Building A Mercruiser 350 Few Questions.

[jws123]

I am trying to build a 350 for my speed boat the old engine was 100% trash and is gone nothing was salvageble except some small parts. The motor had salt water in it sat for years it was a 1985 merc. I have a auotomotive GM shortblock 1973 first gen? block #3970014 bored 30 over I already installed brass freezeout plugs.

My question is for the camshaft I currently have a flat tappet cam from a mercruiser 305 would that work in a 350? or is it to diffrent I am getting conflicting awnsers if they are the same or if it would be less HP?. I also have a roller cam from a newer mercruiser 350 but from what I gather I would have to use retrofit lifters. The cylinder heads I plan to use are from the newer engine that had a roller cam if that makes any diffrence? Its the only good set of rebuilt heads I have laying around currently.

 

[Scott06]

I am trying to build a 350 for my speed boat the old engine was 100% trash and is gone nothing was salvageble except some small parts. The motor had salt water in it sat for years it was a 1985 merc. I have a auotomotive GM shortblock 1973 first gen? block #3970014 bored 30 over I already installed brass freezeout plugs.

My question is for the camshaft I currently have a flat tappet cam from a mercruiser 305 would that work in a 350? or is it to diffrent I am getting conflicting awnsers if they are the same or if it would be less HP?. I also have a roller cam from a newer mercruiser 350 but from what I gather I would have to use retrofit lifters. The cylinder heads I plan to use are from the newer engine that had a roller cam if that makes any diffrence? Its the only good set of rebuilt heads I have laying around currently.

If the 305 flat tappet cam is a marine 305 cam and is from the pre 1985 vintage like your block should be ok.

The big differences from a automotive 350 are cam, freeze plugs, head gaskets (marine wont corrode in raw water), block circulation pump, and electrical components.

I would recommend using newer vortec heads for the HP gain . Heads and more specifically the valve springs and retainer to seal clearance have to be matched to the cam. The spring pressures and lift will dictate what machining needs to be done to the spring pocket, valve guides/seals/ and retainer clearance. You can easily measure installed height and retainer clearance for the cam you are using.

What heads are you thinking.

@Scott Danforth will likely have some thoughts, like build a stroker....

 

[Scott Danforth]

What heads are you thinking.

@Scott Danforth will likely have some thoughts, like build a stroker....

second the head question

if the PO didnt have a short block, building a stroker is only a few $ more than a stocker

I am trying to build a 350 for my speed boat the old engine was 100% trash and is gone nothing was salvageble except some small parts. The motor had salt water in it sat for years it was a 1985 merc. I have a auotomotive GM shortblock 1973 first gen? block #3970014 bored 30 over I already installed brass freezeout plugs.

My question is for the camshaft I currently have a flat tappet cam from a mercruiser 305 would that work in a 350? or is it to diffrent I am getting conflicting awnsers if they are the same or if it would be less HP?. I also have a roller cam from a newer mercruiser 350 but from what I gather I would have to use retrofit lifters. The cylinder heads I plan to use are from the newer engine that had a roller cam if that makes any diffrence? Its the only good set of rebuilt heads I have laying around currently.

a few of the accessory holes may have changed between 1985 and 1973.

Need to know specifically what heads you plan on running

you will need marine head gaskets, and your automotive water pump will need to be replaced with a marine water pump.

hopefully there was additional clearance on the bores as boat motors are generally built sloppy with an additional .0010 - 0.0015 of clearance to allow the pistons to expand more than the block will being raw water cooled.

cam from 305 will work in a 350.

 

[jws123]

Yes the 305 cam is marine I will get the numbers off of the heads i plan to use they are non vortec I am building this thing on a budjet. It is not a high dollar boat but need it to run decent thanks for the input this far.

 

[Scott Danforth]

its a boat, dont cut corners

 

[jws123]

This is the numbers on the cylinder heads Only set of good heads I have they where low hour from my old boat. Would i be fine using these with the 305 cam/push rods or do I need to just buy new 350 rods.?

