How to Use an Automotive Dwell Meterby Don Bowman
The dwell meter is a necessary piece of equipment for tuning early-model vehicles that use a conventional points type distributor. The coil, which is similar to a capacitor, is charged for the length of time the points are closed. The length of time the points are closed is the dwell time. Obviously, the longer they are closed, the more the coil is charged. The dwell meter gives a visual measurement used for the proper adjustment. Point gaps are set at .018-inch with the feeler gauge. In lieu of a feeler gauge, a matchbook cover can be used -- it's the same thickness.
Raise the hood and connect the dwell meter to the coil -- the red lead to the negative terminal on the coil and the black lead to a good ground.
Start the engine and observe the dwell meter. The meter has scales for four-, six- and eight-cylinder engines. The dwell on an eight-cylinder is 32 to 34 degrees. The dwell time rises with the reduction of cylinders since there is one lobe per cylinder on the distributor shaft. As the point gap decreases, the dwell rises, and as the point gap increases, the dwell decreases. Shut the engine off.
Adjust the dwell by using a feeler gauge or an Allen wrench if the distributor is so equipped. Some of the earlier vehicles have points that are not adjustable from the outside. They need to be adjusted with a feeler gauge, while the later models have a metal door on the side of the distributor cap and the points have provisions for an Allen wrench. For distributors that do not have a metal door, go to Step 4.
Remove the distributor cap, using the common screwdriver. Remove the rotor to make it easier to gain access to the points. Mark the distributor housing location and loosen the distributor hold-down nut using a wrench. Rotate the distributor housing just enough to put the foot on the points on the highest point of a lobe on the distributor shaft. Loosen the screws on the points base with a common screwdriver. Insert the screwdriver in the adjustment slot on the points, then insert the feeler gauge (set at .018) between the points. Adjust the point gap until there is a very slight drag on the feeler gauge when extracted. Tighten the points and replace the cap. Recheck with the dwell meter.
- Don Bowman, A.S.E. Certified Mechanic
Things You'll Need
- Dwell meter
- Common screwdriver
- Set of wrenches
- Feeler gauge
- Set of Allen wrenches
- Phillips screwdriver
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).