On Wed, 31 Aug 2005 12:53:46 -0500, "Jim Burns"
wrote:

I've been researching how to replace an old AC Spark Plug CHT probe in our
Aztec. AC doesn't make them anymore and the replacement Rochester brand
probe operates at a different resistance range requiring the gauge to be
removed, shipped out and recalibrated. Not a fun proposition.

Rumor, and a couple parts houses, have told me that the American Bonanza
Society published an article about this problem and a solution is to install
an 82ohm resistor inline with the probe to account for the difference
between the AC and the Rochester gauges. Sounds easy enough.

Is there a group member that belongs to the ABS that could verify the
article and possibly post or email me a copy??

Any other thoughts or comments about this??

IMHO, an accurate CHT indication is one of the things that can tend to
contribute to engine longevity.

Unless you were planning on installing a PMA'd primary replacement
http://www.buy-ei.com/Single%20Primary.htm or
http://www.buy-ei.com/Dual%20Primary.htm
at some point in the near future, I would recommend doing the "right"
thing and getting your probe replaced and your indicator calibrated.

I probably would consider installing a resistor to be a minor
alteration, but would still recommend getting the system
checked/cal'd.

Actually, I would recommend getting both CHT gages cal'd and replacing
both probes. I allegedly used to maintain a bunch of working GA
aircraft (including PA23's), one of the things we ALWAYS did at engine
o-haul was replace the CHT and oil temp probes, and have the gages
cal'd (APoLH). Did the EGT/TIT systems also, but we had the
capabilities to do 'em in-house.

Compared to the cost of engine overhaul/installation, this is cheap
peace-of-mind.

Remember, this advice is worth exactly what you paid for it...

TC