Video How-to: Time-Sert Permanent Repair for Spark Plug Thread
Spark plug thread damage is increasingly more common, mostly due to the popularity of
aluminum cylinder heads on automotive and OHV engines. This HD video how-to demonstrates the Time-Sert®
permanent repair for damaged spark plug threads. This insert kit allows for head-in-place installation of new
spark plug threads. The candidate shown is a popular Honda XR650R motorcycle. The affordable repair saved a lot
of time while providing a major improvement over OEM spark plug
Time-Sert® is a permanent repair for spark plug threads. The #4412 Kit that we
used in this project came with each of the tools shown at right. The #44111 16.8mm length inserts were selected.
(Sold five to a package, we only used one on this single cylinder "thumper".) This tooling permitted a repair with
the cylinder head in place on this Honda XR650R motorcycle engine. Follow the comments and steps in the video, and
consult the Time-Sert® catalog or online listings at http://www.timesert.com.
At left are the damaged spark plug threads, the cause is overuse and heat distortion.
At right is the 16.8mm length replacement insert package, one of these inserts made a permanent repair on the Honda
XR650R cylinder head. Motorcycle engines with aluminum heads are even more vulnerable than the automotive
applications, as motorcycle plugs get removed far more often.
Cutting threads with the Time-Sert® two stage tap uses the first stage to align the
tool with the original spark plug threads. The "Standard" inserts work with loose or slightly damaged threads that
can still support the pilot portion of the tap. There are even "Oversize" inserts available, and these kits address
common washer seat, tapered seat and Ford Triton type spark plug designs.
The cutter at left is a unique part of the Time-Sert® spark plug thread repair kit.
This is a two-phase cutter that first cuts the chamfer for seating the top edge of the Time-Sert® copper-coated
steel insert. At right is the driver tool and special lubricant that thread the insert into freshly cut threads,
pushing through the insert to form and expand the insert's special locking threads. See the video for
CAUTION: When cutting/tapping the
insert threads, be certain to remove all debris from the cylinder! We elected to perform the tapping
operation with the piston rising on its compression stroke and all valves closed.
On this Honda motorcycle engine with a decompression mechanism, the valve lash adjusters must be backed
off to provide full seating of the valves before performing this procedure. Some
perform this procedure with the exhaust valve(s) open and use compressed air to move the thread cutting debris from
the cylinder and out the exhaust. To avoid risk of clogging the exhaust system, our choice
was all valves seated and the piston down in
the cylinder on the compression stroke, far enough to clear the cutting and installation tools. After
tapping, we used a strong shop vacuum to pull debris through the spark plug hole. Make sure all debris
At left is the finished Time-Sert® insert installation. The spark plug washer's seat
is like new, the insert seating squarely and neatly, flush with the washer threads. This provides a perfect
compression seal and restores threads to, in this case, better than new! At right is a sensible method for
installing spark plugs into recessed, difficult to access aluminum spark plug threads: A rubber hose on the plug
end enables finding the threads with the lightest of pressure. This helps prevent false starts and forced damage to
the spark plug threads. Many performance engine builders install Time-Sert® spark plug inserts into their custom
aluminum cylinder head work!