Rear triangle alignment - use Sheldon's method?
 

My vintage English 3-speed has a chainline issue. I finally traced it to the RH chainstay being pushed over to the right side. Using Sheldon's string method described here

Bicycle Frame/Hub Spacing

I determined that the difference between right and left with respect to the seat tube is about 8mm. (I ran fishing line around the head tube, tied it off to both rear fork ends, and used a ruler to measure the difference between the seat tube and the string on both sides. The right side was +8mm more than the left. Incidentally, the rear clearance is around 118 mm--a bit wide for the standard 110 mm spacing on these old hubs. Pushing the right stay 8mm inward would both close this gap and fix the alignment issue).

I called the LBS, and upon mentioning "frame misaligned" they declined to do the work. I did locate a guy who is in town and is a framebuilder (and has a frame alignment table), but he mentioned that I would need to install a bottom bracket insert. I'm not sure if these inserts will fit my bottom bracket or not. The bike is an old English 3-speed with cottered cranks.

So should I attempt the Sheldon method on my garage floor. Are there any improvements to the method that I should try? The method seems pretty crude, but I do trust Sheldon's wealth of knowledge. The frame is lugged steel, and is pretty mild--unlike more modern steels.

You can use a treaded rod and nuts and washers . Put the rod into the dropouts and tighten the nut on the side that next to be move in . Measure the distant until it where you want it . Remove the rod and hardware and the frame should stay at the distant . You might have to do this couple times until the frame stop spring back out . I feel this is easier on the frame too .

There is nothing that will guarantee which stay will move in how much using that method - you could end up making much more work for yourself, as only one side has to move. I would simply lay the frame on its side with the too far out side facing up. Then have someone hold down the main triangle while you carefully push on the rear triangle with a slight bouncing action. Measure, repeat until it's correct

On a vintage English 3-speed you probably can get by without the levers or threaded rod and simply do the cold setting with your hands. I use a metal meter stick from the head tube to the dropout rather than a string and work each side of the rear triangle until I'm satisfied with the result. Don't neglect to check that the dropouts are parallel.

Yes. You will find that changing the alignment with the Sheldon method will be much easier than you expect. Do a couple tries with gentle pressure until you get a feel for when the frame takes a permanent set.

Keep in mind that an 8mm measured difference using the "string method" actually means your stays are only 4mm out of alignment, so don't get too carried away when you cold-set it.

Works well if you follow Sheldon's instructions. No reason not to try it yourself.

But I need to move the right stay 8mm to the left, no? If I move it in 4mm, I'd need to move the left stay 4mm to the left (out) as well. But as I mentioned the rear dropout width is about 8mm too large, so I should just push the right stay 8mm left? (That's assuming I want to keep the old hub with a 110mm OLD). Just trying to make sure I got this right before I attempt it.

if i needed to move one dropout/chainstay/seatstay closer to the centerline of a frame while insuring i did not disturb the other side, i would support the frame on a large bench with the side of the rear triangle i did NOT want to alter, hanging over it and closest to the floor. so as the headtube, BB and seattube only touched the bench. then apply pressure to the side that i wanted to move inward.

OTOH, it's entirely possible that the side that needs to be permanently moved will have to be moved beyond the other side before any permanent change can be made. is so, you're in a pickle. :) progress could possibly be made by applying the force closer to the chainstay's short support bridge near the BB. and, god willing, not dent the chainstay in the process. :lol:

but before i went to any trouble at all with bending a frame i would take a LOT of time a trouble (applying a straight edge along the chainring and rear cog at least, not that i think the OP has not performed due diligence) to determine that it needed to be done, although, i'll admit that 118mm width measurement is compelling...

Again, Sheldon's instructions account for isolating the stay you want to bend and other potential gotchas. You don't need to think about it too much, it's all been figured out.

No, you want to move both stays 4mm to the left, to keep them centered.

I've used that method a few times. It works well for me.

If I do that, they will be centered but the rear spacing will still be 8mm too wide. I need to close the gap by a total of 8mm. How many mm do I need to move each stay to close the gap and make them centered?

Mr. Thompson is wrong in this case. His advice is only correct if the rear spacing is OK. If one side is out 8mm too much AND that is the excess in spacing, then the dropouts have to be centered after moving that stay in. You can't have identical measurements and it not be centered, period. Please just move the one rear triangle in by 8mm, as originally instructed. If you move both 4mm to one side then you will have to move both 4mm toward the center.

You're right; I missed that the spacing was off as well. Sorry about the confusion. :(

Where ever did the "threaded rod" method originate?

It's still comes up, all these years later, so must have been published at some point?

Can you even imagine trying to determine how much over-movement (due to the considerable elasticity) would need to be dialed in to those hex nuts?
And can one imagine how many such time-consuming releases and re-tensionings, perhaps thousands of nut rotations, would need to be applied in order to to "home in" on the needed correction?
And that assuming that one chainstay wouldn't do all the bending, which it pretty much always would.

Can this threaded-rod method ever die?

It must be published somewhere, if perhaps only in the internet rumors archives. Perhaps it was even demonstrated in a Three Stooges skit, can you imagine?

As for me, I've corrected hundreds of fork legs and chainstays over the years, using only my foot, by myself, using balanced dynamic application of body mass and energy through my four limbs, which literally can make for some strenuous exercise.
Trial and measure, repeated iteratively and patiently, with an understanding of visual sighting, measurement, metal-bending behavior (varies wildly among various tubings) and steering behavior.

In the field, one can even use the bike's wheel axle as a width-measuring indicator as one proceeds (using no tools) to heave bent chainstays or fork blades into perfect alignment. A carefully-sized and placed block of wood placed on the ground, used as a stop, can prevent the likelihood of over-bending or buckling a tube. And a glove here and there can protect bike parts like saddle from abrasion against terra firma.

It's always good to learn the needed techniques on less-precious frames, though the late Sheldon Brown's published methods make this about as fool-proof as can be. And yet I learned using my feet.

One thing that I'm puzzling over in Sheldon's description is why the 2x4 only extends about 3-4" past the seat tube. Also, can someone explain why he advocates pushing down on the 2x4 directly over the seat tube and not on the portion extended past the seat tube (pointed towards the head tube)?

Bicycle Frame/Hub Spacing (scroll down to see pics of frame and 2x4)
http://bikeforums.net/attachment.php...hmentid=493376
Can someone explain this bit to me?

the part that's on the seat tube is in the air and the part that's extending out the back is pushing on the floor. At least that's how I see it as the best way. It only needs to go 3-4" past the seat tube, don't think going farther out will help you

The long end of the 2x4 (to the left of the picture) is apparently resting on a stool or something of the sort. He recommends you press down on top of the seat tube to bend the bottom stay up (narrow the distance between the two stays). What I'm trying to figure out is why he says to press straight down on the seat tube instead of pressing on the short end of the 2x4 in the main triangle (overhanging the seat tube).

leverage and the chance of over bending things. I much prefer to first position the 2x4 to run past the head tube then squeeze it and the HT together. I find this to be more controllable. Andy.

There's really no difference. It's all in the leverage anyway. I would press down on the 2x4, just to keep it from slipping sideways.

As I said before: with your mild steel frame, you will be surprised at how little force it takes to move the stays. It's sometimes tempting after the first couple of spring-backs to really heave on it. DON'T!. Just keep applying a little more pressure, then a little more, etc. etc. Eventually you will sense when the frame takes a permanent set.

Some of us were trained this way in the shop by other mechanics .

Well, as I NEVER miss things I can't forgive you :rolleyes:.

I tried the threaded rod method once, just out of curiosity. I had to use Sheldon's method to straighten out the mess I made.