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Thread: SBC 350 questions

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    Default SBC 350 questions



    So I am working on bringing a 78 SBC350 back to functional life. It is the classic 'was running when pulled' and supposedly only has 12k miles on it after a rebuild - how much of a rebuild, I don't know. I would generally consider any engine I couldn't hear and see running as a rebuild core, and that may be what this one is. But I know the seller as they have helped me out with my cj5 quite a bit, and so I paid a bit more than core with the idea that this should not need a full, machine shop rebuild, but rather, a minimal disassembly with cleaning, near seals and gaskets, and get it back running mostly as is....I also got a rotating engine stand, floor engine stand/cradle, alternator mount, shorty block hugging headers, and probably a useless late generation Q-jet carb saddled with emissions and EGR stuff....so, maybe I basically paid core price....


    So I pulled the valve covers, and it was a bit sludgy, and more concerning was having trouble getting oil to flow up the pushrods and onto the rockers....But in theory, that should be taken care of with some cleaning etc.
    Next up - pulled the intake and heads, and found a lot of hard carbon build-up on the combustion side of the valves:


    That lead to enough concern to pull the valves (disassembly of the heads was not in the original plan, but getting new valve seals can happen now), and finding more carbon build up. This stuff is not so easy to clean off, and not sure how 'aggressive' I can be with mechanical cleaning, abrasives, etc?


    For those of you familiar with old SBCs - how salvageable is this with just some cleaning and putting back together? Or am I beginning to see a valve job from a machine shop?
    Still have to drop the pan and take a look at the bottom end.
    ___________
    James Orofino
    1970 CJ5
    1958 Willys Wagon
    2010 Tacoma TRD

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    Default Re: SBC 350 questions



    Good margin on the valves, and they sit proud in the chamber. Clean it up and continue inspection.
    ___________
    The Lost Boys motto: We don't know where we're going, but we'll be there for awhile. :)

  3. The Following Member Says Thanks to Hypoid For This Post:

    FINOCJ (1 Week Ago)

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    Default Re: SBC 350 questions



    Well, I clean up #1 valves a bit to see how it would look. My biggest concern is some pitting on the valve seats and some wear where the valve seats. I don't have any experience with what is 'catastrophic' and what is not ideal, but for this non-performance usage, might be acceptable for use....It was suggested I should lap the valves....


    Here is the intake valve cleaned up about as much as I can do with the tools I have....good enough to work I hope?
    ___________
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    1970 CJ5
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    Default Re: SBC 350 questions



    Making some progress - mostly just doing a lot of cleaning of all the valve train parts....Here was the worst valve in terms of carbon build-up....I think this was #5...


    But a lot of cleaning and lapping - I like how the intake valves look, and I think I got the seats looking better. The exhaust seats were better than the intake seats to start, and look pretty good now, but the intake valves are still rough even after a lot of compound work. But at some point, seemed it was as good as it was going to get and decided to test them....hard to see it, but the closest combustion chamber (#2) here is full of water....its not perfectly water tight, but its only a couple seepy 'drips' over 10 min or so...I think (hope) its good enough...still have the driver bank to lap, but all the cleaning and prep work is done....
    ___________
    James Orofino
    1970 CJ5
    1958 Willys Wagon
    2010 Tacoma TRD

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    Default Re: SBC 350 questions



    The carbon on that valve is crazy thick! I've never seen anything that bad.

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    Default Re: SBC 350 questions



    That donít look like 12k worth of carbon. That much looks like it need valve guide service.
    rhat will include a full valve job which will include a full head rebuild.
    or just find a good set of aluminum heads.
    ___________
    In a never ending search for the proper mix of dirt & rock !

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    Default Re: SBC 350 questions



    The StRanger previously posted:
    "That much looks like it need valve guide service."

    My check of the valve guides clearances suggest they are okay....one suggestion is that the valves were never properly lapped during the previous work. The really bad carbon build up pictured was also immediately adjacent (and connected) to the passageways associated with the EGR valve plumbing....Some of the EGR stuff in the intake is also completely stuffed with carbon build-up - this is outside of my knowledge, but guessing something with the EGR was causing issues? My hope is going with the older style (no EGR) q-jet and intake that is on the 283 will help alleviate the issue?

    The StRanger previously posted:
    "rhat will include a full valve job which will include a full head rebuild.
    or just find a good set of aluminum heads."

    Not in the budget for this project...The sad part is you can buy an all new crate engine for less than you can have all the machine work done for a rebuild....I am channeling all my redneck heritage and slapping this thing together while drinking Budweiser...SBCs are supposedly a forgiving engine and will hopefully run ok at 70-80% function. I don't need the power, just need it to run like a used engine with 100k, and not puke oil everywhere. With a little luck, maybe it will only consume a quart of oil every 3k miles - although even if its a quart every 1k miles, I could live with that for now. The current 283 is consuming a quart every 250-300 miles.
    ___________
    James Orofino
    1970 CJ5
    1958 Willys Wagon
    2010 Tacoma TRD

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    Default Re: SBC 350 questions



    The StRanger previously posted:
    "That donít look like 12k worth of carbon."

    that's what I was thinking.

    J.
    ___________
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    Default Re: SBC 350 questions



    I have seen carbon like that before on a Mercury V6 outboard many years ago. The guy I got it from tried to get more performance out of it by putting some very wrong jets in the carbs and raising the floats so high that it was dumping more fuel than it was burning, and he got rid of the oil pump and ran thick premix. The whole thing was black inside but worked well after two rounds of seafoam. I mention it because of the weird Qjet it came with, the emissions stuff is likely the nightmare stuff from the 80s and could lead to a lot of bad combustion. You might have a decent engine and a crappy carb.

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    Default Re: SBC 350 questions



    FINOCJ previously posted:
    "My check of the valve guides clearances suggest they are okay....one suggestion is that the valves were never properly lapped during the previous work. The really bad carbon build up pictured was also immediately adjacent (and connected) to the passageways associated with the EGR valve plumbing....Some of the EGR stuff in the intake is also completely stuffed with carbon build-up - this is outside of my knowledge, but guessing something with the EGR was causing issues? My hope is going with the older style (no EGR) q-jet and intake that is on the 283 will help alleviate the issue?


    Not in the budget for this project...The sad part is you can buy an all new crate engine for less than you can have all the machine work done for a rebuild....I am channeling all my redneck heritage and slapping this thing together while drinking Budweiser...SBCs are supposedly a forgiving engine and will hopefully run ok at 70-80% function. I don't need the power, just need it to run like a used engine with 100k, and not puke oil everywhere. With a little luck, maybe it will only consume a quart of oil every 3k miles - although even if its a quart every 1k miles, I could live with that for now. The current 283 is consuming a quart every 250-300 miles."

    That works....
    my last rebuild was a can of krylon
    ___________
    In a never ending search for the proper mix of dirt & rock !

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