[T3] How's the trip going?

Jim Adney jadney at vwtype3.org
Mon Jun 20 20:03:37 PDT 2022


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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