None, but the pipe threads on >>plastic<< fittings are close enough (and soft
enough) that they will "form" to the spark plug hole threads, making a good
enough seal for a cheap (like 89 cents) leak-down tester.
We verrrrrrrry tight!
On Wed, 25 May 2005 22:06:24 -0500, Elton Clark wrote
> Okay, I'll bite: What kind of engine uses pipe threads for sparkplugs???
> (Besides the Model T Ford, of course.)
> Eric wrote:
> > It might be worth rigging up a leak down tester to find out where/why the
> > compression is low. I've done this (cheaply) by screwing in a plastic hose
> > fitting (pipe threads on one side, hose barb on the other) into the spark
> > plug hole.