Stripped Threads Spark Plug Hole

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
carl51
G-First Sergeant
G-First Sergeant
Posts: 148
Joined: Sun Jan 17, 2010 2:58 pm
Location: Modesto, CA

Re: Stripped Threads Spark Plug Hole (LESSON LEARNED)

Post by carl51 » Fri Feb 24, 2017 4:16 pm

Obviously I don't play well with others and did not listen to the collective advice of my peers. So, this is a follow-up post of a what not to do. Hopefully, it will help others avoid my mistakes.

Seemingly confident in my skills, I purchased this OEM "one-tool-does-all" to repair the stripped plug hole threads in the cylinder head myself without taking off the cylinder head.

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The concept is that the first tapping threads on the tool match the 14mm plug threads in the stripped hole and will pull the tool into the cylinder head so that the 2nd larger tapping threads can cut threads which match the threads of the plug insert. Unfortunately, the reach of the spark plug is 3/8" which is the thickness of the cylinder head. The gap between the 1st tapping threads on the tool and the 2nd larger tapping threads is about 3/8". So, there was not enough metal in the cylinder head for the tool to properly pull the 2nd tap through to cut the larger threads. Resulting in my wallowing out the spark plug hole instead of cutting new threads for the insert. Oddly, the OEM tool includes 3/8", 1/2" and 3/4" plug inserts. I intended to use the 3/8" for this job. While the tool may have worked fine on a different engine for the deeper 1/2" and 3/4" plug inserts, it does not work for the 3/8" plug hole on an L134. So, please avoid my error and do not use this tool with the L134 head on the engine.

Because the engine was recently rebuilt and had never been test fired, the cylinder head was very easy to remove. Took less than an hour. Turning over the starter with only 3 spark plugs set easily popped the head gasket seal. The next day I took the head to my local machine shop and had a Helicoil Spark Plug insert installed with High Temp. Loctite Thread Sealer.

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It looks so good I probably should have had the shop place inserts into the other 3 plug holes. But if it's not broke don't fix it.
Tomorrow, I will reinstall the cylinder head, fire her up and hope for the best.
Carl
MVPA #36317
MVCC #1762
GPW #117302 DOD 5/21/43 Louisville, KY
MB #210593 DOD 2/11/43 matching frame & body under restoration


Joe Gopan
Jeep Heaven
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Location: Proving Ground

Re: Stripped Threads Spark Plug Hole

Post by Joe Gopan » Sat Feb 25, 2017 4:23 am

All's well, that ends well. :wink:
2011 MVPA PIONEER AWARD - MVPA #1064
HONOR GRAD-WHEELED VEHICLE MECHANIC SCHOOL 1960 - US ARMY ORDNANCE SCHOOL(MACHINIST) ABERDEEN PG 1962 - O-1 BIRD DOG CREWCHIEF - 300,000+TROUBLE FREE M-38A1 MILES
LIFE MEMBER AM LEGION-40/8-DAV
7 MIL SPEC MAINTAINED MV'S
COL. BRUNO BROOKS (ARMY MOTORS) IS MY HERO

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