Replacing OMC 4.3 w/ Chevy Block

[bcastro22]

New to this:
bought a '90 Four Winns (OMC 4.3) Had it on the water a few times, no problems. On the fourth time out, it got hot. shut it down after about 5 minutes... Too late, water in the oil can not manipulate or get compression.
Found a chevy block, good shape, good compression. I know I need to replace the CAMs to start with. I wanted to ask for any other advice???

Thanks,

B

 

[IVAZ]

Re: Replacing OMC 4.3 w/ Chevy Block

Welcome to iboats.
The cam is fine if it came in a truck. The core plugs need to be brass and the head gaskets has to be made from a material that won?t corrode.
Do you know if the new engine is compatible with the old one? I?m referring specifically to the rear seal.

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

That's good news about the cam! The block is out of an 86 Chevy van. I was under the impression that I'd have to buy new gaskets and seals. Am I right or wrong with this thought process?

Thanks

 

[IVAZ]

Re: Replacing OMC 4.3 w/ Chevy Block

Only the head gasket needs to be changed. All the other gaskets are fine.

 

[IVAZ]

Re: Replacing OMC 4.3 w/ Chevy Block

I do believe the rear seals are different on the 1986 from the 1990. Have you verified that?

 

[Bondo]

Re: Replacing OMC 4.3 w/ Chevy Block

I do believe the rear seals are different on the 1986 from the 1990.

Ayuh,... I Know they're Different...

Finding the Same Vintage is important with the 4.3s Especially...
Otherwise, you'll have All kinds of funky differences to build around....

 

[180shabah]

Re: Replacing OMC 4.3 w/ Chevy Block

Yes the '86 has a two piece rear seal, the 1990 has a one piece rear seal. If you do this you will also need a new flywheel and engine coupler ($5-600). You really need to stick with the same vintage engine you have now (87-95). The '96+ engines used different heads(vortec), so you would not be able to reuse your existing intake manfold, but they do make for a noticable power upgrade.

 

[Bondo]

Re: Replacing OMC 4.3 w/ Chevy Block

You really need to stick with the same vintage engine you have now (87-95).

Ayuh,... Aren't you forgeting about the Elec./ Mech. Fuelpump Issues,+ the Balanceshaft or Not issues...
This is the 4.3 remember....

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

Thanks for all the advice! I will keep you all posted on my progress

 

[180shabah]

Re: Replacing OMC 4.3 w/ Chevy Block

Aren't you forgeting about the Elec./ Mech. Fuelpump Issues,+ the Balanceshaft or Not issues.

Forgotabout that - 87-91 then....

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

So I have everything pulled apart I found the thermostat stuck / welded to the top of the T-stat housing. I assume this is not normal. Further down the exhaust system rabbit hole I found that the baffles / flappers inside the bellows have been cooked and a re shriveled up. These were both products of the overall failure... So my question is... Is it possible that the T-stat was the component that failed allowing water into the manifold, then into the cylinders themselves? Your thoughts and suggestions are most appreciated

 

[Howard Sterndrive]

Re: Replacing OMC 4.3 w/ Chevy Block

I found the thermostat stuck / welded to the top of the T-stat housing. I assume this is not normal.

that's normal. They stick in there. That is not an indication of a t-stat failure at all. But if you want, you can boil it in a pan on the stove and watch it easy enough.

Neglected raw water impeller in the outdrive is most likely root cause of the failure.

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

My first thought too! The impeller is in decent shape (not shredded, no missing fins) I have a new one and will replace it when the new motor is in. Just trying to figure out which component is the culprit! Thanks again for all your help!

 

[Howard Sterndrive]

Re: Replacing OMC 4.3 w/ Chevy Block

next on the list is manifold and riser - are they letting water out? or are they all clogged with decades of rust....

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

UPDATE: I got replacement motor in! Turns out it is an '87 block! swapped out rear seal / head gaskets / manifold gasket / oil pan gasket. over the next several days I will be attaching all accessories. Is there any advice or tricks to avoiding any pit falls?

Thanks


-B

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

Sterndrive,

both manifolds are in decent shape. no holes rusting through that I could find.

 

[bcastro22]

Re: Replacing OMC 4.3 w/ Chevy Block

Gentlemen,

I have everything back together! Motor cranks along happily! The remaining outstanding issue is timing the motor. I could not get this to time by ear. I've replaced the harmonic balancer, and HB plate. My question is: How would you all go about timing this? Next Steps?


Thanks

 

[Bondo]

Re: Replacing OMC 4.3 w/ Chevy Block

How would you all go about timing this?

Ayuh,... With a Timing Light,..??