OMC 350 Rebuild Questions

swilliams wrote: I agree with Tim. My service manual does have your model number listed but the general specifications say it is a 350. Your block number is definitely not a 350. Do a search on the head casting numbers. Bet they are not for a 350.

Is that bet just with Benni27 or can I get in on it?

Chevy literature says the heads are for a 71-72 350 and they're a pretty good set of heads. Benni has already looked this up by the way. He mentioned that they're 350 heads a few posts back.

The block is a 69-73 2 bolt main 307.

This info probably pertains to auto engines and we all know that marine conversions can be a mix of different parts

The OMC model number says it's a 350 4 barrel like you already pointed out. Model year 1978 according to Marine Engine.com. That's hard to explain.

I see from Benni's pictures that it is a RH rotation engine.

307 wouldn't have come in a '79... 305 took its place several years earlier. Exh manifolds look correct for late 70's, decals suggest a 307 block took the place of the original 350 at some point in the boats life, which was dressed back up with the original 350 parts. Just a theory.

Ben, can you provide me a pic of your raw water pump? Just curious if its the same as mine. I know OMC made a change in them after my year but not sure when. Finding parts for mine is tough. Thanks, Steve

swilliams wrote: I can't send you the manuals but let me see if your model number is included in my service manual. From there I can tell you which manuals to look for.

Steve,
Nice gesture but beware. Here's the notation that marineengine.com has on their OMC manuals:

"† Please Note
OMC created new manuals each year which are specific to various models. When ordering a factory manual you must include the year, horsepower and/or displacement, and most importantly the OMC model number of your engine."

Your OMC is a 76 and Ben says his is a 79.

Quick and Dirty Check was:

Stroke ~3.25
Bore ~3.87

So it must be a 307... Heads are 3973487X 76cc from a 350? I'm a little bit confused, maybe I should order the Parts Manual at marineengine.

What's the best adress to get parts from? I thought about summit?

Thanks :)

swilliams wrote: I also hav e a service and parts manual that could possibly cover your model.

OMC manual

Ben, you are correct about the block being a 307. If we had your model number, that would be helpful. Omc made a 230 hp that would correlate with your block number. I have a 260 hp 350 ci motor in my 76' Martinique. Most engine parts can be found as it is a GM product. Pics are helpful. I also hav e a service and parts manual that could possibly cover your model.

Hey Guys,

I'm thinking about a rebuild of my OMC 350 because of bad Heads, low Compression and ~2500 hours on it. I took of the Heads an all assembly's and had a look at the Block number: GM3970020. Google told me that it is a GM 307 Block (5.0L?!) instead of a 350. Does someone have more information about the OMC 350? Did they build a 350 out of a 307 Block with 350 crankshaft an pistons?

Boat is a Ski Nautique from 1979, but I don't know if its the original Engine. Color, Intake, Carb looks like origin...

Thanks for the help

Ben