Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

[Starcraft Enterprise]

Has anybody ever done or seen a swap from the 2.5/3.0 to 4.3 in a Starcraft? Anybody ever contemplated it and done any of the research? Please share any of the details and pictures you found, especially the motor mounts.

 

[ezmobee]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

The guys in the I/O repair forum will surely be able to tell you everything you need to know about the motor swap. Not sure about the mounts. However, Bond-o has a SC and may comment. I'll move this thread there....

 

[Don S]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Going to start by assuming you have a Mercruiser, and NOT an OMC stringer.
There is a lot more to it than just changing an engine. First, you need a complete engine with exhaust manifolds and all the electrical and fuel system coupler, etc. Then you need the proper exhaust Y and hoses for that engine and transom shield.
You also need stringers for the side engine mounts on V engines. The 3.0L has a front mount that the V6 doesn't. Then you will need to change the gear ratio in the drive, and no, just changing the props won't do it.

Your best hope would be finding a doner boat with a good engine and drive to make the swap. Then just change everything over.

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Going to start by assuming you have a Mercruiser, and NOT an OMC stringer.
There is a lot more to it than just changing an engine. First, you need a complete engine with exhaust manifolds and all the electrical and fuel system coupler, etc. Then you need the proper exhaust Y and hoses for that engine and transom shield.
You also need stringers for the side engine mounts on V engines. The 3.0L has a front mount that the V6 doesn't. Then you will need to change the gear ratio in the drive, and no, just changing the props won't do it.

Your best hope would be finding a doner boat with a good engine and drive to make the swap. Then just change everything over.

I agree with finding the donor boat and everything else you mentioned.
The main part that concerned me was properly mounting it, the stringers. That is why I originally posted this in the Starcraft forum. I assumed they would be specific to the mounting for an aluminum boat.
Maybe somebody can explain to me exactly what the purpose is of each mount?
Does the transom take all of the load for pushing the boat and the stringers on the floor are just for holding the engine? Or do they also play a part in pushing the boat? If they did not before, does the increase in horsepower require them to now play a part?
I am not so much looking for an increase in speed, although that will be a nice benefit. I am more interested in being able to maintain my current top speed (about 35 mph) without working that poor little engine so hard and at such high RPM's. The boat travels very nicely at that speed, but I feel guilty for going that fast for more than short bursts.
This is the boat.
18' 1969 Starcraft Starchief with a Mercruiser 120.

 

[Don S]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Yes, the transom shield is what takes all the force. The front mounts only hold the mounts at the proper height. On a boat that I have swapped types of engines, I usually get the transom shield installed, then set the engine in and bolt down the rear mounts. Get the alignment bar and adjust the front of the engine up and down with the hoist till I find where the alignment is right. Now, measure to where your stringers will be, pull the engine back out and build your stringers.

It's not just a Starcraft that would require this, I have done it on many boats going from gas to diesel, 3.0 to V6 or 8 and Ford to Chevy. They all have different mounts and have to be modified.

Your boat may have stringer in there now, but they may be too low or not spaced properly.
Since this isn't really a Starcraft specific, or an engine problem, I will move this over to the restoration forum. You will get a lot more views on how to upgrade the stringers.

 

[system-f]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

I don't know what kind of space you have but what about the Merc 165 straight 6 motor? If you have enough space up front to move the front mount forward then this engine might be a much easier swap (assuming you can find one with a marine manifold). The gears are still different though at 1.65.

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

I don't know what kind of space you have but what about the Merc 165 straight 6 motor? If you have enough space up front to move the front mount forward then this engine might be a much easier swap (assuming you can find one with a marine manifold). The gears are still different though at 1.65.

I gave that one serious consideration due to it being the easier swap.
I researched it, thought about it and thought about it some more. But considering it's obsolence and bang (hp) for the buck I figured I was better off with the 4.3.

 

[Don S]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Why don't you post some pictures of the engine area, in front of the engine and each side showing what you have for stringers. Then maybe someone can see what you have and how to fix.

