18 mm X 1.5 + 6E tap

I took out my manual to see how to replace the oxygen sensor. Sounds
simple. Maybe I'm making this complicated, maybe not. I see the above
18 mm x 1.5 + 6E tap to clean out the threads on the exhaust manifold.
The manual says MUST be cleaned out. Imperative.

Okay, nowhere else have I read anything about tapping the threads. Not
here so far and not in allpar.com, which has a little section on taking
out oxygen sensors. On some cars it's not as simple as it sounds but on
my 1994 3.0 L Mitsubishi V-6 Voyager?, have not read anything yet but
don't know if I can get to it from the top. Hope so.

But is this necessary to clean out the threads? Never read anything
before about using a tap to clean something out although it makes
sense. Is this another tool to buy to get the oxygen sensor which needs
a 22 mm socket and perhaps some extension or special doodads if there
is not enough room. In the manual, it looks as though it's sitting all
by itself nice and simple, just waiting to get screwed out.

Does anyone do this before swapping out the oxygen sensor? Have not
read anyone mentioning this in their accounts of changing out the
oxygen sensor.

 

Probably your downpipe is mild steel not stainless, or the sensor goes
into the cast iron manifold, and that's why they're telling you to clean
out the threads? No matter - IIRC 18mm x 1.5 is a spark plug thread
IIRC so just ask for a spark plug thread chaser at your FLAPS and you
should be good to go.

There are special crowsfoot tools to remove O2 sensors in places where
there's limited accessability. I've got a cutaway socket that doubles
as an O2 sensor tool and an early watercooled VW upper strut nut socket,
also, but it requires a little more room than a crowfoot.

good luck,

nate

 

Thanks, that's a great suggestion. And they are 14mm and 18mm and fit
inside a 13/16" sparkplug socket if needs be. I also what you mean by
needing maybe a special socket. Found a 7/8" wrench which is off the 22
mm by .01" but it's a long wrench so probably not enough room. We'll
see.

 

I would only recommend you chase the threads with a tap if the o2 sensor
hole is
very, very accessible, or if something goes wrong on extraction and you lose
part
of the sensor thread in it. Otherwise, just wire brush them - a battery
post cleaner
round wire brush works for this. You should use the appropriate grease on
the new sensor threads - it contains glass beads as I recall - and may be on
the sensor threads already when you buy it.

The problem with chasing threads with a tap is that unless you are
extremely careful and you have experience feeling around for the thread,
it is easy as pie to cross-thread a tapped hole, and destroy the strength
of the threads as a result. If you can't see what your doing - as with
many of these O2 sensor hole placements - it is going to be very risky
to fool around with a tap in there.

Even in the best of environments chasing threads can be a hair raising
experience. The last time I did it was about 2 weeks ago with an old
aluminum head lawnmower engine I was fixing. I was putting the head
back on. One of the threads had already been destroyed by some previous
moron who apparently lost one of the head bolts and substituted a bolt
that was too long then kept cranking on it when the bolt bottomed. I
heli-coiled that one. The rest of them I chased with a tap, and one of
the holes was so bad that it took me 10 minutes of work with the tap
before I was fairly sure that I had it in the correct thread, and even then
I was still not sure until I got the tap in far enough to be committed to
it.
(it was, fortunately, and the mower runs fine now)

Years ago I worked in a machine shop and there was a part that we
would get from the hot galvanizers which had a tapped and threaded
hole in it, and half the time the protective material they put on the
thread to protect it during galvanizing would be burned off, and the
threads half filled with zinc. We had to chase the threads on all of those
parts, of course. Even with a fixture specially made to position the
tap, and even by starting the tap by hand, we would still every once
in a while cross-thread the damn thing.

Ted

 

Thanks for the reply, Ted. Your suggestion to use the battery terminal
thingee is great. I even have a spare, a premade circular wire brush. I
also found your comments about installing your O2 very helpful at
allpar.com.