1992 Four Winns 225 Sundowner with an OMC 5.8 & King Cobra outdrive. I just completed and transom replacement and now I’m moving to the engine. I was curious to know if an OMC 5.7 will bolt up to my existing setup. Any info would be greatly appreciated.

Ayuh,..... Welcome Aboard,..... The Ford motor, 'n the King Cobra suffer from the same problem,....
Parts are nearly, to impossible to find,.....

Donno how much of a problem it'll be to swap from Ford, to Chevy power, especially with the King Cobra,....

 

[Lou C]

What you’d have to do is go thru OMC parts manuals to see what parts are different between the GM engine versions vs Ford. Likely items to check:
Bellhousing
Exhaust Y pipe
Exhaust down pipes

If it were me I’d take this chance to swap the whole thing over to Merc; if you want to keep the boat long term. 5.7 Chevrolet & Alpha 1 Gen 2. Could do it with used parts & sell off the OMC stuff; there is a market for it.

 

[Lou C]

INTAKE MANIFOLD, EXHAUST & COOLING - 1992 Stern Drive 5.8 584APLAMH | Crowley Marine

View parts diagrams and shop online for INTAKE MANIFOLD, EXHAUST & COOLING parts, 1992 Stern Drive 5.8 584APLAMH. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

Ford exhaust
PS GM Y pipe is the same so you probably could re-use the parts from the upper exhaust pipes, and hoses from the Ford engine with the manifolds and elbows required for the GM 5.7

TRANSOM PLATE, FLYWHEEL HOUSING & MOUNTS - 1992 Stern Drive 5.7 574APEAMH | Crowley Marine

View parts diagrams and shop online for TRANSOM PLATE, FLYWHEEL HOUSING & MOUNTS parts, 1992 Stern Drive 5.7 574APEAMH. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

GM Flywheel housing

Ford is different so you'd need that:

TRANSOM PLATE, FLYWHEEL HOUSING & MOUNTS - 1992 Stern Drive 5.8 584APLAMH | Crowley Marine

View parts diagrams and shop online for TRANSOM PLATE, FLYWHEEL HOUSING & MOUNTS parts, 1992 Stern Drive 5.8 584APLAMH. Offering discount prices on OEM parts for over 50 years. FAST $4.95 shipping available.

www.crowleymarine.com

post a pic of what drive you have, engines in this time frame came with both the standard dog clutch Cobra and the King Cobra cone clutch. In fact some were called King Cobra and came with the standard dog clutch drive, which is easier to get parts for.
the only engine that was only used with the King Cobra cone clutch the GM 454 as far as I know. Small block Fords and Chevrolets could come with either.
King Cobra could mean:
1) standard dog clutch Cobra with higher performance engine
2) Ford 460 with standard Cobra transom mount and upper gear housing and HD lower housing from the V8 Evinrude outboard (used 87, 88, 89 years)
3) KC Cone Clutch, totally different no shared parts

the reason why they did this was that just like with the Merc Alpha, the standard Cobra lower was strong enough for the small block V8s but not the big blocks. It was a slightly modified Evinrude/Johnson V6 lower gearcase. Properly maintained and with a good shift cable they can last a very long time. I have one and like it but just try to find someone to work on it, difficult!
In my garage I have a complete spare transom mount, 4.3 outdrive (needs to be redone though) and many Cobra parts

that's all I got, I'd still convert to Mercruiser!

 

[Bondo]

that's all I got, I'd still convert to Mercruiser!

Ayuh,.... I agree, that's no doubt the best way forward,....

 

[Retired SFC]

I have the King Cobra Cone clutch outdrive "Big Daddy." The OMC GM motor I am looking at is complete with flywheel cover and risers. Would the front motor mounts match up to the 5.0 on the stringers?

 

[Retired SFC]

I did consider the Mercruiser swap but I was concerned about the transom cutout and mounting holes. I was afraid that the bolt holes would not match.

 

[Scott06]

I did consider the Mercruiser swap but I was concerned about the transom cutout and mounting holes. I was afraid that the bolt holes would not match.

Cobra and Merc Alpha and Bravo use the same transom cutout. OMC was so far behind Merc in sales they wanted the cobra drive to be easy for boat manufacturers to use interchangeably with merc so they used the same hole.

If you have the Chevy 5.7 complete it will be easier but hard to say if all pieces including exhaust will fit up. Without having it in front of you measure hard to say, but you've put this much work into it... swap it over for a Alpha gen 2 or bravo one and you will be good to go parts wise vs hard to find

 

[Retired SFC]

Would the gen 2 or bravo one gimble housing mounting bolts match up with the OMC King Cobra holes?

 

[Scott06]

Would the gen 2 or bravo one gimble housing mounting bolts match up with the OMC King Cobra holes?

Yes I believe so. Even if the bolt holes need to be filled and re-drilled the transom cutout if the same.

@Bondo can you confirm

 

[Lou C]

I also believe that is true about the transom mount.
Now you have the chance to get away from the OMC parts & repair headache I for sure would do it. Plus it makes the boat way easier to sell if you do want to sell it

 

[kenny nunez]

Some OMC flywheel housings have a dual bolt pattern for Ford or GM.
Is the 5.7 a OMC version or a Merc?

 

[Retired SFC]

The one I have found is an OMC version

 

[kenny nunez]

In that case then it should be a slam dunk. Especially if the GM engine has the electrical. The Ford probably was fuel injected, if not all the better as you will end up with extra electrical components.
What was wrong with the Ford engine?

 

[Retired SFC]

It blew the head gaskets. I replaced the all the gaskets, water pump, freeze out plugs. I still have to ground hop it. I was just making contingency plans.

 

[Lou C]

Did the HGs blow because of an overheat? If so did you get the cyl heads checked out by a machine shop? Overheats can cause small cracks in the cyl heads that you can’t always spot but that can cause leaks. Oftentimes the block is still good when that happens.

 

[Lou C]

FORD Cylinder Heads

machineworldny.com

if your cyl heads got cracked in an overheat (usually what blows HGs) reman units are available.
I got mine from this place (Machine World) in Long Island, $275 each