The distributor would be the heart from the ignition system. Its three fundamental functions are to trigger the firing on the ignition coil, to control timing advance, and also to route or distribute the coil’s large voltage output on the person spark plugs.

On older applications with breaker stage ignition techniques, the contact points switch the ignition coil’s principal voltage on and off. The points are mounted on a movable plate during the distributor housing. Cam lobes on the distributor shaft rotate against a plastic block around the points to open and close the points. On newer applications with electronic ignition programs, the distributor includes a magnetic pickup or Hall effect switch rather than factors to create a signal for your ignition module (which switches the coil on and off). On a lot of applications, the ignition module itself can also be found in the distributor (GM HEI) or mounted to the distributor housing (Ford TFI).

DISTRIBUTOR Put on

Wear during the distributor drive gear can introduce play that may retard timing, while worn distributor shaft bushings (normally the outcome of infrequent oil changes and varnish buildup about the shaft) can lead to erratic timing. The two problems can impact engine overall performance, fuel economic climate and emissions. Should the distributor is worn, replacement will be the only repair option.

SPARK ADVANCE

With respect to timing, the distributor on older applications has both a centrifugal advance mechanism and vacuum advance diaphragm. Flyweights and springs inside the centrifugal advance mechanism add timing advance as engine speed raises. Bushing wear, rust, or weak or broken springs may well result in the centrifugal advance mechanism to overadvance or retard timing. Lubricating the mechanism with high temperature dielectric grease and/or replacing weak or broken springs may remedy a sticking issue, but worn bushings call for distributor replacement.

The vacuum advance diaphragm rotates the breaker plate to advance timing when intake vacuum is substantial to improve fuel financial system, and retards timing when the engine is below heavy load to avoid detonation (spark knock). If your diaphragm can’t hold vacuum, the diaphragm should be replaced (if readily available separately).

DISTRIBUTOR ROTOR & CAP

The distributor rotor directs the ignition coil’s higher voltage output for the various spark plug terminals inside the distributor cap. The condition with the cap and rotor are very important, as may be the “air gap” or distance between the tip of the rotor and cap terminals. If the cap or rotor are cracked, worn, eroded or have carbon tracks, either or the two should be replaced.

Sometimes a distributor will “eat” caps. Often this is due to excessive end perform during the distributor shaft. Too much end play allows the rotor to push up against the cap and put on down the center button. The rotor may well even contact the terminals and damage or break the cap. Shimming the distributor shaft may well reduce the end play, but replacement may also be necessary.

REPLACING A DISTRIBUTOR

If your engine needs a distributor, buying a remanufactured unit can usually save you money compared to buying a new one.

A used distributor from a low mileage vehicle in a salvage yard should be okay, but you may have to buy a new cap and rotor for it. Watch out for used distributors at swap meets because they could have been modified for a performance engine and will have the wrong spark advance curves for a stock engine.

Older breaker point distributors usually come complete with new points, condenser, rotor and cap. The factors are usually preadjusted so the unit can be dropped right in and the timing set. Some on the newer electronic distributors come complete with a module, rotor and cap while others do not.

One very important stage to note when installing GM HEI and Ford TFI ignition module in or on the distributor is to apply a coating of dielectric grease to the underside in the module. Grease is needed to conduct heat away from the module. Forget the grease and the module will likely fail within a few thousand miles.

distributor installation The index position of your distributor is very important because it need to be aligned correctly with the camshaft for proper ignition timing. Before you remove the old distributor, rotate the engine until the #1 piston is at top dead center (use the timing marks to the crankshaft pulley). Remove the cap and see in case the rotor is lined up with the cap terminal for the #1 piston. If it is not, rotate the crankshaft 180 degrees so it is lined up with the #1 spark plug terminal. Then remove the distributor hold down nut and clamp, note where the vacuum advance is pointing, then pull the distributor out from the engine.

When you install the new distributor, line up the vacuum advance in the same direction as the old distributor was pointing, rotate the shaft so the rotor will be pointing approximately inside the same location as the #1 spark plug terminal, then slide the distributor into the engine. The angle with the drive gears will bring about the rotor to rotate slightly and the distributor slides all the way into the engine. Replace the distributor hold down clamp and nut, but do not tighten.

Start the engine and use a timing light to adjust the timing to specifications (typically 6 to 10 degrees of advance with the vacuum advance hose disconnected and plugged at 550 to 650 rpm idle speed). Refer to the emissions decal below the hood, a service manual or online service information for the timing specifications and procedure for your engine, because they do vary quite a bit. If your engine has computer controlled spark timing, no adjustment is possible. Just lock down the distributor.

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