Logo
FULL SITE MENU

3.7 to 4.3 swap

M

Markhodges78

Member
OK guys I have a 21 foot 1985 citation cuddy cabin with a 3.7 MerCruiser engine that has a cracked block. I also have a donor boat a perfectly good OMC 4.3 Engine the boat is sitting in my garage due to a rotted floor that I have not got around to replacing.... Now I am entertaining the thought of just junking the boat and putting the 4.3 in the citation my question is what am I going to run into as far as wiring and brackets since the donor engine is OMC.... I do realize I will need to put stringers in for the engine melts that's not an issue

Thanks Mark
 
Markhodges78 said:
That's it no electrical no cables or cable brackets that's a lot better than I thought
Click to expand...

Ayuh,... That's not true,.... Only the Long Block motor will easily swap,....

Everything OMC has to go, 'n be replaced with Mercruiser dressin's,.....
 
Not exactly. GM to GM, you should be fine except to say the mounting for the control cables will be a little different so you may have to alter the ends of your cables with the OMC adapters that you can get from Teleflex. The other thing is that the harness for the engine might not have the correct length wires to reach where they need to reach. The wiring is pretty much the same tho. All engines have connection for ignition circuit, charging circuit, senders, electric choke. There may be little things like the wire ends may have spade terminals rather than ring terminals or vice versa. Just compare the two wiring diagrams (you can probably find them on google) All boat wires are the same colors dating from the late 1960s Sender colors the same, ignition wire the same, charge circuit the same...The plugs are the same too, so yeah you could plug a 9-pin OMC engine harness into the 9-pin Merc dash/key harness. Not sayin it's 100% plug and play, but it's so similar that you might be OK with what's there already.
Going from GM to Ford, or Ford to GM...that's a LOT different. Yeh you can use the wire harness, but the physical layout is all different; especially the exhaust.
 
where the water will enter the Thermostat housing from the drive, Most v6-v8 enter from the right side when facing the motor
 
from this
mVx_WKMAbU5B8tfqiKQvFLA.jpg

To this
mndrs2owjtGpVPQuVyeYLhQ.jpg
 
OK so I actually had a brain fart today and I was thinking if I have a donor boat with a perfectly good 4.3 OMC engine and perfectly good OMC sterndrive why not just swap the whole Power package and convert to omc
 
bondo said:
Because OMC has been outa business for several Decades,......
Click to expand...

Yes but with aftermarket vendors parts are readily available and it seems like if the drive ever goes out for what I would pay for converting the exhaust I could get a conversion kit for the outdrive to convert to mercruiser
 
Bt Doctur said:
from this

mVx_WKMAbU5B8tfqiKQvFLA.jpg


To this
mndrs2owjtGpVPQuVyeYLhQ.jpg
Click to expand...

Mark, while these may appear to be slightly different, either of the GM V-8/V-6 T-stat housings can be made to work if this engine is Raw Water Cooled.

Markhodges78 said:
OK so I actually had a brain fart today and I was thinking if I have a donor boat with a perfectly good 4.3 OMC engine and perfectly good OMC sterndrive why not just swap the whole Power package and convert to omc
Click to expand...

I would NOT want an OMC stern drive system...... no matter what!

As per Bill, OMC's last produced stern drive was in 1993.
By 1994, the new cone-clutch stern drive design was Volvo Penta.


Markhodges78 said:
Yes but with aftermarket vendors parts are readily available and it seems like if the drive ever goes out for what I would pay for converting the exhaust I could get a conversion kit for the outdrive to convert to mercruiser
Click to expand...

I'll suggest that you look on e-Bay for good used Merc parts.



.
 
Last edited:
OK guys UPDATE it warmed up a bit here so had a chance to got the boat running. It does not have a cracked block that assumption was made do to the deal i got on the boat. And I wasn't confident that the owner winterized it correctly ... The boat starts up and runs nice but after it gets up to about 190 degrees there is white smoke coming from the PVC vent breather I don't believe its oil. I am convinced its moisture when i pulled the hose from breather I seen a few beads of water. So does this seem like a head gasket issue to you guys?

Thanks Mark...
 
The boat starts up and runs nice but after it gets up to about 190 degrees
Click to expand...

Ayuh,..... 1st thing to do is figure out Why it's runnin' so hot,.....

I'm guessin' the "Smoke"yer seein' is steam burnin' off condensation in the oil,...
 
Markhodges78 said:
Okay so I tore the lower unit off today and this is what I found.......... so I will replace the water pump and let you guys know

View attachment 16983
Click to expand...

Mark, you will want to retrieve the missing impeller vanes.
This will involve taking certain parts of the cooling system apart...... but it will be well worth it in the long run!

If you DO NOT retrieve them, they may become lodged and may restrict flow somewhere within the system.
This could result in over-heating issues.




.
 
RicardoMarine said:
Mark, you will want to retrieve the missing impeller vanes.
This will involve taking certain parts of the cooling system apart...... but it will be well worth it in the long run!

If you DO NOT retrieve them, they may become lodged and may restrict flow somewhere within the system.
This could result in over-heating issues.




.
Click to expand...

Ok willing and ready where do I start ....
 
I would start at the curved hose that leads from the bell unit to the transom unit… I would then go from there all the way forward.
Leave no stone unturned!
 
Back
Top