Bad cap and rotor

[whc03grady]

I did my valves today and noticed this damage to the center contact on the cap, and the funny pattern on the rotor. What would cause this kind of damage? The bus ran fine, and I replaced both these pieces. The distibutor is a, uh, ahem, 009 [ducks].

[LiveonJG]

It looks like there may be some endplay in the rotor. That contact in the cap is spring loaded and I'd guess that at the point of ignition for each cylinder, the cap contact is on a different part of the rotor contact. That's what caused the 4 burned spots. This is a pretty far out theory, I know, but it is Friday. Anybody else?
-John

[DurocShark]

Why is the fat end of the rotor so beat up? You may be looking at a sloppy distributor shaft. Sounds like a great time to buy an SVDA or at least a stock vacuum distributor.

[Amskeptic]

I did my valves today and noticed this damage to the center contact on the cap, and the funny pattern on the rotor. What would cause this kind of damage? The bus ran fine, and I replaced both these pieces. The distibutor is a, uh, ahem, 009 [ducks].

Occasionally, a rotor will not be properly seated on the shaft, thus pissing off the brush in the cap. Also, there are thrust shims between the drive lug and the bottom of the distributor to keep the shaft from sticking up too high. Do not indict your distributor if the shaft has a bit of axial movement, it is normal.
Colin