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Home inspection and clean up of V8 block

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  • Home inspection and clean up of V8 block

    I was looking over the shop manual instructions on checking a block and pistons for wear and deciding between refresh or rebuild. I have read the sections a number of times and perhaps I am overthinking what the shop manual says...

    On page 32 of the v8 section of the Lark shop manual there is an illustration of an upside down piston in the bore with the mechanic using a feeler gauge and a spring scale. if the pull on the feeler gauge does not fall within a given range, clean up the bore and try again or eventually replace the piston

    My questions here are why am I doing this and where does one get the tools to do this test.

    A few pages later on page 35 it looks like a dial indicator on some sort of handle to check taper. I think I can get a dial indicator almost anywhere but what do you do for the handle or should I see about borrowing a micrometer and using a telescoping T gadget.

    I've pulled apart and rebuilt a number of engines over the years and I have usually just let the machine shop do all of this but those were the days when I was single

    Well any advice anyone can give

    Jeff T.

    "I'm getting nowhere as fast as I can"
    The Replacements.
    \"I\'m getting nowhere as fast as I can\"
    The Replacements.

  • #2
    I just went through the same thing myself with a 55' 259. I was in wonder that they used a scale and pulled the piston through the bore. I see the logic and it is a simple test. Except for the fact that you have to disassemble the rod from the piston and that, in itself, could possibly, open up another can of worms with the pinch bolts and how to tighten them. When I was young and dumb, we would put a feeler gauge (.004") down the side of the piston... if it went, we knew that we had .002 a side... or whatever fit ie., .005,.006 etc.. .004" was about the max we would like to see. If there was scuffing or gaulding of a cylinder wall, it was off to the machine shop. The rings would be fit into the cylinder and the butt gap measured... back then there were 1st and 2nd oversize rings to take care of any problem there, usually to be filed to specs found in a Motors Manual. I don't know why Studebaker did not come out and say how many thousanths clearance (min and max) should be in the piston to bore... dragging a piston with a scale is kinda archaic or whatever...and those particular scales are not cheap. New cars have different alloy pistons that cause their coefficient of expansion and contraction to be more compatible with todays fuel and heat. Their clearances are a lot tighter than the old cars... If you looking at an engine and the bores are not gaulded and you have a micrometer and some snap gauges, personally, I would look for no more that .005" clearance...at at least 4 spots in the cylinder. My personal opinion from experience....and no more than .012" clearance in the ring butts. I am sure that somebody out there will have something to say about this method... just keep an open mind.

    1955 President one owner
    Moncks Corner, SC

    Comment


    • #3
      Jeff, it is basically an either/or situation. Either you will decide to take your chances and re-ring with standard rings, or you will step up and pay the money for a rebore, and the necessary oversize pistons and rings. All you really need to know about the wear in the cylinders is this: are they worn so bad that new rings won't last long enough to justify the work?

      I have an inside micrometer set, so I can measure bore taper directly. Taper is what gets you; the rings can't maintain a seal if the bores have too much taper.

      Lacking a micrometer, simply remove the rings from one piston, then put the piston in a bore, and move it near the bottom. Slip one of the compression rings into the bore, and push it down until it is flat against the piston crown. Drop the piston a little lower, and carefully measure the ring gap with a feeler gauge, and record that. Now use the piston to push the ring up into the wear area, say about 1/2" below the ridge, and measure the gap again. It will be larger.

      Subtract the smaller figure from the larger, divide by pi (3.14), and there is your bore taper. Example: I measure a gap of 0.016" at the bottom, and 0.027 at the top. Difference = 0.011; divide by pi, and I get .0035" of taper.

      Ring manufacturers publish tables of acceptable taper limits, either expressed in absolute terms, or in terms of taper per inch of bore diameter. I'm sure you could find this information on their Web sites, now.

