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Investigating rust-related frame crack

Old 04-02-20, 11:00 AM
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Laingod
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Investigating rust-related frame crack

Hello!

So I got my hands on an unusual "Miyata 621ST" last November for cheap. After a long search, I was thrilled to get my hands on that baby: perfect size for me (54cm), nice green paint... my dream! I was so excited I barely inspected it and took it home.

Except I could hardly find info on it, not to mention the head badge said "Made in Taiwan" which disappointed me because I have a very high esteem of Japanese work.
Anyhow, I had to park it outside on my balcony for the winter, bike isn't exactly mint condition so I thought "That's fine".
Last week I took it inside to get it ready for a ride, however the crankset was pushing against the chainstay... What? After a quick inspection I spotted a crack underneath (oh noes!) and the tube seemed as though it had considerably expanded, swollen and was now pushing against the smallest chainring.
I did not inspect that area thoroughly before I put it in storage but the bike was riding just fine a few months ago. Stripped all the parts and now looking for another one... no use crying over spoiled milk.

My questions are these:

- Could water have gotten stuck inside the tube and then frozen? I have seen a similar crack on bursted-out copper pipes before, the ones you forget to blast with air before the deep frost comes.

- Is it simply rust acting over the years I failed to notice? Could it be that in fact this frame has been under the effect of corrosion for a while already? I felt guilty for exposing it to rain and ice for the whole winter, yet I am suprised to see it reach that state so quickly.

Attached are pictures, would be appreciated if someone had some insight on rust-related issues. Thanks!





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Old 04-02-20, 11:49 AM
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Those are clear indicators that the stay was filled with water and froze, causing it to bulge and split. Water probably got in through the seat tube and pooled in the stay.
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Old 04-02-20, 11:50 AM
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Originally Posted by Laingod
Could water have gotten stuck inside the tube and then frozen?
Yes.

Originally Posted by Laingod
Is it simply rust acting over the years I failed to notice? Could it be that in fact this frame has been under the effect of corrosion for a while already? I felt guilty for exposing it to rain and ice for the whole winter, yet I am suprised to see it reach that state so quickly.
Maybe.
Try to avoid storing a bike outside at all costs as this is what happens.
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Old 04-02-20, 12:25 PM
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[QUOTE=Crankycrank;21397197]Try to avoid storing a bike outside at all costs as this is what happens.[/QUOTE
Agreed. To bad for the OP, but hopefully this post will help others realize that their bikes need proper storage.
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Old 04-03-20, 12:54 AM
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Bummer about the cracked tube. Certainly looks like water froze inside the tube. On another note, the only tig-welded Miyata frame made in Japan was the original Ridge Runner, everything else was lugged, including their titanium frames. Otherwise they sourced the tig frames from Taiwan, and I believe Southern Cross was a big supplier for those frames. For the Miyata aficionado, please correct me if warranted.
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Old 04-03-20, 01:59 AM
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From the last image it does look like damage caused by expansion (split - pushed away from each other) rather than a stress fracture or general corrosion.
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Old 04-03-20, 09:25 AM
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Wow. That frame is toast!
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Old 04-03-20, 01:22 PM
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Frame is not necessarily toast as it can be repaired. I have replaced chain stays twice. The cost of having someone do it for you will easily exceed the value of the bike, but if you can do it yourself, it is not a hard job and will only cost the price of a tube, filler, paint. Need a torch, but if you don't have the flame, forget the project as it will become costly rather quickly.
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Old 04-03-20, 02:23 PM
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Originally Posted by TiHabanero
Frame is not necessarily toast as it can be repaired. I have replaced chain stays twice. The cost of having someone do it for you will easily exceed the value of the bike, but if you can do it yourself, it is not a hard job and will only cost the price of a tube, filler, paint. Need a torch, but if you don't have the flame, forget the project as it will become costly rather quickly.
Technically possible, yes. Feasible, how much money do you want to put into a 30 year old rusty commuter?
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Old 04-04-20, 11:50 AM
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Originally Posted by TiHabanero
Frame is not necessarily toast as it can be repaired. I have replaced chain stays twice. The cost of having someone do it for you will easily exceed the value of the bike, but if you can do it yourself, it is not a hard job and will only cost the price of a tube, filler, paint. Need a torch, but if you don't have the flame, forget the project as it will become costly rather quickly.
I'm the kind of person willing to indulge in such projects, especially when it comes to old and valuable steel. That being said, I currently don't have the means to do so nor the knowledge, so I suppose this one will be recycled one way or another (wonder if that steel is good for knifemaking?). Had it been an 80s miyata 610 or so I'd maybe given it a chance though

I find it quite unusual though for water to pool in there - I would have thought the level rises to the point it reaches the next hole. Not to mention I've been leaving my current commuter bicyle outside for 4 years now and riding it in the snow and all. The guy's really taking a beating but looking good, it's a Jamis chromo frame as well.
Also didn't think the ice would expand sideways instead of trying to go up the tube. Then again I'm no physics expert.

Proper storage for a proper bike is what I'll remember.
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Old 04-04-20, 03:33 PM
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Nothing really valuable about a rusted bike that was mass produced. It may be a great bike heck it could have been at the top of the range when it came out but if it is in rough shape as this one there is not much there for someone to want. Bikes should be taken care of and kept inside and there is almost never a reason to store a bike outside it is pretty tough to not be able to find a storage solution inside these days with all the various products already on the market and neat hacks that many people have come up with. Even if you had to store a bike outside for some odd reason there is no reason it should get damaged in that way as it should be frequently checked and maintained and at the absolute minimum should be covered to prevent water getting in from the top of the bike. Plus leaving a bike outside makes it an easy target for thieves.

We need a group People Against Bicycle Abuse (PABA) to help teach and prevent this stuff from happening.
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Old 04-04-20, 09:40 PM
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It will be interesting to find out if this stay was blind to the shell but still vented at the usual spot, a half inch ahead of it's drop out end. If so then a build up of water inside over many miles of wet conditions, or just the right outside storage, could produce a significant amount of water that wouldn't drip or evaporate out easily. I suspect that the stay will be nearly eaten away along it's bottom and up the sides a bit. If this frame were to be repaired I strongly suggest replacing the other stay and checking out the top tube's condition. Andy (who has drained 1/4 cup of water out of a frame a few times).
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Old 04-05-20, 06:45 PM
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Originally Posted by Andrew R Stewart
It will be interesting to find out if this stay was blind to the shell but still vented at the usual spot, a half inch ahead of it's drop out end. If so then a build up of water inside over many miles of wet conditions, or just the right outside storage, could produce a significant amount of water that wouldn't drip or evaporate out easily. I suspect that the stay will be nearly eaten away along it's bottom and up the sides a bit. If this frame were to be repaired I strongly suggest replacing the other stay and checking out the top tube's condition. Andy (who has drained 1/4 cup of water out of a frame a few times).
This frame needs a THOROUGH inspection before proceeding! If the chainstay is THIS bad, I'd expect lots more issues elsewhere. Inside bottom of the seat tube at the BB would be the next place to look. Even then, probably worth finding another bike or frame that's a better candidate for your time and effort. Unless it's pristine everywhere else, it's not worth taking a torch to. Even if it were, no framebuilder would accept a job like this. Repair work exceeds value of frame and liability. At least that's my take on the situation.
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