Omc 3.0 140 hp

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misiek

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I have a 1985 ThunderCraft 3.0 140 HP OMC with a cracked block. Can anyone tell me if I can replace it with a 1976 3.0 OMC? I know that there is a slight gear ratio difference. Can it be corrected with replacing the fly wheel and coupler with the old parts from the bad engine I am replacing?
 
Bifflefan

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Re: Omc 3.0 140 hp

misiek said:
I have a 1985 ThunderCraft 3.0 140 HP OMC with a cracked block. Can anyone tell me if I can replace it with a 1976 3.0 OMC? I know that there is a slight gear ratio difference.
Click to expand...

The block doesn't have a gear ratio....the drive does.


Can it be corrected with replacing the fly wheel and coupler with the old parts
Click to expand...

Again, no gear ratio here either.
 
Howard Sterndrive

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Re: Omc 3.0 140 hp

the long block engine itself will be identical
coupler and flywheel is the same 76 and 85
 
zbnutcase

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Re: Omc 3.0 140 hp

Howard Sterndrive said:
the long block engine itself will be identical
coupler and flywheel is the same 76 and 85
Click to expand...

As long as its not an early Cobra, some of which started to trickle out in late 85,then you will have to change coupler.
 
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misiek

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Re: Omc 3.0 140 hp

What is the earliest model of the GM block that will fit? I see the difference in the exhaust manifolds, carburetors but are the engines any different?
 
Bondo

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Re: Omc 3.0 140 hp

What is the earliest model of the GM block that will fit? I see the difference in the exhaust manifolds, carburetors but are the engines any different?
Click to expand...

Ayuh,... All of the Blocks,... From the begining will fit...
It's everythingelse that's bolted to 'em that changes....
 
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misiek

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Re: Omc 3.0 140 hp

How can I identify which engine do I have? Please look at the photos and advise. Thank you.
 
Howard Sterndrive

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Re: Omc 3.0 140 hp

misiek said:
How can I identify which engine do I have? Please look at the photos and advise. Thank you.

P1010036.jpg
Click to expand...

the big "3 Litre" sticker kinda says it all, no?
(I always wondered why OMC wrote Litre instead of Liter
they tryin' to be all French?)
 
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misiek

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Re: Omc 3.0 140 hp

What I meant is it a pre 1986 block? Not a cobra, right?
 
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misiek

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Re: Omc 3.0 140 hp

Here are the pictures. I need to be sure that this is not a COBRA before I'll go engine shopping. Most of the late 70's and early 80's engines that I saw are painted blue and my engine is painted silver and that's what confuses me. Thanks.
 
Howard Sterndrive

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Re: Omc 3.0 140 hp

misiek said:
I need to be sure that this is not a COBRA before I'll go engine shopping.
Click to expand...

no you don't, actually. A 3.0 from a 1986-1989 Cobra will work for you just fine.
If all you need is the long block engine, any 3.0 from 1970 to 1989 will BOLT RIGHT IN. It can be from any OMC, or Mercruiser powered boat with a 3.0L, 181 cubic inch GM Marine engine older than 1990

What you absolutely MUST AVOID, is a 1990 or newer 3.0L from any boat. Your drive coupler on the back of the crank will only work with engines 1989 and older.

Your drive is not a Cobra, it is a "400 Series Full Mechanical Shift Stringer Mount OMC Sterndrive" - or at least that will identify it well
Technically, according to OMC, your drive is simply a 983486
 
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misiek

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Re: Omc 3.0 140 hp

Is there a lot of difference in power and performance between the 2.5L and 3.0L engines? My boat is a 17 footer. There seems to be more of 2.5's available on the the market so should I consider them to replace my 3.0L with. Thanks.
 
Bondo

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Re: Omc 3.0 140 hp

Is there a lot of difference in power and performance between the 2.5L and 3.0L engines?
Click to expand...

Ayuh,... 20hp...

Resize your pictures,... They're Too Big... use 480x640....
 
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misiek

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Re: Omc 3.0 140 hp

I know it's 20 HP difference, but how does it translate to the overall performance? Speed? Pick up?
 
Howard Sterndrive

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Re: Omc 3.0 140 hp

misiek said:
I know it's 20 HP difference, but how does it translate to the overall performance? Speed? Pick up?
Click to expand...

big difference.

you will notice the power difference immediately on holeshot and top speed.

15% less power

maybe do a search - pretty sure somebody was here cursing themselves for going the 2.5 route not that long ago...
 
CobiaXL

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Re: Omc 3.0 140 hp

Howard Sterndrive said:
it is a "400 Series Full Mechanical Shift Stringer Mount OMC Sterndrive" -
Click to expand...
The best drive ever assembled..... JMHO

Sorry I just wanted to be included,lol
I will add that the 3.0 chevy block is same as 2.5

Good luck on your search
 
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misiek

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Re: Omc 3.0 140 hp

Just out of curiosity. Would a 165 HP MerCruiser fit as well? The inline 6 cylinder looks very similar. Can they be swapped?
 
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coheej

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Re: Omc 3.0 140 hp

CobiaXL said:
The best drive ever assembled..... JMHO

Sorry I just wanted to be included,lol
I will add that the 3.0 chevy block is same as 2.5

Good luck on your search
Click to expand...

The 2.5 has a 3.875" std. bore and the 3.0 has a 4.000" std. bore
 
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