[old_master]

If the distributor is not centered in the bore of the intake manifold, it will cause the distributor gear to wear. The driven gear, (on the distributor shaft) is slightly softer than the camshaft, making it sacrificial. The distributor bore on the intake manifold is larger than the distributor housing to allow for a slight adjustment of camshaft retard. Years ago, ignition timing was adjusted by rotating the distributor. On 4.3L OBDII engines, rotating the distributor does not affect ignition timing. Rotating the distributor on these engines is how camshaft retard is adjusted. If camshaft retard is off more than 2 degrees, it will cause the spark in the cap to jump a larger gap, (and can also set a P0300). The hotter spark is what causes the terminals of the cap and rotor to burn. This is quite common with aftermarket caps as the placement of the terminals can be incorrect. If camshaft retard is correct, and the cap and rotor terminals burn, you have a faulty distributor cap. If you have an AC Delco cap and the terminals burn, camshaft retard is off.