The Stovebolt Site Forums The Shop Area Engine Shop Something to Dwell on

Since I don’t have a window to adjust my points thru on my 216, I’ve always relied on the feeler gauge. As a matter of fact, since the 1950’s when I first opened a hood I’ve always relied on a feeler gauge. Now I’m not saying that this is better than setting the dwell, cus it’s not one is good enough for government work and the other is right on, I understand and agree with that.
So after all these years, mainly because of just plain curiosity, I thought I would dig out a dwell meter that was buried in the bottom of the cabinet and just check what the dwell was after I set the points with a gauge.
The meter that I have is an old Sears 244.2185 for 6&8 cylinder engines. Scale runs from 0 to the set line, what ever that means. I have no info on this meter, I probably picked it up at when I was out garage sailin’ a few decades ago. I’m assuming that the voltage has nothing to do with the operation and I have no idea of what the dwell is supposed to be for a stock 216. I am also making the assumption that the red lead goes to the point terminal on the distributor and the black lead to gnd. There is a pot adjustment marked SET on the front but again, I have no idea of what I’m supposed to be setting.
Any input???

Denny Graham
Sandwich, IL

Make sure the tongue is firmly planted in the left cheek and that the socks are firmly half pulled up before adjusting the secondary freps.

I done this on mine and it worked out fine!

I'm guessing the SET adjustment is just a mechanical zero adjust for the meter? I don't remember what the dwell reading is for these.

Denny, you are correct with the connections: red to the points/coil negative terminal and black to ground. I don't know about your Sears dwell meter in particular, but typically, the Set line is to adjust the meter circuit for internal battery voltage: you should be able to set the meter needle to the Set line by turning a "calibrate" knob when you have the selector switch set to a position for "calibrate." Also, there should be a small opening in the meter face to use a small screwdriver to adjust the mechanical zero of the meter movement: the needle should be at the mechanical zero when holding the instrument in position for normal use.

Most dwell meters have a position on the scale, either a line or a colored bar, for Distributor Resistance. When the meter is connected for measuring dwell, key on, engine off, points closed, the meter reading at or above the Distributor Resistance line, or within the colored bar, tells you that the DC resistance in the distributor/wiring/points/ground is low enough so as not to upset the dwell reading.

If you can post a picture of the instrument, I might be able to tell you more about it.

As for the dwell setting for your engine, something in the range of 32°-34° comes to mind, but I'm sure someone else can provide the original specification. As a rule of thumb, a dwell setting of 55% of the lobe angle is a good number, absent OEM specifications. The lobe angle is the angle between cam lobes in the distributor: 360/number of lobes on the distributor cam.

Harvester

"Dwell" translates to the number of degrees of distributor cam rotation the points are closed (they "dwell" together). A dwell meter is actually nothing more than a voltmeter. When the points are open, the meter reads battery voltage, since the circuit is not complete, and there's no current flowing. The meter is reading an open circuit with full battery voltage applied to it. When the points are closed, the voltage is zero, because the points are grounding the coil winding, and the dwell meter is attached between the coil and the points. Since the points are operating several times a second, the meter needle reads an average of the open and closed-circuit voltage, depending on how long the points stay grounded.

Let's say the points are closed 2/3 of the time. 1/3 of 12 volts is 4 volts, or 33% of the battery voltage. As the points are adjusted closer together, they stay closed longer, thereby decreasing the voltage the meter sees. If the points are open all the time, the dwell would be 0%, resulting in a dwell reading of zero degrees. That's the "set" line which is adjusted with the ignition on, and the points open. As the points close, the voltage seen by the meter goes to zero, and the needle will go to the full dwell setting, 60 degrees in the case of a 6-cylinder engine. A normal dwell reading of 60% to 66% of the distributor rotation would result in a setting of 36 to 40 degrees. That's about the maximum a 6-cylinder engine can handle. Usually, the dwell is set slightly less, to give the condenser plenty of time to discharge. If the dwell is set too high, the condenser completes its discharge as the points close, resulting in arcing and metal transfer.
Jerry