Good question. Here is what happens. The thread chaser (chaser not tap) has
four relief's cut into the threads from the tip back along the shank. When
running the chaser through the hole dirt and debris is deposited into the
channels. When removed the debris can be scraped off with your fingernail,
or a shop rag. Typically no metal is removed from the head during the
process, only dirt and debris. If the threads are thrashed to the point that
the thread chaser won't go in or threads are missing then it is time for a
thread repair kit (heli-coil or equiv.). When using these products metal
will be removed from the head, but again most if not all is kept in the tap.
Type A personalities may at their option put grease on the tap to trap more
of the shavings. The rest of figure that once the new plug is in place and
the piston comes up on the exhaust stroke the first time any residue will be
blown into the front muffler.
In a message dated 05/23/2000 9:32:07 PM Pacific Daylight Time,
> Hey Rick, answer this. When you chase the head threads isn't there a
> of ending up with
> fine metal parts in the cylinder? Is there some trick to this?