Converting OMC Dressed 305 to Run a Mercruiser Drive questions

[Taylor_T]

Hey guys,

So I am working on rebuilding my boat. It has a 305 chevy with an OMC stringer set up currently. I would like to get away from OMC if possible so I have been looking at getting a donor boat to switch to a mercruiser drive.

The 305 that I have runs great.

I bought a boat on the cheap with a none running motor, intending to use it as a donor. Well, I'm still learning about boat motor's and drives (and motor's in general) and the boat that I got has a mercruiser 888 (MC-1) with a FORD 302 motor. From what I am gathering, I won't be able to use this as my donor because nothing ford fits chevy, correct?

Well, another boat popped up today that could be a possible donor. It is a 1982 galaxy with a Chevy 305, and mercruiser drive system. He says it runs "ok" but has a cracked intake manifold. Since it's a 1982 it's probably pre-alpha, but it's hard to find a donor boat any newer. He is asking $600 obo. I'm really considering getting the boat if I can talk him down a little, but don't want to waste money on impulse again.

So, I guess these are my main questions that I'm hoping the vast knowledge on iboats can help with (this forum is awesome):

1. What exactly do I need to switch out on my OMC dressed 305 to allow it to run a mercruiser drive? I can keep the majority of the motor the same, right? This is something that seems to be hard to find info on.

2. Is a cracked manifold a deal breaker for a donor boat? Is that one of the parts I need to switch out to make the mercruiser drive work? What other problems might this have caused?

3. My thought is, that the donor boat I am looking at has the same foundation (chevy 305), but Mercruiser dressed instead of OMC. So, I think I should be able to just swap the parts I need between the drive systems?

4. Is it still possible for me to use the Ford 302 donor boat, or should I part out what I can and junk it?

5. Anything else I should consider?

I know that I have a lot of questions, but I'm trying to learn the best I can. Hopefully some of you guys out there know about this kind of stuff.

 

[Scott Danforth]

strip the OMC dressed 305 down to block and heads (what came from GM), and build it up with teh Mercruiser stuff

No, not possible to use the ford stuff unless you use all of it from carb to controls to prop

 

[Bondo]

1. What exactly do I need to switch out on my OMC dressed 305 to allow it to run a mercruiser drive?

Ayuh,.... Like Scott says, strip it down to the Long Block configuration, 'n build it back to a bobtail motor with the Merc parts,....

#2, Ya need the Merc manifolds for a Merc drive/ motor combo,....

#3, Ok,...

#4, I wouldn't, Ford is long outa the Marine game,.....

#5, Expand yer market search, 'n budget to get an early '80s or newer,...

 

[gcheves]

Have you made any progress in this change-over. Interested to learn from this because I'll be doing the same thing later this year. I have an OMC setup and want to change over to a MerCruiser set-up.

The transom opening will need to be "changed" too, right?

 

[Bondo]

The transom opening will need to be "changed" too, right?

Ayuh,..... Depends on what yer startin' with,......

Post-'86, the keyhole is the same,.....

 

[Taylor_T]

Hey gcheves,

Sorry I never replied to this... I haven't been on these forums in a few months.

Unfortunately, I ended up buying a different boat that already had the set up I wanted instead of finishing this project (got a 1985 chris craft scorpion 186). So the project never got to the point of doing the conversion.

I had full intentions of seeing the project to completion, and I REALLY didn't want it to end up as another one of those half finished projects on this forum, but... that's what happened lol I still have a garage full of boat parts and 2 full motors I need to get rid of...

If your still looking for an answer to your question...

Like Bondo said, it depends what you're starting with.

I was absolutely going to have to change the transom keyhole because my boat was rigged with the OMC Stringer. The keyhole for the Stringer is just a massive hole in the transom that the outdrive sticks through(outdrive mounts to the motor and doesn't actually mount to the transom at all).

Here's a picture of the OMC Stringer transom for my boat:

Here's a picture of a Mercruiser keyhole:

 

[gcheves]

Haven't started the teardown yet, but I am sure I will need a complete transom repair so I will be converting over to the MerCruiser setup.

Thanks for the replies...