Late 70s 350 SBC rebuild confusion

[salvageyard saviour]

I'm trying to fix-up a late 70s 5.7 GM. Casting numbers show it as "78"

It came out of a 1972 24ft Starfire hardtop with the original OMC electric shift.

My confusion is about the manifolds, carb and distributor.

Question 1: How do I know what parts I have? 72 or 78 ? does it matter?
The intake is stock GM cast and seems to have white paint under the black someone sprayed it with. Carb is a GM QuadraJet with non electric choke. Point distributor.

Question 2: When putting the intake back on, Do I use the seals on the front and back ridges or just beads of sealer?
Do I use the little plates to block the exhaust crossover?
It had none of this when I took it apart.

Question 3: I have a complete "85" with lots of extra parts. GM and Edelbrock manifolds and carbs. Can I use anything from this newer motor such as heads, crank, cam, intake or distributor? Swap entire engine?

The "85" is a crate engine. I have no idea where it's been. I got it with burned main & rod bearings from bad oil pump.
The "78" I assume is a marine app because of the white paint under the black. I got it with a blown head gasket and 2 froze pistons (#1 & #3) from the water in them from the blown gasket.

 

[wrench 3]

#1- There were no changes in the basic engine between '72 and '78.
#2- I prefer to use the seals. A little bit of silicone sealer or permertex two at the ends and make sure that they're still in place before you tighten the bolts.
There should be restricters in the exhaust passages but not plugs. Do you have marine gaskets?
#3- The '85 is the same basic engine again. They didn't change anything until '86. However a lot of the marine parts are different from the automotive. Alternators are ignition protected, fuel pumps have leak protection, (yours should have a glass bole on the side so that you can check for a leaking diaphragm) the carburetors have no external vents, (the quadrajet never had them anyway) and brass frost plugs.They use truck cylinder heads.

 

[salvageyard saviour]

Thanks for replying.
If I don't use the items you mention in #3 can I swap the entire engine? Do I have to switch the electric distributor back to the point style or do I have to keep it as is?

Is the cam anything special or can they interchange?

The wiring is a mess and I'll basically be re-doing it from engine bay to the control console. I believe the old voltage regulator is toast, so changing the charging - ignition system won't break my heart. Can I do it? I have the temp sensors and electric choke available.

I'd rather use the newer motor. I don't trust the cylinder walls of the one with the seized pistons. I honed them and replaced the pistons, rings and rods. Looked good but still don't trust them. There was also a bit of lifter and valve damage from the water (replaced two valves & lapped the others). It sat for almost ten years like that.

 

[wrench 3]

The block and the crank are about the only constant. There are different compression pistons, different compression heads and different cam lift and timing, and this without even mentioning high performance parts. So you can drop an engine in and it will work but it may not give you the same performance. The distributor should definitely be marine. The timing setup is different. They don't use a vacuum advance.
I've never looked up all the specs on the camshafts to get a comparison. If I'm building up an automotive engine for marine use I always switch in the marine camshaft just to be on the safe side. However if there's any rust pitting on the cam lobes, don't use it. The lobes will wear down in no time at all.
Lots of marine engines use electric chokes. So it should be an OK upgrade.
BTW there are electronic conversion kits for most marine point distributors.

 

[kenny nunez]

2Xs on Wrench3. I have seen a few engines that were assembled with the wrong combination and wound up with a real wimpy engine.
Find a real knowledgeable Chevy guy to put you in the right direction. There is a good chance that the 5.7 that was from the electric shift boat was a Mr. Goodwrench replacement engine and had an automotive cam. I have used these engines many times and always swapped the original marine cam into the replacement engine. The performance was as good as the original engine. All the 5.7 Mr. Goodwrench engines were 4 bolt main blocks. If you use the early style intake manifold be sure to have the stainless steel plate under the carburetor to keep the exhaust off of the bottom of the carburetor.

