replacing a 305 with a 350 engine

Discussion in 'Gas Engines' started by mrostkow, Dec 5, 2017 at 6:51 AM.

  1. mrostkow
    Joined: Dec 4, 2017
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    mrostkow Junior Member

    I have a 1984 Searay 210 stern drive with a cracked block (305 2v engine). I am planning on replacing it with a 1977 Chevy C10 truck engine. It is a 350 4v with 55K . Can I do this without any problems?
     
  2. PAR
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    PAR Yacht Designer/Builder

    Both engines are from the same family (first gen SBC), so yep, it's an easy swap, though some things will need to be transferred and adjusted, like brackets on the front of the engine, etc. Also find out what drive you have (likely an Alpha), as the Alpha 1 drive can't handle much more than 220 HP and a 350 can easily exceed this. This would be as simple as a cam change from the 305, if it's still good.
     
  3. gonzo
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    gonzo Senior Member

    Does the truck engine have a mechanical fuel pump?
     
  4. Angélique
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    Angélique aka Angel (only by name)

    Here's a thread about this swap for cars, maybe some of the info is useful for boats too, except for the boat specific things of course, which PAR mentioned here.
     
    Last edited: Dec 5, 2017 at 4:08 PM
  5. gonzo
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    gonzo Senior Member

    Luckily, everything from the 305 will fit the 350.
     
  6. Angélique
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    Angélique aka Angel (only by name)

    BTW, 55K sounds a bit low to me for a 1977 truck, that is if 55K means 55,000 miles, which would mean the engine is just broken-in, and that seems doubtful to me at that age, or the engine must have been replaced. If so, is there any evidence about this, and what does the engine's appearance tell you . . . ?
     
  7. PAR
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    PAR Yacht Designer/Builder

    Depends on which 350 Gonzo, but yes you're correct everything should fit, if their both first gens (2 piece mains, standard coolant flow, without vortec or swirl-port TBI heads, etc.). You can still use these heads, but you'll have to go to a different intake. On a 1977 truck, the engine is a first gen (2 piece main, standard coolant flow) and with 55k miles on it, I'd suspect it's 155k as most speedo's back then weren't 7 digit back then. If it is 150k, do a compression check and pull a valve cover to inspect the condition of the engine, as with this mileage on a first gen, it's likely in need of a full rebuild, at the very least a top end job, if the compression is good.
     
  8. mrostkow
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    mrostkow Junior Member

    How do I identify outdrive? Alpha I, III, etc...the paint and decals are all faded and worn if that is where it is labeled...[​IMG]
     
  9. mrostkow
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    mrostkow Junior Member

    Engine comes from the salvage yard owner who is a friend of mine, It is original and compression check ranges from 175 - 185 all around...
     
  10. Barry
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    Barry Senior Member

    A marine engine has different components than an automotive engine and they mainly revolve around making the engine compartment safe if you have a small fuel leak that can create an environment for and explosion or fire.

    1) The 350 will more than likely have a mechanical fuel pump. Most marine mechanical fuel pumps will be of a dual diaphragm configuration so that if one of the diaphragms break the excess will flow back into the carburetor throat.
    2) The carb will have the float bowls vented back to the carb as well as compared to some of the old Holley's etc that would vent the bowl to atmosphere
    3) The carb needs to have a flame arrestor on it to ensure that any backfire will not ignite fumes out side of the arrestor
    4) A marine starter will have an o-ring that seals the starter armature to ensure that fuel vapor cannot connect with the spark at the brushes
    5) The alternator will also have an extra o-ring and flame arrestor screen over the openings for the same reason.
    6) The distributor also needs to be o-ringed (?) for the same reason. No sparks available to the engine compartment
    7) I doubt that you would have an open contact voltage regulator on the new 350, pretty sure this was much older

    You need to check and see if the 305 had a return fuel line from the fuel pump back to the fuel tank.
    My recollection from 33 years ago about this is a little sporadic. In the late 70's and early 80's our engines up to but not including the 454 did not have a return fuel line but I believe that mid 80's all marine engines had the return unless
    it was modified at the factory to omit this feature. So the 1977 305 should not have the return line or its line back to the fuel tank. The 350 might have this return line feature.

    As we mainly purchased marinized engines from people who did this for a living, Berkley, Redline, Kodiak we never had an issue but when we had a custom engine built, these items above had to be dealt with to comply with
    ABYC standards

    You do not have to worry about the legs ability to handle the increased horsepower UNLESS you change the prop. The current prop will only absorb so much horsepower for a given RPM. If you change the prop one that can absorb more hp for the same rpm then you can be loading the leg up more. . But if you push the rpm (with the same prop) past what ever the max rpm is now on the 305, then more hp will be generated, more contact pressure on the gears, meaning higher temperature in the legs oil etc.
     
    Last edited: Dec 6, 2017 at 12:04 PM
    Angélique likes this.
  11. mrostkow
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    mrostkow Junior Member

    What do you mean by LEGS?
     
  12. Barry
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    Barry Senior Member

    Sorry the stern drive portion is often referred to as the leg, I should have been more succinct and said out drive

    I mentioned that there might be an external voltage regulator to check. While I seriously doubt that by 1977 that they used such a regulator, you can easily check.
     
    Last edited: Dec 6, 2017 at 12:01 PM
  13. mrostkow
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    mrostkow Junior Member

    How do I know what stern drive (outdrive) this is?? see pic below...
     

    Attached Files:

  14. Angélique
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    Angélique aka Angel (only by name)

    Like I said, 55K on an original 1977 truck engine seems doubtful to me at that age. But it's not impossible, so you're lucky if you have found one from a reliable source.
     
    Last edited: Dec 6, 2017 at 1:16 PM

  15. Angélique
    Joined: Feb 2009
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    Angélique aka Angel (only by name)

    From: Nautica Marine ServicesEngine Main Page

    SERIAL NUMBER LOCATION

    [​IMG]

    ‘‘ The Engine Serial number is located near the starter at the Flywheel housing, the Rocker Arm or Flame Arrestor Cover.

    The Sterndrive Serial number is located on the Upper Driveshaft housing Starboard side or on the Back of the housing.

    The Transom Serial number is located on the Upper part of the Transom Assembly. ’’

    Where it says ‘‘Sterndrive’’ in red in the drawing, that's often called ‘‘the leg’’, meaning the part going down.

    P.S. - - Where it in the above posts said ‘‘legs’’, it was meant to say ‘‘leg's’’.
     
    Last edited: Dec 8, 2017 at 5:28 PM
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