ShuSin

I found a Raleigh Twenty folding bike on the street one day. I thought it was abandoned because of all the rusty parts, but when i got on it and started pedaling, I noticed i was lopsided on the saddle and steering–well, there was practically no steering. I decided to ride the bike home anyways and, not knowing anything about Twenties, I searched on the net. To make a long story short, I have gotten rid of all the components and basically have two halves of the folder and am determined to fix the seat tube that is bent. I want to bring this ol' fella back to life. So here's the trouble:
The seat tube is bent exactly where the down tube joins it. There's no cosmetic damage to the frame, which leads me to believe that the 'accident' probably impacted the seat post and bent the frame here. If you are not familiar with Twenties, see this pic of an almost-stock Twenty:
https://4.bp.blogspot.com/_CGYQGxEMol...h/PIC-0038.jpg
My frame is bent where you see the cable of this yellow Twenty meet the seat tube, just at the top of the down tube. It is bent away from the chain drive.
Here's the other trouble: in order to bring this bike back to life, I will have to spend quite some cash as this bike appears to be very quirky in its details–quite a challenge for someone inexperienced like me! What that means is I can't take the frame to a frame builder and dish out $$ to true the seat tube, I need to save the $$ for the extinct Shimano BB and Phill Wood rings.

Question: How can I true this tube myself without damaging it? I tried putting it on shims and jumping on it... didn't even make a sound! I am thinking of propping it against a heavy concrete ceiling, shimming both ends, and putting a 2x4 on a car jack and pinning the center of the tube on the other end of the 2x4 and jacking up.
I'd be delighted to hear anything you have to say. This tube is quite stiff and the diameter is about 1.5 in. (the force that bent it must have been tremendous!)

echotraveler

i would suggest that you take some good pics, and post them on the frame builders forum... they will surely help fast.

griftereck

Ive not tried to straighten a frame damaged there.

but could try clamping the seat tube in a vice above the down tube. then getting a heavy steel tube thats a tight fit in the bb shell. then heating the area thats bent. Then pushing back on the bb mounted tube.

Youve got to watch as the downtube is brazed on. so dont use to much heat that would melt the brass. The blow torch would wreck the paint job.

Also it would be good if you could check the alignment. Some use bits of string. Others rulers. Ive got a laser line, it shines a red line out of it. Came from the Pound shop, er dollar store.

You can also set out an alignment table. Measure out all the widths of tubing on your bike. Then make wood or metal blocks to the thickness that so that the frame, if straight would lie parralel to the table top. then you can see where and how much the frame needs straightened.

you can see them measuring this mountain bike frame on this video.
https://www.youtube.com/watch?v=jrQqTVV1aBk

rhm

I'm not sure I followed your description of the damage, but no matter.

I rather like your car jack idea. I don't like Griftereck's suggestion that you use heat; if you can't do this cold, don't do it. Obviously you have to be careful not to crush any of the tubes. When you are done bending it, expect it to spring back part of the way; the trick will be to correctly guess how much it will spring back. I'd suggest you measure carefully before you start, figure out exactly how much it has to bend, then try bending it. Take careful notes. Measure again while the frame is in the bending press; then let the pressure off and measure again. With care and luck you should be able to figure how much over-bend you need to apply.

By the way, unless the original crank is totally trashed, I'd keep it. Getting a cotterless crank on a Twenty is possible, but it is complicated and (bottom line) not going to save you that much weight.

Oh, one more thing. ShuSin, as in the fourth king of the third dynasty of Ur? WTF?

Bacciagalupe

I don't see the point.

You've got a compromised frame and need to replace a ton of parts. You'd be better off finding another R20 that's in better shape.

phatatude

It's the thrill of the chase... The story behind the stitches... The one that ALMOST got away ...

What color is your R20?

R20's - If you dont know, you better ask somebody...

Come check the lack of progress
https://web.mac.com/phatatude/Green_S...enty_Blog.html

ShuSin

In fact, they suggested I post here too.

ShuSin

I don't trust myself with a torch as I've never used one (perhaps once a long long ago to make crčme brűlée)... and most the reason is because of the bend's proximity to the downtube brazing.

