1969 Starcraft holiday 3.0 mercruiser - Possible swap to 4.3

[Bow4game]

Hello all, first post and new to the forums. First off I bought an aluminum boat with an inboard needing a lot of love but he price was right and I have never seen one before. The original motor runs but has some repairs to the block. So I bough another motor. Well turned out the block was cracked on it also in the water jacket. So I start tearing down a little farther because I wanted to see what the cylinders looked like I’d they was rusted or not. And I found a piston that has some damage what I’m wondering is your thoughts? Find a replacement motor? Fix the block and run the piston it will be fine. Or fix the block and replace piston. I don’t wanna have a lot of money in a motor that’s cracked or I would just rebuild it. I’ll try to post pic thank you.

 

[Bow4game]

Also this is the crack.

 

[Rick Stephens]

Forget about that one. Sorry to say. It is not worth spending money when in all likelihood there are additional internal cracks. Cheaper to find a block without fatal flaws. Ofttimes the best way to get a motor is find entire boats with decent motors that the boat is ready for the dump. Great way to get a decent motor and even later model outdrive.

 

[Bondo]

Ayuh,..... Welcome Aboard,....... Now you've got 2 junk motors, That piston is detonated, Badly,....
But you learned a great lesson on buyin' a used motor,......

To look for block cracks,........

Now it's time to try again,...... Search yerself up a Good used motor,.......

 

[matt167]

3.0L's until '73 IIRC were high compression rated at 140hp..

Just about any 2.5/ 3.0L will work. Since it's a '69, find a rotted donor boat and swap everything. The '69 MC1 is serviceable still but getting old

 

[Scott Danforth]

3.0L's until '73 IIRC were high compression rated at 140hp..

Just about any 2.5/ 3.0L will work. Since it's a '69, find a rotted donor boat and swap everything. The '69 MC1 is serviceable still but getting old

Are you sure about that?

The 3.0 changed in 1991 then they changed the crank. Up to then, the compression ratio is the same. However about 1985 and below were crank rated, where about 1986 and up is prop rated.

1991 and up were redesigned to use the same pistons as the 5.7 when they redesigned the crank and block.

I would look for a 1992 or newer 3.0 doner with an alpha 1, g2

 

[Bow4game]

Okay I’ll look out for another motor. Well I knew the motor in the boat has had repairs to block. Probably done in the 80s lol. It works but idk how reliable that one is. The other motor I got came with everything but the boat so I got a newer alpha one outdrive and all the exhaust stuff. So all is not a loss I got a great deal on the parts. I’ll be sure to only look at running motors and a compression test on the next one. But there is still lots of good parts off that motor I can use. Wonder what caused the detonation issue. Way to far advanced you think?

 

[Rick Stephens]

Wonder what caused the detonation issue. Way to far advanced you think?

All it takes is a crudded up carburetor running lean.

I have no problem with stating that you can EASILY sell off your old drive, and any new parts that might come with a decent 3.0 motor. When I did my swap from a 3.0L to a V6, I swapped EVERYTHING, even the steering. After selling everything I pulled off the boat and replaced from a donor boat, I broke even. Getting a good price on a bad motor and decent drive is a big plus. You can part it out or use it and come out ahead.

Get a good motor. If it comes with a good drive train, so much the better. Then you can start selling off stuff.

Good luck!

Rick

 

[Bow4game]

I have actually been tossing the idea around about doing a 4.3 and alpha swap. It’s a 69 18’ holiday and I’m redoing the inside I have it down to the bare hull so I’m still flexible. But I have heard that maybe it could be a bit to much weight, idk if it just doesn’t drive good or what the issues was. I do mostly fishing from the boat but also pull skier and tube. I believe I would like the fuel economy of the 3.0. But as light as that boat it’s probably not much different. Anyone done the swap to a boat like this. What’s your opinion? Find another 3.0. Or try to upgrade to the 4.3? Thanks.

 

[Rick Stephens]

No idea what you mean by 'a boat like this'. Post a pic maybe.

My project was a 17 ft ski boat I turned into a fishing barge. This is what it looked like before the mods. Suppose I should have afterwards pics, but never took any.

Fuel use is the same for a given speed. The V6 is a LOT quieter than the 3.0L. And top speed is a bunch higher. I mostly just fish with it, so the added horsies is just get there and back speed. It was fun project. And I know every nut and bolt.

 

[matt167]

Are you sure about that?

The 3.0 changed in 1991 then they changed the crank. Up to then, the compression ratio is the same. However about 1985 and below were crank rated, where about 1986 and up is prop rated.

1991 and up were redesigned to use the same pistons as the 5.7 when they redesigned the crank and block.

