RubeRad

Short story:

I'm facing a Suntour VX RD (looks exactly like this one, as far as I can tell) with a frozen hanger attachment bolt. I've tried soaking oil in, and if I force it I can get it to reluctantly move, with an angry creaking noise. Is this just a case of waiting for the oil to seep in , or have to go with something specifically penetrating?

Long story:

So I came across this bike in the wild with a DSO (derailleur-shaped-object), or rather not even quite shaped like a RD, but more turned inside out. Looked exactly like it caught a spoke and tore the cage plate almost off, but no evidence of trauma to spokes or metal dork disk (extends at least an inch past 28T largest cog on 5sp). I wanted to be a good samaritan, so I left a note with my email on the bike saying I could help replace the RD. He got in touch, I found this Suntour VX on CL for only $8 and sent him to go get it, then he brought me the bike, I got the chain open and old RD off no problem (old RD had integral hanger), next step screw the VX onto a hanger I happen to have handy.

But at this point, I cannot screw it on because the bolt is froze. I cannot screw the hanger backwards onto the bolt, because of the b-screw tab. So unfortunately, I had to send this soul off to the bike shop to see if they can install this RD. Light chain oil from every direction did not set it loose, except the slotted lockring (?) was able to come out.

Further backstory, he got the bike from CL, it originally had some different RD on it (probably also Suntour, to match the FD and shifters), and one day it "just fell off". Some LBS (that I am not familiar with) replaced it with this super-cheap monstrosity about a month ago, it mysteriously got turned inside-out about a week and a half later, out of frustration and busyness he hasn't taken it back to the shop yet. I'm hoping they'll be cool and do what it takes to install this RD for him for free.

Unfortunately, I can't finish the job for him, as I'm heading out of town. Is there any advice that I can forward to this guy?

onespeedbiker

If you plan on keeping the derailleur, your going to have to remove the pivot bolt. There is slotted locknut on the back of the hanger bolt that needs to be removed. While there is specific locknut tool to remove it;but good luck finding one. I'm sure you be able to use a spanner wrench or a small screwdriver and hammer to unscrew it. Best to put the correct size allen wrench in a vise and place the pivot bolt on top so you are looking down at the locknut; then work on getting it off. Here is a diagram of a similar derailleur with the same locknut. https://www.yellowjersey.org/cyclone.html

dsbrantjr

Forget chain oil for difficult fasteners. Get yourself some PB Blaster or even better Kano Kroil which are specifically formulated to loosen stuck fasteners. Apply liberally, tap the fastener firmly a few times to help work the oil in, wait a while and do it again. It may take overnight or longer but it will loosen eventually. Use an unworn, properly fitting tool and you should eventually get it free.

RubeRad

Yes, this has the locknut (faintly visible in the ebay pic too), and after the first shot of oil it easily came loose. The rest, not so much.

RubeRad

WD-40 does this a little bit too, right?

demoncyclist

WD-40 doesn't even come close. It is a water dispersing solvent (WD). I swear by PB Blaster for loosening stuck objects- it literally dissolves the rust. I removed a seatpost that had been stuck for a decade with an overnight soak.

HillRider

It sounds like the derailleur's mounting bolt and the hanger you provided had different thread configurations and that's why the mismatch. AFAIK, all Sun Tour rd mounting bolts have M10x1.0 threading. If the hanger had SAE threading that's your problem.

RubeRad

Maybe with the locknut removed though, I could clamp the RD in a vise and tap the pivot bolt out with a hammer? (If I had it anymore, I sent it off with the guy and his bike to take to LBS for installation)

RubeRad

I have no idea whether the threading on the mounting bolt and the hanger match, the problem is the mounting bolt will not spin, so I cannot attempt to screw it into the hanger.

HillRider

OK, I didn't read your OP in sufficient detail. Now I see what you are dealing with.