Engine swap issues?

[C.Walker]

Hi, i'm new to this forum and i'm just getting into boating. I'm going to be getting a 19' Renken cuddy cabin with a 2.5L OMC engine. The engine looks pretty beat (and weak), and maybe i'll get a summer's use out of it, but im looking to swap it out for a small, lightweight car engine that has the same power as a marine v8, but more effecient. I have a good bit of expertise in the automotive department, but these marine engines are a lot differnt on the outside. It appears that the exhaust manifold is water cooled or something. And the engine is only covered by, essentially, a wooden box. So i'm assuming it must run sorta cool. I'd like to either swap in a turbo 4-cylinder or a straight 6. I was worried that these engines, especially turbo'd ones, might be a fire hazard if they ran too hot. Also, has anything like this been done before? Marine engines are too expensive to buy and maintain lol.

 

[Boomyal]

Re: Engine swap issues?

Marine engines are no more expensive than auto engines. The only substantial differences are in the accessories.

Marine Carb,
Marine Alt
Marine Distr
Marine exhaust manifolds
Marine water pump.

All of these are necessary and legally required for safety.

When it comes to swapping to a different engine, you need to make sure that it mates to your outdrive and the outrive is both geared and strong enough to handle the new engine.

That all being said, if you do not start out with a complete marine engine setup, it will bankrupt you trying to provide all of the marine rated accessories. You need to stick with an engine type that has been marinized. There are many automotive engines that never had marine parts built for them.

The only thing different with the basic engines are the head gaskets, brass freeze plugs and a suitable marine cam. Many truck cams would be suitable. A marine engine is cammed for low end torque and moderate rpm. Valve overlap is a big consideration so that the engine will both idle down low enough to shift into gear and will not suck exhaust water back into the intake valves.(known as reversion)

And BTW, welcome to iboats. There are a lot of knowledgable and helpfull people here. And if you like to get in spittin matches, come on down to dockside chat and add your $.02 worth.

 

[Don S]

Re: Engine swap issues?

Good Job Boom............. That pretty much covered the basics of everything.

 

[C.Walker]

Re: Engine swap issues?

Well, I was thinking about it because.. A fuel injected 300HP Mercruiser engine is $6000. I can get a 300HP turbo nissan engine for $1000, AND you get a cool sound, and I can get parts for it at autozone. I'm assuming I would need a marine alternator, but its distributorless ignition, and doesn't have a carb.

Also, i'm not quite sure what's going on inside marine engines, but, why do they have a special exhaust manifolds, and what do you mean by exhaust water getting sucked back up? Also, assuming i'd have a closed cooling system, why would I need a special water pump and freeze plugs?

Thanks for all your help so far.

 

[Haut Medoc]

Re: Engine swap issues?

You will never find a transmission that it will bolt up to.....
Either find a direct replacement for the 2.5 or forget buying this particular boat.......
With an OMC outdrive your options are very limited......
In fact, if you have no experience with marine propulsion, I would not buy a boat with an OMC, period.....
I'm sure it seems like a good deal, but it isn't......
My advice is keep looking for another boat....

 

[C.Walker]

Re: Engine swap issues?

I'm sure it won't bolt up without some custom made parts. Is OMC bad or something? I can get a Mercury Alpha One drive for like free if that's better. The engine is there too, but it's missing a carb.

 

[WillyBWright]

Re: Engine swap issues?

Give it up. You think a Chevette drivetrain would last long with a Corvette motor under the hood? Doubt it! That outdrive will grenade with 300Hp. Now put that Corvettte powered Chevette on the road. You think you're going to accelerate without burning those poor little tires bald? Doubt it. With a small prop, all you'll do is burn a hole in the water.

You also have no marine starter availability or cooled exhaust manifold availability. A turbo will definately run way too hot in a doghouse. That's why they don't use them in boats. That, and the exhaust is water cooled in a boat. No turbo is made to do that. Many internal engine parts are also marinized with brass and stainless steel parts. Car motors are run with antifreeze. Boats cool with plain water. Regular steel moving parts (like a water pump shaft) won't last long.

Regarding overlap, there is a short time where both the intake and exhaust valves are open at the same time at the top of the piston stroke. When the piston starts moving back down, some water from the water-cooled exhaust has the potential to be pulled into the cylinders through the exhaust valves. Marine cams are designed with the valve timing a bit advanced to prevent that. The period of time where both valves are open is slanted towards opening the intake valve earlier and closing the exhaust valve at TDC.

