500 hours is reasonable, but it depends on who made the plug and how
it's cleaned.
We have had terrible luck with Champions; the electrode wear is
OK but the internal resistor fails much too soon. It will often quit
sparking at pressures below 120 psi, and sometimes you can hear it
arcing internally during the test. I have had brand-new Champs fail
right out of the box.
I prefer the Unison (AC) plug; it uses the Auburn design, having
an integrally molded resistor rather than Champion's loose one (which
is held by a spring) and we get 500 hours without much trouble. Less
cost, too.
Some spark plug cleaners use silicon carbide grit. This stuff is
really harsh, and can cause a lot of electrode erosion and shorten
plug life. We use glass bead. Much gentler, and cleans every bit as
well.



Justin Case wrote in message . ..
500
On Thu, 14 Aug 2003 03:38:19 GMT, john smith
wrote:

How many hours of service should one expect from a set of spark plugs?
(i.e.- Lycoming IO-520 in a PA32-300)