Mercruiser 3.0 to Mercruiser 4.3 swap

[markhodges78]

I have a 1994 seapro with a mercruiser 3.0 engine that I am going to be swapping out with a 1999 4.3 engine.

I have everything from the 4.3 from the engine to the prop. I have taken the measurements in the engine bay. And the area is actually a few inches wider than the area in the boat that the 4.3 came out of.

Also, I believe that the 4.3 was an option for this boat. The only difference is that the boat only has a front engine mount bed, so I'm looking for some guidance on how to build the engine beds.

Do I just build them and tab them onto the bottom of the boat or do I run them all the way back to the transom.

Also was wondering would I be better off running from one side of the bay area to the other side and tabbing them into the side of the stringers?


Thanks Mark

 

[Scott06]

Do I just build them and tab them onto the bottom of the boat or do I run them all the way back to the transom.

Also was wondering would I be better off running from one side of the bay area to the other side and tabbing them into the side of the stringers?

yes build them out of built up plywood or hardwood blocks , grind the arae down , bed them in peanut butter, tab in. Place engine on rear mounts , drill holes for front mounts and lag in place with 5200 on lags …


side to side wont work will hit oil pan and interfere with bilge drain age . @Rick Stephens did the same swap and has posted pics of mounts .
link to merc engine instal dwg so you can figure height off rear mount location…https://samerwebapp01apncus01.azure...phawithtwo-pieceexhaustmanifold_1996-2001.pdf

 

[Scott Danforth]

Unbolt all 3.0 stuff

Bolt in 4.3 transom shield. Drop in motor on rear mounts (while hanging on hoist)
Align motor

Measure the mount blocks

Build mount blocks

Screw in mount blocks

Remove motor

Remove transom shield

Fiberglass in the mounts

Install transom shield, motor, align, mount drive, go boating

 

[markhodges78]

Unbolt all 3.0 stuff

Bolt in 4.3 transom shield. Drop in motor on rear mounts (while hanging on hoist)
Align motor

Measure the mount blocks

Build mount blocks

Screw in mount blocks

You say screw in mount blocks but I'm not sure what I'm screwing them into the only thing at the location of where the mount will be is the floor I am posting a picture of where I believe the mount blocks should go

 

[Scott Danforth]

You say screw in mount blocks but I'm not sure what I'm screwing them into the only thing at the location of where the mount will be is the floor I am posting a picture of where I believe the mount blocks should go


View attachment 371632

No. you screw the chunks of wood to the stringers and have them angled to match the bottom of the hull. the V-engines get mounts on the side.

 

[alldodge]

Building wood blocks is how most build the supports
Can also use Steel or aluminum like some boat builders do and thru bolt. My Formula is done this way

 

[markhodges78]

Building wood blocks is how most build the supports
Can also use Steel or aluminum like some boat builders do and thru bolt. My Formula is done this way

View attachment 371634

Problem with this is I have no access to the other side of the stringer on either side. The floor of my boat is glassed over and gelcoated and really would prefer not to cut into it..

 

[Scott Danforth]

Problem with this is I have no access to the other side of the stringer on either side. The floor of my boat is glassed over and gelcoated and really would prefer not to cut into it..

You have to do fiberglass work to make the swap

 

[Scott06]

The floor of my boat is glassed over and gelcoated and really would prefer not to cut into it..

well thats no fun…
grind the gel coat to scuff it, glass the blocks of wood into hull and stringer, no cutting really

 

[markhodges78]

You have to do fiberglass work to make the swap

Yes I realize that I have to do fiberglass work would just prefer to keep it limited to the bay area and not cut a hole in the floor of the boat to do a thru bolt mount

 

[markhodges78]

well thats no fun…
grind the gel coat to scuff it, glass the blocks of wood into hull and stringer, no cutting really

This is most likely what I will be doing

 

[markhodges78]

Before I go all in on the swap how can I find out for sure if my boat was offered with a 4.3 engine if I go nada it has the v6 as an option

 

[Scott Danforth]

Before I go all in on the swap how can I find out for sure if my boat was offered with a 4.3 engine if I go nada it has the v6 as an option

what does that have to do with anything?
just curious

if you are worried about horspower or engine size and insurance.
being an I/O, if you wanted to install a 40000000 hp jet engine you can. restrictions are on outboard installation and have to do with transom height, etc. I/O's do not have these restrictions

if you are worried about resale value. sell what you have and buy what you want.

 

[markhodges78]

what does that have to do with anything?
just curious

if you are worried about horspower or engine size and insurance.
being an I/O, if you wanted to install a 40000000 hp jet engine you can. restrictions are on outboard installation and have to do with transom height, etc. I/O's do not have these restrictions

if you are worried about resale value. sell what you have and buy what you want.

Yup I was just worried about any restrictions on engine size

 

[alldodge]

Don't see an issue with the HP increase but could check with your insurance company to make sure

 

[Scott06]

no one is going to bother you if you go from a 135 hp 3.0 to a 175-220 hp 4.3. It wont be a race car... do the swap and enjoy it

 

[markhodges78]

no one is going to bother you if you go from a 135 hp 3.0 to a 175-220 hp 4.3. It wont be a race car... do the swap and enjoy it

Cool Thanks

 

[markhodges78]

can I leave my Transom plate and gimble housing as it is and just use the upper dive from the 4.3 along with the 4.3 engine

 

[Scott06]

can I leave my Transom plate and gimble housing as it is and just use the upper dive from the 4.3 along with the 4.3 engine

Yes you can also probably use the 3.0 drive by increasing prop pitch. I did a 4.3=>5.0 swap that should have also ‘required’ a 1.81=>1.62 drive swap. Went from a 19” pitch to a 21” pitch and hit wot rpm perfectly.

 

[Scott Danforth]

I have a 1994 seapro with a mercruiser 3.0 engine that I am going to be swapping out with a 1999 4.3 engine.

I have everything from the 4.3 from the engine to the prop.

can I leave my Transom plate and gimble housing as it is and just use the upper dive from the 4.3 along with the 4.3 engine

thought you were swapping in the whole long-tail

I would try to keep the drive whole vs splitting if you have access to the whole drive from behind the 4.3