Cleaning Spark Plugs is a Simple Job...

wrote:

.... good info snipped...

We've recently had trouble with AC plugs; the internal resistor
seems to be failing. Champs have had that problem for years.

Dan,
I recently used my Fluke 77 DMM to check eight Champion REM40E
spark plugs, which have a built in radio suppression resistor. I
measured Ohms between center electrodes and threads (all Open). I then
measured the resistance through the center electrode from the wire end
to the electrode end, and noticed that two of eight plugs were "Open"
(10MegOhm), while the other six ranged from 1.4K to about 7K.

I expected all of these to be the same resistance, but was surprised at
the variablity plug to plug. I am puzzled at the two that read open.
They were not misfiring before removal. What's going on?

btw- I also measured 12 brand-new RHM40Es; 4 of 12 were open end to
end???

"mikem" wrote in message
ups.com...
(10MegOhm), while the other six ranged from 1.4K to about 7K.

I expected all of these to be the same resistance, but was surprised at
the variablity plug to plug. I am puzzled at the two that read open.
They were not misfiring before removal. What's going on?

No problem. The ones that read open had a sub-thousandth crack on the
resistor and would arc across the crack before going to the two orders of
magnitude larger crack called a spark gap.



btw- I also measured 12 brand-new RHM40Es; 4 of 12 were open end to
end???

QC strikes again. They only "bomb test" the suckers. If there is a minute
crack between the resistor and the plug, they figure that the plug gap will
predominate in the sparking mechanisms. With the obvious comment that a
spark in oxygen rich atmosphere will wear down a contact MUCH further than
in the combustion chamber. Thus a failed plug in a few hundred hours. I'd
suggest you reject the opens. Unless we all continue to do so, plug
manufacturers will be getting away with this slop.

Jim

We learned a long time ago to bomb-test even brand-new
plugs. We've had new Champs fail right out of the box. It can't be just
a tiny crack in the resistor; there has to be something else going on
here. When I remove that screw inside the barrel and take out the
spring and resistor, I can't find anything wrong with it. And if I take
that stuff out of a working plug, it doesn't want to work again after
reassembly. I think there's something wrong with the spring-loaded
resistor concept.
The old Auburn plugs had a molded-in resistor that seldom
failed, and AC copied that idea but have had some trouble anyway.
Now here's a debate: The resistor was originally to reduce
radio interference in automotive plugs. Since aircraft plugs are
shielded, that's not necessary. The textbooks say that the resistor is
there to shorten the spark duration and reduce electrode erosion.
Wouldn't it be better to leave the resistor out and accept shorter but
consistent plug life?

Dan

wrote:
: Now here's a debate: The resistor was originally to reduce
: radio interference in automotive plugs. Since aircraft plugs are
: shielded, that's not necessary. The textbooks say that the resistor is
: there to shorten the spark duration and reduce electrode erosion.
: Wouldn't it be better to leave the resistor out and accept shorter but
: consistent plug life?

It *may* be acceptable, but the shielding isn't 100". Also, the increased
distributed capacitance of the shielded plug wires would lead to extra-high currents
if there were no resistance in the loop. I think that plug life is already pretty
low... it would probably be horrid without the resistor.

-Cory

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************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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