Distributors & Parts

All late model cars and trucks are equipped with electronic, distributorless ignition systems. On the latest COP (Coil on Plug) systems an ignition coil is directly connected to the spark plug in each cylinder and spark timing is computer controlled based on input from sensors and internal programming. But from the early days of the automobile until well into the 1980s, combustion in an engine’s cylinders was initiated by voltage from a single coil that was directed to each spark plug by a distributor and spark plug wires, and for most of that time the distributor also mechanically controlled spark timing with breaker points and advance weights. Distributors contain a number of wear components that require periodic adjustment or replacement, and distributor defects can cause no-starts, hard starting, and poor performance and fuel economy. Whether you’re doing a tune-up and regular maintenance or want to repair an engine operating problem, you’ll find all the distributor components you need right here on our digital shelves.

A typical distributor consists of a shaft that rotates on bushings inside a cast iron or aluminum housing. Attached to the bottom of the shaft is a gear that’s driven by the camshaft. The distributor shaft also drives the oil pump on many engines. The distributor rotor is mounted at the top of the shaft and along with the distributor plate and triggering and advance mechanisms it’s enclosed inside a distributor cap. The distributor cap, made of phenolic or plastic, attaches to the top of the distributor housing with clips or screws. It contains terminals at the cap perimeter for each cylinder and a terminal in the center that connects the rotor with the ignition coil. Most distributor caps have a center terminal that connects to an external coil with a high tension lead, but on some distributors the coil is mounted directly to the cap. The rotor distributes the ignition coil voltage to the individual cylinder towers on the cap as the distributor shaft rotates. The spark plug wires attached to the distributor cap cylinder towers deliver the voltage to the spark plug in each cylinder.

Current flowing through the ignition coil’s primary windings creates a magnetic field. When that current flow is interrupted the collapsing magnetic field produces an electric current in the secondary windings, which is stepped up to the 15,000 – 40,000 volts needed to jump the gap between the spark plug electrodes and ignite the air/fuel mixture in the cylinders. Current flow is interrupted by the triggering mechanism in the distributor – mechanical breaker points or electronic components. In the mechanical system, a cam on the distributor shaft has lobes that correspond to the number of cylinders. The breaker points, also called a contact set, are mounted to a plate adjacent to the cam. A rubbing block on the arm of the point set rides on the cam, with the lobes opening the points. When the points are closed, current flows and the magnetic field builds up in the coil – this is the dwell time. When the cam lobes open the points, the magnetic field collapses and voltage is sent to the spark plugs. A capacitor called a condenser is included in the circuit to reduce arcing and burning of the contacts.

While it’s reduced by the condenser, during engine operation there is still some arcing at the points, which causes erosion of the contacts, and coupled with rubbing block wear this changes point gap, dwell and timing, adversely affecting performance and emissions. To eliminate the frequent adjustment and replacement required by breaker points, vehicle manufacturers began switching to electronic triggering mechanisms in the late 1960s and early 70s. Electronic control offered several advantages; there were no mechanical parts to wear and more voltage to the spark plugs could be provided for more efficient engine operation. In place of the cam on the distributor shaft, electronic distributors have a reluctor with teeth that correspond to the number of cylinders, and instead of breaker points a magnetic pickup or hall effect switch is mounted on the distributor plate. As the distributor rotates and the reluctor passes the pickup or sensor, a signal is sent to an ignition module, which contains a transistor that closes and opens the primary circuit to create and collapse the magnetic field and produce the voltage sent to the spark plugs.

It takes time to fully ignite the mixture in the cylinders, so spark plugs are typically timed to fire a number of degrees BTDC (Before Top Dead Center) on the power stroke, so the full force of combustion can be applied to the pistons. This is called initial timing. However, as RPM increases the spark plugs must fire even earlier. To advance the timing distributors have a centrifugal advance mechanism consisting of weights and springs. As engine speed increases and the distributor shaft rotates faster, centrifugal force pushes the weights outward, which in turn moves the distributor cam to change timing. The springs control the rate of advance. Beginning in the 1950s, vehicle manufacturers began installing vacuum advance mechanisms. Vacuum advance advances the timing during vehicle operating conditions like highway cruising, when engine load is light and vacuum is high, to increase engine efficiency. The vacuum canister is mounted to the distributor housing and contains a diaphragm that is attached to the distributor plate. Engine vacuum pulls on the diaphragm and the plate to advance timing. Eventually spark advance also became electronically controlled on distributor ignitions.

Along with breaker points and condenser, the distributor cap and rotor are also considered wear items that must be periodically replaced. Check the cap terminals and rotor for evidence of corrosion, erosion, carbon tracking and cracks. Voltage must jump the gap between the rotor tip and distributor cylinder terminals, and these are common wear areas. Although electronic triggering mechanisms are much more reliable than breaker points, distributor shafts and bushings can wear, resulting in excessive play and an improper gap between the reluctor teeth and pickup or sensor. Vacuum advance diaphragms can fail, and centrifugal advance mechanisms can get sticky and immobile, resulting in insufficient advance, poor performance and overheating, and centrifugal advance springs can break, causing too much advance too soon and pinging.

No matter what vehicle you’re working on or whether you have mechanical breaker points or electronic ignition, we have the replacement distributors and related components needed to restore proper performance, reliability and fuel economy. We offer distributors and components that are manufactured to original equipment specifications, so when repairs are completed you can count on the performance your vehicle was designed to deliver. In addition to an extensive selection of complete distributor assemblies, we also offer all the distributor related components needed for tune-ups and repairs including contact sets, condensers, distributor caps and rotors, ignition pickups and sensors, reluctors, vacuum advance canisters, and much more. And if you want better performance and reliability with less maintenance, we have electronic ignition conversion kits to replace the mechanical breaker points on most popular vehicles.

Upgrade your factory distributor with a performance cap and rotor. We offer tough, alkyd compound caps with brass inserts, which resist corrosion and provide better conductivity. Get more precise and consistent spark timing, and eliminate the need for breaker point replacement with an electronic ignition conversion kit. Or get these features and more with a performance distributor. Our distributors are available with dual points or electronic ignition, and some even feature preprogrammed or custom advance curves, with housings turned from billet aluminum and shafts that turn on oil lite bushings and/or ball bearings.