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Why don't you post some pictures of the engine area, in front of the engine and each side showing what you have for stringers. Then maybe someone can see what you have and how to fix.

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

I borrowed these pictures from wrfalpacas. This is the same model as my boat to show the structure under the floor.

 

[Don S]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Doesn't look to me like you have enough room in there for a V6. The width on the outside of the manifolds is around 32" as I recall, and the centerline of the front engine mounts is around 22" to 24" .

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Doesn't look to me like you have enough room in there for a V6. The width on the outside of the manifolds is around 32" as I recall, and the centerline of the front engine mounts is around 22" to 24" .

I measured the inside of the aluminum rails and they are exactly 24".
The distance between the seats was also 24". So if the manifolds are 32", that leaves 16" for new seats, which is the same width as the front seats.
The pics show the points I measured from.
Do I have enough room for the 4.3 V6?

 

[Bondo]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Do I have enough room for the 4.3 V6?

Ayuh,... Only if you build a new motorbox, seats,+ trimming out the aft cockpit...

I did my Islander 10 years or so ago,...
I bent up a set of motor mounts out of .090 sheet aluminum,+ pop-riveted 'em from the top of the stringers, down to the hull's ribs...

I built a New motorbox,+ completely did away with the aft seating for better transom access for fishin'....

As noted somewhere above, finding a Donor boat with the driveline of your choice is the Best way to go,...
That way you'll have all the tiny expensive pieces you'll Need...

I have a few pictures that might help you visualize it all,..
But,...
I'm having 'puter problems at the moment,+ can't help with 'em, at this time...

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Ayuh,... Only if you build a new motorbox, seats,+ trimming out the aft cockpit...

I did my Islander 10 years or so ago,...
I bent up a set of motor mounts out of .090 sheet aluminum,+ pop-riveted 'em from the top of the stringers, down to the hull's ribs...

I built a New motorbox,+ completely did away with the aft seating for better transom access for fishin'....

As noted somewhere above, finding a Donor boat with the driveline of your choice is the Best way to go,...
That way you'll have all the tiny expensive pieces you'll Need...

I have a few pictures that might help you visualize it all,..
But,...
I'm having 'puter problems at the moment,+ can't help with 'em, at this time...

Thanks for the input.
Which engine did you put in your Islander? How many feet is it and what was the performance and handling results?
When you get your computer problems straightened out, pictures would definetly be appreciated.

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Anybody have any idea or sources on how to buy late model salvage (wrecked) boats from insurance companies?
I live in the Ohio/Indiana area.
I figured this would be a good way to buy a complete drivetrain for this conversion.

 

[Bondo]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Ayuh,... It's a 74 Islander 221,... Fully charter dressed for lake Ontario salmon/ trout/ walleye fishin'...
The 3.0l did a fine job at the begining,... 28/ 32mph on a Good day...
Then I wacked the drive,... put on a runner that was the wrong ratio...
That winter, I needed either the right drive, or more Horsepower...
I bought a Merc. bobtail crate motor 4.3LX 92/ 94 vintage, that was the take-out with a freeze Cracked block from a local marina...
Replaced the Block casting,+ it's been runnin' over 10 years,+ about 1200/1500hrs...
Updated the transom,+ drive all at that time...

Still today, with a 1.65 drive,+ Torque-Shift prop, it'll pull 43/44mph locally,+ 51/52 in the Saltwater off Maine...

 

[Starcraft Enterprise]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Thank you for that info, it has been the most helpful so far. At least now I know the conversion is possible.

 

[Bondo]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Ayuh,... Not the Best, but you can see the motor mount plates in thiese pic's...

 

[Bob_VT]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Isn't that CAT yellow!!! Oh..... QC is going to love that!!

 

[Bondo]

Re: Swap 2.5/3.0 to 4.3 in an aluminum Starcraft?

Isn't that CAT yellow!!! Oh..... QC is going to love that!!

Ayuh,..... Sure as 'ell Is....

I was painting Dozers when I built that motor......