1977 OMC sterndrive GM 305/5.0 hp? Cam?

[Jessman93]

Hey guys,
I just bought bought my first boat and am in the process of rebuilding the engine and have some questions. Sorry if this has already been asked previously, I couldn't find it.

I picked up a 1983 4winns marquise 180 with a gm 305 sbc engine (original engine was a 4.3l v6). I could not find any information on the engine anywhere, other than OMC , GM, a date for '77 and casting number 46077 on the block (77-79 gm 305 2 bt main) and 375450 on the cylinder heads. I was told originally that it was an old 350ci sbc engine and should have ran the casting numbers. I know these engines weren't very powerful in cars (130-150 hp) and they had camshaft issues. I'd like to put a 350 in it, but that will likely be a winter project.

Does anyone know the horsepower for this motor? Or what size cam would be in it?

It had a high idle issue and I found that the carburetor needed to be rebuilt, intake gasket leak, water in oil (head gaskets blown), and also some electrical issues that I fixed. May also need replace the gears on the outdrive, because the guy put it into gear at a 2k+ rpm idle.

I have it stripped down to the block and have ordered replacement heads, all new gaskets, edelbrock 1409 marine 4bbl carb, edelbrock 2701 performer rpm intake, and new plugs and wires. So it will basically be totally rebuilt on the top end.

I am wondering, if OMC kept the same camshaft and cam drive gears used in autos, if I should go ahead and get them replaced now with a better one.

Does anyone have any recommendations on what to use, or leave it stock?

 

[Scott Danforth]

you know that OMC has been out of business for decades..... and your stringer drive was obsolete back in 1983 when the boat was new, right?

a 1983 boat could never have a 4.3 in it from the factory, as the 4.3 didnt come into existance until 1985

your 1983 OMC would have had a 3.8 liter (229 Chevrolet V6) or a 5.0 (305). however based on the pics, that looks to be the original 305.

in 1983, the 229 V6 put out about 155hp, the 305 put out about 205hp and the 350 put out about 250 or 260hp. these are all crank ratings. so assume a 25hp drop to get to prop ratings that are the norm after 1986

the gearing in the stringer drive would be different between the V6 and a V8, so you would have to confirm what gearing you have in the drive

if you want to put a 350 in it, no problem, however you will need to change gears as well as go thru the drive and fix all the things that need fixing, like the vertical 3-piece drive shaft, and the drive most likely needs a set of ball gears. do not go nuts, as the stringer drive wont survive

what ever you do, do not damage the shift cable. that cable will most likely cost more than you have in your boat.... that is the most expensive marine product that exists by weight.

No, OMC bought GM marine motors. nothing like a car motor, more like a truck motor. GM's marine engines come out of the industrial engine plant (Tonowanda NY) and are truck long blocks with marine specific gaskets, a marine water pump, a marine cam and brass core plugs. the pistons, crank, block and heads are all the same as the trucks. automotive cams would have too much overlap and you would have reversion issues.

since you have a stringer drive you are stuck with using a 2-piece RMS block because there are no button couplers for the stringers that will mate up to the 1-piece RMS pattern. you can take the ford adapter, and pay a machine shop about $150 to modify, however that would be it.

did you check the stringers and transom and motor mount boxes in your 1983 boat? you will most likely find them wet and rotting.

hope you love that boat, because you will sink $1500 into the drive alone, and like every other OMC owned boat from the 80's (yes, fourwinns was owned by OMC), the boat most likely needs a full hull restoration)

my suggestion, check to see if you need a transom first before you do anything mechanical to the motor and drive. this involves test drilling (tap test means nothing, its been proven hundreds of times, wet and rotting wood sounds just like dry wood when encapsulated in fiberglass) if you do need a transom, rebuild everything, throw away the OMC stuff and convert the boat over to a Mercruiser or Volvo Penta motor and drive.

 

[Bondo]

Does anyone know the horsepower for this motor?

Ayuh,....... Welcome Aboard,........ Just over 200 hp, with a 2bbl. carb, 'n 'bout 225/ 235 hp with a 4bbl. carb,.....

If ya change the cam, be very careful,...... to much duration, 'n it'll kill the motor, by suckin' water into the cylinders,.....

 

[Jessman93]

you know that OMC has been out of business for decades..... and your stringer drive was obsolete back in 1983 when the boat was new, right?

Thank you Scott for a very detailed response.

I did know that they had gone out of business but didn't know when exactly. I have service records that came with boat and they are for a 4.3l V6 and the stringer drive says V6 on it.
It makes sense that they were probably both added later on. I thought the stringer drive was original. But I do know the engine is older than the boat and installed last year.

If the OMC outdrives are that problematic i may be best to just reassemble the engine and see if I can get some use out of it this season. If it ends up needing a transom or major repairs to the outdrive I would probably just sell it. Its just a $1500 boat that I bought for some fishing/camping trips this year. I should have done a lot more research prior to purchasing. Sounds like I'm probably at a loss here. At least I saved the original parts and I'd have a good running marine 305 to sell. I could pull the performance parts to use on a 350 build I want to do in the winter.

 

[Scott Danforth]

Not much value in pre 1996 motors, less for OMC parts. However we are here to help

 

[southkogs]

Do you know if you have a full mechanical shift? Or hydro-mechanical? IF the boat is in good shape (good hull, deck and stringers) and you have a full mechanical shift that works - rebuilding that engine and making it go wouldn't be awful. You're halfway there, right?

The Stringer is a finicky bugger, but if it's runnin' and you can keep it runnin' - it's not all bad.

I wouldn't get crazy with it, or try to make it any more than what it is. But making a boat go for some fun at the lake wouldn't be too bad.

 

[Scott Danforth]

1983 would have been the last of the mechanical shifts. hydro-mechanical went out in 1981.

stringer drives still suffer from the design flaws
the 3-piece vertical drive shaft that needs to be replaced as the splines either wear out or get rusty and simply disappear.
ball gear seals that tend to eak
ball gears that wear and need replacing every few years
tilt sector clutch packs that leak
tilt motor that is prone to get moisture in it
a very fragile lower shift cable that costs about $750 to replace
and a lower foot that has a very weak pinion