Anyone that works on a plastic saw will run into this eventually... Stripped thread. Stihl, Husky and most others have models where threads are formed by the factory insertion of the screw, and subsequent reinsertion has to be done really carefully at low torque or it strips out. I'm not talking about the big fat screws that hold the handles or buffers onto the likes of a 440, but the fine threaded screws found all over "occasional use saws".
Common repair techniques are :-
- Epoxy in the hole and screw the screw in. Great... until it needs to come a part. Thanks ebay seller...
- Put a short length of nylon trimmer line into the hole first - works well in non-critical holes.
- Stuff in a toothpick first, hmmm..
- Soldering iron in the hole - melt it. hmmmm... not if you need to apply torque...
-etc
You can get way with many of the above in non-critical positions, but if you need to apply torque and to adjust the held device, a better approach is needed.
This example is an MS290. The problem is the coil securing screws. Mine was stripped out on the top location. The coil needs to be adjusted and held securely.
I used brass woodworking inserts made for threading machine screws into wood. They were 10-32 by about 1/2 inch, but I re-threaded them in seconds (no drilling required) to M5- 0.8 - much more "stihl-like" and with better bolts available. They have a slot for a screw driver blade for insertion but this DOES NOT work in plastic - just breaks off...
Insert an M5 x 16 torx screw into the insert with the blade slot end DOWN. The slot acts as a cutter to cut the required threads.
Drill a 1/4 inch hole. Be carefull on the depth!!! I drill a series of 4 holes each increasing by 1/64 until a 1/4 is reached. This way it's easier to get the new larger hole in the exact same position as the original.
Using a T-handle T27 wrench, screw in the insert. It takes quite a bit of effort!
Finished result - better than new!
A dab of Loctite 242 (removable) on the new M5-20 screw, and it's finished.
