In need of a new block

randelf

Cadet
Joined
Apr 18, 2017
Messages
12
First thank you all for the help so far.
I have a boat with a 990255v comes back as a 1979 OMC 230. My question is a SBC the same thing and if it is will all my parts bolt on it? I did read about changing freeze plugs and getting marine gaskets. And as long as its a truck engine. Will this work?
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
First thank you all for the help so far.
I have a boat with a 990255v comes back as a 1979 OMC 230. My question is a SBC the same thing and if it is will all my parts bolt on it? I did read about changing freeze plugs and getting marine gaskets. And as long as its a truck engine. Will this work?

Howdy,

Welcome aboard!

In general yes, You can easily replace a marine 305/350 with a similar year (up to a point) 350 truck block.

If you're operating in salt water, you *should* replace the core plugs (with SS or brass), head gaskets with marine type, and use a marine type circulating pump. The rest of the marine "stuff" Starter, dist, carb, fuel pump, etc should (.....must, according to USCG/ABYC guidelines) also be used.

There are some rear crankshaft seal issues that you must consider that I believe becomes a factor in the mid 80's.

There may also be some issues with the bellhousing mount/flywheel mount for the coupler etc.
One of the "Stringer Dudes" will probably jump right in here with details!

Regards,

Rick


I guess I should have remembered you asked some questions about your boat in another thread!

You must have discovered a cracked block?
 

randelf

Cadet
Joined
Apr 18, 2017
Messages
12
Thanks Rick yep its me. I bought this boat stupid me never pulled the dipstick. Yes its milky oil I have not torn into it yet just the comments on here tell me the block is probably cracked. So just looking around to see what's out there. My question was is OMC and chevy interchangeable? Thanks for your help guys
 

HT32BSX115

Supreme Mariner
Joined
Dec 8, 2005
Messages
10,083
If the engine is a GM block (OMC did use Ford too) you can replace the engine with a similar year GM truck engine and it will work fine. There is a year (mid 80's I think) where the rear main crank seal is changed. I don't know what it might mean for your applicatiom (maybe nothing) but someone should jump in here with info. Otherwise, you can use nearly any truck 350
 

southkogs

Moderator
Staff member
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Jul 7, 2010
Messages
14,785
I think that should be a Chevy 305 block on the OMC 230. If I get it right, that should bolt right up.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,300
1985 or earlier SBC from a truck, strip down to block and heads. Install brass core plugs and marine head gaskets. Then transfer oil pan, water pump, all electrics, etc from your marine motor over to replacement
 
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