1987 OMC Cobra block swap.

[WinnerCobra]

Alright so i have a 1987 OMC Cobra 350 wich i think is the 5.7l my block is cracked and i temporarily fixed it with some JB weld over the last summer. Now my question is can i swap in any old 350 block? Will the heads match up? I would rather just get a cheap block compared to replacing the entire motor. If not is welding an option at this point? The crack is only on the exterior block from previous owners who did not properly winterize the boat. Appreciate any and all hope thanks in advance if you have any questions that i need to answer feel free to ask.

 

[HT32BSX115]

Howdy,

Yes, you can use a "wrecking yard" truck 350 out of a similar year GM truck and swap all the marine "stuff" over.

It's advisable to use brass core plugs and carefully inspect your manifolds because they may be cracked too.

I don't know what years the flywheel flange changed but I believe there's an issue with newer engines (with a different rear seal) that might be a problem fitting your flywheel and/or flywheel cover and starter etc.........

The truck engine will have a camshaft that is close enough to a marine cam to work ok.

Someone should jump in with the correct years that are compatible with your 87 installation.

Regards,


Rick

 

[wrench 3]

The first thought that comes to mind is, why would you want to go older than an '87?
That said, there were three basic versions of the GM 350. The first had a two piece rear main seal. Then they went to a one one piece seal and changed the bolt pattern for the flywheel so they won't interchange. Next they put in a roller cam and went to the vortec heads. So you need to stay with the same version unless you go for a complete drop in.
If you go for an automotive block and have a raw water cooling system, you will need to change the frost plugs to brass ones. The marine engines usually use a different cam shaft as well.

 

[wrench 3]

I did a little searching and found that the automotive blocks changed in 1986 and again in 1992. The only problem is that the marine engines are often a little behind the automotive, so you will have to take a look at yours to see what you have.

I hate it when my post overlaps some one else's. Sorry HT32BSX115!

 

[jerryjerry05]

If you can find someone who can weld the cast iron.
Go for it.
You'll probably need to pull the motor but still cheaper than buying a new block.
The older marine motors will probably be the light duty truck motors that Volvo/ OMC used.
They have the 2 piece rear seal and have a different crank and need a special flywheel.
Make sure the new crank matches the old.

 

[Bondo]

Alright so i have a 1987 OMC Cobra 350 wich i think is the 5.7l my block is cracked and i temporarily fixed it with some JB weld over the last summer. Now my question is can i swap in any old 350 block? Will the heads match up? I would rather just get a cheap block compared to replacing the entire motor. If not is welding an option at this point? The crack is only on the exterior block from previous owners who did not properly winterize the boat. Appreciate any and all hope thanks in advance if you have any questions that i need to answer feel free to ask.

Ayuh,.... So ya patched the block,.... Did ya get any water in the oil,..??

If Not,..... Run it til she pukes,.... No reason to swap blocks, til the problem, Is a problem,.....