 

[salvageyard saviour]

Thanks for all the great information.
I'm a fairly competent backyard mechanic with daily drivers. 4 cylinder Fords (Mazda) and 60's Hondas have been fun. Although I've had a "69" 120 Merc a long time, V8 Chevy's are kind of new to me and I'm also clueless about the marine differences besides the starter/alternator spark hazard.
I put all new bearings and polished crank in the 85. The look of the old bearings told me it was really "tired". So I think it will be best to use the complete 78 which seemed to look fairly good inside (after repairing the seized pistons). It seems staying with what I know is marine would be best and save the truck engine as a spare.
It's good to know I can upgrade the ignition. When I start putting it back together, I'll make that decision by how much of the old stuff is bad.

Can I use an automotive voltage regulator? The one looks pretty melted. I don't think the auto will mount on the thermostat housing, but will it work?

Also I'll use the old QuadraJet and manifold that I pulled off.
Because it's not an electric choke, should I use the restriction plates in the manifold exhaust cross over?
They weren't there when I took it apart. I'm so confused about these 4 barrels !

I've never seen this boat run, so I'm not sure it was re-assembled correctly before I got it.

 

[kenny nunez]

I always used the restrictors. If you have the original Quadrajet just put a rebuild kit in it, they are good carburetors and I have always had good results repairing them. Just take some time inspecting the intake manifold in the area under the carburetor for any exhaust cracks where exhaust gasses will mix with the intake charge.

 

[Scott Danforth]

I'm trying to fix-up a late 70s 5.7 GM. Casting numbers show it as "78"

It came out of a 1972 24ft Starfire hardtop with the original OMC electric shift.

My confusion is about the manifolds, carb and distributor.

Question 1: How do I know what parts I have? 72 or 78 ? does it matter?
The intake is stock GM cast and seems to have white paint under the black someone sprayed it with. Carb is a GM QuadraJet with non electric choke. Point distributor.

Question 2: When putting the intake back on, Do I use the seals on the front and back ridges or just beads of sealer?
Do I use the little plates to block the exhaust crossover?
It had none of this when I took it apart.

Question 3: I have a complete "85" with lots of extra parts. GM and Edelbrock manifolds and carbs. Can I use anything from this newer motor such as heads, crank, cam, intake or distributor? Swap entire engine?

The "85" is a crate engine. I have no idea where it's been. I got it with burned main & rod bearings from bad oil pump.
The "78" I assume is a marine app because of the white paint under the black. I got it with a blown head gasket and 2 froze pistons (#1 & #3) from the water in them from the blown gasket.

1 - doesnt matter, as there is minimal change between 1972 and 1978
2 - I use a bead of sealer. or you need to dimple the china rail
3 - if the '85 is marine, you can use the stuff. no non-marine electrical or carb stuff on a boat. heads would be ok, however there are much much much better heads out there. however prior to swapping heads, you need to know what you have for current heads, pistons, etc. many of the mid 70's motors were low compression. head volume could be 62cc, 64cc, or 76cc

your 1985 is a core motor. it will need to be rebuilt. if the rods went, then the crank is bad, the cam is bad, the lifters are bad and the debris got circulated thru the motor. so you have a core motor. the crank is cheaper to buy new than to recondition.

on your 78 never assume anything. paint doesnt mean anything. with 2 holes full of water (most likely from the exhaust and not the head gasket), and rusted, you have a core.... unless the rust pitting is deep, then you have an anchor.

since you have to rebuild anyway. I suggest you go with a 1996 and later SBC. then you get a one-piece rear main seal, roller cam, vortec heads and other improvements

 

[wrench 3]

I forgot that the early engines were using an external voltage regulator. It needs to have ignition protection also. So it definitely needs to be a marine unit.

 

[salvageyard saviour]

Thanks Wrench3 and Kenny, I'll do as you say putting the original manifold back on.

