What is the best method to repair stripped threads in plastic?

[ham]

I'm replacing the rear handle and freshening up my MS290. The threads for the brake assembly cover, both screws backed the threads out with the screw.

Any thoughts? It's not a stressed part. I was thinking of doing a wrap of teflon around the screw. Or maybe using a blazing hot soldering iron and dimpling in the plastic

 

[miller755]

Probably at least 5 different ways will work.
Many wraps of teflon tape, like you suggested
Stick the end of a zip tie in the hole, like the toothpick in a wood screw hole trick.
Could shoot some hot snot in the hole right before assembly
Could tap for a slightly larger thread
Could helicoil, and use a machine thread screw thereafter.

 

[miller755]

Also i feel like some manufacturers screws that go into plastic are more aggressive than others. In fact i think that old stihl screws for plastic and new stihl screws for plastic are slightly different, one or the other may get enough bite.

 

[old guy]

I am having good luck with weed whip plastic string, I cut a piece the depth of the threaded hole then skive the end a bit for a taper so the bolt doesn't just push it down.
just drop it in the hole & put the bolt in.

 

[irhunter]

I am looking at a similar problem on the recoil side. Anyone have a solution using Decon or JB Weld?

Roy

 

[Jeff Lary]

I have made a repair like this 2 different ways.
One is to fill the hole with JB then when it's hardened drill and tap to your desired size. The second and easiest way is use a grease of some sort Vaseline or Lubriplate even grease gun grease. Coat the screw / bolt threads lightly so the threads are still prominent and then fill the hole with JB Weld or the epoxy of your choosing . Then put the bolt back into the hole into the wet epoxy and let it set up overnight. In the am if you want to unscrew the bolt. The epoxy will take the shape of the bolt threads thus making a perfectly threaded hole. You may have to use a piece of tape to hold the bolt down into the hole while the epoxy hardens up.

 

[irhunter]

I have made a repair like this 2 different ways.
One is to fill the hole with JB then when it's hardened drill and tap to your desired size. The second and easiest way is use a grease of some sort Vaseline or Lubriplate even grease gun grease. Coat the screw / bolt threads lightly so the threads are still prominent and then fill the hole with JB Weld or the epoxy of your choosing . Then put the bolt back into the hole into the wet epoxy and let it set up overnight. In the am if you want to unscrew the bolt. The epoxy will take the shape of the bolt threads thus making a perfectly threaded hole. You may have to use a piece of tape to hold the bolt down into the hole while the epoxy hardens up.

I was thinking of both of your methods. Do you have a preference?

Roy

 

[HarleyT]

I would try a hot glue gun, you would have to be quick.

 

[AGoodSteward]

I've had good luck heating up
screws and tapping new threads with it.

 

[Brushwacker]

Lot of people don't know before you screw those screws used in plastic downward, you should turn the screw outward to allow it to drop in the original threads otherwise they easily catch the side of the hole and rethread or tap another thread inside the originals. The more it happens, the weaker the threads become until their shot. Prevention is the easiest solution however it doesn't always happen, especially when you work on preowned saws.
You fellows have lots of good ways mentioned here to make or recondiition those boogered up threads to work again. I usually looked for a bigger, self tapping screw when i run into that.

 

[Termite52]

I'm replacing the rear handle and freshening up my MS290. The threads for the brake assembly cover, both screws backed the threads out with the screw.

Any thoughts? It's not a stressed part. I was thinking of doing a wrap of teflon around the screw. Or maybe using a blazing hot soldering iron and dimpling in the plastic

If you don’t need the chain brake then gut it and put it back together using a nut wager and bolt .

 

[Termite52]

If you don’t need the chain brake then gut it and put it back together using a nut wager and bolt .

Nut washer and bolt .

 

[edisto]

Lot of people don't know before you screw those screws used in plastic downward, you should turn the screw outward to allow it to drop in the original threads...

Beat me to it. I just learned that one this past year.

 

[Vintage Engine Repairs]

Strimmer line or cable ties

 

[RED-85-Z51]

Ive had limited luck with long term fixes on plastic stihls but some other brands i heat the screw and drop it in...then cool it quickly.

Sent from my LM-G820 using Tapatalk

 

[Brushwacker]

Beat me to it. I just learned that one this past year.

Hasn't been much longer then that for me. I was told it was taught in the Stihl tech seminars.

 

[Jeff Lary]

I was thinking of both of your methods. Do you have a preference?

Roy

The grease on the threads works pretty good just be sure the threads are lubed well but "clean" if that makes sense.

 

[ham]

I ended up finding these. Heat set threaded inserts. It’s overkill for my particular situation but am going to go ahead and epoxy in a few in the interest of “doing it right”

 

[anlrolfe]

I'd lean towards using a quality 2-part epoxy. Clean, dry, and degreaser most important.
If there was enough meat around the hole, I'd drill it oversized and tap to a larger hole to give fresh clean surface area to bond to. I'd fill the oversized tapped hole with epoxy and tap to the correct size for the OEM screw. If you insert a coffee stir straw into the epoxy you'll have your pilot hole, just seal the end and brace centered in place.

 

[hotshot]

Way overkill & too much $$ for securing a cover, but just my 2 cents.

Before you order all those brass inserts & tools, call your local Stihl dealers & check stock or order two # 9074 477 4130 screws. Couple of dollars at most, your existing screws are D4x15mm & these are larger M5x16. Drill the two cover holes out to M5 major to clear.

If you can strip those out, then proceed on!