OMC Cobra 4.3 to Mercruiser Alpha 2

[208Cuddy]

I have been seriously contemplating doing a complete repower (engine & outdrive) for a few years. My BIG hangup is the hole in the transom- I've seen a couple posts that say the Cobra and A2 cutouts are the same. But 2 local shops have said "Oh NO it's totally different- and you'll have putty or bondo or redo the entire transom at a glass shop. I've also heard talk of needing bushings for the bolt holes.

One post by HT32BSX115 has done it, but with a King Cobra to a Bravo III. Does anyone know for sure, without a doubt, that the cutout for a 1991 Cobra 4.3L will work with an Alpha Gen II ?? I'm planning on a newer 4.3L.

Has anyone out there done this job?

Thanks for reading & any help you can offer...

 

[Bondo]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

Ayuh,.....

Other than Possibly alittle tuning with a grinder, or small fills with putty,.....

They're the Same......

 

[HT32BSX115]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

Most of the boat shops are thinking either Stringer or older VP when they say it will not fit. I went to a couple of shops up here in the NW and they told me it could not be done. Then I went to a shop up east of Seattle and the guy told me that it's an easy swap. everything is the same. After getting conflicting reports I came here and got the "real skinny"!

You may have to drill 2 more bolt holes (top) if you go to a Bravo or a newer Alpha but all the Cobra (OMC/Volvo) cutouts are the same.

Evidently the hull manufacturers wanted to be able to have some flexibility in eng/drives and in the mid 80's OMC/Merc/Volvo must have agreed to standardize the cutouts.

The 1987 King Cobra inside transom plate I have has the same part number across all the Cobras for that year.... the bolt pattern is identical. I did a little re-glassing in the hole because the original cutout was a little rough. It did not match up very well with even the Cobra transom shield. I'm surprised it didn't leak!! It looked like the guy at FW must have used a sawzall and needed glasses (and forgot them at home!!)

I used fiberglass and MAS epoxy to do it. I also had some moisture in the lower part of the transom wood that had to be dried out. It took me a month or so just to dry it out. Luckily it was not rotten anywhere. I pumped a lot of epoxy mixed with milled fiberglass into the bottom of the transom. There was a rather large gap at the bottom of the actual transom wood and the fiber glass at the bottom. Seems that Four Winns didn't do a very good job of bonding the transom wood to the actual bottom of the boat. Any water or oil that made it into the transom drain saturated the transom!

Below are some pictures Before/After to see what it looked like. You'll have to click on them. The pictures are too large to post in this message.

http://i14.photobucket.com/albums/a317/nixypixy07/dscn0667.jpg
http://i14.photobucket.com/albums/a317/nixypixy07/dscn0666.jpg
http://i14.photobucket.com/albums/a317/nixypixy07/new1.jpg
http://i14.photobucket.com/albums/a317/nixypixy07/new4.jpg


Cheers,


Rick

 

[Lou C]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

WOW great job there Rick, looks like a new boat! and neater than most new ones!
Everthing I ever read said that the opening was the same for Merc/OMC, but I guess you don't know till you actually try it.
I have been toying with the available options when I can no longer get Cobra parts, or if it eventually needs a rebuild.....volvo conversion ...way less work, but drive is double the cost of Alpha....or convert to Alpha....but then have to pull engine and change everything.....
I think it may be well worth spending more on the volvo up front...since to pull the engine would be very diffiuclt for me because of limited space....we'll see when the time comes....Sierra makes just about anything I would need for a Cobra and as long as my mechanic is still working....might be a long time

 

[rock_doctor]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

We converted from an 87 OMC Cobra to an alpha gen 2 with a 300mag. The yard said it was an easy swap. Everything was there and no problems what so ever. If you have the cash go for it but make sure you check around. We got prices that ranged from $25k to $15k. We went with the 15 and they have done an awesome job. Also get it done over the winter time. Most yards are slow and are happy to have the work.

 

[HT32BSX115]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

If you have to pay someone else to do it and you buy a new eng/drive/transom it WILL be expensive anyway you slice it!!

Luck smiled on me every step of the way!

I have a huge shop to work in. (actually it's an airplane hanger....I live at the airport!)

One of my neighbors loaned me an outstanding huge portable overhead hoist for an almost indefinite time.

I found a boat up north of Seattle ( a 98 24' Bayliner 454/Bravo III, never in salt, always trailered, 122hrs since new) that was severely damaged in a windstorm (a tree fell across the front of the boat....INS co totalled it)

I bought EVERYTHING in the back eng/drive/transom/harness/cables/controls......everything for $5000


I did the whole swap by myself, had fun learning as I went and asked a lot of questions here!

(for you noise haters, I did NOT re-install the Capts Call...the thru hulls are still there.....if I can find decent(quiet) marine mufflers I may do it someday though!!)

I probably have $6500 total in the whole job (including the San Juan Engr closed cooling system that I added before putting the engine in)

Now the boat just flies!! About the same speed as before but it just ROCKETS out of the hole......it NEVER did that even when my big brother bought it new in 1987!



Best Regards,



Rick

 

[rocket1968]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

Rick, what paint type/enamel did you use to cover the transom?

 

[HT32BSX115]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

I had a fair amount of damage in the back from batteries on both sides leaking so I did a LOT of grinding with a very coarse sanding disk all over the back. The fiberglass job in the back was pretty poor also so I actually put almost a complete layer of cloth over the whole back. I used MAS epoxy instead of polyester resin.

I tried putting some color in the last coat of resin but that didn't work very well. The resin actually can be colored but it's still sort of opaque so I sanded it all down and just used regular gray Interlux Bilgekote. They do have a primer that you should use on epoxy and I did use it.

I also used an HVLP sprayer to apply it (my first experience with one) and it worked pretty well. there was almost no over spray.

 

[Spinnaker]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

I see that this thread is a couple years old but I'm hoping to get verification on what I'm reading. I have pulled a 2.3L and omc cobra from my boat and am installing a 350 with alpha type one drive.
Can somebody please confirm that the cutouts are the same?

 

[HT32BSX115]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

Howdy,


It's really better if you start your own thread but, yes they are the same.

From mid 1986 to current, you can bolt a Mercruiser any where a Cobra or Volvo SX went. Back in the 80's the Boat manufacturers wanted to be able to offer different engine/drive options but didn't want to have to build the boats with different engine mounting..... so they evidently got OMC/Merc/Volvo to agree to build their engine packages to be similar.

If you want to use a Bravo, you'll need to drill 2 additional holes because it has 2 additional mounting studs. I could be wrong, but I think the Alpha GEN II also has 8 transom mount studs.

Just make sure you check the transom and stringers for water intrusion and/or rot.

Regards,



Rick

 

[achris]

Re: OMC Cobra 4.3 to Mercruiser Alpha 2

If you want to use a Bravo, you'll need to drill 2 additional holes because it has 2 additional mounting studs. I could be wrong, but I think the Alpha GEN II also has 8 transom mount studs.

Rick

Not wrong, and the 2 additional holes are at the top.