Sonic tester frustration, experienced users please chime in

[My427stang]

So I bought a sonic checker, and was getting to know it on the 445 block because it was the cleanest and on a roll around stand.  Also considering buying Barry's 4.09 pistons if I thought the block had enough life

I had a hard time getting repeatable results with two different types of transducer gel, and ended up using white grease and the smallest diameter transducer, with this combo, I was able to repeat measurements and do them very quickly, so I felt like all was well.

I only did one bank, C6ME block, 4.08, clean and crosshatch showing, came up with a thinnest thrust at .157, thinnest non-thrust at .145, (pin direction on side toward fan).  Better cylinders were slightly above .200 in areas, but all the thrusts made sense to each other best being about .176, and each direction seemed about the same (all on one bank)

The issue I am running into is I cannot get the proper distance between two cylinders at the deck as a check distance.  Mine is .550 measured, which is also spot on for calculation at bore spacing - 1/2 of each bore at 4.08.  However, my sonic test on that deck area check reads .712, and it is repeatable from bore to bore.  Switching back to the 2 types of purpose-made transducer gel did not help me read properly.

I can check my tester against any flat piece and it is spot on, to include calibration block testing and any measurable flat piece of stock I have around.  It concerns me, because if I adjust my sonic checker to make the cylinder to cylinder distance right, then that will indicate a much thinner wall. (as thin as .119 thrust)

Thoughts?  I have not shaped the transducer, but the small one is pretty small, 5/16-ish and doesn't seem to have significant rocking issues, unlike the big one in the kit, similar to the ones most of us have that are closer to 7/16 OD.

Thanks in advance

[Heo]

You have different settings for different material? cast iron
has a different setting than regular steel. Atleast the checker
i use.
I usualy calibrate it on a resonable flat spot I.E china wall where
i can meassure with calippers . One time i chased my tail and got
some inaccurate readings. I found out the batteries was low

[Joe-JDC]

I think you will find the flat head will not read the gap right, even though it may read consistently.  I paid for a block that was supposed to have .235 walls, and they had used a new sonic tester without arcing the transducer head.  When I tested it with my sonic tester, I was quite a bit different, and took the block to my friend who does this on all Y Blocks before boring them.  His tester confirmed my readings, which were about .065-.070 less then the seller's claim.  What I did to my tester's transducer was arc it to a bore by inserting a sheet of 400 grit sandpaper in the bore and moving the head up and down until it matched the arc of the bore.  Works well if you take your time and keep the head level/perpendicular to the bore.  The test results with white grease always seem to be repeatable with more consistency than the glycerin gel.  I just use the white grease now.  Joe-JDC

[My427stang]

I think you will find the flat head will not read the gap right, even though it may read consistently.  I paid for a block that was supposed to have .235 walls, and they had used a new sonic tester without arcing the transducer head.  When I tested it with my sonic tester, I was quite a bit different, and took the block to my friend who does this on all Y Blocks before boring them.  His tester confirmed my readings, which were about .065-.070 less then the seller's claim.  What I did to my tester's transducer was arc it to a bore by inserting a sheet of 400 grit sandpaper in the bore and moving the head up and down until it matched the arc of the bore.  Works well if you take your time and keep the head level/perpendicular to the bore.  The test results with white grease always seem to be repeatable with more consistency than the glycerin gel.  I just use the white grease now.  Joe-JDC

Thanks Joe, seems like your experience is matching what I saw today.

You have different settings for different material? cast iron
has a different setting than regular steel. Atleast the checker
i use.
I usualy calibrate it on a resonable flat spot I.E china wall where
i can meassure with calippers . One time i chased my tail and got
some inaccurate readings. I found out the batteries was low

Yes I do, since I posted, I tried to do exactly that, to get there I had to change from the 5900 velocity setting (iron) to the 4600 velocity setting (brass), then the deck measured right, but it put my cylinders at .1177, seemed low to me

Tomorrow I am going to do a drill bit test and get an idea how thick things are.  .550 between bores minus the gap should tell me more or less the thickness of the walls and tell me how far off I am.