Your 4-banger probably doesn't have power steering. You'd want that with anything over 150Hp.

Your motor needs an oxygen sensor. With water-cooled exhaust, it won't work.

Your motor also might circulate gasoline back to the fuel tank via the EFI system. Return lines are USCG forbidden.

Then what about a fuel pump? Marine electric fuel pumps are not mounted in the tank. Another USCG no-no. They are also made with many regular steel components which won't last long in a boat.

 

[RubberFrog]

Re: Engine swap issues?

CW, I was excited like you when I got my first cheap boat. We all were! Knew all about car engines. It was going to be great! Wrong.

Boats and cars are completely different.

You can't fab jack shiite for a boat. So forget custom bell housings or exhaust manifolds. By the time you spend the dough, you could have bought a WAAAAYYYYY nicer boat with a gofast motor already in it.

Bummer. We've all cried a tear when we came to this realization.

Sorry.

 

[DukesFin]

Re: Engine swap issues?

Bummer. We've all cried a tear when we came to this realization.

Sorry.

Hopefully, this realization comes before the $$ is dropped on the system that will not work!

Take everyone's advice... We know you are knowledgable about car mechanics, but trust me, (and trust the others more), keep looking... You'll post a "Thank You" thread if you follow the advice here!

Good luck!

 

[Bondo]

Re: Engine swap issues?

Is OMC bad or something?

Well,....Being an Auto Mechanic,...
Have you tried to buy Parts for a Rambler lately,..... It's Pretty Tough Ain't it.....
That's because they've been Out of Production for Years........

That's Also the Big Problem with OMC drives,.....They've been Out of Production for Years as well......
OMC, like Rambler is nothing but a page in History.......

I can get a 300HP turbo nissan engine for $1000, AND you get a cool sound, and I can get parts for it at autozone. I'm assuming I would need a marine alternator, but its distributorless ignition, and doesn't have a carb.

As stated above,...... This is a Dream that will Not Happen,.....
Even without a Dist.,+ Carb,..... You Still need a GC Approved, Spark-Proof Ignition,+ Fuel Delivery system......Along with Water Cooled Exhaust,+ Turbo....
And,....... It's Torque, down Low that moves a Boat.....
A High Winding Jap motor builds it's Horsepower with Big RPMs......
Marine Drivelines,+ Props are limited to about 5000rpms.......Tops.......

I can get a Mercury Alpha One drive for like free if that's better. The engine is there too, but it's missing a carb.

That would make Your life Easier..........
The Mercruiser drives Are Still in production,+ There have been Millions More of them produced......
That makes both New,+ Used parts Easier to Find,+ Usually Cheaper........

 

[Silvertip]

Re: Engine swap issues?

And as for the closed cooling system, its a water to water style. A pump in the lower unit is required to get water from the lake/river/ocean up to the the cooling system. Just like the water pump in your car, it doesn't suck worth a darn. Water is circulated through the engine by the engine water pump. The exchanger has two paths, one for the engine water, another for the raw water. One cools the other. It works much like an intercooler on forced induction cars only water is used instead of air. Exhaust is out through the prop hub. Sucking water back up the exhust and into the engine can and does happen. As for your theory on high rpm engines, remember that there is no transmission in a boat. You have high gear only. Marine engines need low end grunt and except for racing are rarely twisted above 5000 RPM.

 

[C.Walker]

Re: Engine swap issues?

Ok, so I have some stuff to think about.... where can I find a list of all these coast guard boat/engine rules and regulations.

Also, how do the Mercruiser MPFI engines operate without a return line?

 

[ziggy]

Re: Engine swap issues?

go to regulations, then boatbuilders handbook.....check the whole site out. it is pretty cool really.......

these guys above gave ya really good (great even) advise man....take heed if ya can.....

http://www.uscg.org/CoastGuard.aspx?tabid=54

 

[Don S]

Re: Engine swap issues?

Is OMC bad or something? I can get a Mercury Alpha One drive for like free if that's better.

Do you realize that you just can't pop a Merc outdrive on an OMC transom plate? ? ? ? You also haven't mentioned what year this boat is. You could have an OMC stringer which makes matters even worse. Even if you had a Mercruiser drive, transom plate and everything else the hole in the transom would have to be filled in and recut and possibly stringers remanufactured to work with anything else.
There are also gear ratios that have to match an engine, (No it can't all be done with the props. ) Then you have the exhaust system to deal with,

Also, how do the Mercruiser MPFI engines operate without a return line?

