I was re-installing the derailleur and stripped the first few threads. How hard is this to fix? I know I just need to chase the threads with a tap but how difficult is it to do successfully?
I watched the Park tool video and it looks do-able. Park makes the right size tap (online reviews are good). Is their tap handle decent quality?
I know the threads are mostly ok because I installed the derailleur backwards (from the inside) and it went in smoothly.
Any advice from a pro that's done lots of these? The frame is a steel Surly LHT.
Thanks!
by minimK
11 Comments
I would take it to a bike shop just to give you the best chance of not making it worse. They’ll do it right and it won’t be a super expensive job.
Don’t mess about with drilling and tapping it for a helicoil just use a dropout saver.
Old school problem easily solved by an old school fix.
https://www.bikemonger.co.uk/bikemonger-dropout-saver-26695-p.asp?_=&variantid=26696&srsltid=AfmBOoq8wJ9tcYrJ26SSWPP9VyvQkqsvNR6abiQiM6S8U2mPxh5L2lLUzxk
You just need to drive the tap in backwards like you did with the derailleur. Use cutting oil and every few threads go backwards to allow the metal shavings to fall into the grooves in the tap.
You need enough material for a tap to work. This looks extremely buggered and I doubt tapping would do anything here.
First you want to see if the minor diameter of the hole is still in tolerance for the threads. But fuck all that, someone mentioned a dropout saver and you should go that route.
M-10 Heliocoil
Could you just get a new hanger? Seems like it’s probably less expensive than getting tools to fix it, or bringing to a shop?
When you’re certain you only stripped the first 2 oder 3 threads I would say get the tap and rethread it from inside out, the same way you tested by installing the derailleur from the inside.
Had to do so myself last summer.
That way you smooth the threads you fucked up and you can gently reinstall your derailleur the correct way but (!) be careful this time.
And if you have any doubts just clean it before and apply some threadlock.
In generel threads are considered usable when there are 3 full turns in good shape.
Edit: by retapping backwards you allow your derailleur to reach to the threads in the back that are still good. Of course the first few threads/turns will be nearly nonexistent after
A bike is not a watch or a precision tool, just try it this way first before you go all the way with helicoil or similar measures.
Advice comes from a german mechanic, qualified CNC operator after 3 years of industrial apprenticeship and 5 years of work experience if you have trust issues 😉
A thread restoration tool would be ideal because it doesn’t remove material but will reform the threads. That’s assuming there’s enough material left.
Mechanical engineer here…my own solution would be take it to a welding shop to get material added, redrilled on a pillar drill, and then retapped.
Means you have less tolerances to deal with in the likes of dropout savers and brings it back to original spec.
Might cost a little more but im assuming you’ve already spent a significant amount on the bike.
If it’s a bolt on one look on AliExpress. Use discretion when looking. You will get one for cheap Vs a lot of money in a bike shop. No disrespect to bike mechanics I was one for about 15 years.