Started by DaveVA78Chieftain, August 13, 2009, 11:15 PM
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Reformated and updated article: Hemming Motor News Article - Hemmings Muscle Machines - JANUARY 1, 2007 - BY RAY T. BOHACZ
Back in the day when every spark ignition engine was equipped with breaker points, it was hard enough to find someone who really knew what they were doing when it came to working on a distributor. Today that quest is almost impossible. But if you own a muscle car that was produced prior to 1975, with only a few exceptions, the coil is fired through breakers. Thus, it would behoove those owners to become familiar with the proper service procedures for breaker point ignition systems. This installment of "The Lost Art" series will focus on the Chrysler breaker point and electronic ignition distributor. This style of distributor was used from the early 1960s until the last carburetor-equipped V-8 was delivered from a Mother Mopar assembly line.
An ignition system has two basic circuits. The primary, which consists of the breaker points, condenser, ignition switch, and primary windings of the ignition coil. The secondary part of the ignition system includes the secondary windings of the coil, the distributor rotor and cap, along with the spark plug wires and the spark plugs.
The ignition coil can be considered a transformer because it takes the 12 volts supplied by the battery and raises it up to around 30,000 volts. This is required so that the electricity can bridge the gap of the spark plug under cylinder pressure.
The breaker points control the flow of current through the ignition coil and allow the field to build. It can be considered a very accurate on/off switch. When the breakers are closed, the ignition coil is charging (dwell period). When they break open, the field in the coil collapses and induces the higher secondary voltage. On the average V-8 engine the breaker points open and close approximately 150 times per second at 60 mph. Under those conditions the points are closed for around 0.005 of a second for each spark plug firing.
In that brief interval, current has flowed through the coil primary, building up a powerful magnetic field. As the points separate, the primary current tries to keep flowing and arc across the opening contacts. The condenser, however, being connected directly across the primary circuit, absorbs the electrical energy at the breaker, accomplishing two things. First, the points are protected against arcing. Second, the energy stored in the condenser "kicks back" and helps in the almost instantaneous breakdown of the magnetic field in the coil.
If the breaker points are in poor condition, a diminished spark output from the coil will be the result. Points in good condition have a light frosty-gray color. If the points are black after a few thousand miles, it indicates that oil or grease has gotten on them. An excessive amount of oil on the distributor cam may be the cause of this condition and can result from a faulty breather or PCV system, causing the oil to come up through the distributor-shaft bushing.
If, under inspection, the points have deep pits and craters, the condenser usually is defective or has failed. When the crater is developing in the ground point (the stationary side) the condenser does not have sufficient capacity. When the crater is on the point connected to the moving arm, the condenser has excessive capacity. The moving member is the positive side while the stationary member is the negative side.
A faulty condenser or excessive charging output voltage is responsible for excessive wear of the electrical contacts. Wear of the rubbing block will cause the length of time the contacts are closed to increase and will result in gradually retarding the ignition timing. In contrast, if the point contact surface erodes from excessive current flow, the ignition timing will advance.
Properly installed points always have the outside diameters registering so that contact is made at approximately the center.
Point alignment is something that is very important and is often overlooked during installation. Proper alignment can be accomplished by bending the stationary contact and never by bending the moving arm between the rubbing block and the contact. Alignment of the fiber block of the moving arm with the cam is accomplished by bending the arm between the hinge pin and the block. The fiber block should never be filed or sandpapered.
Breaker point spring tension adjustment is critical, but will almost be impossible to check today unless you can find an old application specific spring tension gauge. For a Mopar, the breaker point spring tension should be set at 20 ounces. This value will reduce as the rubbing block wears. Adjustment to the spring tension is accomplished by moving the end of the spring either forward or backward under the screw, which fastens the free end to the breaker base plate. Excessive tension will create a high rate of wear at the rubbing block, but allow high rpm. Too little tension will cause point bounce and poor performance at high engine rpm.
The only way to properly service a Chrysler distributor, or any other brand that has the mechanism under the breaker plate, is to remove it from the engine (Delco distributors had the weights under the rotor). Trying to do a proper job with the distributor in the engine is impossible since all of components that require service cannot be accessed. So follow along as HMM shows you "The Lost Art" of Mopar distributor maintenance!