OMC COBRA TO MERC SWAP... Complications??

[Celebrity240]

Im finally pulled out my OMC Cobra 95 Chris Craft Concept 27 and Im ready to start working. I got it with no Motor or drive, but everything else is there including the transom, cables wires etc... I got another dump ready boat with a great condition Merc 454 with Bravo drive. Before I start ripping apart, what difficulties might I encounter? Will the transom swap fit properly? Has anyone done this before?

Any feedback will be appreciated.

Thanks!

 

[Bondo]

Re: OMC COBRA TO MERC SWAP... Complications??

Im finally pulled out my OMC Cobra 95 Chris Craft Concept 27 and Im ready to start working. I got it with no Motor or drive, but everything else is there including the transom, cables wires etc... I got another dump ready boat with a great condition Merc 454 with Bravo drive. Before I start ripping apart, what difficulties might I encounter? Will the transom swap fit properly? Has anyone done this before?

Any feedback will be appreciated.

Thanks!

Ayuh,... Get rid of the rest of the OMC stuff, 'n the Merc should pretty much bolt into the same place, pretty much the same holes....

 

[HT32BSX115]

Re: OMC COBRA TO MERC SWAP... Complications??

Im finally pulled out my OMC Cobra 95 Chris Craft Concept 27 and Im ready to start working. I got it with no Motor or drive, but everything else is there including the transom, cables wires etc... I got another dump ready boat with a great condition Merc 454 with Bravo drive. Before I start ripping apart, what difficulties might I encounter? Will the transom swap fit properly? Has anyone done this before?




Any feedback will be appreciated.

Thanks!

Howdy,


Sure. What would you like to know?

I removed my previous 1987 OMG 460 King Kobra and installed a 1997 Mercruiser 454/Bravo III.



1. You should carefully inspect your stringers, transom, and engine mount-points.
Look for rot, soft wood, stripped lag-bolt holes(engine-mounts) etc.
Also drill some holes near your transom drain and see if you "strike water"

2. If you cannot get a drilling jig or template you can still drill the 2 additional holes (top of gimbal)
in the transom.

3. Now is a good time to clean up the entire engine compartment....do a little sealing with some sanding/glass/resin

BEFORE:

AFTER:

Notice the 2 holes at the top of the "cut-out".

Also, I filled in the holes in the engine mount "pads" using resin mixed with milled fiberglass and wood powder. (you'll most likely need to redrill the engine mount holes.)

I also used lag bolts that were longer than the originals (I can't believe that FW used such short bolts!!!) DO NOT drill through the bottom!!!!!!!Don't laugh, it's happened!!!!)

Comparison.

I think everyone is getting tired of my pictures!!!



BPost pictures!


Cheers,


Rick

 

[Celebrity240]

Re: OMC COBRA TO MERC SWAP... Complications??

Wow Rick, that came out beautiful. So for the transom, you only added the 2 holes at the top, the rest lined up?

And you mentioned that its better to dill up the old engine mount holes and drill new ones, was the spacing between the motor and transom off??

 

[HT32BSX115]

Re: OMC COBRA TO MERC SWAP... Complications??

Wow Rick, that came out beautiful. So for the transom, you only added the 2 holes at the top, the rest lined up?

And you mentioned that its better to dill up the old engine mount holes and drill new ones, was the spacing between the motor and transom off??

Well, I don't remember what you have in your boat now but the engine mounts most likely will not be in exactly the same place. So filling them in and re-drilling is probably going to be required.

Everything does line up. I think OMC, Mercury and Volvo got together with manufacturers in the late 80-90's and agreed to standardize the cut-outs so customers would have engine/drive choices without having to replace the transom.

Also you can tell that the distance from the propshaft to crankshaft center-line is the same too. That was intentional too I'll bet. Boat builders didn't want to have to completely redesign the engine compartment/mounting to offer either engine/drive.


The only other feedback I can offer is that I REALLY agonized over getting the Bravo III because I wanted a Bravo I.


The Liberator is a pretty fast boat. I had heard that a Bravo III would "slow it down".

The 460 with the King Cobra was no slouch for performance EXCEPT for being sluggish out of the hole(even when new....my brother bought it new) .

Otherwise, once on a plane it REALLY FLEW! 60mph at 5000 RPM! (1.43:1 drive, 20p 3 blade SS)

Since the 454 is similar in HP to the OMC 460 (460--340(crankshaft) hp, 454--330 hp) .......... I expected to lose some top speed...........Well, I did. About 3 MPH. (1.81:1 drive, 26p Props, 4600 RPM, 57 GPS mph)

BUT THE DIFFERENCE IN HOLE SHOT! (WOW!) It just ROCKETS out of the hole now!

My brother came up and drove it after I got it running and he couldn't believe it!

I wouldn't even consider a Bravo I now. If you have any access to a "III" lower, it would definitely be worth it on a boat your size. (aside from the low-speed and reverse handling etc the Bravo III is unparallelled)

 

[Celebrity240]

Re: OMC COBRA TO MERC SWAP... Complications??

You read my mind with the drive suggestion. I was having nightmares all winter long... BRAVO I, BRAVO III... But i guess its definitely worth the extra grand for the III. Thanks alot for your help. Will update the situation and include some pics when the job is done.