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Repairing Stripped Machine thread in plastic hole

Terry Hennessy

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If you have machine thread bolt hole stripped in plastic, what is the (best) way to repair? I tried epoxy with vaseline as release agent, but see teflon tape maybe better for a release agent, but is there a (specific) product (maybe locktite?) that works best? (I.e. proven in the pro shop). Specifically, SIL has a 455 rancher w/ oil pump mounting bolt problem. I did a quick job before, but (maybe?) pulled bolt too soon, (afraid it might not back out to install pump), and think saw (maybe) leaking again.
 

Gritz

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Stick a straw from a Wd-40 can in the hole and start the screw in next to it. It's not permanent, but it works. You will have to trim the straw so it doesn't stick up out of the hole. It is really easy to strip those self tapping screws in plastic. Always turn them counterclockwise in the hole until they fall into the old groove, then tighten.
 

stihl_head1982

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Is a heli-coil not a viable option?
 

Terry Hennessy

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Stick a straw from a Wd-40 can in the hole and start the screw in next to it. It's not permanent, but it works. You will have to trim the straw so it doesn't stick up out of the hole. It is really easy to strip those self tapping screws in plastic. Always turn them counterclockwise in the hole until they fall into the old groove, then tighten.
NOT self-tapping, this was machine thread into plastic
 

Gritz

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NOT self-tapping, this was machine thread into plastic

That trick will still work. If not, hopefully you can post a pic of the screw and the hole so we can better identify how bad it really is. Almost all of those screws are self-tapping. They don't look like a self tapping screw you might get from a hardware store. The threads will be sharp though, might have a slight taper to the end, and should cut into the plastic/aluminum. They are installed at the factory into a blank hole. If you order a new case for those, none of the plastic screw holes will be threaded. Most of the major manufacturers do the same thing - even on most of the aluminum parts.
 

295 tramp

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I had a shock mount on a stihl tank that stripped the hole the upper tank shock on the starter side.
Anyway I used a coarse thread brass thingamagiggy. its used on wood to have machine thread holes.
they come in all sizes and probably in only standard threads. It depends on how much meat there is wear the screw goes.
If its to long you can cut off some to. I found it at a hardware store. Drill out the hole just smaller than the insert.
The same as a heli coil. 20160125_182933.jpg
20160125_182857.jpg
 

Stump Shot

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Had a Husqvarna 55 air dam that had a stripped stripped hole on the manifold. I showed it to my cousin and he replied that he could repair it to be just like new. I was a bit skeptical, but here is what he did: He drilled and tapped the hole to an oversize thread that fit a nylon bolt/screw (that you can acquire at a hardware store) but short tapped the hole so when he fit the nylon screw it tightened up really tight, kinda like pipe thread does. Then he trimmed the nylon screw off flush, and re-drilled for the original screw. I honestly had to admit, the repair was as good as new, and performed flawlessly when I reassembled the saw. Saw has been in service for a year now, with no problems reported and is holding up well so far.
 

willie

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If it's a machine screw thread and there's no metric m6 x 1.25 tap in your toolbox, you can always
dremel or file cut a slot (or 2) into the screw. Voila, instant self tapping machine screw!
 

Stump Shot

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I see Husqvarna has thread inserts for plastic and aluminum. The one for an MT6 screw part number 503 27 40-01, the other for a PL5 screw part number 503 27 39-01.
 

customcutter

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Try sticking a few pieces of fine copper wire down in the hole then inserting the bolt. I saw that on a video on you-tube the other day on a stripped hole in Al. I'm going to try it on a stripped hole in my carb on my 350 husky.
 
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