I pulled the crank off my winter bike ('93 MB-3) and was pretty dismayed to see the state of the chainstay. It's pretty messed up, I gather from the chain getting wedged in there before I installed the jump-stop.
How worried should I be about this? On one hand, it seems like a bad place to have a frame failure (is there any good place)? On the other hand, it's been that way for who knows how long - I installed the jump-stop ~2 years ago following a nasty drop on the way up steuben st. and haven't dropped the chain since.
I know it's kind of hard to tell from the photos, but it's really pretty compressed, with a couple good chain link shaped divots. As far as I can tell it's just bent not broken though. Should I take it to a shop and have someone look at it?
i doubt it would be worth the money to fix it if its even repairable. i'd just ride it till it dies. a frame failure there really won't be that big of a deal. it will startle you and you'll drop a couple inches and have to rack it home, but thats about it. if you are going to have a frame failure, thats about the best spot to have it.
You could try and fill in the dent with some aluminum reinforced body filler. Might strengthen the area and protect it from further chain damage. They sell this at most auto parts stores.
well, with the jump-stop i'm not too worried about the chain coming off again... i guess that's about the best news possible.
well, you know how people say "if you think you hear noise coming from your bottom bracket, it's probably coming from somewhere else instead"? but, sometimes it is the BB... 
the split bearing is a nice touch. the spindle cone is jacked up too, so i need to find a new one.
The frame has certainly seen better days; at some point it will likely break if not repaired. If you want to try to fix it, I'd be happy to form and mig weld a patch over the top of it, although I won't have the time to help for a week or two. I have some cold rolled steel sitting around from another project that would work well. It should take about an hour and would be no sweat off of my back.
Having worked with similar products, I feel that Greasefoot's suggested fix is excellent for protecting the area from further damage, but unfortunately would add a very modest amount of structural support. It is well worth doing, in my view, so long as you recognize that you won't be adding any real strength to the frame.
Any form of a filler will not strengthen the area.
Wow, that is super generous of you, thanks! Although, I do wonder if it's worth it, I've been thinking about buying a new commuter with disc brakes anyways and maybe this is a sign I should just do it.
I don't ride offroad much anymore and when I do I was already nervous about using this bike given its age, my not-as-svelte as it used to be figure, and the abuse I give the bike with slogging through the salt all winter.
So, while there is a lot of sentimental value in this bike for me (it was my first "real" bike and I rode it a ton offroad and on) it sounds like it might be time to just face up to grim reality... 
Sorry about your frame. I do like the word svelte, though.
I would ride it til it dies. I don't think there is anything you can do otherwise, and it might keep going for another ten years for all we know.
I also wouldn't reinforce it with any sort of filler or hit it with a MIG welder.
I agree with Brad. Also, just throw a cartridge bb in that thing and be done with it.
Guys, I'm curious why you feel that MIG welding is not a viable fix. I ask this not to be argumentative, but instead with great respect for your views and experiences, and I honestly want to make sure I'm not overlooking something. I should add that I can think of about 6 reasons that adding a patch via MIG would be fairly tricky, thus part of me agrees that leaving it alone and riding it until it breaks is the better thing to do.
The cost of a new steel bicycle frame is relatively cheap when you divide the cost by miles you expect to ride. A patch is a better short term fix in order to get home than a dependable repair, nevermind that it's probably not going to be all that aesthetically pleasing to look at.
On an older frame, I'd be afraid of metal fatigue near the welds PDF The weld itself could result in an area more likely to fail than the damage caused by the chain in the first place. I think it's a toss up. For that reason, I'd also say the best bet is to just keep riding it until it fails (if it ever does).
I agree, you could make matters worse by trying to weld in a patch. You have to assume that the frame hasn't rusted inside to the point where it is too thin and rusty to even weld (the result is you blow holes in the frame). You also have to contend with the brittleness that I have read can occur if chromoly is welded cold, i.e., without a little preheating. Preheat the frame too much and you risk melting the brazing out of the lugs. Then you have the complexity of possibly welding steel of different thicknesses, which is that much harder if the metal is rusted inside. Add in the risk of setting the frame on fire and it could be a real can of worms!
A patch would be a good way to fix this but MIG welding thin wall tubing is tricky and takes some talent.
I would suggest finding an old junk frame with a similar chain stay and cut out a tasteful patch from it. Then epoxy it into place with Lord Fusor. It’s an industrial 2-part auto body repair epoxy with tiny glass beads in it. When this stuff sets it has twice the tensile strength of a weld.
Believe it or not this epoxy is OEM in the manufacturing of new cars and insurance companies require it rather then welding for repairs. You can buy a small tube with the mixing applicator gun at any auto body repair supply store.
The LORD stuff might work out, but I would be careful assuming it has the same strength as a weld. There is some context in that description that can get lost very quickly.
In this instance it might do the trick, others, who knows.
Interesting discussion, as is the norm here. I'm aware of the modern epoxies with glass beads, but have never used them. I've been looking into them and plan to use a variety (3M 9323 or Loctite Hysol 9430) soon on a car project. I understand that they're very strong, assuming proper surface prep, and that the glass beads ensure that the glue maintains a certain minimum thickness. Given the comlexities of welding there, whether via MIG, TIG or oxyacetylene, bonding a steel patch might be the best repair of all. It would also let you get the patch up against the lug, which you can't do with any welder since the weld won't stick to the brazing. That said, all things considered, it still may or may not be worth the effort.