ShuSin

rhm, thanks... I think that's what I'll end up doing. Though I'm still not sure what's the best method. I know I can rely on the bottom bracket shell for supporting one end, the other end is the tricky part. The original crank was wrecked as well, I've already ditched it.

hahaha, I didn't make that connection with the king of Sumer and Akkad... but that's a happy coincidence since I'm from the fertile crescent. Actually Shu and Sin are the first three letters of my first and last names.

ShuSin

That's exactly it, phatatude... and btw, i'm still waiting for your new posts!

ShuSin

How can you explain obsessions? this bent frame stares at me challenging me to fix it... and i'm determined not to go broke in the process. (well, perhaps if i acquire another obsession along the way, say... of getting a campy track hub and building a rear wheel for it.)

Sirrus Rider

If you pull it off it would be one more back from the brink.. Sometimes it's not about the money, but the challenge.

kraftwerk 

Steel can be repaired, unlike aluminum which is dodgy to repair and carbon fiber well forget about that...
the R 20 is a frame worth saving.
If you want to build a jig table I have an unbent frame for reference in Brooklyn.

ShuSin

Thanks. I will keep that in mind. Next weekend I'm going to go around the hood to find a car body shop... they might be willing to take on un-bending this frame for much cheaper than a frame builder might ask for. If nothing comes of that, i've already found a car jack!

randya

I once unbent a Columbia 20" mild or hi-ten steel frame that looked like it had been driven over by a car by propping it up on 2x4 blocks and jumping up and down on it, when I was done you couldn't even tell the bike had been damaged. I still have the bike and used it for this year's Mt. Hood bomb.

https://www.youtube.com/watch?v=X7V-q8UX108

Ya Tu Sabes

It would be cool if you left the frame then bent a seatpost in such a way as to accommodate for the bent seat tube. I mean, if we're talking about quixotic bike-fixing missions and all . . .

griftereck

Im thinking of getting rid of all my stuff. Ive got 3 normal R20s. Solid frame, not folding.
But geuss thats no use to you. As I live in Scotland

ShuSin

I successfully did that with my fork steerer for the Twenty, but I'm not going to use it anyways. The frame, however, would not even budge a little. Last night I did unbend it! i will post later with photos to describe. It's pretty satisfying, as you probably know. Cheers.

ShuSin

That would be great to have in the States as they are hard to come by (the non-folding type). But as I mentioned, my obsession is to get this frame trued on my own. I can happily report that I did it last night. I'll write later when I have time with explanations. Cheers.

stevegor

That's scary Griftereck, so have I......you wanna be my friend?

griftereck

Hi Stevegor, you can be my freind.

theres my BSA 20 that I put suspension forks on.
A brown 20. Think its a Raleigh. Its a frameset just now. Got an experimental cartridge BB in it
And a light blue 20 thats a complete standard bike. but rough

I dont want anything for the bikes/ frames. I live in a village near Dundee. So probably too far from anyone that wants them.
Well apart from the kids that stole saddles from my Brittish eagle shopper, an Apollo mtb and my gold bike, last week. Thats sickened me alltogether that I cant leave stuff in my back yard with out it getting stolen.

ShuSin

At long last, I did it and I am proud of me. hopefully the images will explain enough. Here's the link:
https://www.flickr.com/photos/1578255...7622827107290/

I just want to add that it was simpler than I thought, but did require plenty of patience. When torquing the jack, i reached a point after which the wood stopped compressing and it became difficult to torque with a screw driver. i proceeded with real caution after that (the first try the 2x3 slipped and hit my left ear and many unpleasant words left my mouth, after which point i put on my bike helmet). After a couple of turns, i began to HEAR the steel bending. It had a crackling sound almost like stepping on broken glass. I didn't have sophisticated measuring tools so I just did it by instinct. I took off the rig and checked after the first go and i was within half a degree of a straight tube. I rigged again and this time I measured. I went 1/8" down and when i lifted the jack, the tube returned about half that amount. And that was it!

rhm

Cool!

I look forward to hearing how the bike rides.

Schwinnsta

Well thought out and executed.

Foldable Two

Is the rear triangle a little "off" to the right side of the bike? (which would be to the left in your picture with the white line)

Just curious.

You came up with a very simple way to do the needed bending. Like it.

Lou