Replacing 95 merc 4.3 with 87 OMC 4.3

[markhodges78]

Ok I just purchased a 95 marada with a Mercruiser 4.3. The engine has water in the oil and the guy I got it from said when he backed it in the water that engine was locked up. I'm thinking it was hydro locked. None the less, it's been a year with water in oil and possibly cylinders, I have a good 1987 OMC 4.3 engine that I've been holding onto . My question is, will the parts from the 95 Mercruiser engine swap over to the 87 OMC engine ? to convert the omc over to mercruiser ?

Thanks Mark

 

[Scott06]

Ok I just purchased a 95 marada with a Mercruiser 4.3. The engine has water in the oil and the guy I got it from said when he backed it in the water that engine was locked up. I'm thinking it was hydro locked. None the less, it's been a year with water in oil and possibly cylinders, I have a good 1987 OMC 4.3 engine that I've been holding onto . My question is, will the parts from the 95 Mercruiser engine swap over to the 87 OMC engine ? to convert the omc over to mercruiser ?

Thanks Mark

Strip the omc one down to the long block and it should swap over to use all the mercruiser accessories. Underneath it they are both chevy 4.3's. would keep the flywheel and balancer with the donor engine incase there are any balancing variance between the years.

would look at the exhaust manifolds before you reuse them as they are a common cause of hydrolock

 

[markhodges78]

Strip the omc one down to the long block and it should swap over to use all the mercruiser accessories. Underneath it they are both chevy 4.3's. would keep the flywheel and balancer with the donor engine incase there are any balancing variance between the years.

would look at the exhaust manifolds before you reuse them as they are a common cause of hydrolock

Yes the exhaust manifolds will be replaced as I'm sure that was the root of the issue . I believe that there was a balancer difference between the years. will the coupler from either of the motors work ?

 

[stresspoint]

one motor is later vortec the other is early vortec often said to be non vortec.
? confused so was i when i bought a replacement early motor thinking it was a swap and go affair.

https://www.thehulltruth.com/boating-forum/1211569-giving-some-much-deserved-love-restoration-thread.html

start at post 30 that's where the drama began

 

[markhodges78]

one motor is later vortec the other is early vortec often said to be non vortec.
? confused so was i when i bought a replacement early motor thinking it was a swap and go affair.

https://www.thehulltruth.com/boating-forum/1211569-giving-some-much-deserved-love-restoration-thread.html

start at post 30 that's where the drama began

yeah looks like you went through it with that engine

 

[Bondo]

one motor is later vortec the other is early vortec often said to be non vortec.
? confused so was i when i bought a replacement early motor thinking it was a swap and go affair.

https://www.thehulltruth.com/boating-forum/1211569-giving-some-much-deserved-love-restoration-thread.html

start at post 30 that's where the drama began

Ayuh,..... Both the '87, 'n the '95 do Not have vortec heads,....

Previous to '96, vortec meant absolutely nothing,.... just a word on the valve covers,.....

 

[Scott06]

Yes the exhaust manifolds will be replaced as I'm sure that was the root of the issue . I believe that there was a balancer difference between the years. will the coupler from either of the motors work ?

None of the OMC items will work (with exception of starter and intake manifold) so you can toss or sell them.

keep the balancer and flywheel that came on the 87 with it. You may have some fitment issues to work through on the pulleys and you may need a different mercruiser coupler if the flywheel is a different size between the 95 and 87 engines. If they are both 14" flywheels the 95 coupler will work no issue.

Bottom line until you get it all in front of you hard to say what will or will not work

 

[Scott Danforth]

Light reading. https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

the 87 is a gen 2 4.3 - non balance shaft, 1-piece RMS
the 95 is a gen 4 4.3 - balance shaft, 1 piece RMS

the 87 will need the squishy engine mounts because the motor shakes like a dog passing a peach pit

 

[04fxdwgi25]

the 87 will need the squishy engine mounts because the motor shakes like a dog passing a peach pit

Now that was funny

 

[markhodges78]

Light reading. https://forums.iboats.com/threads/complete-history-of-the-4-3-liter-with-casting-numbers.693935/

the 87 is a gen 2 4.3 - non balance shaft, 1-piece RMS
the 95 is a gen 4 4.3 - balance shaft, 1 piece RMS

the 87 will need the squishy engine mounts because the motor shakes like a dog passing a peach pit

Wow Scott that is a lot of information compiled on the 4.3

Thanks

 

[stresspoint]

yeah looks like you went through it with that engine

yes it was a learning curve let me tell you , point being , don't expect a bolt an go with that early OMC motor , it will work "but "you will have to strip to a long block and go from there ,end of the day IMO it will be no where near as good the later model balance shaft version.

