Chevy 350

Discussion in 'Gas Engines' started by mikealston2428, Jun 17, 2013.

  1. mikealston2428
    Joined: Jul 2011
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    mikealston2428 Senior Member

    Hi all,
    I am about to reinstall the intake manifold on my 350 chev.
    The gasket kit I have has 4 stainless steel inserts for the manifold.
    We're do these go ?
    There is already a stainless plate covering the centre hole on each side if the manifold.
    Not sure if I need to put the 4 that came with the kit, they all have a round hole in them were as the one on in side that us already in place in solid with no hole completely blocking the port.
    Any help would be great.
    Cheers mike
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I'll assume this the exhaust crossover port, located in the center of the manifold flanges. This crossover is used to warm the plenum in cold weather start up situations. If you live in a warm climate and/or have a mild to high performance engine, most block them off, which is likely how the gasket set came (blocked). The metal inserts are for those that wan to open the ports.

    [​IMG]

    This is typically how they come and you can see the exhaust crossover ports are blocked.

    [​IMG]

    Sometimes they're like this, but again the ports are blocked.

    You can drill both styles or use the inserts provided with some sets. Personally, I always keep them blocked, but in Florida, I don't have to worry about cold start situations.

    Were your previous gaskets ported? What is the application for this small block?
     
  3. mikealston2428
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    mikealston2428 Senior Member

    Wow thanks that answer every thing
    Attached is pic of what I have
    The manifold has the middle hole cover with a plate glued over the hole so I think I can throw the inserts away
     
  4. PAR
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    PAR Yacht Designer/Builder

    You picture didn't come through, but yep, you can toss the inserts. Most aftermarket performance manifolds come with the crossover blocked off and you have to drill them out, if you want the heat. On a custom manifold I made some years back, I didn't install any crossover tube and just had the flange cover the hole in the heads. It looked great with the big gap under the plenum and I used to toss ice on the windage tray under it for 1/4 mile runs, to cool the intake air mass.
     
  5. mikealston2428
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    mikealston2428 Senior Member

    Thanks mate'
    Another question
    Before I put the roller rocker arms back on should I replace the valve steam seals ?
    I'm not real sure if I need to do this or not ?
     

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  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It depends on how many hours on the engine and it's general condition. Personally, I'd toss some on, just because it's easy and you can measure spring heights while you're there, to insure everything's okay.
     
  7. Dave T
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    Dave T Senior Member

    Whether to have the exhaust crossover blocked or not can depend on what type of choke the carburetor has, that is if it's not fuel injected. A lot of older 350's had a choke that was controlled by a coiled bi-metal spring that set in a well cast in the intake that opened the choke as it heated and in this case you would not want the crossover blocked or the choke wont open soon enough. If the choke is electrically heated or manual then I'd leave it blocked.

    Dave T :)
     
  8. Dave T
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    Dave T Senior Member

    If your about to install the intake manifold then I assume you must have already installed the cylinder heads. If so it's a little late to think about replacing the valve seals. It can be done by applying air pressure through the spark plug holes to hold the valves shut but it's not easy and it would be quicker to remove the heads. Were the valves and seats re ground and were the valves and valve guides checked for wear ?

    Dave T :)
     
  9. Mark Cat
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    Mark Cat Senior Member

    For upper engine rebuild, I pull the heads for inspection. If you need to change the valve seals, just pull the heads and do it.

    The new intake gasket ports (size, outline) should match the head and intake ports. I usually glue/seal my gaskets in place on the heads so they don't move around. Products like Edelbrock Gasgacinch Gasket Sealer.

    For older USA GM, Ford small blocks, I use high temp gasket making RTV on the front and back of the block (in place of the small thin pieces) overlap a little onto the head intake gasket and torque the intake down in three steps (let it skin then wait 5 minutes between steps). This compresses the RTV in an even way. Make sure all the surfaces are clean. This is a common way to seal the front and back of the intake/block for older USA V8 engines. Some engine builders will put a small bead of RTV on the head intake gasket, and at times even the intake.

    All for now,

    Mark Cat
     
  10. Dave T
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    Dave T Senior Member

    I agree with Mark I never used the rubber intake end seals I used to use RTV silicone. the rubber seals tend to squeeze out from under the intake when you torque it down especially if the heads have been planed and then you have an oil leak. We used to center punch a line of punch marks about a half an inch apart along the top of the engine block and the underside of the intake where the end seals go to make sure the RTV had something more to hold it in place. Later I used whats called Great Stuff which is a real good gasket making stuff available at most parts stores.

    Dave T :)
     
  11. mikealston2428
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    mikealston2428 Senior Member

    Hi all,
    Ok now I am abit confused about blocking the crossover intake.
    My choke is the spring type that opens as the engine warms up.
    These ports were blokes and the engine ran nice.
    So should I bloke or leave open ?
    A funny story how I found out about the spring choke, I took the boat out one day and it was blowing black soot out the exhaust and wouldn't run, found out the clip that holds the spring had fallen off the the choke stayed closed was a real sim
     
  12. Dave T
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    Dave T Senior Member

    There were several different types of spring operated chokes that were used some like I described had the spring in a well in the intake manifold and if so the exhaust crossover should be open this depends on the design of the intake. Other spring operated chokes had the spring in a housing mounted on the carburetor it self and had a tube that ran down to the exhaust manifold and then had a vacuum line that connected to the back of the carburetor or intake manifold to pull the hot air through the spring housing. There were also ones that were electrically heated and just had wires that connected to the spring housing. If you could post a picture of the carburetor and intake manifold showing the choke mechanism it would help. Do you have the old intake manifold gaskets. We're assuming this motor is being used in a boat that will only be used during warm weather. Is it a stock manifold or an aftermarket performance manifold is it 2 barrel or 4 barrel ?

    Dave T:)
     
  13. mikealston2428
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    mikealston2428 Senior Member

    Hi Dave I will take a few pics and post them of the choke spring system I have and she what you think what I need to do with the crossover
    Am I correct by understanding your advise on not using the rubber seals either send of the intake manifold but use rtv instead and not use the seals at all ?
    Thanks mike
     
  14. powerabout
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    powerabout Senior Member

    yes you can leave out the rubber strips,
    late builds from GM did this but be sure you use the correct sealant
    GM sells it if you cant get an equivalent
     

  15. Dave T
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    Dave T Senior Member

    Yes I don't use the rubber end seal gaskets I've used both high temp {RTV silicone gasket maker} made by permatex it's in a red tube and available at most hardware stores and at places like Wal Mart . What I prefer though is a product called {Right Stuff} gasket maker also made by pematex but it's only available at auto parts stores and is much more expensive and comes in a 5 ounce cartridge that goes in a caulking gun. It maybe available in smaller tubes now it's been quite a few years since I've bought any. I've never had any problems using either product just make sure the surfaces are real clean and you put down a good bead that will fill the gap between the block and the intake and let it set for at least 24 hours before starting the engine.

    Dave T :)
     
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