Re-powering Sundancer with twin 485s

[markline800]

Hi,

I have a 1979 Markline 800 (Sea Ray 260 Sundancer built in New Zealand as Markline) which originally had single OMC (Ford 351W) with Stringer 800 Sterndrive. Having rebuilt the sterndrive last season sea water got into the engine on its maiden voyage and wrecked it so I have been thinking about re-powering options.

I have just been offered a pair of Mercruiser 485's complete with legs, controls, gauges etc. for a good price - $5000 AUS - the engines have had $16,000 spent on them 2 years ago (yet to see the paperwork) and the legs (Which I am told are Alpha I's Gen II - although this is yet to be confirmed) are operational.

Is there anything I should look out for with these engines especially as I am going from single to twin - I know I will have to have the transom re-glassed. (Anyone done this?) I will be engaging the services of a mechanic to check out the engines/legs prior to them being pulled out of the seller's boat.

Your comments will be most welcome

By the way I am based in Sydney, Australia

 

[STIHLBOLTS]

Welcome to the board. There are a few folks that have some experiance in that area for you so hang on till they poke in. :grin:

 

[jetmac]

If it were me i'd say no to the twin option and put that same money into a new V8 OR maybe even a small diesel, it just depends on what your looking to gain, power or speed.
The reason i say this is that the twin would be a major undertaking requiring everything to be changed (wiring, trim, controls, transom, etc.). Mine came this way and it's a pain because of the dual systems, but it's a really neat old boat that came that way originally, so i suck it up and drive on.
As far as the 485's go, they are simple to work on but not when there side by side (very tight on my boat). The main problem that most people have with them is the original charging system. The fix for that though is the alternater kit that you can find on e-bay.

 

[Cap10Pat]

(Is this working right? How come I have to fill in a Subject when replying to this topic?)

Anyway, I have a 1980 260 Searay - Weekender model. Single 5.7L Mercruiser. Having two engines would provide redundancy, maybe increase power, and improve handling.

But the downsides would be limited space in such a small boat for two engines, using smaller engines to fit into the space, and maybe the biggest issue - too much weight for such a small boat. I think you would be much better with a single engine.

That boat has a fairly deep V, so when you move the outdrives outward they are going to come up pretty high - they can't be down where your current drive is located. And, your engines will be so close together that they won't provide as much mobility as you might expect.

Way too much work and too little improvement for the effort.

 

[why/not]

has anyone convert from inboard to outbord 34 saden

 

[Spookeay]

If you had gutted the boat and had a clean slate I would say yes go for it all. However, to just mod a single to a twin and think it's just popping another engine in and wiring it up that's not the case by far. You need to make sure the transom will take it. Move everything from the old engine over. Change all the cabels, stearing system and make sure you have clearance for the second Engine. Then you start to confront the things like a entire new dash panel for gauges, Twin throttles, drive separation to prevent cavation and a lot of detials that you only discover when you are committed and can't turn back. Don't get me wrong, It can be done and I have done a few but it only sound simple,,If you have never done it before... You will learn fast on your first one....,, :huh:

When it comes down to doing it,,, it can be rough and just add 200 Hr's to how long you think it will take... :wow:

Again to make sure I am not coming across as a "YOU CANT DO IT" type,,I assure you, you can do this... However,,,It's a advanced undertaking and not for the faint of heart or will or mechanically declined.:thumbsup:

 

[cpt. sundancer]

i would take out the 5.7 and replace with a 7.4:thumbsup:

 

[JVM225]

I would think that the original 5.7 probably put out about 230 - 260 HP. I would look in to getting another small block that puts out more HP. Maybe 300 - 330? I think that with the weight savings over the big block you would get just as much performance gains as going to the 7.4, and probably a much easier swap.

 

[keokie]

Looking at the original post, I see the question was asked three years ago. Anyway, I would go with the big block. A higher horsepower small block will give no noticeable improvement in performance. I have done that exact engine swap on the exact boat. The higher horsepower 350 did nothing, but the 454 made a world of difference.