<VV> Thermisters (Now Thermocouples)

[Sethracer at aol.com]

In a message dated 8/15/2005 9:51:25 AM Pacific Daylight Time,  
RoboMan91324 at aol.com writes:

I have  always wondered if there is any issue with sparkplug thread depth 
when 
you  use an under-the-plug thermistor.  Obviously, the sparkplug will sit a  
little higher in the hole by the thickness of the thermistor.  If any  of the 
threads in the head are exposed, wouldn't there be a problem with  carbon 
build 
up?  This could cause a problem if you ever remove the  thermistor for any 
reason.  The carboned threads would cause  interference with the plug that 
would now 
want to go deeper.  Also,  if the plug is at all recessed in the plug hole, 
could this cause an  ignition problem?  I understand that some plugs already 
have 
a depth  problem even without the use of an under-the-plug thermistor.

Inquiring  minds want to know.

Doc



It is not a problem, Doc. It is not a thermistor which goes under a plug.  
All of the other Head-temp gauges are thermocouple types. They use a bi-metallic 
 junction crimped into a ring terminal. The ring terminal replaces the 
original  plug gasket - at least on the Corvair. The plug "height" is virtually the 
same  as original. I suppose you could retain the original gasket, but it 
might alter  the heat range of that plug, since it would add insulation into the 
cooling path  of the plug- but not much - since most of the heat probably goes 
through  the threads. Many people just crimp the two wires into a smaller ring 
terminal  and mount it in another location. If you have either removed the 
stock  thermistor or snap switch, or the head is not equipped with a sender 
(like all  non-Corsa/Spyder models) you han mount the ring under a really short 
bolt in the  stock location. - Seth Emerson