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Old 10-01-2003, 08:25 PM
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Join Date: Mar 2003
Posts: 34
stripped sparkplug threads

in 113 aluminum head...when removing sparkplug, aluminum threads were annealed to sparkplug (1) ...have found a tapered tap w/heliocoil at NAPA, just the two pcs.. NO Directions...any pitfalls here, any guidelines for doing this job...thanx
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Old 10-01-2003, 09:06 PM
I told you so!
Join Date: Jun 2002
Location: Motor City, MI
Posts: 2,817
A couple of tips I can think of.

- Make sure the piston is near the bottom of its stroke to give you room for the tap.

- Pack the tap with grease to catch the aluminum chips as you cut new threads.

BTW, the aluminum galled onto the threads, they didn't 'anneal'.
95 E320 Cabriolet, 147K
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Old 10-04-2003, 05:13 AM
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Join Date: Mar 2003
Posts: 34
did not work

tapped out head perfectly with tool, then inserted heliocoil (napa brand) on sparkplug as directed and tried to install unit into newly threaded sparkplug hole, no way, could not catch a thread and ended up buggering top thread, seems to me a mismatch somewhere..Napa now says that maybe the napa brand insert is not compatible with K-D brand tap threads, I am also being told that contrary to what I am being told that there is a special tool for inserting heliocoil into head and not putting it on sparkplug..I am in big trouble here as machine shops say now head must come off for them to work on it. has anybody done this job? thanx
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Old 10-04-2003, 05:40 AM
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Join Date: Sep 2003
Location: Oxford UK
Posts: 7
The helicoil should be inserted into the head using special tools then fit the spark plug. Unless you can pick up the existing thread with the helicoil tap you are in all kinds of trouble which are best sorted with the head off.
Mad Englishman who like a challenge
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Old 10-04-2003, 05:56 AM
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Join Date: Jul 2003
Posts: 78
There are two types of thread repair inserts. One is a solid sleeve, the other is a wire coil. The coil wire insert is designed for a smaller size thread and does require a special tool for insertion. (The K-D tool that I've seen taps a thread designed for the solid inserts, not the coil wire insert.)

As far as I'm aware, all the solid type inserts are the same thread size and can be inserted using a spark plug, including one also made and branded by helicoil. (If not, just get the matching insert for the tap you used!) If the tap you used is designed for the wire coil insert, the thread/hole is too small for the solid inserts. I'm not sure, but I don't think the wire coil insert will thread into a hole tapped for the solid insert either.

I doubt the head has to come off. You must simply obtain the correct insert for the tap used. When you sort it out, I would loctite (green) the insert in otherwise there is apparently a good chance it will come out in the future with the spark plug.

Last edited by deaconblues; 10-04-2003 at 06:12 AM.
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Old 10-04-2003, 09:21 AM
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Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
My advice is get a KIT. The kits come with the correct tap and insert. If you have taped the hole with the KD tool, the get the rest of the KD kit. Tap the hole again to clean up the upper threads, then follow the instructions that comes with the kit.
Save the kit for future repairs.
84 500 SEL (307,xxx miles)
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Old 10-04-2003, 09:30 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
As Deacon points out, the simplest solution is to get the insert or coil for the tool already used. You can not start over at this point with anything but a custom insert.

In real bad cases an insert of any size (so to speak) can be cut and inserted, but you will be best suited to get the insert the tool inetended.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 10-06-2003, 05:43 AM
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Join Date: Mar 2003
Posts: 34
wrong parts

I trusted my NAPA dealer to give me the right parts..they DID NOT....I have now bought and installed the correct insert w/top lip and correct thread count....when doing this job never buy anything less the the complete KIT..thanx al.l.
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Old 10-06-2003, 08:51 AM
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Join Date: Jul 2003
Location: Northern Virginia
Posts: 1,070

Just sharing my experience with both helicoil and threadsert. My 80 KZ1000 had a stripped spark plug hole. I changed plugs often and regularly. The helicoil installed by the previous owner didn't last more than three plug changes. I had a professional install the threadsert and problems were solved. Numerous plug changes and still tight as when first installed. To me, really the difference between rookie and pro.

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