There are myriad products available today designed to replace the mechanical contact points found within a conventional distributor and convert it to electronic operation. While such conversions are quite popular, there remains a large number of vintage Pontiacs occupying today's roads that still contain yesterday's technology, and they require occasional maintenance and eventual component replacement to maintain peak operating condition.
While such tasks seem relatively simple for those familiar with points-type systems, many novice hobbyists are unfamiliar with the characteristics of contact points, and consider the maintenance and replacement a science similar to quantum physics, but nothing is further from the truth. Follow along as we install a fresh set of contact points in a conventional Pontiac distributor, and prepare it for countless miles of trouble-free operation in less than an hour.
Contact Points Basics
The contact points within a conventional distributor transfer electrical current from the coil to the spark plugs, and its action is controlled by a small cam that rotates about the distributor's mainshaft. A magnetic field builds within the coil while the points are closed. The duration that the points remain closed, which is expressed in degrees of rotation, is referred to as "dwell angle." As the points open, the magnetic field collapses, and an intense electrical spark travels the air gap from the spark plug's electrode to its ground strap, igniting the compressed mixture.
As the contact points surface and plastic rub block wear during normal operation, the dwell angle changes. As dwell exceeds its specified range, spark intensity degrades (and spark advance changes), ultimately affecting emissions and performance. Periodic contact point adjustment is required to ensure that dwell angle remains within a specific range to maintain peak engine performance. Once the contact points wear beyond practical adjustment, eventual replacement is required.
Replacing The Contact Points Set
Replacing a distributor's contact points set is very straightforward. It involves nothing more than simply removing the existing assembly and installing a replacement. The required preliminary dwell adjustment that immediately follows, however, can be the most difficult portion of the swap, and that can seemingly lead to an engine without spark.
In years past, some manufacturers pre-adjusted the contact points sets during assembly, and when installed into a distributor, were found to be within a reasonable dwell range for easy engine start-up and final dwell adjustment. Many of today's contact points sets are nowhere near a reasonable dwell range, and oftentimes require physical measurement to ensure quick engine start-up. The accompanying photos show that process in detail.
Conclusion
An argument against contact points has often been required maintenance, but that's largely a non-issue when we consider how sparingly our vintage Pontiacs are driven today. So if you own a Pontiac that was originally equipped with a points-type distributor, and you prefer its mechanical function over an electronic conversion, expect complete contact points set replacement to take about 30 minutes and set you back around $25. After that, a slight amount of periodic preventative maintenance is typically all that's needed for thousands of miles of reliable performance.
This contact points set has...
This contact points set has obviously seen better days. Though the distributor appears to have been removed from a relatively low-mile engine, it has sat dormant for quite some time, and the contact surfaces of the points set are badly corroded. A fresh set of contact points was among the items we installed in this distributor before placing it back into service.
Contact points sets are available...
Contact points sets are available from various manufacturers, but because of limited use today, not all parts stores keep them in inventory. While the quality of some is questionable, NAPA No. CS89 is an excellent choice for most non-race applications. Retailing for around $25, it's what we regularly use when servicing conventional distributors. This distributor's condenser didn't need replacing, but NAPA No. RR175 is our choice if it did.
After removing the condenser...
After removing the condenser and primary wire leads from the contact points set, we removed the two small screws that secure the assembly to the breaker plate, lifted it away from the housing...
...and installed the new ...
...and installed the new set.
With the new points set in...
With the new points set in place and the associated wiring reconnected, we proceeded with the preliminary dwell angle adjustment. We rotated the engine (which rotates the distributor) so the contact point's plastic rub block was aligned with a distributor cam lobe peak, and using a feeler gauge, adjusted the points gap to 0.019-inch.
This setting should provide...
This setting should provide sufficient dwell angle to get the engine started and make the final adjustment. Before dropping the distributor back into the engine, we lightly lubricated its cam lobes with quality bearing grease.
To reset dwell angle with...
To reset dwell angle with a distributor in an engine, we would connect a dwell meter to the negative terminal on the coil and the appropriate power leads, start the engine, open the adjustment window, and make the appropriate adjustments.
Factory dwell settings range...
Factory dwell settings range between 28 and 32 degrees-we routinely set ours at around 30 and check it annually. Use caution when making under-hood adjustments-you'll receive a sharp jolt if you ground the contact points in any way. Also, remember that dwell affects ignition timing, so be sure to reset timing after making any dwell adjustment.
Vintage distributor testing...
Vintage distributor testing equipment, like this Allen Syncrograph, was specifically designed to test the entire functionality of a distributor and typically included a built-in dwell meter, vacuum pump for testing vacuum advance, and electronic strobe for testing centrifugal advance. It can make servicing a distributor much simpler, since final dwell adjustments can be performed on the machine. It also allows us to spin the distributor at high rpm, and check for any unwanted signs of high-speed points-bounce.