OMC Cobra to Mercruiser Alpha 1

[Cptkid570]

Hey everyone,
I posted a similar thread before asking if my 1985 5.7 liter Mercruiser + Alpha One outdrive would line up if I were to install it into a 1988 boat that had an OMC Cobra w/ 5.7 liter (possibly was a King Cobra).

I got the impression that the bolt pattern and hole in the transom is the same and that my mercruiser should go right in without having to re-glass the transom (correct?)

Next question -- Has anyone does this swap before? What exactly needs to be done to make my mercruiser transom assembly fit where the OMC cobra was? How about wiring? Will I have to rewire everything from the engine to the dash? Or shift cables? Would I need to run my own mercruiser shifter (that doesn't seem like it would be a big deal).

I installed my mercruiser engine in my boat, but don't have the confidence to do it if there are a bunch of modifications to be done. I just can get a good deal on a new boat that looks better than mine, so I'm thinking of swaping my engine package into this boat..

 

[Limited-Time]

Re: OMC Cobra to Mercruiser Alpha 1

If I recall correctly the Cobra, and the Alpha 1 have the same hole/bolt patterns. It should be a direct bolt in swap I'm not sure about the King Cobra though.

 

[HT32BSX115]

Re: OMC Cobra to Mercruiser Alpha 1

Howdy,

It's pretty much a direct swap. You may need to drill two additional holes in the transom depending on how new the Alpha is. (The older Alphas have 6 and I think Gen IIs and Bravos have 8 studs)

I replaced my 1987 King Cobra 460 with a 1997 Merc 454 Bravo III

Kobra:

Bravo:

Bravo on the back in place of a King Kobra!

You may have to relocate the engine mounts. Check the mounting pads carefully for rot and squishy wood.

Also check your transom wood for water. Mine while full of water but was not rotten or squishy. It took me several weeks to dry it out before I could fill areas in there with marine epoxy. I almost entirely re-glassed the whole engine compartment. the original job by FourWinns was pretty crummy.

The paint is Interlux BilgeKote.

Cheers,


Rick

 

[Bondo]

Re: OMC Cobra to Mercruiser Alpha 1

How about wiring? Will I have to rewire everything from the engine to the dash? Or shift cables? Would I need to run my own mercruiser shifter (that doesn't seem like it would be a big deal).

Ayuh,...... It's called a Refit......

You Strip Everything that was for the OMC, Out of the hull,.... Everything....
And,...
Install All of the Mercruiser stuff back into the hull.....

 

[Cptkid570]

Re: OMC Cobra to Mercruiser Alpha 1

All of the wires going to the gauges too? You'd think that I could splice those together???

 

[Bondo]

Re: OMC Cobra to Mercruiser Alpha 1

You'd think that I could splice those together???

Ayuh,....

My point is,... The cannon Plugs are Different,... You can splice things anywhere you want.....
But,....
Everything OMC will Not usually mate up to anything Mercruiser......

 

[Cptkid570]

Re: OMC Cobra to Mercruiser Alpha 1

Gotcha -- would the wires typically be color coded the same though?

 

[JustJason]

Re: OMC Cobra to Mercruiser Alpha 1

Just curious, what did you use to coat your bilge with HT32?

 

[HT32BSX115]

Re: OMC Cobra to Mercruiser Alpha 1

Will I have to rewire everything from the engine to the dash? Or shift cables? Would I need to run my own mercruiser shifter (that doesn't seem like it would be a big deal).

While you probably could maybe use the Cobra harness (the plug will plug in), there are a couple of additional wires (and pins) in the mercury harness plug/socket.... The wiring color code is similar but NOT the same. If you're going to spend for the most part several thousand dollars for an engine, transom, drive, trim pump, props, etc etc etc, a couple more hundred for either a new Mercury harness, or a good used one is WELL worth it! I got everything from the donor boat including the gages. (The gages I had in the Liberator were the ones I used however...they were in FAR better condx!)

Rewire everything to the dash. You REALLY want to minimize crimped spliced connections. Every crimped or spliced connection is a potential future corroded "mis-connection"! I even crimped and soldered every connection at each gage. (I'm a little anal about that stuff!!) Spliced connections should also have heat shrink tubing over them after crimping to seal them against moisture. (which means you have to slide heat-shrink tubing over the wire before you crimp!!)

If your steering wheel & cable and are good you can use it.

You have to change your throttle/shift cables. I also bought a new Teleflex-Morse CH-1700 control and new cables like THIS ONE. (you might be able to use the OMC control but it would have to have different cable positions for the Mercury....... I thought mine was a POS!)

I also went to West Marine and bought a nice fuse panel. The old harness used inline fuses. The new panel uses those cool push on fuses (ATO) like a car uses.

I used a fuse block similar to this one.

That's about it...check your engine mounting pads carefully. the wood underneath might be mush...


Cheers,


Rick