[T3] STUMPED!!???

Jim Adney jadney at vwtype3.org
Thu Nov 28 13:49:49 PST 2013


I took the defective rotor to the physics dept yesterday and managed 
to find where the spark was shorting to ground. I did this by setting 
up a spark generator (Tesla coil) to play HV sparks along the 
insulator surface, to see if there was a particular place that the 
spark wanted to go to get to ground.

I started with the rotor mounted on a grounded distributor shaft. The 
spark played evenly all over the outside surface of the bakelite, but 
what it really wanted to do was go to one of the brass contacts on 
top. It was clear that there must be a puncture from the underside of 
that brass, thru the core of the rotor, to the shaft, but I couldn't 
see anything more than that.

Then I turned the rotor upside down, so the brass pieces were 
grounded and played the spark over the socket where the dist shaft 
normally goes. The spark would always go to the little flat steel 
spring that keeps the rotor snug on the shaft, but I could also see 
the spark jump from the inside end of that spring to one particular 
spot at the bottom of the shaft socket. With the spark off, there was 
nothing I could see at that spot, but the spark always jumped to the 
same place.

So this rotor failed when the insulator punctured right thru the 
middle. The spark still had to jump a small air gap to get to the 
puncture point, so that must have been what let this work some of the 
time.

BTW, this Taiwaneese copy had no resistor between the center and end 
brass contacts. It DID have that "red glue" that normally hides the 
Bosch resistor, but in this case there were zero Ohms.

I may try to cut this apart to see if there's anything visible 
inside.

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