DWELL ADJUSTMENT

The dwell angle or cam angle is the number of degrees that the distributor cam rotates while the points are closed. There is an inverse relationship between dwell angle and point gap. Increasing the point gap will decrease the dwell angle and vice versa. Checking the dwell angle with a meter is a far more accurate method of measuring point opening than the feeler gauge method.

When setting ignition contact points, it is advisable to observe the following general rules:

1. If the points are used, they should not be adjusted using a feeler gauge. The gauge will not give an accurate reading on a pitted surface.
2. Never file the points. This removes their protective coating and results in rapid pitting.
3. When using a feeler gauge to set new points, be certain that the points are fully open. The fiber rubbing block must rest on the highest point of the cam lobe.
4. Always make sure that a feeler gauge is free of oil or grease before setting the points.
5. Make sure that the points are properly aligned and that the feeler gauge is not tilted. If points are misaligned, bend the fixed contact support only, never the movable breakable arm.

   A dwell meter virtually eliminates errors in point gap caused by the distributor cam lobes being unequally worn, or human error. In any case, point dwell should be checked as soon as possible after setting with a feeler gauge because it is a far more accurate check of point operation under normal operating conditions. The dwell meter is also capable of detecting high point resistance (oxidation) or poor connections within the distributor.

   The dwell meter, actually a modified voltmeter, depends on the nature of contact point operation for its usefulness. In this electro-mechanical system, a fiber block slides under tension, over a cam. The angle that the block traverses on the cam, during which time current is made available to the coil primary winding, is an inverse function of point gap. In other words, the wider the gap, the smaller the dwell (expressed in degrees); the closer the gap, the greater the dwell.

   Because the fiber block wears down gradually in service, it is a good practice to set the dwell on the low side of any dwell range (smaller number of degrees) given in specifications. As the block wears, the dwell becomes greater (toward the center of the range) and point life is increased between adjustments.

   To connect the dwell meter, switch the meter to the appropriate cylinder range, as the case may be, and connect one lead to ground. The other lead should be connected to the coil distributor terminal (the one having the wire going to contact points). Follow the manufacturer's instructions if they differ from those listed. Zero the meter, start the engine and gradually allow it to assume normal idle speed. See the Tune-Up Specifications earlier in this section. The meter should agree with the specifications. Any excessive variation in dwell indicates a worn distributor shaft or bushings, or perhaps a worn distributor cam or breaker plate.

   It is obvious from the above procedure that some means of measuring engine rpm must also be employed when checking dwell. An external tachometer should be employed. Hook-up is the same as for the dwell meter and both can be used in conjunction. Most commercial dwell meters have a tachometer scale built in and switching between them is possible.

Single and Dual Point Distributors

There are two methods to adjust the breaker point gap, the feeler blade method and the dwell meter method, of which, the latter is preferred.

FEELER BLADE METHOD

1. Remove the distributor high tension lead and ground it. Remove the distributor cap and rotor.
2. Check the breaker point alignment (refer to the accompanying illustrations). If necessary, align the contact points by bending the stationary contact. Never bend the moveable arm(s).
3. Crank the engine in short bursts, until the rubbing block on the breaker arm rests on a high point of one of the distributor cam lobes. In this position, the gap between the contact points is largest.
4. Insert a feeler blade of the specified thickness between the breaker points. The feeler blade will slide through the contact points with a slight drag when the gap is correct. If your truck is equipped with a dual point distributor, this step and the following steps should be repeated for each set of points.
5. If adjustment is required, loosen the breaker point attaching screws and move the stationary contact and base until the correct gap is obtained.
6. Tighten the attaching screws and recheck the gap.
7. Install the rotor and distributor cap. Reconnect the high tension lead.

DWELL METER METHOD

1. Disconnect the vacuum line from the distributor and plug it.
2. Connect the dwell meter in accordance with the manufacturer's instructions.
3. Start the engine, and run at idle until normal operating temperature is reached.
4. Observe the dwell meter reading. If the reading is within specifications, turn the engine OFF and skip to Step 5. If it is not within specifications, adjust the dwell as follows:

   NOTE: If dwell angle is above the specified amount, the point gap is too small; if it is below the specified amount, the gap is too large.

   1. Turn the engine OFF. Remove the high tension lead and ground it. Remove the distributor cap and rotor.
   2. Loosen the breaker point attaching screws and, while observing the dwell meter, crank the engine. Move the stationary contact(s) and base(s) until the correct dwell reading is obtained.
   3. Tighten the attaching screws. Install the rotor and distributor cap. Reconnect the high tension leads.
5. When the dwell angle check is completed, disconnect the dwell meter and reconnect the vacuum hose to the distributor.