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  1. #1
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    Default Understanding Core Shift in the 455 block- why sonic checking is so important.

    Hi Folks

    Let's talk about the 455 factory block, and dis-spell some myths about the various 455 blocks produced by the factory from 1970-1976.

    This one is a bit lengthy, so pop up a bag of corn and grab a beverage..

    It comes up often in various posts, so I thought I would take some time on this Saturday to illustrate for you all that there is a false "know fact" circulating in our circles.. it goes like this:

    "That's a 75/76 block, so it's the one to use."

    All Buick engine blocks are prone to core shift. What is core shift you ask?

    Core shift occurs at the foundry when the blocks are being cast. The internal core will shift from the external core during casting, resulting in an “off center” block. The biggest problem with this is an un-uniform cylinder bore thickness. It is of utmost concern when using large overbores or very high horsepower.

    The easiest way to check for core shift is to look at the cam and lifter bores. If they are in the center of the cast bulkhead in the block, the core did not shift too much, if they are way off center the core did shift. A block with a moderate amount of core shift will still be okay for mild performance use.

    But that's only the first "visual test" of an engine block.

    To illustrate this, I am going to show the pictures and sonic check of a '75 "Blue block" as they are typically called, that was sent to me some time ago, by a board member, for one of my Level 1A buildups.

    This block is a great example of the exception to the rule, and why every Buick 455 should be sonic checked before rebuilding.

    Before we get too deep into the pictures and sonic check of this block, let's take a minute to talk about what a sonic check is, and how to read a sonic check sheet.

    What is a sonic tester?- the sonic tester sends out a sound wave and then calculates the thickness of the metal by measuring the time for the reflected wave to return to the sensor.


    Sonic check worksheets are the paperwork for the "blueprint" of the cylinder wall thickness of the block. 12 check points are done in each cylinder. The operator then notes the cylinder wall thickness as he tests each point, on the sonic test sheet. The sheet is set up to "look down" on the top of the block. You will understand that when you see the picture below.

    The 4 axis for checking a cylinder are:

    In line with the piston pin (front and rear of the cylinder)
    The major thrust side
    The minor thrust side

    3 check points are done at each of the 4 'sides' of the cylinder. One under the deck surface, one in the middle, and one near the bottom, make up the 12 check points for each cylinder.

    Let's talk terminology for a minute:

    Major Thrust Side

    The major thrust side of a clockwise rotating V-8 engine is the LH side of each cylinder bank, as you face the front of the block. So for the Driver side bank (1,3,5,7) the major thrust side is the inside of the cylinder, or the side facing the lifter valley. On the Passenger side of the block (2,4,6,8) it's the outside of the cylinder block.

    This is the side that sees the highest loads, and should have the thickest cylinder walls.

    Minor Thrust side

    The side of the cylinder wall opposite the major thrust side.

    Pin Sides-

    The front and rear of the cylinder, in line with the piston pin. These will typically be the thinnest parts of the cylinder, especially between the cylinders. The 455 block is not "Siamese" block, meaning that it has water all around the cylinders. A 'Siamese" block has casting from top to bottom,in between the cylinders.

    While the pin sides of the cylinder see little thrust force on them, they are important in keeping the cylinder round, as the piston travels thru it's major and minor thrusts. And a cylinder that is honed round, and stays round in use, is one of the biggest contributing factors to overall power production.

    So.. now your up to speed.. and what I am going to say from here on out will make a lot more sense.

    Let's talk about this specific block.

    It is a 1975 Buick 455 block, identified by it's VIN number- 45X149030

    It decodes as

    4- Buick Motor Division
    5- Last digit of the year of production for the vehicle is engine went in. In this case 1975
    X- Final assembly plant of the vehicle
    The last six are the sequential vehicle number, and they match the dash VIN

    It's often said, and there is some truth to this, that by looking at the holes in the casting for the lifters, you can see how much core shift the block has.. if they are centered in the casting, then the block has little core shift..

    So with this in mind, take a look at this block's lifter bores.



    Looks good..

    Here's a close up of number 4,6,8 lifter bores:



    From these pictures, this block looks like a great candidate for a high performance buildup. Both my customer and I thought so, from initial inspection.

    Now I said that there was some truth to looking at the lifter bores.. and there is, you will see evidence of core shift here. If they are really off center, more than likely the cylinder thickness will correspond to the lifter bore positioning..

    But not always.. and that's the point of this diatribe.

    Here is the sonic check worksheet for this block.



    Two problems were uncovered, and I was surprised to see them.

