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What do I need to replace a 3.0L with a 4.3L

Fish-a-Palooza

Fish-a-Palooza

Member

Hello, this is my 1st post on this Forum and I'm hoping you guys can help me out.

I currently have a 3.0L OMC Cobra that has a cracked block. I am considering replacing that motor with a OMC 4.3L.

Assuming I had an OMC 4.3L Cobra motor complete with risers what would I need to complete the change?

I already know I would need to build the front engine mount towers.

I know I need an exhaust y-pipe and my question on that is; will it bolt directly to the where the single pipe is now or do I need something else?

I believe I need to change out the lower drive unit and possibly the top???? Any advice?

Do the ears on the flywheel cover line up with the current inner support?

How about linkages, wiring, or other things I may not be aware of?

Any help is appreciated so thanks in advance.





 
Hello Wayne.
There are some sharp OMC guys here that are probably busy with the upcoming Christmas events.
They'll no doubt be along soon after.
 
Fish-a-Palooza said:
I know I need an exhaust y-pipe and my question on that is; will it bolt directly to the where the single pipe is now or do I need something else?

Do the ears on the flywheel cover line up with the current inner support?

How about linkages, wiring, or other things I may not be aware of?
Click to expand...

I still have a few unanswered questions in my quote above so I'll try one more time. Thanks!
 
Fish-a-Palooza said:

Hello, this is my 1st post on this Forum and I'm hoping you guys can help me out.

I currently have a 3.0L OMC Cobra that has a cracked block. I am considering replacing that motor with a OMC 4.3L.

Assuming I had an OMC 4.3L Cobra motor complete with risers what would I need to complete the change?

I already know I would need to build the front engine mount towers.

I know I need an exhaust y-pipe and my question on that is; will it bolt directly to the where the single pipe is now or do I need something else?

I believe I need to change out the lower drive unit and possibly the top???? Any advice?

Do the ears on the flywheel cover line up with the current inner support?

How about linkages, wiring, or other things I may not be aware of?

Any help is appreciated so thanks in advance.
Click to expand...

Ayuh,.... The 3.0l outdrive is geared wrong for the 4.3l motor, so, ya need a different outdrive...

I don't know if the downpipe can be swapped to a y-pipe...

The rear motor mounts, Oughta be the same...

'n only after ya do the swap, will ya know if the cabling, 'n wirin' is long/ short enough...

To be Honest,... With that amount of work, 'n rebuildin',....
NOW is the time to scarp the whole OMC thing, 'n drop in a Mercruiser, or Volvo, so ya can buy Parts to keep it runnin' for a good long time....
 
bondo said:
  1. The rear motor mounts, Oughta be the same...
  2. To be Honest,... With that amount of work, 'n rebuildin',....
NOW is the time to scarp the whole OMC thing, 'n drop in a Mercruiser, or Volvo, so ya can buy Parts to keep it runnin' for a good long time....
Click to expand...

1... I was curious about that, Bill.
With the Merc, the inner transom plate is not the same between certain engine models.... but I do not know about the OMC Cobra.

2... Now Bill............ Volvo Penta? You sure 'bout that? ..... :mad:

(just kiddding.... I made this suggestion to Wayne already! :D )


.
 
From what I have located so far if I switch over to Merc or Volvo SX expense goes up exponentially. I keep finding complete drop in OMC Cobra setups which works for me. I’m not having any problems finding anything for an OMC Cobra thanks to all the OMC bashing over the years.
 
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RicardoMarine said:
1... I was curious about that, Bill.
With the Merc, the inner transom plate is not the same between certain engine models.... but I do not know about the OMC Cobra.

2... Now Bill............ Volvo Penta? You sure 'bout that? ..... :mad:

(just kiddding.... I made this suggestion to Wayne already! :D )


.
Click to expand...

Ayuh,.... Since the intro of the Cobra, Merc., OMC, 'n Volvo are all pretty much usin' the Same key-hole cut-out, 'n bolt pattern.....

The inner transom plate/ motor mount spacin', changed when the MC-1 went away....
Not sure if it's the "R" change, or the "MR" change, but the motor mount spacin' changed 'round '80/ '81...

'n,... F-a-P,... Ya need a different Outdrive. 'n motor now,....

