Eng replacements

D

d2wtr

New Member
May 9, 2020
9
Boat Info
SR 300 DA Sundancer 1987 x2 350 5.7L 260hp
Engines
260 Merc 350 5.7L w Alpha drives
Hello, like to have some one that replaced his\her 1987 Sundancer 300 DA from marine engines to vehicle engines. these engines are GM 350 5.7L 260 hp what do i need to do too exchange these engines. Mine are a closed system, any one out here can lend some knowledge on this would be really appreciated
 
Marine engines are in most ways the same as vehicle engines except for the camshaft specs and in your 1987 Sundancer which probably has one reverse rotation engine.An automotive engine in a boat with wet exhaust will most likely develop exhaust "reversion" which means due to camshaft timing it will suck water backwards into the engine and cause serious engine problems. Proceed at your own risk.
 
Hi and thanks for the response, so if i wanted to change out the cam, too a marine one, because i don't know much at all on engines, ok so, if i did the swap, is this a possibility or ??. Is there any other way besides paying that enormous amount for a marine eng. I am limited on my funds so i'm looking to replace my failed engines in the most least expense.
 
If you are limited on engine knowledge, you will have a very difficult time replacing a camshaft.

If both engines have failed 2 replacement long blocks could be purchased for around $7000 and you’d then need another (I’m guessing) 30-40 hours labor to replace both of them.


2 new or rebuilt complete drop in motors would be more expensive but involves considerably less labor time, probably 4 hours each to install.
 
d2wtr said:
Hi and thanks for the response, so if i wanted to change out the cam, too a marine one, because i don't know much at all on engines, ok so, if i did the swap, is this a possibility or ??. Is there any other way besides paying that enormous amount for a marine eng. I am limited on my funds so i'm looking to replace my failed engines in the most least expense.
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Espos4 said:
If you are limited on engine knowledge, you will have a very difficult time replacing a camshaft.

If both engines have failed 2 replacement long blocks could be purchased for around $7000 and you’d then need another (I’m guessing) 30-40 hours labor to replace both of them.


2 new or rebuilt complete drop in motors would be more expensive but involves considerably less labor time, probably 4 hours each to install.
Click to expand...
ok thank you. i'll look it all over and decide on some thing
 
Let's start at the beginning. What is wrong with engines and who diagnosed them? The older 300 Sundancers with Alpha drives are known as fairly high maintenance especially in salt water. Where are you located? Maybe add you location to your profile it helps for us to answer your questions much easier.
 
Both engines on your 1987 300 Sundancer are standard rotation. I had one of those boats for many years and repowered it while I owned it.
 
Freeze plugs are different on marine engines. Why not buy marine engines?
You’ll end up w more problems and costs trying to cut corners.

There’s a reason engine builders specify application when ordering.
 
JVM225 said:
Both engines on your 1987 300 Sundancer are standard rotation. I had one of those boats for many years and re powered it while I owned it.
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Hi, yes your right, all the mechanics for mercruiser been telling me that that is impossible, I tell them, show them the part in the manual but they still won't except it. So believing any mechanic around here is hard. i have talked persons that did use automotive engines with no problem but i cant find them now. been a long time. So now, did you repower with a 5.7L from an auto? When i bought this boat, the starboard eng was taken apart, no good. the port ran but rough some times. the eng developed a knock so i stopped running it. temp would rise . so now its rusted pretty bad and time to replace. What suggestions would you have on this.
 
Only difference on the long block would be the cam, head gaskets and core plugs. How rusty are your bolt on parts ?
 
all bolts on top are good, but the bttm is all rusted..the core plugs are the frezze out plugs?
 
freeze plugs if you want to call them that. Post up a pic of this rust ball. So we can tell what's usable and what isn't
 
d2wtr said:
Hi, yes your right, all the mechanics for mercruiser been telling me that that is impossible, I tell them, show them the part in the manual but they still won't except it. So believing any mechanic around here is hard. i have talked persons that did use automotive engines with no problem but i cant find them now. been a long time. So now, did you repower with a 5.7L from an auto? When i bought this boat, the starboard eng was taken apart, no good. the port ran but rough some times. the eng developed a knock so i stopped running it. temp would rise . so now its rusted pretty bad and time to replace. What suggestions would you have on this.
Click to expand...

No, I bought two new motors from MichiganMotorz. That was almost a decade ago.
They were Carb to pan and circulator pump to flywheel including ignition, plugs and wires.
Personally, I would go with new motors on a boat I was looking to hold on to.
But I have helped a friend swap automotive motors in to boats several times.
He ran an auto repair shop (now retired) and would sometimes buy boats with hydro-locked motors, put used auto motors in them and use them until someone gave him what he wanted for them or a better boat came along.
He would usually take apart and freshen the motors up before installing them though.
Offhand I can think of the following:
As others have said, you’ll need to get a Marine spec cam and kit, and swapping out the freeze out plugs for brass ones is a good idea.
Replace threaded plugs on both sides of blocks with drains.
If the automotive motors you use have temperature senders in the heads you’ll have to remove them and replace with brass plugs that don’t interfere with installation of the exhaust manifolds.
Use the oil pans, dipstick tubes and dipsticks from your old motors.

If you’re going with used motors you are better off looking for truck motors with 4 bolt mains. From what I can remember, it’s been a while, the cams in some of those are spec’d closer to marine cams for the torque too.
The problem you’ll face with used motors is that it’s been a while since GM installed the old small blocks in vehicles so anything you find will likely have a lot of mileage on them and will probably be pretty tired.
The good news though is that new parts for them are plentiful and cheap so if you got a couple of solid cores you could rebuild them on a budget.
 
JVM225 said:
No, I bought two new motors from MichiganMotorz. That was almost a decade ago.
They were Carb to pan and circulator pump to flywheel including ignition, plugs and wires.
Personally, I would go with new motors on a boat I was looking to hold on to.
But I have helped a friend swap automotive motors in to boats several times.
He ran an auto repair shop (now retired) and would sometimes buy boats with hydro-locked motors, put used auto motors in them and use them until someone gave him what he wanted for them or a better boat came along.
He would usually take apart and freshen the motors up before installing them though.
Offhand I can think of the following:
As others have said, you’ll need to get a Marine spec cam and kit, and swapping out the freeze out plugs for brass ones is a good idea.
Replace threaded plugs on both sides of blocks with drains.
If the automotive motors you use have temperature senders in the heads you’ll have to remove them and replace with brass plugs that don’t interfere with installation of the exhaust manifolds.
Use the oil pans, dipstick tubes and dipsticks from your old motors.

If you’re going with used motors you are better off looking for truck motors with 4 bolt mains. From what I can remember, it’s been a while, the cams in some of those are spec’d closer to marine cams for the torque too.
The problem you’ll face with used motors is that it’s been a while since GM installed the old small blocks in vehicles so anything you find will likely have a lot of mileage on them and will probably be pretty tired.
The good news though is that new parts for them are plentiful and cheap so if you got a couple of solid cores you could rebuild them on a budget.
Click to expand...
 
Hi, thank you for your advise, i'll look into this. Thank you again.
 
thank you every one for replying ..
 
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