nm9stheham
Well-Known Member
I wanted to get one of these for measuring cylinder wall thickness, but the price on the 'shop' grade ones is over $1k. So took a chance on a 'chinesum' one. Found one on Amazon for $180 shipped. Model is TM8812.
Got it here and it seem to work OK. First measured some non-vented brake rotors where could measure the thickness exactly with calipers, and the ultrasonic gauge read within .001-.002", when averaging a few readings. The resolution is only .004" so finer individual readings can't be had with this unit.
With that done, I measured 2 blocks and it seems to read as it should. Without another sonic gauge available to compare it against, the calibration versus a flat rotor is the best I can do to check this unit's accuracy. You hold the probe so that the line in the middle of the probe's face is vertical in the cylinder bore (i.e., parallel to the bore axis). I stayed about 3/4" from the top of the bore and at least 1-1/4" or more more from the bottom of the bores, to stay away from the areas where the casting thickens.
The probe with this has a flat surface, so to make it conform better to the curved cylinder wall, a fine file was used to slowly take material off of each side of the probe head. Do this so that the head is slightly convex across the face, with the vertical line in the middle (where the sonic waves are launched). I made sure to not touch the vertical line with the file. (You can kinda see how the probe surface is convex in the pix of this higher priced gauge and probes: PR-82 Sonic Tester Racing)
Instructions are not the best as expected. Learned that:
Got it here and it seem to work OK. First measured some non-vented brake rotors where could measure the thickness exactly with calipers, and the ultrasonic gauge read within .001-.002", when averaging a few readings. The resolution is only .004" so finer individual readings can't be had with this unit.
With that done, I measured 2 blocks and it seems to read as it should. Without another sonic gauge available to compare it against, the calibration versus a flat rotor is the best I can do to check this unit's accuracy. You hold the probe so that the line in the middle of the probe's face is vertical in the cylinder bore (i.e., parallel to the bore axis). I stayed about 3/4" from the top of the bore and at least 1-1/4" or more more from the bottom of the bores, to stay away from the areas where the casting thickens.
The probe with this has a flat surface, so to make it conform better to the curved cylinder wall, a fine file was used to slowly take material off of each side of the probe head. Do this so that the head is slightly convex across the face, with the vertical line in the middle (where the sonic waves are launched). I made sure to not touch the vertical line with the file. (You can kinda see how the probe surface is convex in the pix of this higher priced gauge and probes: PR-82 Sonic Tester Racing)
Instructions are not the best as expected. Learned that:
- Calibrate on the disc on the side of the unit only with the unit set for steel
- Use white lithium grease for best coupling to the cylinder bores; other greases may work. Oil is OK too. Spit works in a pinch LOL
- This unit can be set for different materials with presets; use preset 'cd10' for cast iron
- Or, it can be set by sonic velocity of the material with a 'VEL' button
- The display update speed is slower than commercial units claim to be
- The resolution is only about .004", but IMHO the casting surface irregularities on the water jacket side are that much or more.
- Readings were pretty repeatable. When I went back to re-check a few spots, I could only go by the prior 'grease spot' to determine location, and I'd expect cylinder walls to vary a few thousandths if not in the exact same spot, simply due to the casting irregularities.