The consideration that needs to be made on the epoxy is how it is used. It is for bonding panels. Without knowing 100% specifics of their product I am assuming they have great shear strength in part because of the bonded area. I do not know that the panels they are bonding are subject to too great of loads nor to I believe the weld they would be able to use in those panels is too strong, thus the reason the epoxy is better.
Yeah, I think I'm leaning towards just putting it back together and pretending like I didn't notice... The last time I remember dropping the chain was summer '09 so it's probably been that way for quite a while, if not long before. I'll ride it this winter and probably buy a disc LHT in the spring, then the MB-4 can become the bike I ride when I have to lock up outside for extended periods or something.
I’ll be the first person to admit I was very skeptical of this epoxy when I saw someone using it the first time.
I attach a set of Global West sub frame connectors to my Mustang with the (long set) Fusor. The car has a 400HP motor and twists the frame when I drop the hammer. Every once and a while I’ll check to see if the bond has cracked or if rail connectors have moved, and they are in the same exact place I attached them 3 years ago.
Damn, Greasefoot, that's some strong stuff! Thanks for sharing your experience. I can relate - I welded subframe connectors into my old Mustang GT and drove my brother's Cobra with and without them welded in. There was a big difference in unibody flex, especially under throttle. Those connections are highly stressed, to say the least. With 400hp and enough traction you might pull the left front wheel off the ground at a dragstrip, if you don't rip the upper control arms out of the frame!
Any tips on making it work, besides the obvious need for proper surface prep?
The new Lotus cars have their frames almost exclusively bonded. They also used honeycomb where possible. Really awesome stuff.
The GW connectors have a lot of contact area and fit perfectly around the rails so I believe this is the main reason it worked. I had a few people tell me to stay away from the less expensive bolt on rail connectors.
The prep as you mentioned is important. Cleaning 40 years of dried undercoating off the frame rails was a project. The frame connectors from GW are powder coated so removing it from the inside contact surfaces area with a wire wheel took a long time.
I did one rail connecter at a time and applied the Fusor to all the clean contact areas liberally. Then used a 1-inch paintbrush to make sure it was worked in to all contact points. I used a jack and press each side of the connector into place around the rail. I needed 2 jacks to hold both sides of the connector in place over night. The next day repeated the process to the other side.
Originally I was going to weld them in per the manufactures instructions but I did not have the hart to lay heat on my original rails and toque boxes. They had survived so long without a spec of rust that I was not going to introduce anything that would disturb the steel. But I needed the connectors, so I decided to use the Fusor. I had a back up plan and if needed I was going to drill some holes to add some 5/8’s grade 8 bolts.
I have not yet put in my 2c, which is unusual, so
a. That is some hella damage, just from dropped chains!
b. Filler - I'm thinking is not a good idea, you would not want to cosmetically cover damage like that, keep an eye on it.
c. If there are any cracks, drill some (tiny) termination holes at the farthest ends of the crack to stop them going any further, braze the cracks to stop any movement in the crack itself, and to keep water and crap out of the tube.
d. Put it back together and ride it.
Nice work. I would have used the Fusor as well for exactly the same reasons. I'm modifying the chassis/roll cage on my FFR Type 65 to SCCA GT specs and may try the Fusor on it. Two optional diagonal braces will be steel at the ends, carbon fiber tube in the middle, welded in, and removable via Ballistic Fab connections (akin in function to S&S couplers on travel bikes). I basically need to glue the carbon tube to the Ballistic Fab connections on each end. Oddly enough, I've read to powdercoat the steel first, abrade the powder coating, then bond them, since bare carbon-on-steel contact causes electrolysis and/or rust. In researching this I read that people are developing techniques to repair structurally deficient bridges in the same manner, and a challenge is ensuring that the electrolysis and rust issues are addressed.
I apologize for this thread going astray; hopefully it is also interesting.
edmonds - i don't recall anything else ever getting wedged in there but it's been so long i don't trust my memory. it has just the right amount of clearance that the chain can get *seriously* stuck in there, i remember last time (riding up steuben) it took a few minutes for me to get it unstuck then i had to improvise with the tools i had on hand to bend the chain back into some semblance of straight so it wouldn't skip.
$12 well spent: http://www.gvtc.com/~ngear/
Well, I bought a new sealed BB, put everything back together and finally started riding the bike this week with the snow and all. I still love riding the thing even if it's big and heavy and obsolete. It feels like riding a tank compared to my other bike, which is both good and bad - but mostly a welcome change of pace.
Kind of an embarrassing story, I was dismayed to find it was still making a terrible noise when I pedaled. I convinced myself it wasn't coming from the BB, it seemed to be coming from the rear wheel. Sure enough when I got to work I grabbed the wheel and I was able to shake the whole thing left and right by a truly alarming amount. Somehow I completely messed up adjusting the rear hub - it wasn't even close, I had to turn the cone 1/4 of a turn if not more. Not sure how I did that, so bad news there but happy I was able to diagnose and fix it before I did any real damage.
