I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
Thanks–
Chris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
Chris
In the past I have used an old plug with two grooves cut across the threads
with some success. Depends what’s happened. This will get rid of crud in the
threads but if they’ve been cross threaded probably not good enough.
I’ve always thought the thread was 14mm but I’ve never actually checked
this.
Eric
Church Stretton, UK----- Original Message -----
From: “Chris XK150” crmcaviney@gmail.com
To: xk@jag-lovers.org
Sent: Sunday, May 03, 2009 4:52 AM
Subject: [xk] spark plug threads 3.4l
I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
ThanksChris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
Go to the oldest parts store in town and find the oldest employee. Tell him
the problem and he/she will have you fixed in no time. As I recall,
Champion spark plugs co. makes a thread chaser.>I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
ThanksChris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
Chris
A couple of champion plugs measured to be 13.8 mm across the thread diameter
so the nominal size is 14 mm diameter by 1.25 mm pitch.
Be careful when you chase the thread. You get only one chance to get it
right and don’t drop the shavings down into the “innards”.
Good luck
Klaus W. Nielsen
812394
815666BW-----Original Message-----
From: owner-xk@jag-lovers.org [mailto:owner-xk@jag-lovers.org] On Behalf Of
Chris XK150
Sent: Saturday, May 02, 2009 11:52 PM
To: xk@jag-lovers.org
Subject: [xk] spark plug threads 3.4l
I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
Thanks
Chris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
No virus found in this incoming message.
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14:23:00
In reply to a message from Chris XK150 sent Sat 2 May 2009:
Chris
They make a thread chaser for the 14mm spark plug holes. Coat the
tap with grease before you use it so the aluminum shavings don’t
fall into the cylinder. They also make a kit to re-cut the threads
for a steel spark plug insert. I like it better than the Helicoil
kit, because you don’t have to fish that tang out of the cylinder
when you’re done. All auto parts stores sell any of these tools.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
In reply to a message from ex jag sent Sun 3 May 2009:
Thanks all for your input. Had a close look inside the
problem hole, it appears that just the first couple of
threads are not as they should be. Will try the chaser/tap,
if that does not work I will have to go the insert route. I
am a tool and die maker by trade and familiar with the
grease on the tap to collect swarf, but thanks for the
reminder. Will let you know the outcome.
What irritates me is that I had the head rebuilt last year
and did not specifically mention that the the spark plugs
holes should be checked (I was not aware of the problem
until this week). Maybe it is just me but if I were
rebuilding a head for someone I would check everything.
Thanks for the rant ;-0–
Chris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
Chris;
Snap-On made, some years ago (I bought mine in the late '60’s), a
“Sparkplug Thread Chaser/Surface Cutter” tool. One simply put a dab of
grease in each of the three flutes of the “tap”, then gently screw it into a
sparkplug hole until the spring-loaded “cutter” contacted the cylinder head,
continued until the spring was completely compressd, then removed. The
grease captured any “chips” from the tap. The “Cutter” simply resurfaced the
“gasket area” of the cylinder head. Could be used on alloy or cast iron
heads… Could NOT be used on heads that used “tapered seat” sparkplugs
(Fords and the like).
As far as the “size” goes, they were (then) sold in the “standard” 14mm
Sparkplug size as well as the 18mm and the “new” 12mm plug size. The Jaguar
XK uses 14mm sparkplugs.
Any good automotive tool supplier (Snap-On, MAC, Proto, Blackhawk, etc.)
should carry this tool or one like it.
I should note, this is not a “Tap” in the strictest sense of the word… it
will NOT “cut” threads, it only “chases” them.
Charles #677556.----- Original Message -----
From: “Chris XK150”
I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
ThanksChris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
1 Like
In a message dated 5/2/2009 11:54:01 P.M. Eastern Daylight Time,
crmcaviney@gmail.com writes:
I need to chase the threads in the spark plug holes can
anyone tell me the size and type of tap I need. And where to
get one’’
Thanks
Chris,
Snap-On has them, I was going to send you the link but the web site is
down for maint. till 3 P.M. Monday.
Regards, Otto M.
**************Access 350+ FREE radio stations anytime from anywhere on the
web. Get the Radio Toolbar!
(http://toolbar.aol.com/aolradio/download.html?ncid=emlcntusdown00000003)
In reply to a message from Ottman0401@aol.com sent Tue 5 May 2009:
Otto
Thanks, I did the same thing.–
The original message included these comments:
Snap-On has them, I was going to send you the link but the web site is
down for maint. till 3 P.M. Monday.
Regards, Otto M.
–
Chris McAviney - S836006DN, S830747, GCJ17 RR 20/25 89 XJ-S
Calgary, Alberta, Canada
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –
Greetings!
I realize this is an older thread, but I have the same problem with my Mk 2’s 3.4l engine. A web search turned up this product: https://www.sealey.co.uk/product/5637192178/14mm-reverse-action-spark-plug-thread-chaser
Does that look right? I happen to be in England at the moment and noticed there’s a location not far from me that should carry this product. (Will call in the morning.)
Cheers!
Rick
1 Like
The reverse action sounds great!
Somewhere in my pile of tools, I have one of those! It’s quite a handy tool, and you’ll still need to use a little light Grease on it when you use it.
Even cheaper on ebay, $6.
I’ve used the 14mm end many times. Used the 18mm end once on a 1928 Dodge back in 1969.
Thanks for the replies. Checked the websites of several of the nearest suppliers, and none list the Sealey product. Will check what’s online when I get back (the eBay shipping price seemed quite high).
The Sealey product looks very different from the Lisle product. I can assume they work the same?
Reverse chaser at Amazon’
Reving an old thread is good once in a while: always new stuff to learn:
good tip on the Sealey reverse: ! sounds that you have visually inspected the one problem spark plug thread and can see anomalies…just checking–that first step is be sure all threads are clean and free of grit. As you know a plug should thread all the way in to seated by fingers…then Champion says, if new gasket about 3/4 of a turn, if a used gasket far less–about 1/8th…anyway just finger tight and then a little more with the wrench–do not over tighten, NGK says: 18-21 ft lb for aluminum head. I prefer 16-18 in our valuable heads… I have found that some “things” you might thread in other than spark plugs–bind–some thread ini compression testers that are supposed to be 14mm do not thread…if it doesn’t go with fingers, same as a new plug does…never do it. Since these are extended tip plugs–one can see on an take out one, that the few threads closest to the electrodes are exposed in the chamber–when I use antiseize I do not apply it all the way down…and very sparingly above near the seat.
Nick
Excellent reminder, and my method was to never use a ratchet or a speeder handle to put in plugs, but only to screw them in by hand.
1 Like
Yeah. I saw a guy who was in a hurry use an air impact wrench. Stripped them right out. Not in a hurry anymore. 
on the xk head, i just use fingers…not even a spark plug socket , without extension or wratchet…–as the socket can still have the plug be off center. fingers to spin in–and that way one can feel any bind or grit. If a used crushed gasket–do not tighten much…beyond nice and firm. You can feel a new gasket crush…then become firm tight. The plugs of course sit in an indent–the bottom mating surface can have grit etc. Use a small rubber stopper in the plug hole and clean out the grit where the plug will seat. By the way…a conical rubber stopper is an easy way to find the compression stroke…put the stopper in --it will pop out smartly on compression when turning engine by hand.
Nick
But, don’t forget, and be leaning over the engine… and have someone crank the engine.
Don’t ask. 
1 Like