The Versatile Dial Indicator

Checking Disc Brake Runout

A warped rotor can cause a pulsating sensation when you step on the brakes, and it can cause uneven pad wear and premature wheel-bearing failure. Use the dial indicator to check the runout of the rotor every time you change the pads, even if you buy new rotors or have the old ones turned. The reading should be no more that 2-3 thousandths in either direction of zero.

Setting Up a Ring-and-Pinion

Many home mechanics shy away from setting up a rearend, but the dial indicator is really the most exotic tool required for this job. Once the correct tooth contact pattern has been established, the indicator and base are essential for properly checking the backlash between the ring-and-pinion gears. To measure it, hold the pinion steady and rock the ring gear up and down while reading the needle. Follow the gearset manufacturers’ recommendations for proper backlash.

Dialing In a Bellhousing

In a high-revving manual transmission car, the pilot-bearing hole in the bellhousing must be exactly centered in the back of the crankshaft to ensure smooth, high-rpm shifts. If the misalignment is great enough, the input shaft can bind enough that the trans won’t shift into Fourth gear at high rpm. Most factory bellhousings are surprisingly close, but aftermarket scattershields are hit-and-miss. We’ve used several that were spot on, while others were so far off that we guarantee there would be a shifting problem if not corrected. The bottom line is that every one needs to be checked. Setting up the indicator inside the bellhousing is the toughest part of the job because there’s limited room for a bulky base. It may be easier to bend a short bracket out of a piece of metal strap and bolt it to the crankshaft. Once the indicator is zeroed, rotate the crank in the direction of engine rotation, take readings at the 12, 3, 6 and 9 o’clock positions. Maximum runout should be no greater than +/- 0.005 inch from center in either direction. Offset dowel pins are used to correct any misalignment.

Checking Piston-to-Valve Clearance

We’ve written several articles on this subject in recent years, but it’s still surprising how many experienced car crafters still don’t understand that net valve lift is far less critical to piston-to-valve clearance than camshaft duration is. As a rule of thumb, any cam with more than about 230 degrees of duration at 0.050-inch tappet lift is likely to be very close to interfering with stock piston valve notches. P-to-V can be checked with a dial indicator by installing checking springs on the valves, zeroing the indicator on the retainer, and depressing the valve while rotating the engine. This is best done in conjunction with a degree wheel, because the valves are always closest to the pistons at 9 to 11 degrees before top dead center (BTDC) on the exhaust side and 9 to 11 degrees after bottom dead center on the intake side.

Checking Deck Height

Piston deck height is an important measurement to have when calculating an engine’s compression ratio. With the piston at TDC, a dial indicator and base can be used to check the depth of the piston in the bore by zeroing the indicator needle on the deck surface, then swinging the needle onto the top of the piston and measuring the difference. If the rings are not installed, rock the piston to each side and average the two measurements.

Checking Crankshaft Endplay

Installing a crankshaft with inadequate endplay will wipe out the main thrust bearing in a hurry. With the indicator and base set up to read off the crank snout, shift the crankshaft fore and aft in the main saddles with a large prybar and read the movement on the dial indicator. On a small-block Chevy, endplay should be about 5 to 8 thousandths, although many engine builders will tell you that “some endplay” is good enough. No endplay is the bearing killer.

Degreeing a Cam

In conjunction with a degree wheel, the dial indicator is mandatory for measuring lobe lift while degreeing a camshaft. Depending on the technique, a special cam follower fixture can be mounted to the dial indicator, or you can simply install a solid tappet in the lifter bore and read the lobe lift off the pushrod or the valvespring retainer.