as you probably noticed from the thread link ,i have a bitsa ATM in the boat but all Mercruiser , its a very powerful and solid motor , it has parts from motors ranging from 2008 to 2015 in it with HTtec extractors , a HEI distributor ,a quadrajet 4bbl carb and lots of machine shop work , so the Hp is well up there in the 250 + range with reasonable torque, it is solid and reliable as that was my aim and on a realistic budget.

in retrospect a V8 would have been easier and cheaper to get more HP ,but now i have the little 4.3 working i am glad i went that path because this thing just sips fuel and sounds amazing @5500 rpm (the limited RPM i allow) . you guys are blessed with availability of 4.3 parts in the USA so it will be easier for you to get a good 4.3 working. here in AUS they are a neich motor so parts are few and far between so it made for a project .

 

[markhodges78]

None of the OMC items will work (with exception of starter and intake manifold) so you can toss or sell them.

keep the balancer and flywheel that came on the 87 with it. You may have some fitment issues to work through on the pulleys and you may need a different mercruiser coupler if the flywheel is a different size between the 95 and 87 engines. If they are both 14" flywheels the 95 coupler will work no issue.

Bottom line until you get it all in front of you hard to say what will or will not work

The flywheel that came on th 87 ( omc engine ) won't work with the mercruiser coupler because it isnt drilled and taped for the triangle style coupler I have .. but I can use the flywheel from the 95 mercruiser engine according to Michigan Motors it was the same from 87 on

4.3L Flywheel (1987 & Later Engines, 14

4.3L Flywheel (1987 & Later Engines, 14" diameter)

www.michiganmotorz.com

So I think I'm ok what do you guys think ?

 

[markhodges78]

Also should I leave the ignition system that came with the 87 omc engine or should I replace it with the mercruiser ignition from the 95 engine

 

[Scott Danforth]

Also should I leave the ignition system that came with the 87 omc engine or should I replace it with the mercruiser ignition from the 95 engine

the mercruiser TB ignition is better

 

[Scott06]

If your flywheel is not drilled and tapped for the triangular coupler I wonder if the engine is earlier than 87. Typically in a change over year there is a lag in what marine engines are in the assembly que.

Is the '87' flywheel 14" in diameter? if not the older style merc coupler for smaller flywheel bolts to the crank via studs in where the flywheel bolts on.

I would just be 100% sure before swapping flywheels that the balance is the same. very hard to tell with changes to rotating assemblies over the years if it is ok or not. @Scott Danforth - do you know if the flywheel will work

on the ignition keep the later distributor and wiring harness off the merc engine likely it is a better merc thunderbolt set up. Thunderbolt works great unless you need to buy a new module ($$$)

 

[Scott Danforth]

@Scott Danforth - do you know if the flywheel will work

if the flywheel housing is set up for the 168 tooth flywheel, then yes. the motors are internally balanced which is why the crank changed from the non-balance shaft motors to the balance shaft motors.

 

[stresspoint]

the early ( non balance shaft ) Mercruiser flywheel will bolt up to early motor , the problem you could run into as i did is the ring gear teeth being a different pitch , as from what i found there are 2 types of early non balance shaft FWs one is for a geared starter (vortec type) and the other is for the big bulky chevy type..
i am not sure about the harmonic balancer so i used the balancer from the crank and FW as a matched set when i set up the early bottom end. .
i bought a new balancer for the motor that is in the boat now, it needed a few drill marks to set the balance on the motor ( don't ask me what the story was there ,that was the machinists doing).
Scott , i have both FWs in the shed , i can count teeth and report back if required , just let me know and i will venture down there and check.

 

[Scott Danforth]

Scott , i have both FWs in the shed , i can count teeth and report back if required , just let me know and i will venture down there and check.

no need. a 11" clutch flywheel is 168 tooth, a 10" clutch flywheel is 153 tooth. sometimes incorrectly called a 14" flywheel and 13" flywheel

been that way since the birth of the SBC/BBC all SBC/BBC ring gear pitch has been the same since the beginning as well. copied over from the early in-lines

 

[markhodges78]

Both flywheels are the same size and they both came from engines with a 1 piece seal. I do not believe OMC ever had the triangle shaped coupler so I believe ( do not know for a fact ) that this is why its not drilled. and according to Michigan Motors there its the same one but I'm going to call them

 

[Lou C]

OMC did not use the triangle shaped coupler it’s a cylinder shaped one with studs that go into the flywheel/crankshaft and nuts that hold the coupler to the studs. Just like what’s seen on a Volvo SX in fact probably the same part!
I used a PMGR starter to replace the old Delco starter on mine with no issues so I don’t think that there is any difference in the thread pitch. However due to the addition of the balance shaft I always wondered if there was any difference in the flywheels from the pre balance shaft to balance shaft.