Workshop tales, trials and disasters.
Maintenance tips, techniques and myths.
Technical discussion, description and outright lies
6 posts • Page 1 of 1
I spent some time aligning and cold setting some frames using the Sheldon Brown methods before they go to the powdercoater's this afternoon. The pink bike in the photos needed a fair bit of work, but the other two (an Apollo and a Peugeot) didn't need much.
Using string to gauge alignment - make sure the string comes out from the same place on each dropout, taking into account the tendency for knots to deviate the string.
Measure this side against the other to determine whether the dropouts are evenly spaced. For this frame I was aiming for a dropout spacing of 126mm.
This results in bending the dropouts inwards:
I've done this before with a bike that was shipped to me without dropout spacers. Some frames are easier than others; this pink one was really flexy, but the Peugeot needed a fair bit of convincing on the left hand side while the right hand side bent more easily due to the compressions on the chainstay for tyre/chainring clearance.
The forks on this pink bike were also pretty out of whack. I tested it by aligning the steerer tube alone a straight line and measuring the dropout distance from the centre of this line. By mounting the steerer tube into some wood padded square steel I was able to bend the forks from their ends to align perfectly.
If I was being more pedantic I'd fuss about the dropouts being parallel, but these builds aren't really anything special.
Thanks for posting, but I wouldn't recommend bending forks. If they are bent, just replace them. If a frame breaks, there is still a good chance you may stop before crashing, but if a fork breaks you are usually going down hard.
Yeah, i wasn't too sure about it either. The ones that needed straightening weren't too far out and the joins seemed solid; it was like they'd been knocked from one side without the wheel in. I inspected for imperfections after I'd done it but couldn't find any.
But you're right, it's a valid concern.
Thanks for posting this! i was reading that page last weekend and was going to give it a go this weekend on an old frame.
n=10 (2013 & 2004 roads,2010 track,2x 2009 foldups,1990 hybrid,1992 trainer,2007 rental,1970's step through,1980's zeus)
I've done it as well.
The thing you have to watch (which Sheldon doesn't mention) is that the brake bridge can be knocked off centre as a result of one seat stay bending/giving slightly more than the other.
The string method won't detect this, but you will easily see if the brake bolt hole is off centre by mounting a [true] wheel.
Fortunately, it is easily correctable using Dave Moulton's method for straightening stays: http://davesbikeblog.blogspot.com.au/2007/11/straightening-bent-seatstays.html
My local bike shop preferred to file the wheel seat lug thinghamy's to even up a slightly bent fork rather than re-bend. Said if it was a new bike, they'd just replace the fork, much safer, but on my old brick tank of a bike, they just filed it a bit and it was good as new again.
6 posts • Page 1 of 1
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