[T3] How's the trip going?

john carartbyjohn.com john at carartbyjohn.com
Mon Jun 20 20:36:36 PDT 2022

Thanks for the info tonight Jim. Still trying to track down a new rotor.

I pulled the old rotor.  Shouldn't there be continuity between the center and the tab that swipes by the 4 plug wire locations in the cap?  I don't get and reading there at all.

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From: type3-vwtype3.org <type3-vwtype3.org-bounces at lists.vwtype3.org> on behalf of Jim Adney <jadney at vwtype3.org>
Sent: Monday, June 20, 2022 8:03:37 PM
To: type3 at vwtype3.org <type3 at vwtype3.org>
Subject: Re: [T3] How's the trip going?


Nice to get that call from you tonight. I'm 99% sure that the rotor is the

My favorite tool for diagnosing HV spark problems is an inductive timing
light. The inductive pickup senses CURRENT, so, in this case, you'd see
current going into the distributor but not coming out.

Since that current is bound and determined to get to ground somehow, it has
managed to get there somewhere within the distributor. There are only 2 HV
insulators in the distributor: the cap and the rotor.

The cap is easy to inspect. Sparking to ground in the cap will either be via a
carbon track, which is easy to see, or by way of dew (yes, been burned by
that!) inside the cap.

The spark can also puncture right thru the rotor, to the grounded shaft. This
is made more likely by the OG sharp corners on top of the shaft. I file a
radius on these whenever I rebuild a dizzy. You won't be able to see the
puncture. It's completely invisible, but you can find it with a HV source that
sparks along the insulator surface. If there's a puncture, the spark will go
RIGHT THERE. If there's no puncture, the spark will flow evenly along the
whole surface.

I've encountered this twice. Once on a customer who was stranded
somewhere. Couldn't figure that out until I swapped him the rotor from my
Square. I'll tell you the rest of that story when we see you on Thursday.

It happened to me on my ugly/rusty '73 a few years ago. That car had
become hard to start and would sometimes have trouble pulling away from
stoplights. It was oddly intermittent. Unfortunately, it never happened when I
was home, near tools. That was an aftermarket rotor, now in the
basement,marked bad. Out of curiosity I took it to campus and ran one of
those hand held Tesla coils over it. The spark went right to a place where
the corners on the top of the shaft would have been.

Good luck on the rest of your journey. See you Thursday.

Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA

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