mercruiser 470 3.7 motor swap

[rockolan]

i have a 1977 Starcraft 22' with a 470 mercruiser 3.7 I/O motor 170hp and i would like to know what a good replacement motor would be . after trying to start this motor it seems to be seized and frankly after looking at the motor i am not impressed with the technology , so instead of dumping a bunch of money in updates alone on this motor i would rather put something better in it .

Does anyone know if if another motor will work with the outdrive?
or should i go with a GM 3.0 or 4.3 motor & outdrive

Thanks

 

[Lyle29464]

Re: mercruiser 470 3.7 motor swap

You will need to change everything but the out drive.
The gear ratio will not be the same but you might be able to re prop enough to make it work.
Best bet is to find a donor boat and switch everything. Then you will not have the gear problem + you can sell all of the old stuff.

 

[dubs283]

Re: mercruiser 470 3.7 motor swap

Best bet is to find a donor boat and switch everything

too much work!!

sell what you have and get something better

 

[stonyloam]

Re: mercruiser 470 3.7 motor swap

i have a 1977 Starcraft 22' with a 470 mercruiser 3.7 I/O motor 170hp and i would like to know what a good replacement motor would be .

Forget it, the switch is not worth it, way too much time and money. If you like the boat, your best bet is to find a good used second generation 470 with 4" exchanger (post 83 I think) and drop it in. Can do it in a weekend. Part out the old engine to recover some money. IMHO

 

[Bondo]

Re: mercruiser 470 3.7 motor swap

Does anyone know if if another motor will work with the outdrive?
or should i go with a GM 3.0 or 4.3 motor & outdrive

Ayuh,... The motor bed will be close for the 3.0l, but the outdrive ratio is too tall...
The 4.3l will work with the outdrive ratio, but it'll need a new motor bed...
Either swap is possible, but with complications...

 

[Bifflefan]

Re: mercruiser 470 3.7 motor swap

There are some places that you cen find a rebuilt one to put in, then all you may need is a 4" heat exchanger. Those are not really hard to find, and I found a few for less than $150. Then you dont have to go through all the changing over of stuff.

 

[Eric 3.7LX Alpha 1]

Re: mercruiser 470 3.7 motor swap

It might be worth looking into what is wrong with the engine at least. Investingation wont cost anything but time.

Are you sure the issue is the engine and not the drive? Broken top gears in the drive could jam the engine as well.

Or might be a top end issue in the head like a bent valve and the bottom end is ok.

Just sayin I think I would find the cause before I wrote it off. Then you can see where you stand with it before dumping money into it.

 

[rockolan]

Re: mercruiser 470 3.7 motor swap

Update
I put a battery in that i knew was good and it turns over and it does have 4" cooler update but i really dont want to put much money into this motor.
gonna try to get this 3.7 running next week and see what it needs and go from there

Will the 4.3 bolt to my drive unit or will i need something else? any certain year or hp to look for?

if i have to pull that 3.7 for anything and the 4.3 will bolt to my drive unit 3.7 is gone as i have the resources to easily instal the 4.3
changing the drive and the cables looks to be more work to me.

Thanks for all your input

 

[nola mike]

Re: mercruiser 470 3.7 motor swap

Bigger problem with the 4.3 is the different mounts. May not physically fit/bolt down without stringer mods. Not to mention the 4.3 will be more weight, little if any more power unless you go with a newer model...

 

[Bondo]

Re: mercruiser 470 3.7 motor swap

Will the 4.3 bolt to my drive unit or will i need something else? any certain year or hp to look for?

Yes,...

Like I said, there'll be Complications,...

Ya needa Fully dressed Mercruiser transplant motor,...
'n a Chevy patterned flywheel cover that matches the rear motor mount spacing of yer inner transom plate...

 

[elkhunter338]

Re: mercruiser 470 3.7 motor swap

Just for your info if you by chance come across a complete 3.0 and drive for a good price and swap everything. The 3.0 in a 21 foot cheiftain, similar to a islander will push the boat at 28 mph wot. runs good a 20-22 mph. Enough hp for fishing but no speed demon.
That is a boat fully loaded, kicker motor, 50lbs fishing/downrigger weights, full fuel, 4 full size adults.
At sea level.
Good luck keeping what you have running.

 

[stonyloam]

Re: mercruiser 470 3.7 motor swap

Update
gonna try to get this 3.7 running next week and see what it needs and go from there

First order of business should be a compression check. Let us know how you make out. Good luck.

 

[rockolan]

Re: mercruiser 470 3.7 motor swap

Yes,...

Like I said, there'll be Complications,...

Ya needa Fully dressed Mercruiser transplant motor,...
'n a Chevy patterned flywheel cover that matches the rear motor mount spacing of yer inner transom plate...

my friend can make or mod any mount that i need we just dont want to get into modifying a shaft or other moving parts as we have no way to ballance them and if my motor doesnt workout i will get a fully dressed replacement motor like you said.
thanks

 

[Bondo]

Re: mercruiser 470 3.7 motor swap

my friend can make or mod any mount that i need we just dont want to get into modifying a shaft or other moving parts as we have no way to ballance them and if my motor doesnt workout i will get a fully dressed replacement motor like you said.
thanks

Ayuh,... The parts ya need are available, but not as a package, per'se...

Vintages will complicate the complications...

 

[rockolan]

Re: mercruiser 470 3.7 motor swap

This boat is aluminum and is very light and i will just be using it for pearch & walleye fishing on Lake Erie so a 3.0 140hp would proly move it ok as we are using a 80hp outboard on a 17.5 foot fiberglass right now but if i have to change the motor i will keep that in mind
thanks

 

[rockolan]

Re: mercruiser 470 3.7 motor swap

Just for your info if you by chance come across a complete 3.0 and drive for a good price and swap everything. The 3.0 in a 21 foot cheiftain, similar to a islander will push the boat at 28 mph wot. runs good a 20-22 mph. Enough hp for fishing but no speed demon.
That is a boat fully loaded, kicker motor, 50lbs fishing/downrigger weights, full fuel, 4 full size adults.
At sea level.
Good luck keeping what you have running.

Thanks for the info
The Cheiftain is a nice boat. how do you like the ride? it will be a while before i can take out the islander and yours is simular , have you had it in 3' - 4' waves? , thats what ill be running into and i was just wondering how they handle the waves.
thanks

 

[solar7647]

Re: mercruiser 470 3.7 motor swap

I think the best and least hassle way would be to get a hole new set up via CL or EBay. The more mods you have the more room for issues you have. You probably rap the hole thing up for about 3k.