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-   -   Repair thread rear derailleur b-tension screw (https://www.bikeforums.net/bicycle-mechanics/1008797-repair-thread-rear-derailleur-b-tension-screw.html)

mooder 05-16-15 06:44 PM

Repair thread rear derailleur b-tension screw
 
Hello everybody,

I damaged the b-tension threading. I wonder how I could repair it or make a bigger threaded hole.

How To Repair Damaged Threads or Add Stainless Steel Threads to Any Project

This technique requires special tools. I wonder where I could find one and how to know the right size? Do LBS carry these kind of tools? Would it be expensive for one to do that?

FBinNY 05-16-15 06:48 PM

need more info. Derailleur model, nature and extent of damage, etc. A photo will help.

Odds are you don't have to do anything exotic, which would cost more than the derailleur is worth, but nobody can suggest the cure until they know the disease.

dsbrantjr 05-16-15 08:08 PM

HeliCoil inserts are available in sizes down to M2X0.4, however besides the inserts you will need special tooling; drill, tap and insertion tools which are quite costly. Some machine shops MAY have them but unless the item is extremely rare or irreplaceable purchasing the tools for a single repair is uneconomical. http://www.stanleyengineeredfastenin...c2000-rev9.pdf

rmfnla 05-16-15 08:11 PM

This is not a high-torque application.

If you can obtain the correct tap you can probably just run it through and clean out the threads...

SkyDog75 05-16-15 08:22 PM

Or if the threads are completely trashed, you may be able to tap it one size bigger.

mooder 05-20-15 01:11 PM

Thanks a lot for the suggestions. Do you guys know by chance the correct size (specs) of the shimano ultegra 6600 b tension threading and what would be the greater size?

It's a shame to not be able to use bike :(

Black wallnut 05-20-15 01:18 PM

Locktite form-a-thread would work in this application if only the threads in the derailleur are damaged but the screw is fine. Available in nearly any auto parts store for a fraction of what a helicoil kit would cost.

70sSanO 05-20-15 01:50 PM

First question... are the threads on the screw stripped/messed up?

Here are a few thoughts...

If the screw threads are bad, you may be able clean up the threads in the derailleur with a tap as suggested above. Or the "quick and dirty and hope it works" method is to go to Ace Hardware and pick up a 2 or 3 stainless M4 screws that are little longer and run them into the derailleur tension screw tab to see if cleans out the derailleur threads.

If the derailleur tension screw tab threads are bad and won't hold with a new screw, spend another quarter, or 2, and get 2 M4 stainless jam nuts as thin as possible. Depending on how far you need to screw in the tension screw, you can use either 1 or both of the nuts. What you are going to do is sandwich the derailleur tab between the head of the screw and the jam nut, or between 2 jam units. This is one reason why you want to get a longer M4 screw and use at least 1 jam nut width of adjustment.

If the new screws threads keep stripping out when you try to clean out the derailleur threads, I'd drill out the hole and use the jam nuts. This whole thing should only cost you a few bucks.

John

rmfnla 05-20-15 04:20 PM


Originally Posted by Black wallnut (Post 17822890)
Locktite form-a-thread would work in this application if only the threads in the derailleur are damaged but the screw is fine. Available in nearly any auto parts store for a fraction of what a helicoil kit would cost.

I'd never heard of this stuff; good to know... :beer:

mooder 05-22-15 01:31 PM

I will try the locktite suggestion. The threading of the screw seemed fine. I don't remember I threw it away... but the threading inside the socket (where the screw goes in) is quite damaged. The screw goes in but it will stop near the end, it's impossible no matter what to screw it in.

Black wallnut 05-22-15 02:05 PM

If the screw threads in and then stops it is likely that you could just chase the threads with a tap of the correct size.

dddd 05-24-15 12:41 AM

I can't really see any kind of adhesive filler getting sufficient purchase on such a thin metal stock. I believe it probably wouldn't even survive the tapping operation.

You might try forcing a slightly-larger #8-32 SAE screw in the remains of the hole, and if you can get it started straight, then it may hold up.

Next size up would be #10 machine screw, 10-32t is so slightly smaller than an M5x.8 that it screws into anM5-tapped hole. But is there enough eat there for an M5x.8 hole to be tapped?

FRANK CANNON 05-24-15 01:54 AM

Easy fix but not worth doing.

Where are you, I have a couple mechs lying around.


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