OK I can report back a little now.
As I said before, in my car, is that the spark is working its way through
the casing of the rotor and grounding on the distributor drive. I cannot
find a crack (even under a magnifying glass), but I can find what appears to
be a tiny hole where the spark has burned through.
I do not know if it is related to the rivet in any way, thought many have
reported problems with the rivet.
What I have been told is happening is that there is a problem with the
strength of the compound that the arm is built with. This is exaggerated by
heat, and as it weakens it can fail by either of the two ways that we are
documenting.
UK Healey (http://www.ukhealey.co.uk/) has commissioned a reproduction of
the larger arm original style rotor. I ordered 2 of these at a total cost
including shipping to the US of $16.38. They arrived today and here are my
initial observations.
I'll start this by saying that I do not have any precision instruments to
measure this, so everything I say is to be considered approximate.
The ignition rotors from UK Healey are very different than the Lucas Green
box rotors that have been the subject of much conversations.
The first, and most noticeable difference is that the arm is longer than the
"green box" version.
The radius's from the center of rotation to the edge of the arm are
approximally:
7/8" for the "green box" rotor
1-1/16" for the UK Healey rotor
For the distance between the center of the button to the brass plug lead
contacts on my NOS Lucas cap is 1-1/8".
Here are pictures of the difference
http://home.earthlink.net/~kpdii/rotor_1.JPG
http://home.earthlink.net/~kpdii/rotor_2.JPG
I would think that the larger gap from the rotor to the contact would
increase resistance, and could be causing the spark to seek an easier path,
combine that with cheaper constructed insulation, and I think I have found
the reason for the burned out rotors.
A worry would arise concerning distributor shaft play. Since this clearance
is very small, I would think that a sloppy distributor would cause the arm
to hit the distributor.
A couple of other differences are apparent. The new rotor does not have the
metal spring on the inside, I do not know if this is important or not, here
is a picture from the bottom
http://home.earthlink.net/~kpdii/rotor_3.JPG
You will see that the new style rotor also uses a different rivet
http://home.earthlink.net/~kpdii/rotor_4.JPG
The writing on the top of the new style says "remove to oil"
The height of the rotors appears the same
http://home.earthlink.net/~kpdii/rotor_5.JPG
I will send along more information as I play with these, and will eventually
place a page on my web site for this. If anyone has a picture of a rotor
with a rivet failure, please send it along and I will include it in the
final.
I hope this information helps someone.
Patton
Patton Dickson - Richmond, TX - '57 A-H 100-Six - http://Austin-Healeys.com
-----------------------------------------
- Marissa: "Wow, that's really loud."
- Frank: "Yeah, thanks, I took the restrictor plate off. ...gives the red
dragon a little more juice. But uh, let's keep that on the downlow! It's not
exactly street legal." - Old School
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