The QuadraJet is not in good shape after setting on that engine the last 10+ years. I'll get the re-build kit for it. I've done other Rochester carbs before but these 4B confuse the h--- out me. I think it's magic in there ! -------What is that vacuum break thing? (thought it was the choke at first)-------- and where is the bi-metal thermo at?

I'm tempted to put the Edelbrock 1409 on it that I have. It looks so much simpler, but I've ALWAYS heard good things about the QuadraJet.

Any thoughts on my question about the Voltage regulator?

 

[kenny nunez]

There is supposed to be a plastic vacuum actuatator on the right upper side that cracks the choke open to keep the engine from flooding. The choke thermostat should be bolted to the manifold with a link rod to the choke linkage
If you go to a large book store like Barnes & Noble you will be able to buy a Rochester manual in the Transportation section of the store which is really helpful.
Try to stay with the Quadrajet if possible. You manifold is made for it. I know the Edelbrock/Carter style are good but I really like Holley marine style for their off idle response.

 

[salvageyard saviour]

I'm definately going to stay with the QuadraJet. Been looking for a kit by the casting numbers and know it is a marine application.

I see that now on the linkage to the vacuum thing. It's been a few months since I removed this from the boat but I'm not seeing anything like a choke thermostat in all the parts, but I think I remember a manual pull knob and connection mess to the carb.

I'll look more in the part diagrams for this. Would it be mounted on the flat piece on top of the edge where the exhaust crossover is?

 

[Lou C]

The Quadrajet is a great carb. They are a bit more complex to take apart than the Edelbrock/Carter carbs but once you figure out the tricks of disconnecting the choke linkage on the side learn how to get the metering rods back in and the air horn gasket on correctly it is not bad. The main thing is to get the emulsion tubes clean. It takes a good soaking in carb cleaner and then blow out with high pressure compressed air (the air cans do not cut it, you need a real compressor, a small hot dog style one will work). For info check out Cliff Ruggles' Quadrajet site. He sells rebuild kits and there is a forum to ask questions. I had a Quadrajet on my family's 1975 Olds Delta 88 350 cu in and we never had any trouble with that carb (pre-ethanol days).

 

[wrench 3]

In regards to the voltage regulator. Check my last post #9.

 

[salvageyard saviour]

Yes, thanks for mentioning spark issues with the automotive styles. I found a few on Ebay for marine use. Most are listed as for the V6 GM, but I don't think it matters.

I think I was typing while your post was going up and missed it.
Besides 4 barrels, forums confuse the bleep out of me also.

Am I correct about the choke thermostat mounting on the flat spot of the middle hump on the side of the manifold ?

 

[aimlow]

Are you sure it's a 350??

 

[wrench 3]

Yes, the choke thermostat mounts to the manifold on the starboard side of the carb. It looks something like this one https://www.iboats.com/shop/sierra-choke-thermostat-18-7667.html

 

[salvageyard saviour]

Thanks for that link . An easy place to get one.

Good news! Just got another 72 Electric shift outdrive with both intermediate and housing adapter ($200). Talked him into giving me the exhaust manifolds and the flywheel/coupler for another $40. He only wanted the SBC 350 they were on.

The best news is, got to see how the manifold / QuadraJet stuff went together. I Saw the choke thermostat and I know I never had that. I'll also need the cover and linkage rod.

That Quadrajet website is super informative. It seems that this model is either a Marine 4M or 4MV. Thanks for all the help.

I believe I'll use the manifold restriction plates and I'll get the parts to do the divorced choke on the manifold. The QuadraJet will get a rebuild kit too. thanks again

When the weather gets warmer I'll start repairing the transom and stringer mounts so This thing can get put in

 

[aimlow]

Yes, the choke thermostat mounts to the manifold on the starboard side of the carb. It looks something like this one https://www.iboats.com/shop/sierra-choke-thermostat-18-7667.html

I'll bet ANY small block Chevy engine mounts thar way.

 

[wrench 3]

I'll bet ANY small block Chevy engine mounts thar way.

Only the ones with a Quadrajet.