 

[jws123]

its a boat, dont cut corners

Not trying to cut corners to bad just within reason I paid $2000 for the boat plan to spend another 2k getting it Decent. I just pumped the fuel tank and re sealed the outdrive drive changed bellows and bearing so thats good to go now. It needs some other maintainance stuff done besides the motor the boat sat for about 7 years its a 19ft glastron carlson.

 

[alldodge]

Thinking the last digit is 7
14096217...55-86...350..........Crate motor, 285hp/300hp, 64cc chambers,
72' or 90' center intake manifold bolt angles

 

[jws123]

Thinking the last digit is 7
14096217...55-86...350..........Crate motor, 285hp/300hp, 64cc chambers,
72' or 90' center intake manifold bolt angles

Yes correct 14096217

 

[kenny nunez]

You need to check the flywheel bolt pattern between the original and the 73 model engine. You may need another flywheel and a new drive coupler.
Quite often a hard freeze would catch the local boat owners off guard, resulting in a lot of broken blocks and manifolds.
I did the 305 to 350 swap many times using the GM “Target master & Mr. Goodwrench engines. I always had good results by re using the original cam and keeping the lifters in order to their respective cam lobes.
If the 305 had a Quadrajet it will work on the new engine without touching it.

 

[jws123]

You need to check the flywheel bolt pattern between the original and the 73 model engine. You may need another flywheel and a new drive coupler.
Quite often a hard freeze would catch the local boat owners off guard, resulting in a lot of broken blocks and manifolds.
I did the 305 to 350 swap many times using the GM “Target master & Mr. Goodwrench engines. I always had good results by re using the original cam and keeping the lifters in order to their respective cam lobes.
If the 305 had a Quadrajet it will work on the new engine without touching it.

Thanks for the info the carb it came with was a quadrajet but its shot have to find aother one or a diffrent carb setup. Basically the boat sat witht the engine uncovered for a long time.

 

[kenny nunez]

Cliff’s Quadrajet rebuilding service and there are others that can restore the carburetor and jet it for the 350. You can buy an Edelbrock from Summit or Jegs also. The main thing is that it is a Marine carburetor.

 

[Bondo]

Ayuh,..... Another, probably minor issue can be that the dipstick switched sides of the motor, in I believe, 1979,.....
If ya got an oil pan mounted dipstick, no problem, if the pan will fit,.....

 

[jws123]

Thanks for all the info been very helpful thus far will post a vid if this thing actually runs ahaha. All the new parts come in this week then will be slapping it all together .

 

[jws123]

Ayuh,..... Another, probably minor issue can be that the dipstick switched sides of the motor, in I believe, 1979,.....
If ya got an oil pan mounted dipstick, no problem, if the pan will fit,.....

I have another pan off a older 350 that bolted up but I did not pay attention to the dip stick as I have not installed it yet hopefully it works.

 

[jws123]

Yep the dipstick wont work going to have to figure something else out.

 

[Scott Danforth]

Yep the dipstick wont work going to have to figure something else out.

OMC dipstick and adapter. it screws into bottom pan drain

 

[jws123]

OMC dipstick and adapter. it screws into bottom pan drain

I will look it up thanks.

 

[kenny nunez]

One other option is the remote oil drain kit. It has a hose that will go out of the bilge drain. The fitting has 2 female 1/4 pipe threads that screws into the pan drain. The one side not used can be the dipstick side. I used to make up the tube with 3/8” steel tubing and just form it where you want it to mount. Then put 4 quarts of oil in the pan and start clipping off the excess tubing until the dipstick reads correctly. Then add the last quart.

 

[jws123]

Ran into a slight issue while putting it together today. The crank bolts from my old 350/305 dont fit this motor.. to small in diameter. What other size crank bolts did they use? motors technically a 1973 ish block number#3970014