Another thing you seem to be missing is that things have changed from year to year, so there is no 1 answer fits all to that question. But trust me, they do not return to the tank. Some had VST tanks, other systems on other engines. Come up with a Merc SN and we can tell you how it works.

But you REALLY need to start putting some model numbers and years on things. Engines and drives change a LOT..

Here is a year 2000 Mercruiser installation manual. May help you understand a littl of what is going on.
http://www.boatfix.com/merc/Install/gas/86017211.pdf It's almost 3MB in size, so may take a while to load.

 

[C.Walker]

Re: Engine swap issues?

Sorry if i'm asking really stupid questions or being a bother. I'm just trying to learn some stuff. Umm, well regardless of whether I get a marine engine or convert a car engine, I'm going to try and run the existing OMC this season. I'll probably need to rebuild it. Here are some pictures so you can see what i'm dealing with...
<p>
They are full size so you can see detail.
<p>
Here is the boat itself. It's like a 1986? 19' Renken Cuddy<br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/boatfrontright.jpg">Front right shot of boat</a><p>

Here's the OMC 2.5L Engine<br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/boatengineleft.jpg">Left view of engine</a><br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/boatengineright.jpg">Right view of engine</a><br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/boatenginefront.jpg">Front view of engine</a><br>
<p>
Here's the outdrive..<br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/outdrive.jpg">Outdrive picture</a><p>

The propeller (is in bad shape)<br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/boatpropeller.jpg">Prop picture</a><p>

And here's a 3.0L mercury engine that I could use. There's also the mercury outdrive in this boat that isn't attached.<br>
<a href="http://home.comcast.net/~et3rnal360/source/boat/mercuryengine.jpg">Mercury engine in other boat pic</a>

<p>Ok, so maybe that'll help you out a little. Idk if you can tell me by looking at the big pictures but, do you think the OMC engine will run for another season with some work? Does the cooling system on that run straight seawater through the engine? If so, could the inside of the engine be completely corroded and useless? I can see that the t-stat housing or w/e that is on the top is rusted and cracked open.. I'll have to rewire it too... i'm not sure those wires should be cut with wire nuts on them. =/

 

[Don S]

Re: Engine swap issues?

None of you pictures will show up. Since you say they are large, just get the complete URL of the picture, then click on the

icon above the text box at the bottom of this page. Then copy and paste your picture URL in the box that comes up and click ok. Then it will work. Not sure what you used, probably that attachment thing in this software that has NEVER worked.

 

[180shabah]

Re: Engine swap issues?

Can't see the pics - but it doesn't sound good. Broken t-stat housing(hopefully not freeze damage, or there will be more), wire nuts, etc.

Sounds like you have a serious project here, It should have been a free boat with the OMC on it.

 

[C.Walker]

Re: Engine swap issues?

Ok i fixed the pictures. The tilda ~ was confusing the forum software, so I redid it in HTML.

Yes it's a serious project. I like projects d. I need somehting to work on when i'm done my Jeep. It's only $300 and I think it's a really cool looking boat. Those newer ones really don't impress me too much.

 

[mtnrat]

Re: Engine swap issues?

If you have the boat already, and you think you can get a season out of it, do that. Have you seen it run yet??? If it works baseline the fluids, looking for milky looking oils. Tune it up if possible and take it out. Not too far to start. Get used to it. Use it for the summer.
Research here and other forums and learn as much as you can, then you will start to understand what can and cannot be done with marine powerplants.

If you don't have it yet, don't get it. Take you time and with the help of those here check out a few boats. There are LOTS of cheap and inexpensive boats out there. All you need to do is give Make, Model, Year, Engine type and size and outdrive type and Model. Serial numbers are particularly helpful. Some of these guys around here are walking encyclopedias and have been in the boating business for many many years.
Good Luck.

 

[Don S]

Re: Engine swap issues?

Well, it's got a stringer drive, so an easy swap to the Merc is out of the question. You also don't need pictures that big. Because looking at pictures won't say if the engine will run or not.
YOU, have to do some checking. Start it up and see what it sounds like. Or even if it will turn over, do a compression check, how is the fuel? may need a tuneup, may need a carb rebuild, may have a locked up engine, who knows.
Change the gear lube in the drive and see what it looks like! any water? ? ?, that is not good for bearings and gears ya know.