    1. Look at the major thrust side, vs the minor. The block is shifted exactly the wrong way, with the major being thinner than the minor. For high performance blocks, I always look for the block to have at least .200 cylinder wall thickness on the major thrust sides of the block. I prefer that number to be closer to .250. And the higher the performance required from the block, the more picky I become with these numbers.

    2. Look at the rear of the pin side, on number 2, 4 and 6 cylinders. Remember, this is before boring.. this block was scheduled to be bored to 4.350 (+.038) so we would be taking an additional .019 thousands off each side.. that would leave us with a very unacceptable .055 thick cylinder wall, at the thinnest point on number 6.

    Needless to say, this block was set aside, and is holding the concrete floor down in the shop, as I type this.

    Now, here is the picture of the actual block used to build this customer's motor, in the assembly room. You will note that the lifter bores look about the same as the first block.


    But look at the sonic check worksheet..



    This block is shifted, (as they virtually all are) but the major thrust sides are considerably thicker than the first block, and there is no point under .100
    before boring.

    This block went on to have a very streetable build, at over 550 HP.


    So as you see, year of the block, as well as visual inspection does not always tell the whole story, and it's well worth the extra $75 or so to sonic check every 455, before you invest a lot of money in it.

    And building a high HP or stroker motor, makes this even more important.

    In later posts, we will discuss grouting the water passages for cylinder stability, the pros and cons.



    JW
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  2. #2
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    :tu:
    MIKE

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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    very nice.

  4. #4
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Jim,

    Excellent information presented in a very well written and educational manner. I would suggest you submit this and other tech articles for publication in some of the leading peformance magazines and websites. You have a talent in your communication style that is on par with your technical knowledge, a rare and refreshing combo.

    Please keep sharing and educating the masses. I know I need all the help I can get!

    Thanks,

    Rob
    Rob Sarlan
    -------------------------------------
    1970 GSX #425 * QQ * 4 Speed * Authentic Iron Head Stage 2 Engine
    1965 Corvette Roadster * L79 * 4 Speed
    2004 Honda S2000
    -------------------------------------

  5. #5
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by TORQUED455 View Post
    Thanks for the informative post!

    If the walls are too thin, would this possibly lead to engine overheating or a catastrophic failure in a high HP application? Is a sonic tester a common machine shop tool?
    Too thin a cylinder wall has a number of potential results.

    1. Poor ring seal- the cylinder actually distorts in use.
    2. Inability to re-hone the cylinder easily during a motor freshen up.. so instead a just a light hone during a race motor freshen, you have have to take .002 or so out of it.. and either run bigger clearances, or in some cases, order a new set of custom pistons. A good Buick bore will hone up nicely with just a few swipes of the hone, with an overall size increase of just .0003-.0005. This is important for race motors that come apart often for freshening up. A hip engine builder will run the pistons down to the very minimum allowed clearance on the first build, to allow room for later freshen hones. But if the block takes .002 or more to get it straight again, then that doesn't work well. This is mostly a concern for a race engine, but should be considered for all performance buildups.
    3. Cracking- This is the worst, and potentially most severe side affect. If you get lucky, it will just crack and leak water, and start blowing smoke.. or it could lead to total engine failure.

    The overheating issue is regard to cylinder wall thickness has been overblown in my opinion. Yes, a thinner wall will be a less efficient heat sink, but in reality, we fill these blocks in some applications to 1" below the decks, or sometimes all the way up, which effectively makes the cylinder wall transfer very little heat to the cooling system.. I have built quite a few of these motors for street and strip, and none have had a water temp problem.

    I believe that most likely, this urban lore about "too thin a cylinder walls and overheating" came from guys who built a high performance motor, which, as we know is actually a heat pump, and then installed it in a car that had a marginal cooling system. Maybe it just got by removing the heat from a 350 HP motor, but could not handle the heat from another 100 or so HP. This would account for the "I just built the engine, and now it overheats, and it didn't before, must be too thin cylinder walls" syndrome.

    And yes, a sonic checker is standard equipment in any full service machine shop.

    JW
    Owner/operator

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    Jim Weise
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  6. #6
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    thanks for the informative read JW - Much Appreciated

    ... nice way to spend your day off
    Alan W

    BPG # 1048 - Charter Member
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    Quote Originally Posted by 442w30 View Post
    ... They have awkward proportions from certain angles, and they look dumpy compared to their GM brethren
    ....'68 SportWagon400 "Sportn'Wood"..............'69 GS400 Convert "BigRed"..........