On craigslist 'round here, rotten hulls, with complete runnin' 4.3l/ Alphas are runnin' Under 2 grand....
'n that way, ya get ALL the expensive tiny pieces to make it work....

'n,... I'm not bashin' OMCs, but I am realistic 'bout expectations of life....
 
Bondo, of course I know you aren’t bashing OMC, and thanks for replying. I'm saying; thanks to all the bashing that has gone on over the years, OMC is cheap and easy to acquire. I just don't share the view that lots of people have that OMC Cobra parts are difficult to come by, unreliable, or hard to work on.

You are 100% correct there sure seems to be an endless supply of rotten boats and complete engines on the East coast. I'm not sure why, but I don't seem to find much of the same on the West coast.
 
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bondo said:
1. .... Since the intro of the Cobra, Merc., OMC, 'n Volvo are all pretty much usin' the Same key-hole cut-out, 'n bolt pattern.....

2. The inner transom plate/ motor mount spacin', changed when the MC-1 went away....
Not sure if it's the "R" change, or the "MR" change, but the motor mount spacin' changed 'round '80/ '81...

3. I'm not bashin' OMCs, but I am realistic 'bout expectations of life....
Click to expand...


1. Bill, I was suggesting an AQ series Volvo Penta to Wayne, not necessarily the Gimbal System V/P.
The cut-out of course is not the same.... the AQ series requires a much larger cut-out.

IMO, the AQ series Main Suspension Fork and Pivot Tube geometry is superior to the Gimbal system geometry.
The AQ series "C" drive style ran well into the 90's.... (1996 I believe)..... and ran into 200X in the Diesel drives.
This is the good stuff, IMO.


2. Bill, correct me on this.... but I'm thinking that with the older Mercs, there is a difference in the center-to-center dimension between the two rear mounts re; a in-line engine -vs- a V-8 engine, for example!
This is why I asked if the OMC inner transom plates were also different!
You would know..... I would not!


3. Same here, Bill.

I have a friend who owns a Marine Salvage yard. His "bread-n-butter" is use OMC parts and drives.
Merc is next.... Volvo Penta trails last.


.
 
RicardoMarine said:
1. Bill, I was suggesting an AQ series Volvo Penta to Wayne, not necessarily the Gimbal System V/P.
The cut-out of course is not the same.... the AQ series requires a much larger cut-out.

IMO, the AQ series Main Suspension Fork and Pivot Tube geometry is superior to the Gimbal system geometry.
The AQ series "C" drive style ran well into the 90's.... (1996 I believe)..... and ran into 200X in the Diesel drives.
This is the good stuff, IMO.
Click to expand...

Ayuh,.... Never doubted yer thoughts on 'em Rick,...
They're just rarely seen 'round here....

2. Bill, correct me on this.... but I'm thinking that with the older Mercs, there is a difference in the center-to-center dimension between the two rear mounts re; a in-line engine -vs- a V-8 engine, for example!
This is why I asked if the OMC inner transom plates were also different!
You would know..... I would not!
Click to expand...

The center to center of the rear motor mounts, I addressed above,...
Nothin' to do with I-motors, Vs: V-motors...

The I-motor, Vs: V-motor is 'bout the Chevy I-motors, with the MC-1s, used a shorter, by a inch, Input shaft on the drive....
The Merc 470 is the exception to this rule,... 'course, the 470 is the Exception to most rules,...

That too, changed 'bout, or at the same time, the rear motor mount C to C went to 9"s, from the previous 15"s...
'n I'm pretty sure, that was when the MC-1 finally died...


3. Same here, Bill.

I have a friend who owns a Marine Salvage yard. His "bread-n-butter" is use OMC parts and drives.
Merc is next.... Volvo Penta trails last.
.
Click to expand...

Agreed,... You, 'n I are Usually on the same page, Anyways,.... ;)
 
Well the decision is made. I picked up a newly rebuilt 4.3L Cobra Friday morning. Complete from the engine to the prop and everything in between. I know the motor itself is good. Heard it run and got compression readings of 170 psi on every cylinder. The outdrive is believed to be good, has clean oil, seems to shift properly but wasn't attached to the motor. Until this Cobra outdrive proves to be bad it's what I'm going with. Thanks for the advice on alternatives.
 
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