Omc 305 to mercruiser 5.7L swap

[NWUnifite18]

Hi, I've really learned a lot on these forums and now I'm going to do something I've never done... I'm going to swap the omc 305 and cobra drive for a 5.7L and alpha drive... The new(to me) engine and drive came off of a boat that had a tree fall on it. It started and ran great yesterday when I bought it ($1600) . My boat is a '74 tollycraft sportfisher 24. What will I have to do to the motor mounts for this to work? I have started collecting documentation for the swap, anyone have good links for this? Anything else I need to watch/keep in mind?(I'm sure there is plenty) should I be replacing anything in the transfer? While I have everything outside the boat... Thanks in advance.

 

[matt167]

Re: Omc 305 to mercruiser 5.7L swap

If your boat was actually converted to run an OMC Cobra than it's almost a bolt in. If your boat still has the OMC Stringer drive, than you have a new transom to install, and fiberglass work at the very least..

 

[Bondo]

Re: Omc 305 to mercruiser 5.7L swap

Hi, I've really learned a lot on these forums and now I'm going to do something I've never done... I'm going to swap the omc 305 and cobra drive for a 5.7L and alpha drive... The new(to me) engine and drive came off of a boat that had a tree fall on it. It started and ran great yesterday when I bought it ($1600) . My boat is a '74 tollycraft sportfisher 24. What will I have to do to the motor mounts for this to work? I have started collecting documentation for the swap, anyone have good links for this? Anything else I need to watch/keep in mind?(I'm sure there is plenty) should I be replacing anything in the transfer? While I have everything outside the boat... Thanks in advance.

Ayuh,.... Welcome Aboard,.... Matt sums it all up, yer hull woulda had a Stringer drive in '74,....

But if converted to a Cobra, it should be pretty much yank the OMC out, 'n bolt in the Merc...

What vintage was the donor hull,..??

At the top of this forum, you'll find Don'S Adults Only section,...
It's crammed Full of documentation, includin' links to the Merc manuals,...

 

[NWUnifite18]

Re: Omc 305 to mercruiser 5.7L swap

Well, you were right(of course) the outdrive is stringer style... I really hate to saw into the transom as it is solid. I'm pretty sure I could sell the power train I just bought for what I have in it... I am now thinking of having Greg's marine convert it to outboard and make a bracket... I've seen a couple of their conversions/ brackets and they look great. I have a merc 225 I could put on it though that might be a little small for this boat. The conversion I liked replaced the inboard with a fish box...

 

[Bondo]

Re: Omc 305 to mercruiser 5.7L swap

Well, you were right(of course) the outdrive is stringer style... I really hate to saw into the transom as it is solid. I'm pretty sure I could sell the power train I just bought for what I have in it... I am now thinking of having Greg's marine convert it to outboard and make a bracket... I've seen a couple of their conversions/ brackets and they look great. I have a merc 225 I could put on it though that might be a little small for this boat. The conversion I liked replaced the inboard with a fish box...

Ayuh,... You'll be Fillin' in the hole, not cuttin' it out,...

It's yer choice which way ya go,...

Personally,... I've seen more Bad results from outboard conversions, than Happy boaters,...

 

[Scott Danforth]

Re: Omc 305 to mercruiser 5.7L swap

The boat is a 74 with a hole in the transom large enough for a grown man to crawl thru. building a new transom for your new Mercruiser or building a new transom for outboards is still building a new transom. Plus after 40 years, what is the condition of your current transom and stringers?