  7. #7
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    1. Thanks for the post, the photos, and notes are very informative.

    2. I really like your new signature line.

  8. #8
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    question, hopefully i didn't miss this in my reading, what thickness do you like to see on the pin side for a 500 hp build?

  9. #9
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    IN any build, you would like to see as much as possible, but a benchmark for a high perf build for me is .140+ on the pin sides.

    But the reality is that you will look a long time for that block.. so often times you have to settle for one that has maybe just one or two holes with around .100 in that location, as long as the major thrust side looks good. I don't like to see than tht .100 anywhere, before boring.

    The sheet I posted is an example of this, and that motor made 550+ HP, and is in use today 3+ years after it was built.

    JW
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    Jim Weise
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    Most folks are about as happy as they make up their minds to be.
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    thanks a lot for the reply jim!

  11. #11
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by TORQUED455 View Post
    have you ever found the converse to be true (lifter bores off center but sonic readings good),

    Yes, I have in fact..

    or do you normally not bother sonic checking the cylinder walls when you notice core shift in the lifter bores?

    I do have a small pile of blocks like this, that have been passed over on first inspection, but eventually, will be sonic checked to verify that they can or can't be used.

    JW
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    Jim Weise
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    Most folks are about as happy as they make up their minds to be.
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  12. #12
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    why would there be shift in the lifter bores but not the slug holes ? Selective shifting ? Sounds Shifty to me ....
    Alan W

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    Quote Originally Posted by 442w30 View Post
    ... They have awkward proportions from certain angles, and they look dumpy compared to their GM brethren
    ....'68 SportWagon400 "Sportn'Wood"..............'69 GS400 Convert "BigRed"..........

  13. #13
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Are sonic testing and magnafluxing the same or different? I was under the impression they were the same but now I'm not so sure.

  14. #14
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Sonic testing measures cylinder wall thickness. Magnafluxing is a method of detecting cracks in ferrous metals.

    Devon
    Fuel & Brake Systems Engineer
    "I can live with doubt and uncertainty and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong." - Feynman
    "Good data is precious. The problem I have is when some damned fool fails to use it properly." - Slingerland

  15. #15
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    JIm,

    The Buick community as a whole is enhanced each time you write something about our cars.

    Thanks for all you do!

    Philip

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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    So they are different. I wonder if I'm making a mistake by deburring the block for my latest engine build by not having it sonically tested? Any thoughts? BTW, AMC/Jeep 360. It shares a lot of design features with the Buick.

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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by N360LL View Post
    I wonder if I'm making a mistake by deburring the block for my latest engine build by not having it sonically tested?
    The only mistake is in not doing the sonic test to determine the block's wall thicknesses BEFORE you waste a lot of time deburring a potentially useless block.

    The deburring isn't going to affect the sonic testing.

  18. #18
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Very informative thread thanks.

    I have one question: To my knowledge the 430 block and the 455 block have the same exterior dimensions, i.e. the cylinderwalls and webbings are thicker on the 430 ci. If this is correct, would you expect the 430 ci, on average to be more robust (less core shift issues) for a, say, 550 hp combo?

    Thanks,

    Taul

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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Yes,

    Typically 430's can be bored all the way to the standard 455 bore size. (From 4.1875 to 4.312)- they have plenty of meat in the cylinder walls.


    I ran a .060 over 430 for years in my bracket cars. Made 530 HP, and lived a long time.. probably over 500 passes. I ran it for at leased 5 seasons, and freshened it once. Lost it when a stock rod broke.

    Rod upgrade was scheduled for the next freshen, but it never made it.

    Was a good motor, a little shy on the power compared to the nearly identical 464 that followed it, but that's to be expected.

    JW
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    Jim Weise
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    Most folks are about as happy as they make up their minds to be.
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  20. #20
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    OK thanks.

    If the 430 has the same exterior dimensions as the 455, I would expect that in principle one should be able to bore the 430 up to whatever size that the 455's are bored to, on average. Why is it that the recommendation is to bore the 430 "only" up to 455 standard size?

    Regards,

    Taul

  21. #21
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by Taul View Post
    OK thanks.

    If the 430 has the same exterior dimensions as the 455, I would expect that in principle one should be able to bore the 430 up to whatever size that the 455's are bored to, on average. Why is it that the recommendation is to bore the 430 "only" up to 455 standard size?

