Wednesday, February 25, 2009

How to Fix a Bent Seat Stay

I am now officially hard-core. Or at least medium-core. The Mundo's right seat stay was bent when I bought it, the result of a rear rack being affixed to it, and evidently getting whacked at some point while the thing was in the previous owner's shed. It was almost a deal-breaker for me, but I figured I'd see what I could do. In researching how to fix such a problem, I happened upon Dave Moulton's Bike Blog. Former frame builder and interwebs bike guru, Moulton has all kinds of helpful articles on all kinds of topics. Just so happens, he had one on this.

Mind you, this only works with *steel frame* bicycles (see how I emphasized that?), which are more flexible than carbon fiber, aluminum, etc. and can be bent back into shape (within reason) without loss of structural integrity. So anyway, go read the article, then come back here and check out the pictures below. Go ahead, I'll wait.

So here's my setup:


Instead of wood blocks, which I didn't have in the right size, I used a couple of landscaping bricks with (very dirty) towels over them for padding. I also put supports under the head tube and bottom bracket so the frame wouldn't wobble around. I used a piece of 1" wooden dowel, cut to size, as the spacer between the dropouts. You can see that the bent stay is on the bottom, ready for my foot.

Then, as Moulton says, I stood on the stay where it was bent. But either I'm too light, or this frame is too strong, because it did not bend as easily as Moulton suggested it would. In fact, after several tries, and some adjustments to the spacing of blocks, I ended up having to stand on it with 230 lbs. of force (my own 180, holding 50 lbs. worth of weights). After several attempts, during each of which the stay straightened a wee little bit, it came out straight enough to my satisfaction.

Actually, it still seems a tiny bit skewed to me, and I'm not sure if this is just my mind playing tricks, or if it needs a little more. Looking at the photo below, what do you think? (it's the right one). The alignment checks out with the string test, which Moulton also recommends.

Now I just need to get the seat post unstuck. Any suggestions on that? Besides heating it with a torch? I'm not averse to that, it's just that that seems to be the main suggestion for various stuck things, so I'm saying it now to get it out of the way. Oh, and penetrating oil, I know about that, too. Anything else?

17 comments:

  1. Far as the seat post is concerned, what we tell people at West Town Bikes with a stuck seat tube is to attach a seat and start applying dry slide to it and let it soak in, sometimes it needs applied for a few days. Then start twisting. If this doesn't work you can start cutting the seat post from the inside using a Dremel. Putting notches in it to collapse it a little.

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  2. Ah, thanks! Sounds similar to Sheldon Brown's hacksaw blade recommendation. The only problem with using a seat is that this bike didn't come with one, and someone in the past had tried to get the post off with other means (pliers, I assume), and bent it so that a saddle won't clamp firmly to it--just slides off when pulled. Since the post is thus already buggered, I think the Dremel or hacksaw method is going to be the solution. Thanks very much.

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  3. NOw is this some sort of test where you say it's bent so I think it looks bent? I've looked at it several times and I'm still waivering....

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  4. Yeah, and do you see a vase or two faces? A pretty girl, or an ugly witch?

    Right, anyway, the fact that you're wavering makes me wonder if maybe it does need a little more after all. Or is it all just an illuuuusion?

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  5. To get a really good grip on the broken seat tube, drill a hole through it and push a steel rod through. That will work at least as well as a saddle clamp.

    Well done with straightening out the stay. It's straight enough now - stop worrying.

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  6. Thanks for the tip, David, that sounds excellent. And thanks also for the reassurance. I went back out and looked the thing over again tonight, and I think you're right--I'm going to call it good!

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  7. Supposedly ammonia will attack the corrosion product if it can get to the area between the aluminum and steel.

    When all else fails, a drill followed by a reamer always works for stems and seatposts.

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  8. I agree with David, drill The post and use a 10 or 12mm steel rod to start the post turning. If it happens to be a cottered bottom bracket, I'd also take the precaution of turning the frame upside down before drilling to prevent the swarf from falling into the bearings. Use a large screwdrver or lever to slightly open up the split in the top of the seat tube and spray in penetrating oil.

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  9. @ Anonymous: If only my life were that simple! I saw that tip on Sheldon Brown's guide to stuck seatposts, and got all excited until I realized mine was steel, not aluminum. I would be interested to hear from anyone who has used this trick on aluminum, though--does it work?

    @ flaneur brian: Spreading the seat tube was the first thing I tried, and it worked, I was able to open up some space on the backside of the post, but not all the way around. The real problem I think is on the other side of the post, where it has rusted pretty tightly inside the tube. Incidentally, I think this might also make drilling and then turning very difficult. I'll think on it--thanks for the tips!

    That goes for everyone--this is all great stuff. I'll do a post on whatever I end up doing, and link to these comments--very useful, thanks much!

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  10. drilling a hole is a good trick, as well as clamping the seatpost in a bench vise, so you have the whole frame to use as leverage.

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  11. @ gabrielamadeus: Ah, my kingdom for a bench vise!

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  12. I was going to say a large pipe wrench and a cheater bar, a pipe that will fit over the end of the pipe wrench and give you plenty of leverage. The seatstay look straight to me.

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  13. I agree with cycling chicken: a pipe wrench with a cheater bar should solve the problem. Be cautious about the eventual "let go" (think Wil E. Coyote), and also consider the extremely stuck possibility that the frame (where ever you have converse leverage) may bend while you wrench.

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  14. If you go for the torch, I'd get a spray can of chip cooling spray (freon?) commonly sold to try and diagnose circuit board failures,so you can heat the frame and cool the shank/shaft at the same time.

    Apply heat on the out side, cool on the inside, and it should break loose. I'd try this last though.

    I think the frame is straight, it's an optical illusion, caused by the rust spots drawing the eyes that makes it look bent.

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  15. To get a seatpost unstuck in the past, I've used the usual penetrating oil . . . but also clamped a seat back to the post to give some leverage for twisting it. This works much better than simple pulling, and (in my far-from-expert opinion) is less likely to do damage to the frame's metallurgy than heating.

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  16. Dude... that seat stay is beyond good enough. "It's gorgeous!" Good work!

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  17. Many thanks for the tutorial, this article was very important for me to learn how to fix a bent seat stay. Appreciate it

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