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post #1 of 19 (permalink) Old 07-16-2020, 06:05 PM Thread Starter
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Stripped Spark Plug Threads

Garbage picked a relatively new Craftsman mower and discovered the spark plug threads have been stripped. You can see it's quite bad in the picture below.

Picked up a kit from Amazon for $10 to fix the problem. Have watched a couple of videos about it so I know the cover the threading tool with grease and even put some paper towel in the hole before starting to try to catch any shavings.

Anybody done this repair? First time for me.
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File Type: gif Threads.GIF (100.2 KB, 2 views)
File Type: gif kit.GIF (55.0 KB, 1 views)
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post #2 of 19 (permalink) Old 07-16-2020, 07:12 PM
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After you have cut the thread but before you put the insert in wash the hole with petrol
If you can get the hole pointing directly up .
leave it for a few minuted the spin the engine as quick as you can to expel any chips.
I shove a long air duster in the hole and give it a nice long blast .
Then install the insert .
When you break off the tank. use a magnet to pull the tang out.
From now on put a THIN SMEAR of nickel anti sieze on the plug to prevent it gauling and pulling the insert out.

Very important the have the insert 1 full thread lower in the hole so the plug can seal against the head.
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post #3 of 19 (permalink) Old 07-19-2020, 08:11 AM Thread Starter
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Quote:
Originally Posted by bertsmobile View Post
After you have cut the thread but before you put the insert in wash the hole with petrol
If you can get the hole pointing directly up .
leave it for a few minuted the spin the engine as quick as you can to expel any chips.
I shove a long air duster in the hole and give it a nice long blast .
Then install the insert .
When you break off the tank. use a magnet to pull the tang out.
From now on put a THIN SMEAR of nickel anti sieze on the plug to prevent it gauling and pulling the insert out.

Very important the have the insert 1 full thread lower in the hole so the plug can seal against the head.
Thanks for the details. I've used them, particularly the nickel anti-sieze idea and having the insert lower in the thread so the plug can seal against the head.

I have to preface the rest of this with the fact that this is my hobby and I'm here to learn so I may not do what a shop might do in order to make money. I often spend money/time I know I won't recoup in order to learn something from the repair. This one is no exception.

To start with, the repair kit I show above had a tap that was actually too big to get into the hole and start cutting. I had to get a 9/16" drill and bore it out before I could start cutting threads. The over-sized tap led to some slop when the insert was screwed in. You can see that here:


For that reason, I would not recommend this kit.

Second point is I could not see what I was going to leave inside the cylinder, so I took the head off the engine and worked with it separately. I was glad I did as you can see all the shavings involved. Yes the tap was too big, but I'm not about to leave that kind of stuff inside a cylinder. In the end, both sides were nice and clean.
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File Type: gif Shavings2.GIF (102.3 KB, 0 views)
File Type: gif Shavings3.GIF (92.1 KB, 0 views)
File Type: gif CutHole.GIF (106.0 KB, 0 views)
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post #4 of 19 (permalink) Old 07-19-2020, 08:18 AM Thread Starter
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Here I am standing on the head to hold it flat up against the cement floor, carefully turning my socket wrench to keep the tap straight.

With a little trim work on the bottom of the insert in the second picture and I was good to go.
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File Type: gif tapping.GIF (157.4 KB, 1 views)
File Type: gif trim.GIF (115.9 KB, 1 views)

Last edited by Joe Kuhn; 07-19-2020 at 08:48 AM.
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post #5 of 19 (permalink) Old 07-19-2020, 08:34 AM Thread Starter
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Briggs serial number: 128M02-0943-F1 calls for 140 inch pounds of torgue per this link, the line for the 120000 series (128M02 = 120000 model series - note to self: you just use the first two digits):

https://outdoorpowerinfo.com/engine_...ad_torques.asp

Trying to find the torque on the Briggs website was a problem, so I went with the above. Any help finding this on the Briggs site would be appreciated. I've failed there in the past. They could use some help with website design.

Engine started first pull with new oil and new gas. It did not run well though until I gave it a little choke manually. I purchased a thermostat for the automatic choke, which should do the trick. I considered cleaning the carb, but the choke was hard to move manually and I'll see how it runs with the new thermostat first.

Because the tap was so large I had ordered a second kit. Wish I had waited for it to arrive as the tap was smaller and would have worked better. Note the inserts for this kit were made of aluminum whereas the first kit had inserts made of steel. Don't know if that matters.

ABN is the kit with the oversized tap & steel inserts. Autocraft has the correct size tap & aluminum inserts.
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File Type: gif Autocraft.GIF (79.3 KB, 0 views)

Last edited by Joe Kuhn; 07-19-2020 at 08:46 AM.
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post #6 of 19 (permalink) Old 07-19-2020, 11:37 AM Thread Starter
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Looked the mower over more carefully and found that it's a Briggs brand, 725EX.

Also found a repair tag with the owners name & phone number and: "Runs good then loses power." This description of the problem sounds like what I found after fixing the spark plug threads.

Oh and I put gasket sealer on the outside of the thread insert.

Last edited by Joe Kuhn; 07-19-2020 at 12:05 PM.
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post #7 of 19 (permalink) Old 07-19-2020, 12:46 PM
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Thanks for the nice write up and pictures of the install. I can say I have a 1975 Bricktop that has a helicoil that was installed by a servicing dealer many years ago and it has never failed. Also had one installed in my 2000 Toyota 4 Runner when it blew out the #3 spark plug. Still working fine. Bill

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post #8 of 19 (permalink) Old 07-19-2020, 01:43 PM Thread Starter
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Thanks Bill. Didn't see the Helicoil option when I did my search, but it looks like a good option. A bit more traditional, but whatever works!
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post #9 of 19 (permalink) Old 07-19-2020, 05:49 PM
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Quote:
Originally Posted by Joe Kuhn View Post
Trying to find the torque on the Briggs website was a problem, so I went with the above.
This forum (MLF) has a reference library with lots of good info.

https://www.mylawnmowerforum.com/for...atton-manuals/

Experience is something you don't get until just after you need it.
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post #10 of 19 (permalink) Old 07-20-2020, 02:41 AM
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There is no well made product priced so reasonably that some one will not seek profit from the ignorant, lazy or plain cheap by making a bad copy that does not do the job properly.
FWIW I only fit timeserts in plug holes.
They are solid, rather like a reducing bush and have pins that lock in to prevent it from unwinding
Helicoils are used in dry situations
Occasionally a Recoil if I can not get a Helicoil in the right size
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