How Does a Dial Indicator Work ?

You will need the precision inspection instrument to degree in a cam, check cam lobe lift or blueprint your engine. Dial indicators are also great for checking crankshaft runout, crank end play or piston deck clearance. Although a versatile inspection tool, there are other methods you can use that require the use of less expensive tools if you are only doing a rebuild.
The tpical dial indicator consists of a plunger and two dials. As the plunger moves in and out, the dials rotate, indicating plunger travel within an accuracy of 0.001 in. The larger, or outer, dial face is divided into 0.001-in. graduations and the smaller one is divided into revolutions of the larger dial. Each revolution of the larger dial is typically 0.100 in. To provide a convenient starting point, the outer dial face can be rotated on the body of the indicator to zero the pointer. It also has a clamp at the edge to hold the face in place.
Accessories—The most common dial indicators are available in 0.500-in. and 1.000-in. travels. Although more expensive, choose the 1.000-inch-travel indicator because it is more convenient to use. What I consider nice, but not necessary are telltales. These two little pointers on the outer dial OD can be positioned around the dial face to indicate starting or stopping points or ranges for checking tolerances. If the dial pointer does not pass the telltale, you know that what’s being checked is within spec.
You will need two accessories for a dial nidicator: a base and a plunger extension. The base is used to support the dial indicator. It can either be bolted or held in place with a permanent magnet. The magnetic base is the most convenient and usually the best to have, but if the part being checked is non-magnetic, such as an aluminum cylinder head to block, It would be better to have the bolt-on base. I say better because you can always bolt a small steel plate to the part being checked. Although not as convenient, you’ll then have something to which the magnet will stick. Between the base and indicator is the adjustable part of the base. It’s either a combination of rods and clamps or a snakey looking affair that clamps solid once the desired position is achieved. I prefer the rod and clamp type base because it’s easier to set up and is more solid.