Dropout/mech hanger bolts

[robgul]

I have a customer who has managed to break, at the latest count, 3 rear mech hangers on his 2014 Trek Madone 2.1 aluminium frame bike.

Replacing the hanger is simple BUT his latest occurence (and probably damage before that) has "flared" (or increased the counterink) both of the holes in the aluminium dropout so that the two tiny screws that hold the hanger in position on the inner face of the dropout almost pull all the way through - thus not holding the hanger very firmly.   I know that the wheel/axle will actually press against the hanger and hold it in position when the wheel is in BUT it does present a risk if the hanger came adrift (and perhaps didn't snap off)

See pic for the "flare" - both holes in the drop out are pretty much the same - I'm guessing that the breakages have levered on the screws and pulled them through the soft-ish aluminium.



Any suggestions for a remedy? - I've looked at sourcing screws with a large head but to no avail. 

Have to say if it was my own bike I'd be looking at replacing the frame (it's an older frame but with, by the look of it, later components)

[iandusud]

Where have looked for replacement screws with a larger head? What is the thread size. I think that a larger head would be a good idea but I would also look at cleaning up the countersinking with a sharp drill bit. The fact that the countersinking in the frame has been damaged suggests to me that the screws have been coming loose. Do you use thread locking compound on them?

[robgul]

Where have looked for replacement screws with a larger head? What is the thread size. I think that a larger head would be a good idea but I would also look at cleaning up the countersinking with a sharp drill bit. The fact that the countersinking in the frame has been damaged suggests to me that the screws have been coming loose. Do you use thread locking compound on them?

I've been to the local fasteners shop that seems to stock everything known to man - he couldn't match anything with a larger head. 

Drilling out the holes in the dropout is a non-no - there's almost no metal as it is.  Screwing the retaining screws and they go so far in that they protrude on the inside/wheel side of the hanger. 

This is the first replacement I've done - I do know that the two (at least) previous replacements were done by an LBS - no sign of any threadlock on the screws.

The break on this occasion was riding across a field of long grass which jammed in the lower jockey wheel and ripped the hanger into 2 pieces.   I should add the bloke isn't the brightest of sparks when it comes to bikes and indeed anything practical!

[chrisbainbridge]

I think this is a case where your reputational damage will be worse off if you actually do any repairs.  The frame is now unsalvageable a a regular use bike.  If you bodge something it will fail and it will be your fault.

I would tell him that his bike is beyond salvage and you will not be able to repair it.

[robgul]

I think this is a case where your reputational damage will be worse off if you actually do any repairs.  The frame is now unsalvageable a a regular use bike.  If you bodge something it will fail and it will be your fault.

I would tell him that his bike is beyond salvage and you will not be able to repair it.

Indeed.  Having now looked at the dropout closely and measured the remaining metal with a (dental!) caliper there is no way that I'm prepared to fix it - and am about to tell the customer . . . suggesting we try and find a suitable, similar s/h frame and swap all the components over.

[rr]

If it were my bike I might be tempted to try something involving chemical chemical metal as a bodge to get me through until I could source an alternative frame. In your position I would probably take the same decision as you and say can't do a decent job so not going to touch it.

[robgul]

If it were my bike I might be tempted to try something involving chemical chemical metal as a bodge to get me through until I could source an alternative frame. In your position I would probably take the same decision as you and say can't do a decent job so not going to touch it.

I did consider the "metal araldite type stuff" to build up the holes and then re-drill/countersink - but then sense prevailed!

Customer is "pleased" with the result and we're going to try and source another frame .... it's Trek Madone 2.1 58cm (although I have another customer wanting to sell what is probably a suitable machine)

[Feanor]

Does it really matter?

All those screws do is hold the hanger in place when the wheel is out, much like the small shear-o-matic screws that hold a brake disk onto a car's hub.
Once the wheel is on, they don't really serve much purpose, do they?
Or do they?

[robgul]

Does it really matter?

All those screws do is hold the hanger in place when the wheel is out, much like the small shear-o-matic screws that hold a brake disk onto a car's hub.
Once the wheel is on, they don't really serve much purpose, do they?
Or do they?

That is true BUT the way this bloke rides his bike and busts gear hangers the risk is that if he has another similar "grass in the jockey wheel" incident the screws fail it could rip the hanger out from between the wheel and the dropout with possibly dire consequences - bike stops instantly and he flies out of the front door!