Bottom of cooling jacket: Not super thick

Discussion in 'Small Block Mopar Engine' started by nm9stheham, Dec 2, 2018.

  1. nm9stheham

    nm9stheham Well-Known Member

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    It's thinner than I thought at the bottom of the cooling jacket in a couple of SBM blocks checked, while planning some bore notching at the bottom of the bores for rod bolt clearance with a stroker crank, like pictured in this article:
    This 436ci Small-Block Mopar Makes Big-Block Power On Pump Gas

    The bottom of the cooling jacket in the crankcase area on a 273 about 0.5" from the bore was sonic checked, and the thinnest areas varied between .210-.310" for all 8 bores. 2 bores were checked similarly on a 360 block and the thin areas were .275-.290". Measurements with an old style caliper in a couple of spots showed that the sonic checker was telling the truth. I always thought it was thicker down there.

    Some checks of the corner thickness with the old style caliper, where the bottom of the bore ends, showed more like .45" thickness + or - at an angle through the casting.

    To help visualize this, here are a couple of hand sketches of the measurements; 273 is 1st and then 360. (Sorry for the fuzzy pix).

    DSCN2550 (Large).JPG DSCN2552 (Large).JPG DSCN2546 (Small).JPG

    The last pix is the 4" crank in the 273 block with a stock light SBM rod in place, showing the interference. This pix is taken at an angle where the far edge of the rod bolt's nut is moving straight away from the camera at the point of contact with the block so you can visualize the notch angle in the block compared to the far bore wall which is visible. A notch would eat about .20-.25" minimum out of the corner of the casting, where it is around .45" thick. That would seem like a lot to take out with any flexing of the block down there.

    Bottom lines IMHO:
    • Don't go wild with such notches and smooth all the corners nicely.
    • The 'stroker cleared' dimensions on rods like the SCAT's (and maybe Eagles) have their value in all this; they stick out about .125-.150" less towards the lower edge of the bore than these stock light SBM rods.

    Comments, other measurements and sage experience welcomed as always!
     
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    • MOPAROFFICIAL

      MOPAROFFICIAL Well-Known Member

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      Been wanting to see someone put a 4" in a little 273.
       
    • moper

      moper FABO Gold Member FABO Gold Member

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      A note - if the surface of the media being tested is "as cast", your results may vary... Most transducers made for a curved surface will not sit very well on an as-cast finish. I would suggest if you tested on the cast finish you use a bur or sanding roll and smooth it out. Then re-test. The coiupling gel is not "filler". The transducer halves have to contact the surface properly or the reading will be suspect.
       
    • kursplat

      kursplat FABO Gold Member FABO Gold Member

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      between these being average production line castings, and who knows how much core shift when they were banging these things out, i wouldn't be surprised to find an 1/8" of variation in that area. how high are you wanting to twist this thing?
       
    • nm9stheham

      nm9stheham Well-Known Member

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      My big thing here was that I had the impression that this area was something like .5" thick minimum and so grinding with abandon would not be a worry.... does not look like that is the case LOL!

      Roger on the above.... I use white lithium grease as a 'gel'.... seems to couple well, and I do repeated measurements. The sonic tester I have has an indicator on the screen when it is sensing a well-defined reflection (which implies good coupling). I also used old style curved calipers, like pictured below, to reach around the casting and confirm the sonic measurements. The corner thickness measurement was done in this way as I would not expect the sonic tester to be at all accurate there. But I still just may do as you suggested in one place with smoothing it out.

      If I had a junk block I would get out the portable band saw and slice it up to be sure and take pix.

      3 Inch Leg, Spring Joint, Steel, Powder 62393863 - MSC
       
    • moper

      moper FABO Gold Member FABO Gold Member

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      You should buy the right gel. I'm not convinced white lithium is a valid substitute.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      I can understand questioning this, but so you will know..... I use a smooth cast iron brake rotor as my 'test coupon' to calibrate the sonic tester as I can put a caliper around it. The accuracy is as good as I expected, within the resolution of the unit, which is 0.1mm or .004". The readings there don't change dry, or with spit, or with the grease as a coupling.

      The coupling gel is just to make the sonic impulse and reflections couple effectively between the material under test and the impulse head. Even the gel has a different propagation velocity versus the material under test, but it is so thin, the time delay between the impulse and the reflection return is not effected enough. And, with the far side of a casting being rough, the reflections are going to be diffused anyway, crating some uncertainly in the measurement even if the measurement-side surface is perfect. The sonic tester can only look at the earliest time or arrival of the reflections and say that is the distance.

      Is there a reason that the use of a caliper at the same spot to get the same results does not seem like adequate confirmation? I'm not looking for .001" accuracy... I'm looking to see if this is thick or thin.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Not particularly high and not a ton of power. Maybe a bit over 1 HP per ci. But I don't want to get things so thin with grinding that a crack develops and coolant leaks into the crankcase.
       
    • moper

      moper FABO Gold Member FABO Gold Member

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      I guess I understand your perspective. But I'd rather follow what the smarter folks that made the equipment say to do - which is use the correct coupling gel. I'm not going to pretend I know better (not saying you are pretending - just a turn of phrase).
      I'll add - just clearance the block. Give yourself .100" clearance and move on. Ive done probably 20 over the years. Some making 1.7hp/inch with the nitrous. The bottoms of the cylinders are not what one worries about.
       
    • nm9stheham

      nm9stheham Well-Known Member

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      Thank you very much... that's the experience that is priceless and is very much appreciated. I'm going with SCAT or Eagle rods anyway so that will help lessen the interference.

      FWIW, I did run across this on the gels and substitutes; the source link is included.
      "The stuff we use (ECHOTRACE 9000) is water based so it is easier to clean up. Generally speaking most silicone oils & gels, greases, Vaseline (pariffin) and even some hair gels etc can be used if the temperature is not sufficient to make it run out from under the transducers and or be workable in overhead applications. I have found that good quality high temp wheel bearing grease is usually a suitable alternative. Glycerin can give a few extra dB of coupling (it can sometimes help obtain useful readings when there seems to be no reason why it won't work) as it's acoustic impedance is similar to plastics, but it can cause corrosion and or rusting so it must be completely removed."
      Ultrasonic or Acoustic Couplants and Alternatives - wiki