Modern Engine Blueprinting Techniques. Mike Mavrigian
Testers
This specialty gauge is used to measure material thickness, and is especially useful for measuring cylinder wall thickness in an engine block. This hand-held tester has a corded probe that emits a sonar signal that travels through the material. When the signal reaches the opposite side of the material, the signal bounces back to the tester, which displays the thickness measurement.
Probe measurement checks are made from the top of the cylinder wall to the bottom, in all radius directions. It’s especially important to check areas where water jackets exist behind the cylinder walls. Being able to determine existing cylinder wall thickness tells you how much material can be safely removed during an overbore. Walls that are too thin at critical areas deflect more during engine operation and degrade piston ring sealing. In addition, these walls can crack and/or blow out.
Ideally, you want to maintain at least .125-inch wall thickness at the thinnest areas. This requirement can vary depending on the specific block, but this is a reasonable ballpark. Any cylinder wall thickness concern increases if the engine is to be force-inducted with supercharging, turbocharging, or nitrous injection. The higher the cylinder pressures, the more critical wall thickness becomes.
Before using a sonic checker, the unit must be calibrated. Commonly, sonic testers include a machined calibration sample of steel that is milled at specific thicknesses of .200, .300, .400, and .500 inch. The calibration procedure is outlined with the specific brand of tester, but it’s a simple process. Once the unit has been calibrated, apply a dab of lithium grease to the probe face. Contacting the probe against a clean cylinder wall (using moderate pressure on the probe) reveals material thickness.
A sonic tester is a must-have in any engine shop, especially when considering a cylinder overbore job. Instead of guessing about existing cylinder wall thickness, this type of testing equipment allows you to accurately measure wall thickness anywhere in each cylinder. This is a sonic checker kit from BHJ.
With the cylinder surface clean, and after calibrating the tester with the thickness standards included in the kit, a bit of lithium grease is applied to the probe. While applying moderate pressure at the probe against the cylinder wall, the display reveals material thickness at that location. The goal is to check wall thickness at all clock positions and height locations to determine existing wall thickness, especially in areas adjacent to cooling passages.
Don’t just measure one cylinder bore. It’s very common for cast-iron blocks to have variations in wall thickness, so be sure to check each cylinder. If the wall thickness in any given cylinder is marginal, you have the choice of scrapping the block or (depending on the specific block) installing a sleeve/cylinder liner. Checking your block with a sonic tester helps you avoid investing in a block that doesn’t hold up.
Hand-Held Magnetic Particle Testers
Applicable to cast-iron and steel materials only, this process involves placing magnetic poles at opposite sides of a suspected crack area and introducing a ferrous powder onto the inspection area.
The workpiece must be clean before testing. Only clean with solvents, and do not clean with abrasives or anything that might disturb the metal surface. In other words, don’t use glass bead, steel blast, etc. because they may peen crack edges, which makes inspection more difficult.
A hand-held magnetic checker has two magnetic poles. The poles are positioned on either side of the suspect area, and a special easy-to-view metal powder is sprayed onto the area. With the unit turned on, a field is created that draws the powder into the crack for easy identification. Shown here are Goodson’s electric magnetic-particle tester MMP-210, a container of inspection powder, and a powder duster. Goodson supplies a wide range of tools and supplies dedicated to the needs of pro engine builders.
Using the squeeze duster, apply the powder to the surface.
A magnetic (or “mag”) tester is a hand-held electromagnet used to check for cracks in ferrous materials, such as cast iron and steel. The surface to be checked must be clean and dry. Spray a light dusting of special iron powder onto the inspection area, and place the twin-poled magnet onto the surface. Press the momentary ON button to turn on the magnet. When using a twin-post magnetic tester, the best results are obtained if the bases are placed at a 45-degree angle to the suspected crack. Repeat the test 90 degrees from the first test (test in a crisscross manner). This pulls the powder into both walls of a crack for easier viewing.
Place the magnetic particle tester onto the work surface and adjust the pivoting magnet posts to achieve contact.
With the magnet unit in place, press the ON-button to activate the magnets. The powder is pulled along and into any cracks. Note the small crack that runs between these two valve seats.
Also referred to as a magnetic particle inspection station, a dedicated “wet mag” bench has a large-diameter magnetic ring and a black-light setup. Passing the tested part through the ring magnetizes it. A hand-held magnetic field tester verifies the integrity of the part. A special penetrating liquid (mineral spirits mixed with florescent particles) is rinsed over the part and then it’s viewed under the black light. Any cracks show as a brightly colored line. Once the inspection is complete, the switch is flipped to de-magnetize mode to remove the magnetic field. If left magnetized, metal particles continue to cling to the part due to a potential residual field, even during engine assembly, which can obviously cause contamination and wear problems. The handheld field tester is used to verify that it has been demagnetized. The part is passed through the mag ring again. A wet mag testing unit is applicable to any ferrous (iron or steel) component, and is most commonly used for checking crankshafts and connecting rods.