I also think it could be transducer shape, even with the smaller transducer

[My427stang]

OK,

So here is what I did

1 - Shape my small transducer using Joe's method, real easy and didn't change much but did make it significantly more consistent
2 - Did a drill bit test between 7 and 8 at the center of the freeze plug.  Got .215, so using bore spacing and bore calcs that got me to a calculation of  .335 for both, at that exact point, or about .1675 of cylinder wall
3 - So measured those points with the sonic checker.  I got something odd at the iron setting, too thick
4 - So I went back to the deck, and adjusted the velocity to calibrate for the measured cylinder spacing at the deck -  .560.  It took me back to the same adjustment as yesterday, velocity of 4675
5 - I went back down to my point parallel to the freeze plug, and got repeatable .165-.166.  It's slightly thinner than expected, but pretty darn close to the drill bit test and knowing I didn't jam in the drill bit, there was slightly more space than the drill size.
6 - I then measured all the cylinder spacing at the deck and it came up pretty stable

Something to note, #7 cylinder walls clearly get thinner as you approach the deck, at the feeeze plug, the .2150 drill bit was tight and would not slide lower, however it loosened up as it went higher.  This block is pretty clean, it wasn't a lot, 1 drill size, but it was noticeable

7 - So I measured all the thrust sides at about 1.500 down and got a range from .118 to .134, all other dimensions thicker, and as I go deeper it's thicker
8 - I then did a final check against the china wall for sort of a "post-event calibration" and it came up pretty close, not perfect, but it's not machined and it has a good coat of paint on it, so not different enough to concern me.

In the end, Joe's shaping helped, Brent's advice off line to "always calibrate to the deck" was correct, and Heo's quick check gave me a bit of peace of mind.

I will post thoughts in the engine forum on "what next", and later today, likely repeat the process on a standard bore 428 to see if it repeats

[WerbyFord]

x2 what JDC said, I find I always have to "curve" the transducers or they just don't read right.

I also calibrate on an old torch-cut 400M Cylinder wall section, 4.040 bore.
This one had disgusting core shift so the thinnest spot is .036" (no kidding, it ran like that at about 350hp for almost 2000 miles before it split on a 93F summer day...), the thickest spot is about .260".

I also find that things don't "add up" using the (sonic+drill+sonic) = (Bore space - Bore).
I have to allow IIRC 1/32" or 1/64" on each surface for "roughness" - kinda like the Korea "Demil Zone", the sonic doesn't catch it & the drill bit doesn't either, its just "rough iron and air".

Then I use (sonic+rough+drill+rough+sonic) = = (Bore Space - Bore)

It was kinda fun (well, if your kinfolk in the hospital is EVER fun.....) watching the hospital folks to "bladder checks" with a sonic tool, and they'd get confused by erratic readings sometimes. Blood Pressure readings are the same way - there's a LOT of signal processing & voodoo going on inside those machines, its not like checking your points with a feeler gage.
That usually jives.

[Katz427]

Measurements on cylinder walls are tricky even with the best equipment. I have used instruments valued over $5k and still difficult to get good data. I also had the luxury of an oscilloscope, to monitor the signal to observe if the readings looked believable.
It looks as if you are doing the best you can, considering the level of equipment you are using.

[Heo]

When i was a weldor. I spoke with one of the guys that x-rayed
and inspected our welds and sonic tested boiler tubes and such,
to know if it was time for new ones
A nice guy, he used to give me a spray cans for indicating cracks
and magnaflux rods for a bag of doughnuts
He got killed when he was inspecting something on the roof of
a railroad cart and got electrecuted because they had not shut of
the electricity
 He said that castiron was hard to sonic, accurate enough.
But on the other hand his sonics could be the difference between
life and death. Or run the plant another year or rebuild it for a couple of
milions