Logo
FULL SITE MENU

Engine a drive rotation question

G

gearhead

Member
I'm planning on upgrading

I'm planning on upgrading to a bigger boat 25 to 28 feet with twin engines. probably between 1980 and 1990 year models. I know that most twin engine setups spin one prop clockwise and one counter clockwise. Is it because the engine spins backwards of does it chance direction in the outdrive? Are there newer drives that change the rotation and can be used with standard rotation motors? Any help would be welcome.
 
Most later model setups use dr

Most later model setups use drives that have a counter rotating lower unit to them. I wouldn't buy a reverse rotation engine these days.
 
"Could you be more specific ab

"Could you be more specific about what kind of drives use the counter spinning lower unit? alpha one, twoes, bravos? Thanks for the responce. I want to use different engines on the boat and i can't make one spin backwards so i need to find out what kind of drive to look for. What would happen if both drives spun the same direction? Thanks for the reply."
 
"[b]"I want to use differe

""I want to use different engines on the boat"

Ayuh,... What motors,..??

All of the later model Merc. outdrives can be bought in either rotation..."
 
Well I'm probably going to

Well I'm probably going to get flamed for it but here goes. I want to replace the V8s or V6s with mercedes OM617 diesels.
 
"And if the boat originally ha

"And if the boat originally had inboards you will have to make a new transom.
Also may need a fuel return line from the engine
to the tank. May want to do a weight calculation
of new diesels vs old gas - diesels heavier than
comparable HP gas engines. Don't want to put
the scuppers under water (if so equipped) with
a full load of fuel, gear, and people. And the
exhaust risers must be a certain minimum height
above the water at rest with a full load or you
will have water ingestion problems. And I doubt
the flywheel cover/rear engine mounts will match
up."
 
"The Om617 makes 170ft/lbs of

"The Om617 makes 170ft/lbs of torque so i thing an Alpha one should be able to handle it. I can make a fuel return it won't be too hard. I've thought a lot about the weight issue. That is why I'm only looking for Twin V8 boats with Mercruiser outdrives. The OM617 is a Inline 5cyl and should be close to the weight of the V8s they will replace, but I'm going to have to check for sure. Thank you all for your input. I've been lurking on this site for a while and have learned a lot from you all."
 
"Ayuh,...

What are you goin

"Ayuh,...

What are you going to do about the Exhaust,...
The manifolds Have to be water cooled,..??

Are these motors used for boat applications in Europe,..??"
 
drive ratio in the Alpha would

drive ratio in the Alpha would need to change... as would the props to accomodate the lower RPMs...if I'm not mistaken.

you mentioned up to 28 feet and pre 1990. 28 feet is about when you get wide beam twin engines. Just wondering...

Do you have a couple of these Benz engines already? With all due respect... I just can't think of a reason to do what feels like a $40k repower job on a $20k boat.
 
My idea for the exhaust is to

My idea for the exhaust is to do a through hull exhaust using some water cooled mufflers i saw advertized on a website. ( i can't remember which one) I haven't found any marine application of this perticular engine in europe but I know there is a company in Britian that makes conversion kits for other auto diseals to use in boats. I I'm not sure if i will have to change the gear ratios. The Om617 has a stock redline of 4200rpm. Most boats get on plane around 3000rpm that would work for me. These diesels will not preform like the gas engines they will replace. I just want the be able to get on plane and cruise thats it. I checked out the weight. I automotive iron 350 weighs 575lbs the 5cyl diesel longblock weighs 563lbs. fully dressed for marine use they should be close.


I don't have the engines yet but I'm in the car buisness I have a dealer and dismantler's license in GA. I buy wrecked cars weekly. Thecars that have engines i want have weak transmission and and expensive body panels so the get totalled very easily. I saw 1991 300d 2.5 non turbo not wrecked go for $800 in todays Atlanta auction. It was a donation car.

Thanks for the input guys I'm greatful.
 
Ahh... I'm tracking now. t

Ahh... I'm tracking now. the 617 was the 5cyl diesel that was in the 300D's. Lasts forever. Had several. But those transmissions.. when they start wearing out they develop that rough 1-2 shift that nearly spills your coffee.

You would theoretically be able to use those with Apha's from a torque and RPM perspective. The challenge is going to be solving for:

manifolds
water to air aftercoolers
bell housing
engine coupler
motor mounts
closed cooling system parts

No doubt it could be done... if you have pockets and maybe a machine shop.
 
