Stripped bottle boss thread

[Arminius]

The thread on one of the seat tube bottle bosses has been stripped (not my fault, and I'm not delighted about it...).

Does anyone know of a way to sort this, please?! I'm aware that helicoils and similar things are an option that probably wouldn't result in all of the surrounding paint being wrecked (I really don't want to have to get it resprayed), but my drill definitely wouldn't be able to fit into the main triangle of the frame, so I can't drill out the offending thread without going in at an angle, which presumably would be a stupid idea.

If it makes any difference to the solution, it's a steel frame (853) with silver brazed bottle bosses (stainless steel, I guess), and the bosses have been painted over (so there's no exposed metal).

Will I just need to go down the route of a strap-on bottle cage holder, e.g. https://www.sjscycles.co.uk/bottles-cages/rixen-kaul-bottleklick-adjustable-bottle-cage-holder/?

[Brucey]

there may or may not be enough 'meat' in the fitting to accept a helicoil.

Do be absolutely sure that you are using good quality M5 screws and not some 3/16" ones; they will strip the threads as quick as lightning.

One method of recovering the situation is to bond a short length of M5 studding in place using a high strength epoxy. A nut (ideally a nylock if there is room for it) can then be used to fit a bottle cage or w.h.y.

cheers

[Jurek]

If it was me I'd probably use a 5mmø drill.
Drill out the boss, and then tap it with an M6 thread.
Drill any fittings to be applied with a 6mmø drill (or 6.6mmø if you want to split hairs over clearances)
And Robert is your father's brother.

[zigzag]

this might help: https://www.youtube.com/watch?v=kTVBzfgOEAU

[The Family Cyclist]

I'd be inclined to wander to my local smallish engineering company (if I wasn't fortunate to work at one) with some beers in my panniers and ask the grumpy old guy with a beard as everyone knows the grumpy old guys normally very much more skilled then the helpful young apprentice

[Kim]

but my drill definitely wouldn't be able to fit into the main triangle of the frame, so I can't drill out the offending thread without going in at an angle, which presumably would be a stupid idea.

Got enough room for a right-angular drill?  You can get adaptors...

[Feanor]

but my drill definitely wouldn't be able to fit into the main triangle of the frame, so I can't drill out the offending thread without going in at an angle, which presumably would be a stupid idea.

Got enough room for a right-angular drill?  You can get adaptors...

Or a flexible drill extender?

[neilrj]

Where are you located? Someone with the kit locally might oblige - or know a grumpy bearded man who can.

[Bolt]

I would coat the stripped thread with JB weld (industrial epoxy) then retap, or if retapping is not an easy option screw in a M5 bolt covered in a suitable release agent (silicone oil) while the epoxy is still curing.  Some of you may remember that I used JB weld to attach a LH downtube shifter boss to a steel frame, that was over a year ago now and it's still very firmly attached

[hatler]

Use a Dremel flexible drive shaft to get the right angle to drill the hole ?

[quixoticgeek]

Would something like this work with a hex shank drill bit https://amzn.to/2GGJkcG ?

J

[Arminius]

I would coat the stripped thread with JB weld (industrial epoxy) then retap, or if retapping is not an easy option screw in a M5 bolt covered in a suitable release agent (silicone oil) while the epoxy is still curing.  Some of you may remember that I used JB weld to attach a LH downtube shifter boss to a steel frame, that was over a year ago now and it's still very firmly attached

Hmm, this sounds like a method that would involve less powertool use on my part, which is a good thing...

When you say you coated the threads, how did you do that without completely filling in the hole? And what sort of silicone oil did you use? (Looks like there are many types.) I guess if it all went a bit wrong I could still drill it out (thanks for the other suggestions, feanor, QG, et al). I'd prefer to avoid that option if possible, given that it's brazed in rather than a rivet.

I'm based in York, if anyone nearby has the tools and a grumpy beard (I gather this is a requirement for this sort of job). 

[aidan.f]

I would go for a M5 taper tap to clean up the repaired thread.

[Bolt]

Hmm, this sounds like a method that would involve less powertool use on my part, which is a good thing...

When you say you coated the threads, how did you do that without completely filling in the hole? And what sort of silicone oil did you use?

JB Weld is quite thick if mixed at a cool temperature and so you should be able to build up a good layer around the thread using a cocktail stick or similar applicator.  In terms of a suitable release agent I've used silicone lubricant purchased cheaply from Lidl, but I'd say that any alternative that doesn't react with the epoxy will work.   Try experimenting with the process with an old oversized nut and undersized bolt before tackling the job on the frame.

[jsabine]

How badly stripped is it? If there's still a bit of purchase on the threads I'd be tempted to run a tap through them and then just assemble with a bit of loctite, and only resort to a proper fix if that failed.

The next least effort is probably as Jurek suggests, retapping to M6.

[aidan.f]

M6 will require a good thick boss. As for helicoil upthread. I do have everything required and am not far out of Durham. But IMO JB weld followed by a cheap M5  tap is not hard