Stripped thread for mech hanger

[Mark80808]

Due to a transport disaster, I have a bike where the mech hanger can no longer be screwed to the frame, as the hole within the frame has had the thread torn out (the mech hanger was forcibly pulled off the frame). The screw was steel, the frame is scandium allow, and the screw just tore itself out. This means the screw nolonger grips the frame to hold the mech in place.

When the wheel is in place, this is not a problem, as the wheel and thru-bolt holds it all together, but when the wheel is removed, there is nothing to hold the mech and the hanger to the frame. Has anyone had any experience of this and found any decent solutions? Supergluing the hanger in place lasts a couple of months if I am gentle, as the bolt is not needed when the wheel is in place. Maybe a slightly wider screw that might cut a new thread in the frame, or is there anything that can be done by a competent bike builder with a welder? The bike is fine until then back wheel comes off, at which point the rear mech usually detaches itself in a very annoying manor..

 

[Tim Hall]

Would a Helicoil work? It's a doofer that screws into a larger hole and has a thread on the inside. Needs a specialist tool to install and I don't know if a typical dropout is thick enough.

 

[raleighnut]

Even easier get the frame re-tapped for a size bigger thread (If it is an M3 bolt tap it out to M4) then make the hole in the hanger a touch bigger and Bobs yer mothers brother.

 

[Bazzer]

If you go down the helicoil route, try to find a kit for the relevant size, with all the tools you need; bit for bigger size, tap, tool for the insert and tool for knock out. - Unless of course you have the the latter two in particular already from another helicoil kit.
Personally I'd get some thread lock as well.
If you have never helicoiled before, it is straightforward, you just need to take a bit of care. There are some useful videos on You Tube.

 

[midlife]

You can buy a nut that fits on the inside of the hanger which the mech bolt screws to

Shaun

 

[numbnuts]

Even easier get the frame re-tapped for a size bigger thread (If it is an M3 bolt tap it out to M4) then make the hole in the hanger a touch bigger and Bobs yer mothers brother.

This ^^^

 

[Profpointy]

can you just use a nut and (longer) bolt? Ie drill it out a bit - bolt right through and nut on the back - providing there's enough space that the nut doesn't foul the spokes or whatever.

If not then drill and tap it a size bigger as raleighnut suggests

 

[Yellow Saddle]

You can buy a nut that fits on the inside of the hanger which the mech bolt screws to

Shaun

I don't think it is that thread that stripped. It reads like the smaller hole for holding the sacrificial hanger onto the frame. But that said, those mdwafters of yours are very useful.

 

[Venod]

I have used one of these, it is double sided and slips over the dropout, one side is threaded, so the screws clamp it to the dropout, it seemed a bit flimsey and I was a bit dubious how long it would last, but it was still okay when I sold the bike.

http://www.ebay.co.uk/itm/Rear-Gear...283598?hash=item2ef0ca45ce:g:xKQAAOSwKrhVXzbN

 

[midlife]

I don't think it is that thread that stripped. It reads like the smaller hole for holding the sacrificial hanger onto the frame. But that said, those mdwafters of yours are very useful.

Yup, went back and re-read the OP's post and I got the wrong end of the stick as usual

Shaun

 

[Mark80808]

I'm liking the sound of tapping out to a bigger size. Putting "M4 Tap" into Google brings back several suitable looking tools for a few quid, and hopefully they will be small enough to use without dismantling the rear frame of the bike - and also not require power tools... Will have to do some internet ordering over the weekend.....

 

[raleighnut]

I'm liking the sound of tapping out to a bigger size. Putting "M4 Tap" into Google brings back several suitable looking tools for a few quid, and hopefully they will be small enough to use without dismantling the rear frame of the bike - and also not require power tools... Will have to do some internet ordering over the weekend.....

Don't assume the bolt/tap needed will be M4, it may well have been an M2 bolt which needs taking out to M3.

 

[Profpointy]

Don't assume the bolt/tap needed will be M4, it may well have been an M2 bolt which needs taking out to M3.

M2 is a pretty small bolt - well, 2mm diameter funnily enough. Not too many of those on a bike.
Of course, someone will tell me the hanger bolt is 2mm now - but I read it as being the 4mm or 5mm bolt

And to the OP, at the risk of teaching my grandmother to suck eggs, you need a drill the right size to tap the hole - specifically you don't drill a 4mm hole to tap to 4mm ! For M4 should drill a hole 3.3mm for example.
Some sets of taps come with the right drill for each thread size, which isn't a bad idea if buying a set, unless you've already got a set of drills in 0.1mm increments - which most people don't.

 

[raleighnut]

M2 is a pretty small bolt - well, 2mm diameter funnily enough. Not too many of those on a bike.
Of course, someone will tell me the hanger bolt is 2mm now - but I read it as being the 4mm or 5mm bolt

And to the OP, at the risk of teaching my grandmother to suck eggs, you need a drill the right size to tap the hole - specifically you don't drill a 4mm hole to tap to 4mm ! For M4 should drill a hole 3.3mm for example.
Some sets of taps come with the right drill for each thread size, which isn't a bad idea if buying a set, unless you've already got a set of drills in 0.1mm increments - which most people don't.

TBH I've worked in engineering and I'd be wary of doing it myself without having the workshop equipment, some could do it 'freehand' but I wouldn't even attempt doing it And certainly wouldn't use a DIY Tapset.

 

[Profpointy]

TBH I've worked in engineering and I'd be wary of doing it myself without having the workshop equipment, some could do it 'freehand' but I wouldn't even attempt doing it And certainly wouldn't use a DIY Tapset.

Maybe I've been lucky, but I've done a few jobs like that (DIY, never been a proper engineer!) all freehand and all have worked out OK. Not so clever if you snap the tap off half way into the job though - which I've yet to do.
I was fairly meticulous with greasing the tap with the proper stuff, 1 turn in, half-turn back (or whatever it was), and stopping if it got tight, and so on.

EDIT
I should add that I was using a proper make tap and tapping drill rather than some bongo make. Dunno if the cheapies are also OK, but from experience of other tools I rather doubt it. I do tend to use any job as an excuse to buy the right tool (or set of...) , and a high quality one at that. I recall I bought the tap set in the first place in order to cut a thread in the underneath of the bottom bracket for attaching the plastic cable guide when changing the gears around. Thus £70 tap set for one 5 minute job - but I've had it ever since and it gets trundled out once or twice a year for something or other.