Orval Fairbairn wrote:
In article ,
David Lesher wrote:

(Drew Dalgleish) writes:

Kroil probably won't work if it has never seize on the threads but it
can't hurt to try. If it's really stuck it's probably faster to pull
the prop and ring gear than to mess things up trying to work around
it. Flying long enough to get the case fully warmed up may help too.

Not NeverSeize but pipedope, but I tend to agree. Another trick that
comes to mind is a large American Beauty soldering iron applied to
the plug, getting it hot enough to disrupt the pipe dope. (The iron
will not melt the case so that's no worry.)

You are better off heating the crankcase area with a heat gun and
turning the plug with the Allen wrench. Heating the plug will just
expand the plug into the case, whereas heating the case will expand the
aluminum away from the plug.

Lycoming typically uses Teflon pipe sealant on those plugs,
and with age and heat the stuff sets and gets really stubborn.
Heating the entire area or just the plug itself will usually
work. The trick is to let the thing sit for a minute after heating; the
plug and case will come to the same temperature, and since aluminum
expands at twice the rate of steel for a given rise in temperature, the
plug will loosen slightly. More effective than the loosening will be
the relaxing of the grip of the teflon dope. I used to rebuild air
compressors that often had steel plugs in aluminum, and we used to
torch just the plug, let it sit, then back it out. The biggest risk
with this was the tearing out of the aluminum threads, especially with
the softer casting aluminums.
That said, there have been times I haven't been able to get
plugs or other fittings out of the engine core when installing a new
one, and rather than risk damaging the core ($$$) we put in a new
fitting and let Lycoming fuss with getting the old one out. This
doesn't help your situation. The casting around those plugs is rather
massive and will soak up an awful lot of heat before the temp will rise
much, and there's a risk of overheating the case in trying to get the
plug warmed up.
I noticed that the JPI probe has a 3/8"-24 thread on it, which
they claim is a match for the 1/8" pipe thread. This isn't true; it may
fit, but it could damage the threads, because 1/8" pipe has a 27 tpi
thread and is tapered. You sure won't want to force it in too far. Most
people massively overtorque pipe fittings, far beyond what's necessary
to keep them there; the spec is quite low and should be used. We used
to get a lot of compressors and control valves back with split pipe
bosses from overtorquing. Somehow the mechanics felt that the air or
coolant was going to push that plug out unless it was supertight.

Dan