Are you bent out of shape?
 

I have taken on the hopelessly romantic task of rehabbing a 1974 Motobecane Grand Jubilee and need some advice on frame alignment.

I built a nice (and cheap) copy of the Park Tool frame gauge. Follow this YouTube link for your DYI'ers out there:

https://www.youtube.com/watch?v=z9bPiAi_KQc)

Sure enough I found that the rear stays are not symmetrical. I also measured using the old tried and true string test. Both methods yielded the same result… the drive side dropout sticks out about 3/8" further out than the non drive side. Spacing at the rear dropout is currently at 121mm.

I have no problems getting out the ol' 2x4 and leveraging things back, but which stay to bend? Is the drive side too far out (therefore making the non drive too close to keep the 120 dropout distance) OR is the non drive side too close, so I need to bend it out, but then shove the drive side in a bit to keep the 120mm spacing correct?

Seems to me one has to establish a centerline off the head tube/seat tube line then symmetrically space each drop out from that reference line, all the while maintaining your 120mm drop out distance. I'm I missing something here? It really has me bent out of shape!

http://bikeforums.net/attachment.php...hmentid=458715

If the spacing is good but one side is too far out, they both have to be adjusted until the string test yields an equal length. That said if the out of alignment is minimal then you may not notice it.

When the whole rear end is out, those are the hardest to address, where to go first?
I would string another bike, just to get a feel for the numbers you might end up with, yes, not accurate, but it might give some direction.
I would also take my handy Campagnolo straight edge and look at the alignment from between the front chainrings to where it hits the freewheel cogs. It should land at the center of the freewheel, I think it will be one way or the other out, your guess.
That should give you a direction and possibly magnitude to move one side then the other to get to 120 mm, I am assuming a 5 speeds, 120 mm rear end, decide now if you want that or 126.

hey i built a diy park tool too! :)
http://bikeforums.net/attachment.php...hmentid=458749
gaspipe for the gaspipe!
back on topic though, pretty much what has been said. decide on a dropout distance first, then string and work your way to an acceptable alignment. baby steps and lots of mesuring i guess.

First, set the drop spacing to either 120mm or 125mm, depending on the face to face on your hubs.

Next, string test the frame. If the out of alignment shows 6mm, move the closest out 3mm and then move the other drop to meet the defined drop spacing.

That will center the rear drops, offering pretty decent alignment. Don't forget to ensure that the drops are parallel to one another, when finished.

Is this place great or what? :love:

I'm getting really good feed back on how to align the rear stays to the frame. I posted this same question on the mechanics forum and FBinNY comments explain exactly what I see in my frame:

" If the dropout width (separation) is 120mm or so, which is the intended width, then BOTH stays are bent to the right. You'd want to move both to the left by half the right/left difference to establish symmetry.

BTW - it's common for both stays to bend together like this pair did. Figure a bike hit by a car with the wheel bolted in. The rear triangle is bent sideways, but the width is constrained by the wheel's axle leading to what you see now."


Couple that with the above comments and I now know to which stay (non drive) and direction (left) to bend things. randyjawa and others have given me the technique to follow. Now to settle on 120/125 dropout opening and I'm in business. Thought I'd share another link that I found on how to build your own dropout alignment tool. (I'll put that into play after squaring up the frame)

Build your own dropout alignment tool (Park Tool FFG-2)

https://www.youtube.com/watch?v=PsU8IkkFaok