Cross threaded Spark plug threads

I was replacing the spark plugs in a 1989 accord, something I've done
many times on many different vehicles. It's never been a problem until
this instance. When I used the socket to loosen Plug #1, it eventually
loosened but didnt screw out with ease. The other plugs 2-4 came out
with ease and I installed new plugs in them, however everytime I
attempted to install the new plug in the first plug hole I couldnt get
it to screw in. It just wouldnt catch. I then used a light and have
determined that the threads on this first spark plug hole were cross
threaded last time the plugs were changed (by a mechanic) I also
noticed on the block around this spark plug hole its kinda black and
the other 3 spark holes arent black on the metal outside their hole.
Has anyone ever ran into this situation and if so how did you solve the
problem. Someone I work with suggested I get a 14mm thread chaser and I
tried that and it wont catch either... cant repair any of the threads
if it wont screw in. Any help or comments would be appreciated.

 

Yes, several decades ago on an old Ford push rod V8.

The thread chaser worked great for me.

If you can't make it work, you are probably looking at a new or
rebuilt head. I doubt that a Helicoil would work, but even then you
are going to have to remove the head.

Hope this helps

 

Man that's terrible. That's one reason I always change my own plugs out and
everytime I get a new used car have that fear of the first time I pull them
out and check them. Keep us informed on how you fixed it.

 

How do you mean "won't catch"? You can't get the chaser to bite into the
metal and it keeps spinning in place?

 

Hi,
There are specialty tools that would make your job a lot easier. I work
at a small engine shop and we regularly face this problem. I bought a nifty
thread chaser from Lawson Products that is adjustable for hole size, you
can collapse it to fit into the hole, insert five threads or so deep,
expand to cut and it cleans the threads on the way out. Works very well. By
starting in the good threads it works a lot better than starting on the
damaged threads. When you use this tool on an assembled engine, hook up a
shop vac or vacuum cleaner on the blower side and pressurize the exhaust,
turn the engine slowly until air blows out the plug hole and chips won't go
into the cylinder. The only drawback I can see is it may be necessary to
remove the valve cover to get it into the plug hole and see what you are
doing. I also suggest that you try it out first on a nut near the same size
to familiarise yourself with the way it works and to develop a good "feel"
for how it works.
Good luck
Scott

 

This used to be a common malady with VW beetles. Often, the cure was
reaming and tapping the hole to an oversize to accommodate a helicoil.
That would be the option if the threads cannot be cleaned up.

JT

 

A thread chaser is not likely to be useful on the aluminum head; the
remaining metal won't support the spark plug well enough. Got the tee shirt
on that, just with worn threads!

Helicoils work superbly in aluminum heads, and the head doesn't have to come
off. Some people (including the pros where I used to take my cylinder heads
in Phoenix) advocate not worrying about the aluminum shavings; they blow out
when the engine is started. More commonly, people put the engine on the
beginning of the compression stroke for that cylinder and squirt a bunch of
shaving cream into the cylinder. They do the tap and helicoil thing and then
turn the crank until the shaving cream, with the shavings, is expelled
through the spark plug hole. I suppose they change the oil soon afterward
<8^P

All in all, you may want to have a cylinder head shop do the work. Fewer
unknowns that way.

Mike

 

helicoils work just fine.

no, it's done in situ.

 

you got unlucky. if done right, the chaser works perfectly - it depends
on whether it was started where the original threads started or whether
it cuts a whole new thread - /then/ you don't have much supporting metal
and the helicoil is essential. if the head's already off, you can chase
from the piston side as the crossing hardly ever gets all the way to the
bottom of the hole. use a plug from the piston side first too to force
as much of the old thread back into shape as well.

 

Not so much unlucky as I made a poor choice - it was in a Lotus with a
Renault engine, and the threads were not even crossthreaded, just worn out.
I wasn't even accelerating hard when I heard a POP and a sound like a
lawnmower... the plug had probably been in for months at that point.

Maybe a Honda head is more robust and not as sloppy.

Mike

 

those are quite a good little engine!

i've seen this on a honda head - plug had apparently been loose forever.
eventually the plug just pulled/wore out the last few threads, and
then, as you say, loud chugging noises. as long as there's enough
thread to hold the plug, it should be ok. the seal comes from the
gasket/washer on the plug and bolts only need 3 threads to hold under
most circumstances.

 

Scott

Looking on the Lawson website for the part that expands into the thread. ANy more details on this tool I can use to search?