uprightbent

So I scored what I thought was to be a fairly easy fix. Vintage 84' Miyata 610, with a cracked in half Suntour Mountech rd which really bent the derailer hanger inward, somehow not crashing into the spokes.

So I found a replacement NOS Suntour rd, carefully bent the hanger back outward with a large crescent wrench. On the test ride, things seemed very smooth and aligned/ shifted correctly. Then I jumped the chain past the largest cog into the gap where the dork disk was, that I had just removed. This locked up the drivetrain for barely a half rotation of the cranks, yet bent that soft hanger right back into gross misalignment.

I've read this was often an easy fix, but hadn't read these can easily bend back again the wrong way. I'm sure all this movement is not good for the steel, which now must be weak? Do I now have something destined to be a single speed by hacking off the hanger? I'm not sure I see any other options? As a collector that's not my first choice.

By the way, it's a direct mount rd. I do have a correct rd with a claw type hanger, wondering if this might provide its own support and not be affected by the bent or weak hanger built into the frame.

Thanks in advance!

trailangel

You bent the rear hanger with the wheel on, right?
Bend it back again, and this time adjust the RD low stop before riding.

Andrew R Stewart 

Being easy to bend back after the first incident means that it was easy to bend in the first place, and easy to bend after that. Only after a number of bends that is, until the hanger starts to work harden. Then it will want to crack...


I suspect that the drop out is a fairly thin stamped design. Common on low to mid priced steel bikes back in the 1980s and early 1990s. besides the fairly mild grade of steel that was used (so to be easier to stamp and form in the factory and reduce costs) the thickness being, maybe, 2/3 of a forged drop out doesn't help it's stiffness. Forging will improve a steel's strength and I suspect this drop out wasn't made this way. Andy.

dsbrantjr

Check your spokes for damage, where the much-maligned spoke protector (dork disc) was before you removed it.

cpach

Bending the derailleur hanger multiple times is indeed not great for it, but it's not very indicative that it bent when you derailed the chain into the spokes. That would be the expected outcome really regardless of the state of the hanger.

I'd recommend getting the hanger realigned with an appropriate tool--not a crescent wrench, particularly since it's undergone some trauma. If you don't want to buy the tool, and there's not a cooperative in your area, it's not typically a very expensive service at a bike shop. Then for goodness sake, learn to adjust the low limit of your derailleur properly, and CHECK that it is adjusted correctly before riding it by trying to derailleur the chain into the spokes in the stand, first by pulling on the der cable, and then by pressing the derailleur with your hand. The derailleur's movement on its own puts relatively little stress on the hanger, so if you can get it straight without cracking, it'll probably work fine. I'd just take a little extra caution about storing and moving the bike to not bend the hanger. If it does go, a framebuilder could braze in a new dropout, though it'd ruin the paint for several inches.

uprightbent

Thanks for the replies so far. Yes, I did leave the wheel in place as a brace after removing the freewheel for better access, before I taped the dropout and bent it outward in 3 small steps. Also checked before and after to ensure the 126 spacing remained the same.

I guess it is a lower grade stamped dropout, but still surprised how easily it can bend.

JohnDThompson 

+1 this. Vintage dropouts are made from mild steel precisely to allow for bending into alignment. Repeated bending of steel will eventually work-harden the bent area and eventually lead to cracking, but it takes a while with mild steel. Re-align the tab and take care to adjust derailleur travel as trailangel notes so it doesn't happen again.

AlexCyclistRoch

If it were me, I might try to hot-set/anneal it.

Andrew R Stewart 

Some might use the metaphor of "jumping out of the frying pan and into the fire" when the use of heat is mentioned to align a bike frame. Andy

AlexCyclistRoch

If it's been bent back then it's 'sprung' partway to where it had been, then the bend has already 'work hardened', and is now in danger of fatiguing. Since the bike is a crap-can anyways, I would straighten it, then using a MAPP gas pencil torch, heat the area until it is glowing red, then just let it cool naturally (don't 'quench' it; all that will accomplish is to case-harden the outside).

davidad

If you don't have the hanger tool you can use a spare rear wheel to realign the hanger. Remove the rear derailleur and screw the axle from the spare wheel into the hanger (10mm Dia. by 1mm pitch). Use the wheel as a lever to bend the hanger until the wheels are parallel.
A friend dropped his chain and destroyed his rr der and bent the hanger so much that after straightening the hanger with a Cresent wrench I had to run a tap to get the threads in condition to take my alignment tool. We have had to realign the hanger a few times over the last 70k or so miles. Steel can be very forgiving.

Andrew R Stewart 

As John said the road to work hardening is a rather long one. Think about how many bends it takes to crack a paperclip. My first post (#3 I think) referred to this indirectly.


My suggestion of avoiding hear during bending is from knowing that the structure of steel is rather delicate when orange hot. Any one who has welded or brass brazed on a piece under stress has experienced the failure of the piece, steel's "strength" declined rapidly when so hot.


But you suggest a different use of the heat that I didn't initially get. To anneal the after bend. Not a bad idea but I'm not sure this step is yet needed. Certainly if done the person would want to do the homework as to heat level attained, how long held at that level and how slow the cool down was. Additionally the atmosphere this was done in might also be an aspect to consider. Andy

70sSanO

I've had to bend a hanger on a few bikes over the years. I use a crescent wrench and a combination square. It gets it pretty close. I would imagine after years of use and abuse you may be hard pressed to find too much on that bike that is correctly aligned. But you do want your drive train pretty close to avoid funky shifting.

John

kaos joe

There are a few instructional vids on Youtube on how to make an alignment tool set out of 2 pieces of threaded rod. I've done this, being a serial hanger bender and dropout mangler on my steel mountain bikes. The tool works and is easy to use.

AlexCyclistRoch

Well, while a proper anneal might require the services of a heat-treater in a vaccuum oven (I know at least 2 in town), my suggestion was only a sort of half-@$$ed anneal, but at least it would impart a stress-relief on the bend area. I would never do this on any bike that has any value (or forged dropouts..).

uprightbent

What do you mean by this?