"If i keep the engine bay well

"If i keep the engine bay well ventilated i think I'll be able to use the stock manifolds and cool the exhaust after the turbo use water coole mufflers. These motors didn't have intercoolers from the factory I'm not planning on adding one. As for the bell housing. 4x4labs, a small company in britian has a kit that will adapt the Benz to chevy transmision. I think i can use them to adapt to the Mercruiser bell housings. The motor mounts I can make myself I'm pretty handy with a welder. As for the cooling i think i can adapt a generic CC kit or two in this case. My Dad and i already made a Mercruiser CC kit work on his Volvo Penta manifolds and all. As for the coupler..... well i'm stumped."
 
"A coupler can be fabricated o

"A coupler can be fabricated on a lathe if you start with an engine coupler with the correct splines.

Keep in mind that those engines were not meant to sit at steady state under full boost like a big Cummins engine. They just don't have that duty cycle. That and there's no air flow through the engine bay like there is in a car. Those manifolds and turbos are going to be cherry red below decks in no time. I think you need wet exhaust... water cooled manifolds, turbo and aftercooler or your rig is going to look like the space shuttle entering orbit.

I've seen custom fabricated wet manifolds!"
 
I'm going to have to talk

I'm going to have to talk to a machinist about the coupler. You are right about the engines not ment to be run wide open for long periods. That is risk that i'm going to have to live with. I'm going to use the boat on a lake so there isn't going to be alot of high speed cruising for long periods. There is isn't anywhere to go! lol. You are making sense when you talk about the glowing manifolds. I have never seen nor heard about custom wet manifolds. I'll have to find a picture of one. I've built a few custom turbo headers out of weld ells for myself and a few customers. I never thought of making my own wet manifold. Thanks for the the idea!
 
Why not just have chevy mercru

Why not just have chevy mercruiser v8's? Reliable. Parts everywhere. Inexpensive.

Or is it the challenge you're looking for?
 
"I do like a challenge but goi

"I do like a challenge but going to do this for the fuel economy. The thing is I don't really have the money for a boat this size and its upkeep in the normal sense. What i do have is a full shop full of tools and equipment, my skills and the ability to take time off whenever i need it to work on the boat. I can't afford to feed two hungry chevys. My Dad has a 25 ft Marathon Bermuda with a single 350 in it, and it drinks like crazy.

The other thing is I'm worried about the future. My family is from Romania, I was born behind the iron curtain of communisn. With therecent political changes in this country I am uneasy. The politics here are becoming scary similar to the ones i left behind in europe. I am convinced the that gas will be at 5 bucks a gallon very soon. There is no way i can afford a boat at those fuel costs. From all the research i have done the twin diesels will burn half the fuel and last a long time.

I am hoping that an investment now, will let me enjoy boating no matter what the future holds."
 
[b]"With therecent politic

"With therecent political changes in this country I am uneasy. The politics here are becoming scary similar to the ones i left behind in europe."

Amen brotha!! Scary time.
 
"I, like millions of others, j

"I, like millions of others, just hope my investments can get back to last year's level. I too think the political climate is uncertain. Perhaps there will be more historical events take place over the next four years that will make this presidential history seem like a nursery rhyme.
snow.gif
"
 
"[b]"If i keep the engine

""If i keep the engine bay well ventilated i think I'll be able to use the stock manifolds and cool the exhaust after the turbo use water coole mufflers."

Ayuh,....

That Won't Work,...

You're building a Severe Fire Hazard if you don't have Water Cooled Exhaust,..
Right Off the Motor..."
 
"If getting on plane and just

"If getting on plane and just cruising around the lake is your goal, there are lots of 25-28 footers out there that have single gas V8's with Bravo two or Bravo three drives that will do that. If gas goes to $5 diesel will be $6.50.
A single gas may not use much more than dual diesels, less weight, less drag, less maintenance, and, like stated above, parts and
service everywhere.
Not trying to severly discourage what seems an
interesting project but there is a lot to overcome that requires custom parts and lots of
time solving problems. Please do let us know what you decide and updates on progress."
 
"Sanity check!!

You're

"Sanity check!!

You're going to pay a premium for diesel over gas... maybe $0.25.

You're also going to save fuel due to lean burn fuel efficiency... maybe 20%?

my back of the envelope math gets me a fuel savings of $8 per hour of run time. ...so

For every thousand you spend on this project, you are going to have to cruise that home grown rig 125 hours to break even. A boater that runs over 100 hours a year is considered a big user.

Just a thought."
 
your math makes sense. I&#39

your math makes sense. I'm going to pick up the engines anyway just to have them. I'm confident that i can get two cars for around a grand total. I'll use the boat for one season and see how much it cost me. If i get close to the 100 hr mark I'll go forward with the swap. I not I'll sell the engines and probably get my money back. Thanks for all the advice guys.
 
Back
Top