Dwell angle is the amount of time (measured in degrees of distributor cam rotation) that the contact points remain closed. Initial point gap determines dwell angle. If the points are set too wide they open gradually and dwell angle (the time they remain closed) is small. This wide gap causes excessive arcing at the points and as a result, point burning. A small dwell doesn't give the coil sufficient time to build up maximum energy and so coil output will also suffer. If the points are set too close, the dwell is increased but the points may bounce at higher speed, the idle becomes rough and starting is made harder.
Remember when adjusting the dwell angle that the wider the point opening, the smaller the dwell and the smaller the gap, the larger the dwell. Adjusting the dwell by making the initial point gap setting with a feeler gauge is usually sufficient to get the car started and running, but a finer adjustment should then be made using a dwell meter.
Connect the red lead (positive) wire of the meter to the distributor primary wire connection on the Positive (+) side of the coil, and the black ground (negative) wire of the meter to a good ground on the engine. The dwell angle may be checked either with the engine cranking or running, although the reading will be more accurate if the engine is running. With the engine cranking, the reading will fluctuate between 0° dwell and the maximum figure of that angle. While cranking, the maximum figure is the correct one.
Dwell angle is set electronically on HEI distributors, requiring no adjustment or checking.
Dwell can be checked with the engine running or cranking. Decrease dwell by increasing the point gap; increase dwell by decreasing the gap. Dwell angle is simply the number of degrees of distributor shaft rotation during which the points stay closed. Theoretically, if the point gap is correct, the dwell should also be correct, or at least very close. Adjustment with a dwell meter produces more exact and consistent results since it is a dynamic adjustment. If dwell varies more than 3° from idle speed to 1,750 engine rpm, the distributor is worn.
- To adjust dwell on a 6-cylinder engine, trial and error point adjustments are required. On a V8 engine, simply open the metal window on the distributor and insert a 1 / 8 in. hex wrench. Turn the adjustment screw until the dwell meter shows the correct reading. Be sure to snap the window closed when the adjustment is finished.
- An approximate dwell adjustment can be made without a meter on a V8 engine. Turn the adjusting screw clockwise until the engine begins to misfire, then turn the screw outward 1 / 2 of a turn.
If the engine won't start, check:
- That all the spark plug wires are in place.
- That the rotor has been installed.
- That the two (or three) wires inside the distributor are connected.
- That the points open and close when the engine turns.
- That the gap is correct and the hold-down screw, if applicable, is tight.
- After the first 200 miles or so on a new set of points, the point gap often closes up due to initial rubbing block wear. For best performance, recheck the dwell (or gap) at this time. This quick initial wear is the reason the factory recommends 0.003 in. more gap on new points.
- Since changing the gap affects the ignition timing, the timing should be checked and adjusted as necessary after each point replacement or adjustment.
The dwell angle on models equipped with the HEI ignition is electronically set and is not adjustable.