I don't think that Keenserts would work very well in a spark plug hole.
They don't appear to provide any sealing action against the high
pressure of compression and combustion inside the combustion chamber.
The high pressure gas would seem to want to work it's way past the
straight thread insert eventually causing the insert to overheat and
fail.  I can envision the driven keys blowing out under the influence of
heat cycles and pressure.

Has anyone on this list used Keenserts in spark plug holes?  How well
did that work for you?


Mark LaPierre


I have, or similar from NAPA. The tap follows what's left of the
original threads and angle. I ran the output of the shop vac through the
exhaust pipe to keep the chips coming my way.

Then you put the insert on a standard plug (whatever is supposed to go
into that hole) and add a locking compound to the outside of the insert.
Tighten the plug and let it sit for a few hours.

I was gifted a racing head that had two plug holes melted out. The
repair worked perfectly on a 14.5:1 compression engine*.*

245 pounds of cranking compression.
The insert had a small flange at the top that dug into the top of the hole.

Also repaired a Honda MC for my kid's friend. Everyone was happy.

Lynn E. Hanover