motor swap
 

:eek: I need some information. I have a 1987 21' boat with an OMC 5.7 carb. motor and Cobra outdrive. The OMC motor is weak and is in need of a rebuild. I have a fresh 2000 EFI 5.7 Mercruiser Bobtail that is ready to go. I know that both motors are a Chevrolet based 350's, so what problems would I be looking out to swap the OMC out for the Merc. The Cobra outdrive is a fresh rebuild and is top running order and I don't have the funds to purchase a Mercruiser Outdrive at the moment, but who knows about the future. I eventually would like to get a BRAVO outdrive to replace the Cobra, but for now I'm stuck with the Cobra. So am I barking up the wrong tree with a motor swap or should I just do the rebuild on the OMC. Any thoughts would be greatly appreciated :confused:

Re: motor swap
 

there should be no problem swapping those two motors just use all the engine coupler and mount hardware from the OMC on the new engine and it will bolt right in.

Re: motor swap
 

you may need to change the wiring harness, throttle andd shift cable ends, but the bell housing should just bolt right up to the new engine.

Re: motor swap
 

You will be ok. Just be careful.
Most stuff will be obvious.

I have had an OMC "350" and a merc "350" at the same time. the biggest difference is that OMC piles everything on top of the intake like a hat. I have twin OMCs now in that size.
Merc spreads the brackets around.
You'll need the hub from the OMC/chevy of course. Bolt it on the merc/chevy. You'll need to transfer the ESA bracket and everything over to the top of the Merc/chevy. If the intake manifold from the OMC/chevy is ok, I would transfer it over with all the goodies still on top.
A problem area may be the mass connector and AGU fuse holder assemblies, because they are 17 years old, and they were kind of weak designs.
If you have power issues after the swap, check these harnesses first.
Especially if you lose drive trim, or main 12v after the swap.
(weakest link.)

Kind of turn it into a long block swap out, if you know what I mean.

Rock on with your Cobra drive. I have two. Just make sure that your ESA is really dropping those Rs when you want to shift.

The other thing is.... if you like that boat and you decide to get rid of the Cobra, or should it break... look into Volvo. They are the smoothest shifting drive in the business, and they will BOLT RIGHT UP to your existing 80s OMC transom assy. If you try to switch to a bravo you're making a new hole.

And for a 21 foot boat with a 260 horse (ish, I know) the Volvo drive would be fine. I have a friend with two Volvos on a 24 Donzi. They shift so smooth you need to give it a little gas, just to know that it really did pop right into gear.

Good luck. If anything specific comes up, I'll try to help.

Re: motor swap
 

If you can transfer that Intake over, carb and all, that would eliminate the throttle and shift cable end issues.

Take the harness leads off of the block, but use the same harness.

Re: motor swap
 

Yes.... that's right.

A NEW volvo drive will bolt right up to the transom assembly of an 87 OMC.
Of course there is a different shift and trim kit.

Re: motor swap
 

Hey thanks for the input, The mercruiser is complete from top to bottom. I shouldn't have to exchange any of the intake or carb since the merc. is efi.

Re: motor swap
 

That's ok, just more work. I was picturing ways to leave as much OMC stuff on the boat and hooked up as possible in my mind. But this way you get newer carb and intake.

good luck. let us know how it goes. Take pics. :D

Re: motor swap
 

Which reminds me..... take a bunch of pics of the layout before you start tearing the OMC out. Even with a good shop book, it's nice to go back to the pics for reference.

Re: motor swap
 

Hey Thanks again esp. Fund Razor and I've already got the camera working overtime