This was published in the Corvair Ultra Van newsletters in 1996 by Norm
Helmkay <corvair@...>



Poor Man's Dwell Meter
by Norm Helmkay

Want to gap the distributor points without feeler gauges?

Almost everyone has an analog volt-ohm meter (not the
digital type), so you already have an uncalibrated dwell
meter, but probably never realized it.

Try an experiment with your meter on a low D.C. volts
scale, 1.5 to 5 volts. Hold the - probe on the bottom of a
1.5 volt flashlight battery, then rapidly tap the + probe on
and off the top of the battery. Notice the meter needle
stays roughly about the same place on the scale at some
value under 1.5 volts. This reading represents the dwell
time of the probe you are tapping on top of the battery.

If the meter were on a 10 to 15 volt scale with the - probe
grounded and the + probe on the distributor point post, with
the motor running, you would read the pulsing voltage of the
points opening and closing. When closed there is no voltage
across the points. When the points are open, the meter
reads the voltage across them. The average of this on-off
voltage can be calibrated as the dwell. You could calibrate
your own analog meter by comparing it to a real dwell meter
on various 4, 6 and 8 cylinder engines.

Degrees of dwell may be different, even with the same point
gap, as the profile of the distributor cam may be slightly
different. Generally, dwell time will fall into the
following ranges:

Cylinders Dwell in Degrees Point Gap in Inches
4 50? to 64? .019 to .025
6 33? to 43? .016 to .027
8 27? to 37? .014 to .018

If known, always use the manufacturers distributor
specifications.