Peter Conover wrote :
>
> My question is, what can go wrong with a rotor that will make a
> car completely
> stop running without any warning whatsoever. There doesn't
> appear to even be
> anything wrong with it. Weird?
I'm not sure about the 'no warning' part, but rotors can fail by 'carbon
tracking' through the middle, between the brass plate on top, and the top of
the distributor shaft. It can be tough to see, even when you're looking for
it. The only sign is a small spot, inside the rotor where it sits on the
shaft, typically less than 1/16" in diameter, and only a slightly different
shade of black (dull rather than glossy) than the normal rotor material.
It can be caused by something else amiss in the high tension wiring, eg a
bad plug wire, broken resistor, bad connection, bad plug, etc. If you don't
solve the underlying problem, the rotor will fail again. This happened to a
local club member on the way home from VTR last year, the brand new (bought
at the show) rotor on his TR4A died less than 200 miles out of Beaverton.
After eliminating the broken plug resistor and cobbling up a rotor, he made
it home without further incident.
For those unfamiliar with the term, 'carbon tracking' occurs when a spark is
forced to jump through (or even along the surface) of the plastic (bakelite
?) used for distributor rotors, caps, coils, etc. The intense local heat
from the spark causes the plastic to decompose back into carbon, which of
course is a conductor. The factory ignition is usually chosen such that it
cannot reach the breakdown voltage of components like the rotor and cap, but
changes like adding a Lucas Sports coil, or an electronic ignition, can
allow the voltage to go higher (if for some reason it doesn't jump the plug
gap first). Dirt can also play a role in allowing a track to form.
Randall
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