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1983 Honda vt500c Shadow
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37 Posts
Discussion Starter · #1 ·
Well I’ve gone and made a huge mistake. I had a spark plug break off while changing. I Ordered a helicoil repair kit, drilled, tapped and installed the coil. Plug doesn’t thread in. Not sure how but I accidentally ordered a m12 x 1.5 instead of m12x 1.25. Is there anything I can do? Is there a spark plug with 1.5 pitch?
Is it possible to rethread a spark plug?
Can it be drilled for a larger helicoil and larger spark plug? Please help. Feeling pretty down after this. Just want to be able to ride again.
 

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2002, Shadow Spirit 1100
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2,166 Posts
How much too big is it? If you could remove and reinstall the correct helicoil would be best. You may want to try the product below. Put a thread release agent on your spark plug. Then coat the plug with the product below. Screw the spark plug lightly into place where it is secure but not tightened down. Let it dry. Once dry unthread the spark plug from the hole. Clean the threads of the spark plug off. You should be able to insert and torque down your plug. If this doesn't work you may have to pull off the head and have someone at a machine shop repair it. You could have to replace the head.
J-B Weld 37901 ExtremeHeat High Temperature Resistant Metallic Paste - 3 oz,

Here is additional information I found on thread release agents:
Re: How get bolts release from epoxy

Fasteners and Hardware

When you want to install a threaded bolt or screw and be able to later remove the fastener, there are a couple easy options. In our boat building class with the Saginaw Bay Community Sailing Association, we keep a wax toilet ring for on the work bench and stick a bunch of screws in it. We just pull these out as we need them. The wax gets in the threads and we can back the screw out easily after the epoxy has cured. You can also put auto paste wax on a piece of cheesecloth, grab the threads firmly below the head and back it out with a cordless drill in reverse. This applies a nice thin coat of wax evenly over the entire thread pattern.

Pam® Cooking Spray is a quick and convenient adhesion preventer. Simply place the fastener on a paper towel and spray the threads, butter the threads with a bit of thickened epoxy so air isn’t trapped, push the fastener into the oversized, partially filled hole and let the epoxy cure. Back it out after the epoxy hardens and now you’ve cast threads in the epoxy.

Polyvinyl alcohol or PVA is a green liquid available at hobby shops and craft shops. Dip the fastener in or brush it on the threads, let it air dry and install the fastener like I just described for Pam.

There are a number of aerosol mold release sprays on the market. A couple we’ve used around the tech shop are Stoner® E-497 and E-499 Thermoset Mold Release. They work well for all thermoset resin systems used in most boats – epoxy, polyester and vinyl ester. They do not contain any silicone, which you want to avoid in any mold release, especially a spray. Silicone aerosol sprays can contaminate the entire shop if you’re not careful.
 

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At this point, you need the advice of a good machine shop. It can be saved at a cost. Might also look at replacing the entire head with a good used one. Also not cheap. We’ve all made costly mistakes. This is kind of a minor one in the grand scale of things.


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99' Valkyrie/North Central Indiana
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9,546 Posts
You could be beyond "off the shelf" fixes but the "TimeSert" seems to be the best fix. Pulling the head and having it sleeved and welded or get another head are the final options. Having the sleeve ID sized to the tap drill size @ .425/10.8 mm. Goodluck.
 

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05 Sabre 1100
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117 Posts
I did a thread sert for a spark plug decades ago and IF I REMEMBER CORRECTLY the thread sert leaves a bar bif you will that locks into the head so it dosent back out. You may damage the head if trying to pull the sert out. I hope someone with more recient knowledge can confirm or deny this for you..
 

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1999 Shadow 750 ACE VT750CD3 Modified
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4,026 Posts
Is there such a thing as an 'oversized' sert?
Yes, but for 14mm plugs not 12mm.
There is not enough room the heads are pretty tight with two plugs between 3 valves in a heart shaped chamber.
 

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1983 Honda vt750 Shadow
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17,210 Posts
If it is an actual spring type Heli-Coil you may be able to pick the top thread loose and pull out the steel threads. Then get the proper 12MM X 1.25 Time-sert solid insert kit and just do the same process with red lock-tite to hold it .
I believe it can be a solid fix.
 

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3,362 Posts
Fine threads use a larger drill bit for the initial hole. So going to the 12x1.25 helicoil should work. Just get a new set and give it a try.

Eric


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1983 Honda vt500c Shadow
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37 Posts
Discussion Starter · #11 ·
The timesert kit is pretty expensive. Seems like it will work though. As far as the helicoil, would I buy a new tap kit for 12 x1.25 , retap and put coil in or would just buying a 1.25 coil thread into the already tapped hole?
 

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1983 Honda vt750 Shadow
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17,210 Posts
You will have to get the correct tap from Heli-coil to make the 1.25 threads in the head that the new coil will follow.
 

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1983 Honda vt500c Shadow
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37 Posts
Discussion Starter · #13 ·
will there be enough material left to retap if it’s already tapped to 1.5?
 

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2002, Shadow Spirit 1100
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2,166 Posts
Go to YOUTube and type in: Can you remove a helicoil? It looks like there is a removal tool. It may be worth checking out.
 

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'83 VT750C
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1,618 Posts
I would think not. I’m not sure of the details, but my father installed a helicoil on a spark plug hole in my old KZ400 LTD back when I was a teen. Didn’t even get much running. One day I bent my head down to hear a rattle a little better when the plug blasted out if the hole, catching on the wire to change its trajectory. Missed my head by less than an inch…

See if you can get another head or a whole parts bike for cheap. Or take it to a machine shop and ask if they can measure, weld and re-drill/tap the aluminum.
 

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99' Valkyrie/North Central Indiana
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9,546 Posts
Well your hole for the 12 x 1.75 mm helicoil is suppose to be 12.4 mm (.488) and the Time Sert M12 x 1.25 requires 31/64" (.484) thus spending over $100 for the kit that may not work out. On a note, Loctite isn't used in heat applications. I use heat to free up Loctited parts if necessary.

Now I see that JB Weld has a high heat formula boasting a 1000 degree spec. thus lending help in using the Time Sert due to the slight difference in hole sizes.

I did observe that the tooling in the TS kit are setup to be used with a T handle tap wrench thus extensions used for tap's maybe needed also due to the recessed location.
 

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05 Sabre 1100
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117 Posts
But at .004 diff there will PROB be enough coil to head contact to make for the ground....idk...just thinking aloud.
 

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The timesert kit is pretty expensive. Seems like it will work though. As far as the helicoil, would I buy a new tap kit for 12 x1.25 , retap and put coil in or would just buying a 1.25 coil thread into the already tapped hole?
Yes, you will need a new complete kit. Tap, drill, and coils are all different.

Will there be enough material left? This is the tricky part. Measure the OD of the tap you used and compare that to the drill diameter for the new kit. If the new drill is larger you are good to go. If it is a few thousandths smaller you should still be good but you might still see a little bit of the old threads.

Eric


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