      If your bores are worn within that limit, then you can be safe in assuming that a simple re-ring job will be enough to put your engine back in shape, consistent with good trade practice. By that last phrase, I mean that according to the standards of the trade, the re-ring job could be expected to be successful, and to last long enough for an honest mechanic to recommend it, and to stand behind it with a warranty. All the wear specifications you see in the manuals and in parts manufacturers literature are predicated upon that principle: stay within the wear limits, and the job won't come back and bite you.

      If you are doing the job yourself, you have the luxury of choice: how much risk do I assume if I "cheat" a little bit on the wear specs? Depends a lot on how much value you place on your time, and whether you regard overhauling the engine as an adventure or an onerous chore. If you find that engine work is a PITA, and you never want to see the inside of it again, then go ahead, and have it rebored; have the crank ground undersize, and all new bearings, whatever it takes to make the engine "as new", or better. If you enjoy the process, and aren't afraid to tackle it again in a few years, and if money is tight, then go ahead, hone the bores, and throw in a set of standard rings, even if the bores ARE marginal or worse. Install a new set of standard rod bearing shells, and leave the mains alone, barring any signs of obvious damage.

      If you keep the engine scrupulously clean, and don't make any errors in its assembly, the worst possible outcome is that your overhaul simply doesn't last very long, and it goes back to its old bad habits of blowby and oil consumption sooner rather than later. And the couple of hundred bucks you spent on rings and rod bearings is wasted. But you have come away from the whole thing with some knowledge and experience that has value!

      I have a 259 on the bench at home that I plan to use as a "worst-case" test mule. I tore it down in December, and found that it had BAD ridges at the top of the cylinder bores. I had to ream the ridges to pull the pistons out. So I know I can expect to find some serious taper there. The bottom end shows some normal wear, but no obvious damage to the journals. What I propose to do is simply to hone the cylinders well, clean the block thoroughly, and then assemble it using the best (selectively fit) used parts I can find in my collection. I have several sets of pistons, many sets of rings and bearings, etc. I plan to deglaze the wear surface of the used rings with a pass with a fine drum sander on a Dremel tool. I'll selectively
      Gord Richmond, within Weasel range of the Alberta Badlands

      Comment


      • #4
        Gord:
        Please keep us informed on the above experiement. Especially, how the oil consumption turns out on the finished product.

        wagone

        Comment


        • #5
          Jeff, the dial gauge taper tool was basically only to decide if the taper was more than .005. I have one but never use it. Measuring the ring end gap top and bottom asGord mentioned above, is actually more accurate if done properly. A machinist will use an inside micrometer or a snap gauge and outside mike to fit the bore to the pistons if you bore oversize. The old-tech ribbon gauges were used because they were much less expensive than inside and outside micrometers. It was also felt the average garage mechanic wasn't smart enough to read and interpret micrometers. Those were for machinists only. (BTW, the Husky 192-piece tool set sold at WalMart for $99 is way more comprehensive than the typical garage mechanic had back in the day.)

          Gord, We will all follow your po'boy project with great interest. As an aside, the greatest oil consumption on the Stude V8s of my experience has always been through the intake valve guides and seals. I once worked a 100kMi engine with .005" taper, didn't touch the short block, just a valve job, new guides, modern positive valve stem seals, enlarged the oil drain-back holes in the head and this cut the oil consumption back to a quart low at change time.

          thnx, jack vines

          PackardV8
          PackardV8

          Comment


          • #6
            Thanks for the tips on checking my block. If it is nice this weekend I can give the ring gap method a try. I dont mind tearing into the guts of an engine because I find the detail work relaxing.

            With my engine(s) I am pondering a plan of action, my Lark was a daily driver but it has been on blocks for about 11 years : I could get a block assembled so I can least enjoy driving my Lark with a "make due" engine. While I am driving my Lark I could build an engine the right way and have a completely fresh engine that will last for a while.

            I also have a couple ohv sixes but what fun is a six

            Jeff T.

            "I'm getting nowhere as fast as I can"
            The Replacements.
            \"I\'m getting nowhere as fast as I can\"
            The Replacements.

            Comment

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