    Regards,

    Taul
    Because the walls would get too thin. A block is cast with a certain amount of wall thickness.
    Example; ALL Pontiac blocks are the same external dimensions. They started out in 1955 with a 287 cubic inch and kept that block all the way through to 455 CID. The deck height at 10.24 and the bore space at 4.62 didn`t change. Nor did the head bolt pattern. There are no big and small block Pontiacs. BUT, that doesn`t mean one can bore out a 287 to a 060 over 455. One would have to have inch thick walls to do that. The block would be very heavy and would over heat with too thick of a wall.

    Course I left out the 265/301 blocks out. They were late, low deck bastard blocks that most don`t use.

  22. #22
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Nice piece on sonic testing. I am a firm believer in sonic testing as well.


    There is another important factor to consider after sonic testing, and that is final bore position. When I bore a block (after line honing and truing the decks with a BHJ Block Tru) I will have my sonic test data sheet right there to reference.
    After centering the boring head on the BHJ Bore Tru fixture, I sweep the head down in the cylinder bore with the dial indicator and find out where it will be removing the most material to correcty true and index the bore.
    If it looks like it will be cutting heavy on the thin part of the cylinder, you have to decide if correcting the bore position is worth sacraficing bore integrity...sometimes you can split the difference, sometimes you are just left to bore off the original position. in extreme cases, you may need to move the bore over to maintain thickness. This is a "last resort" option and I would never use such a block for a race engine where the bores were that far out of index.

    That said, Block filler goes a LONG way to strengthen the cylinder walls, especially in a thin or shifted block. It will make the engine run cooler, and the rings last longer. If anyone is interested, I could elaborate on that subject a bit more.
    There is almost no engine block that won't benefit from some amount of block filler.

    Ron @ the machine shop.

  23. #23
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by MN GS455 View Post
    Nice piece on sonic testing. I am a firm believer in sonic testing as well.


    There is another important factor to consider after sonic testing, and that is final bore position. When I bore a block (after line honing and truing the decks with a BHJ Block Tru) I will have my sonic test data sheet right there to reference.
    After centering the boring head on the BHJ Bore Tru fixture, I sweep the head down in the cylinder bore with the dial indicator and find out where it will be removing the most material to correcty true and index the bore.
    If it looks like it will be cutting heavy on the thin part of the cylinder, you have to decide if correcting the bore position is worth sacraficing bore integrity...sometimes you can split the difference, sometimes you are just left to bore off the original position. in extreme cases, you may need to move the bore over to maintain thickness. This is a "last resort" option and I would never use such a block for a race engine where the bores were that far out of index.

    That said, Block filler goes a LONG way to strengthen the cylinder walls, especially in a thin or shifted block. It will make the engine run cooler, and the rings last longer. If anyone is interested, I could elaborate on that subject a bit more.
    There is almost no engine block that won't benefit from some amount of block filler.

    Ron @ the machine shop.
    Ron

    I was just asking why moving the cylinder wouldn't work to center the bores in the sweet spot when I read your post. I was wondering if it would wise to sleeve standard bore block back to a standard or .010 bore that wasn't overbored from previous overhauls?

    Slugger

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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Around here a sleeve is 120.00 per cyl thats 960.00 for the whole block. If you just do a couple cylinders I guess it might work. Can you build a race block with sleeves and block fill then bore the snot out of it?
    John & Terry Kemper
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    Default Re: Understanding Core Shift in the 455 block- why sonic checking is so important.

    Quote Originally Posted by Slugger View Post
    Ron

    I was just asking why moving the cylinder wouldn't work to center the bores in the sweet spot when I read your post. I was wondering if it would wise to sleeve standard bore block back to a standard or .010 bore that wasn't overbored from previous overhauls?

    Slugger
    Slugger and Staged 70,

    Most blocks will take a .020" or 030" overbore. I don't know of any shelf stock pistons that are .010" , Sleeving the whole block is kind of impractical from a cost standpoint. I do it now and then with some NHRA Stock/Super Stock engines for 2 reasons though. First, to get a block back to a legal bore size after it is max bored and worn. Second, I can use a thin wall (3/32) sleeve made of ductile material which is 100,000psi tensil strength VS stock which is 30,000. These sleeves offer much better ring seal, bore and ring life. Again, very expensive, but it allows me to index the cylinder from the start as well and have uniform sleeve thickness.

    A block with ductile sleeves requires less block filler to do the same job, and you can't beat the RZ, RPK and RA wall finish capability for the rings. Ductile sleeves love the new Advanced Profiling steel rings from Total Seal too.

    Ron

 

 
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