Automotive Machining. Mike Mavrigian
runout, piston position relative to top-dead-center (TDC) in an engine block, measuring crankshaft thrust, measuring runout on a crankshaft, camshaft, valvestem, pushrod, etc. In each case, the dial indicator gauge must be rigidly mounted to allow only the gauge plunger to move.
Regardless of the application, the method of adjusting and reading the gauge is the same.
Let’s use checking crankshaft thrust/endplay as an example. In the case of an iron engine block, the dial indicator gauge is mounted to a mounting fixture that has a magnetic base (for an aluminum block, a fixture that bolts to an available threaded hole works). Position the dial indicator so that the plunger contacts the face of the crankshaft snout or other available flat surface. The plunger must be parallel to the crankshaft centerline and not at an angle relative to the crank. Adjust the dial indicator so that the plunger contacts the surface and creates a slight preload (about .050 inch or so). The preload is vital to make sure that the plunger remains in loaded contact with the crank at all times. Using a lever such as a screwdriver, between a main cap and crankshaft counterweight, move the crankshaft rearward as far as it will move and remove the screwdriver. Rotate the gauge dial to allow the gauge needle to read exactly zero. Then use your lever to move the crankshaft fully forward, noting the distance of movement on the gauge. Repeat this reading several times. Move the crank fully forward and re-zero the gauge, then move the crank rearward (the same reading should be seen). Typically, depending on the application, you may see .004 to .008 inch or so of crank fore/aft movement.
The use of a dial indicator is the same for all applications, whether you’re measuring for movement or runout. For example, if you’re checking pushrods for runout (warp), a special pushrod runout stand is ideal. Lay the pushrod onto the stand and position the dial indicator at the center of the pushrod. Adjust the dial indicator with a bit of preload. Slowly rotate the pushrod until the indicator gauge reads maximum or minimum. Then zero the gauge dial and slowly rotate the pushrod, noting how far from zero the needle moves. This represents the amount of runout. Generally speaking, a maximum of .0005 to .001 inch is acceptable.
When checking a brake rotor disc for runout, the dial indicator needs to be mounted rigidly to prevent the gauge housing from moving. Several methods are available including a mount with a magnetic base and adjustable-length rods to position the gauge, or a flexible/locking arm that secures to a solid area such as a strut bracket (the gauge must be mounted to a component that does not move independently, relative to the rotor). Place the dial indicator plunger 90 degrees to the rotor (straight onto the disc surface, not at an angle). The plunger should contact the rotor surface about 1 inch inboard from the disc edge. Adjust the indicator with a bit of preload (about .050 inch), and slowly rotate the rotor until the gauge reads at a minimum point. Zero the gauge needle and slowly rotate the rotor a full 360 degrees, watching the gauge needle. The maximum gauge reading relative to zero represents the amount of rotor runout. Always refer to the manufacturer’s runout specifications, but generally speaking, a maximum of about .002 inch should be acceptable.
A pushrod runout checker features a stand and a dial indicator. Position the pushrod on the stand cradles. Adjust the dial indicator so that the indicator plunger contacts the center of the pushrod radius, and adjust the indicator to create approximately .050 inch of preload, then zero the indicator gauge. Slowly rotate the pushrod and monitor the indicator to measure any pushrod runout. This type of checking tool makes it easy to measure each pushrod for runout/bend. Generally speaking, runout in excess of .001 inch is unacceptable.
A magnetic-base dial indicator can be used to measure a variety of dimensions. In this example, the magnetic base is secured to an iron block deck with the indicator plunger contacting a piston dome, which is one method of checking piston location at TDC (top dead center).
Shown here is a dial indicator being used to measure installed valve depth relative to the deck on a racing cylinder head. A bridge fixture rests on the head deck, with the dial indicator mounted to the bridge. This allows checking to measure each valve’s depth, so that the seats can be machined to obtain an identical depth to optimize performance.
Here, a magnetic base dial indicator is used to measure crankshaft thrust. The magnet must mate to a clean, flat surface for proper stability. The indicator is adjusted on the tool’s extension rod to locate the indicator plunger onto the crankshaft snout. The magnetic base is secured to the iron engine block.
Here, a dial indicator plunger is set up to contact the front face of the crank snout. Regardless of the point of contact, the indicator plunger must be set up parallel to the crankshaft centerline, not at an off-angle. If the plunger is at an improper angle, the reading will not be correct. Set the indicator up so that the plunger contacts a flat area of the crank, and push the indicator a bit toward the crank to obtain a gauge preload of about .050 inch. Push the crank fully rearward and zero the gauge. Then push the crank forward and observe the amount of travel. The close-up of this dial indicator shows that the crankshaft thrust measures a tad greater than .006 inch. The gauge needle has traveled just past the .006-inch mark. The small dial seen near the gauge center indicates additional travel in .0001-inch increments. This crank thrust reading is approximately .0067 inch.
If you’re dealing with an aluminum engine block, you may be able to secure the magnetic base to the face of a steel or iron number-1 main cap. Otherwise, a fixture that bolts to the engine block is needed to mount the dial indicator. In this example, an extension has been added to the indicator plunger, as the plunger contacts the crank’s snout base.
When using a dial indicator to measure brake rotor runout, the best style of indicator for this task is one that features a ball bearing tip on the plunger. This reduces the variable of contact chatter and provides a smoother, more consistent reading. Dial indicators are available with either a solid or roller tip.
A dial bore gauge allows you to measure bore diameter in areas such as main bearing bores, cylinder bores, lifter bores, cam bores, etc. A bore gauge kit includes an array of various length anvil extensions that mount to the tool depending on the bore diameter range that you plan to measure.
Keep in mind that a bore gauge does not allow you to measure a bore diameter directly. The gauge is first set up to the target diameter and then zeroed. The gauge allows you to read how close the bore is to the target (at target, undersize or oversize, relative to the target diameter).
Shown here is a typical bore gauge set. The tool includes a gauge and a selection of extensions and spacer washers to allow obtaining a variety of specific bore diameter applications.
To set the gauge up, you need a micrometer. First, set the micrometer to the target bore size. For example, if the bore at hand is supposed to be 2.000 inches, set the micrometer at 2.000 inches.
Then, set up the dial bore gauge with the proper anvil extension that is able to accommodate a 2.000-inch bore. Bore gauge kits include a selection of extensions and spacer washers to allow you to adjust the gauge to the specified bore diameter.
Place the bore gauge between the micrometer’s