I would look for a 1992 or newer 3.0 doner with an alpha 1, g2

yup, it's what a marine mechanic had told my dad when he had his '73 Chieftain. Had a " Premium gasoline only " decal on the valve cover as well. It would ping with regular gas so we knew it was high compression. As far as I know, that early 3.0L/ 140hp is quite different from motors that came shortly after... It was a plenty strong 3.0L, and the 21' Chief had clocked 50 mph GPS over glass

 

[Bow4game]

I don’t have any updated photos. But it’s an 18’ closed bow Starcraft holiday. I have never seen an aluminum boat with an inboard so I had to have it. Couple hundred bucks it was mine and came with a clean title. Trailer needs a little work and the boat needs work but I needed something to do in the winter. Anyone that has swapped the 4.3 into this light boat are you happy? Or recommend staying with the 3.0? Thanks.

 

[Scott Danforth]

yup, it's what a marine mechanic had told my dad when he had his '73 Chieftain. Had a " Premium gasoline only " decal on the valve cover as well. It would ping with regular gas so we knew it was high compression. As far as I know, that early 3.0L/ 140hp is quite different from motors that came shortly after... It was a plenty strong 3.0L, and the 21' Chief had clocked 50 mph GPS over glass

You may want to look at the piston part numbers and the GM parts breakdown

 

[Alumarine]

I don’t have any updated photos. But it’s an 18’ closed bow Starcraft holiday. I have never seen an aluminum boat with an inboard so I had to have it. Couple hundred bucks it was mine and came with a clean title. Trailer needs a little work and the boat needs work but I needed something to do in the winter. Anyone that has swapped the 4.3 into this light boat are you happy? Or recommend staying with the 3.0? Thanks.

Check out the Starcraft forum. Lot's of info and help.
https://forums.iboats.com/forum/owners-groups-by-manufacturer/s/starcraft-boats

 

[Alumarine]

yup, it's what a marine mechanic had told my dad when he had his '73 Chieftain. Had a " Premium gasoline only " decal on the valve cover as well. It would ping with regular gas so we knew it was high compression. As far as I know, that early 3.0L/ 140hp is quite different from motors that came shortly after... It was a plenty strong 3.0L, and the 21' Chief had clocked 50 mph GPS over glass

I'd be thrilled if my 3.0 got my 18 footer anywhere near 50mph.

 

[Rick Stephens]

I'd be thrilled if my 3.0 got my 18 footer anywhere near 50mph.

My 2300 pound (from mfg specification) fiberglass 17 footer would run somewhere near 36 MPH at 4800 RPM with the 3.0L. With the 4.3L runs right at 48 MPH at 4800 running the only prop I ever tried, a 4 blade aluminum purchased as a ski/board puller. Never tried to see what top end would be with a prop designed for that function. Of course the 4.3L weighs in right about 200# more than the 3.0L, putting dry weight of the boat now nearer 2500 pounds.

As far as I know, the only thing changed about 3.0L HP ratings over the years, from what I could see from parts lists and reading up, is how rated horsepower went from flywheel to prop rating, reducing stated values by 8-12% depending on applications. This occurred by US trade agreement in 1983, signing on to Internation Council of Marine Industry Associations Standard No. 28-83 (ICOMIA 28-83).

 

[matt167]

You may want to look at the piston part numbers and the GM parts breakdown

The pistons are the same, but the cylinder head substitutes to a later cylinder head 936-5325 is the original and 936-5544 is the replacement number.. The original likely has smaller chambers and thus higher compression, but without knowing the casting number of both, it's speculation.

 

[Bow4game]

1969 Starcraft holiday 3.0 To 4.3 inboard.

I have an 18’ aluminum Starcraft holiday and the motor Has some damage and I already have it removed to rebuild the transom and floors. Not full restore just making a nice reliable fishing and skii boat. I don’t wanna put the old motor back in it has crack repairs done to block and I want it reliable. My question is has anyone repowered one with a 4.3 motor? What are your thoughts about it? I have read that it’s to heavy for that boat but would like some opinions on someone who has done it. Or should I just stay with the 3.0. I have never driven the boat so I don’t know what to expect from either the 3.0 or 4.3. Thank you.

 

[Kmsp1264]

I have a 1974 Holiday with a 140hp 4 Cyl and was going to put an inline 6 230 hp but decided not to. The boat is rated for a 140 max but I think you can get by with the 230, but the 4.3 v-6 might be too heavy, just an opinion.

 

[jbcurt00]

Yep, 3.0-4.3 swaps been done to 18ft SCs. Heres 1
https://forums.iboats.com/forum/owne...raft-chieftain

Won the SOTY award too....

Look around lots of good info in here, then you dont have to wait for replies to find answers to questions.....

And FYI, I/O boats dont have hp max limits on them like OB boats do, w in reason of course...