Epoxy Thread Repair

for those of you that have M.B.S. (multiple bike syndrome) and have the "silver wing" models.
as our sponsors also have supplies for those bikes and they are popular with the "wing" crowd.

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mytown
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Epoxy Thread Repair

#1

Post by mytown »

I stripped the bolt hole that holds the thermostat housing bracket to the head on a CX650 engine. See here:
cx650 stripped bolt.jpg
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I plan on using Loctite Thread Repair which is basically a two-part epoxy. I don't want to pull the head at this time, but may want to do so in the future. Will I be able to drill the epoxy out such that I can re-tap the hole to take a larger bolt or a helicoil?
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Re: Epoxy Thread Repair

#2

Post by Rat »

Should work .....

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Re: Epoxy Thread Repair

#3

Post by gregforesi »

Yeah, the helicoil drill will be larger than whatever thread size is there (8mm?) so the plastic will all come out when you do the heli-coil repair.

Now I'm not trying to tell you what to do but with the engine out...I'd be doing the heli-coil repair now. I would doubt you can get much torque on an epoxy thread, and if it starts leaking you'll be back where you are today anyway. I'm not sure what the head gasket costs but a heli-coil repair kit from Napa or Grainger can be about $40. You can cross your fingers on the loctite repair, but if it was mine, the epoxy would fail in the first 12 miles.
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Re: Epoxy Thread Repair

#4

Post by robin1731 »

The drill size for a 6mm helicoil is 1/4". Measure the hole in the head and see how big it is. You may be able to drill out for the helicoil without removing the head. It of course is a bit harder to get it all done without doing that but it is doable. That is what I would do. And like Greg said, the engine is out now. Fix it now.

Even if the hole in the head for the bolt to go through is a bit smaller than 1/4" you won't hurt anything by drilling it out some.

Now, the only thing that would stop all the above is if that hole has an alignment dowel in it. Then you will have to take the head off to fix it. I'd still do it now.
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Re: Epoxy Thread Repair

#5

Post by mytown »

Thanks for the replies.
I don't want to pull the head since original Honda head gaskets are no longer available for this engine and aftermarket head gaskets have a history of failing. I've never done a helicoil but am now leaning in that direction. The bolt is 8mm x 55mm fine thread but the hole measures 65mm deep. Can I drill and helicoil at that depth? I'm also considering using a 8mm x 60mm or 65mm fine thread bolt on the theory that there are additional threads towards the bottom of the hole that are not stripped. If the threads are there can I get something like 7-10 ft lbs torque on the additional threads?
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Re: Epoxy Thread Repair

#6

Post by gregforesi »

The short answer regarding how much torque you can get is "maybe enough".
On long blind tapped holes, there is nowhere for the chips to fall out, so you drive the tap drill in farther to leave space at the bottom for clearance for the tap chips. I would doubt there is much in the way of threads down there, but again, maybe.
Helicoils themselves come in different lengths. You can actually drive a short one in deep, and then put another short one on top of it. Some designs of helicoil have a drive tang that would need to be broken off so the screw can get past the top one and into the bottom one. That makes the job fussier, but it's doable.

Bummer about the head gasket situation. I can understand your concern.
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Re: Epoxy Thread Repair

#7

Post by robin1731 »

Use air to get the chips out. Not that hard. I never stack heli-coils. One is plenty. You do have to break the tang off and you do have to remove that tang once you break it off. Magnetize a small, long screwdriver and reach in the hole to get the tang out.

I wouldn't trust the threads further down either.

Where are you located? If your not sure on doing the heli-coil any shop should be able to do it. Buying the kit for one time use isn't worth the cost for most either. If you were close to me I'd do it while you wait. It would take longer to get all the tools out than it would to do the real fix.
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Re: Epoxy Thread Repair

#8

Post by mytown »

Thanks again for the replies. About helicoil, I looked at a few kits online and it looks to me like the tap and insertion tools would not go down far enough into the hole as it sits. Plus the hole is situated such that I would not have much turning room. I'll look at some kits in person tomorrow. In the meantime, since the hole is 8mm, what size bit and insert would I use or what kit would I use? I think going back in with a bolt having 1.25 thread would work, but does it matter that the original threads are fine (1.0)? I looked at several charts but couldn't make sense of them.
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Re: Epoxy Thread Repair

#9

Post by mytown »

robin1731 wrote: Where are you located? If your not sure on doing the heli-coil any shop should be able to do it. Buying the kit for one time use isn't worth the cost for most either. If you were close to me I'd do it while you wait. It would take longer to get all the tools out than it would to do the real fix.
Thanks for the thought. I'm in Carbondale IL. That's about 6 hours from Decatur, but I do have a sister in Fort Wayne. Worse comes to worse I'll load the lump into the car and pay her a visit. :lol:
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Re: Epoxy Thread Repair

#10

Post by mytown »

Another reason I don't want to pull the head is that I've never heard the engine run, having bought it at a junk yard. I did read where combining a few good threads at the bottom with the epoxy increases the chances of success, but I intend on doing what I can short of pulling the head to repair it with a helicoil.
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Re: Epoxy Thread Repair

#11

Post by robin1731 »

21/64" drill bit for the 8mm kit. Stay with the 8mmx1.25 thread pitch. A lot of times there isn't room for the regular t-handle used on the tap. I use a socket and ratchet that fits for those situations. They do make special tools for that but a socket works well.
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Re: Epoxy Thread Repair

#12

Post by mytown »

It appears to me that there is enough "meat' in both the head and block to accommodate a 10mm bolt and I don't see any other issues to be concerned about. I found a long enough bit and the correct tap socket for the helicoil job, but I'm not sure about the length of the insertion tools that come in the kits. It's just starting to look simpler to me to just go up a bolt size to 10mm x 1.25. One 11/32" drill bit of proper length, a tap socket so I can use a ratchet wrench and a 10M x 1.25 tap. Any thoughts on that idea?
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Re: Epoxy Thread Repair

#13

Post by robin1731 »

Do what you want. I hate going to a bigger bolt unless absolutely necessary.
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Re: Epoxy Thread Repair

#14

Post by salukispeed »

I have made step studs for things like this If it is possible to use a stud and still install the housing it may be possible. a 7x1 screw tapped in the head is a 1mm increase in size and the same mm per thread so it could follow/shadow the original without even drilling the 6mm thread. or 8x125 stud machined down and threaded to 6mm for anything above the head surface??? I Not my first choice either.
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Re: Epoxy Thread Repair

#15

Post by salukispeed »

I probably was writing before engaging my brain and assumed that it was a 6mm bolt. I see that it is likely 8mm. Sorry
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