Folding Bikes - Dahon Jetstream derailleur adaptors- help wanted from my Asian friends :)
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In a bid to cure my Jetstream XP's chain drop problem, I'm looking to purchase a front derailleur adaptor (the FD will be a dummy, just as a chain guard- I don't need 54 speeds!). I found these pics of a bike on flickr (http://www.flickr.com/photos/wenham/3055690747/ ) so I knew there was one that would fit, if not specifically for the XP. I dropped Thor a line- he told me there were Jetstream versions and kindly put me in touch with his Taiwanese supplier, who hasn't got back to me at time of writing. I also contacted the seller on Ruten.tw mentioned in this thread http://www.bikeforums.net/showthread.php?t=390549 . He's quoted me $1800 Taiwanese (well, he said $60 US plus $15 shipping, but the sterling rate's better!).
So, for my Asian folding friends- could you tell me if this is a fair and good price for the part? Having searched Ruten, it seemed reasonable enough, but there may of course be suppliers I don't know about...
Thanks in advance.
Chain drop... I have forgotten what your particular issue is? because I cured the problem on my Swift with a device, but would equally easy be cured with a chain guard (which I didn't do on the Swift because I'm a weight weenie there). I know the reason for chain drop on the Swift.
They only have the Speed version shown on the website, but I know they have the Mu. Not sure about the Jetstream, you can try contacting them.
Thanks for the link, Joseff. Thor's supplier's got back to me & his price is a bit better than the other guy I've contacted (apart from which Thor says he's honest, good enough for me). So I'll probably go with that option.
Jur- not entirely sure what causes the problem, though it's a drop inwards rather than outwards. Though the '04 XP has dual guard rings, they don't seem to work that well- though they do at least stop the chain wrapping itself round the bottom bracket. What's most annoying for me is that I can ride the same roads the same way and (as on my ride Sunday) it can be fine going one way and drop four or five times on the return, in the space of four or five miles. Road conditions don't seem to make much difference- yes, it'll drop on bumps, but it's happened on smooth stuff as often. Some rides, no problems at all. The bike's recently had a (very) full service and chainring, chain and cassette were all new on last year. I tried a chain guide suggested by Jay Gaerlan- which made not a jot of difference- and there don't seem to be many if any off-the-shelf parts that'll do the job- either they won't fit the seat post or won't work with a 52t ring. Doing nothing is not an option, I'll go nuts! A dummy FD seems like a straightforward option- it's worked for other people I've met on and off-line, and I've never had a drop on my Cadenza despite riding it the same way. I may have had one on my old hybrid....in seven years and 7k+ miles.....
Hmmm very frustrating. I drop a chain perhaps once a month and that's far too many times for me. I made a chain tunnel thingy for the Swift - not a chance for the chain to drop, and since then it never has. The Birdy misbehaves occasionally.
02-19-09, 05:55 AM
If you just want to stop chain drops there are a bunch of chain guides out there designed to help as well.
The N-Gear Jump Stop, Deda Dog Fang, Rohloff Chain Guide, and the JTek dropstop to name a few.
02-19-09, 12:38 PM
While I've totally changed the gearing from stock on my 2008 Jetstream XP, and you have a different frame altogether on your modified 2004, you might nonetheless consider doing something similar to what I did to solve this problem. After looking at all the off-the-shelf options that have been suggested here and not feeling too good about any of them, I ended up building my own inner "chainguard" out of a piece of 1/8" ABS plastic.
I just experimented with various shapes until I ended up with something that fit and worked. It attaches to the frame with black tie wraps (what else). Proper spacing was achieved by stacking up little 1/8" ABS bits until the required distances were achieved, taping those together into blocks with electrical tape, then screwing each to the main plate with a stainless screw. A little strategic bending/flaring of the "tail" portion to fine-tune the shape to just-barely clear the chain through the full range of gears, and voila!
(Edited to note that I made this piece have such a long "tail" because I am running extra-wide knobbies which the chain would occasionally get bounced laterally against and get sucked down and wedge between the chainstay and the tire--a particularly nasty situation as it would instantly lock the rear tire! The "tail" keeps the chain away from the knobs and out of the crack o' doom!)
Hopefully you can get the idea from the pics below and perhaps adapt something similar to yours. ABS is cheap, durable, easy to work with, and, well, I happened to have a few scraps on-hand from another project. ;)
Since installing this plate last September, in combination with the stock 53T FSA bashring from Dahon (oversized for my now 44T chainring), I have not had ANY more chain drops in 800+ miles of rough (occasionally extremely rough) terrain, so it has proved to be a totally effective fix.
And, despite how it looks in the harshly-lit close-up photos above on a dirty bike, in "real life" I think it actually looks pretty sharp on the XP, being solid black and all...
Anyway, I hope that helps, and good luck in your quest.
Like that one foldsinhalf- something like that, or Jur's mod for his Swift, would be perfect, certainly in terms of price (!). I'm going to pop in my LBS at the weekend, they might be able to do something like that. FD would be neater and tidier, not necessarily better at sorting the problem.
fmattheus- I had looked at those kind of things, MTB bash guards, etc. Either ££££ as in the case of the Rohloff (which cannot fit my seatpost, btw), not available in the UK (and expensive to import), not practicable (due to either the chainring size or the seatpost diameter), or no better than the cheaper options like Dahon's own little plastic doodad. Which doesn't work. Jay Gaerlan sold me a rollerkit (and he knows Dahons)- couldn't fit the right way up, and where it was mounted was no help.
Update: Having looked into the possibilities of a FD mount and other possible fixes (thanks to Thor, Andrew Fudge of Fudges Cycle Store in London and Rick Fair of Dahon for their advice, as well as the contributors above), I took the bike into my regular LBS, Velocity Bikes in Portsmouth, last Saturday, had a word with the co-owner, and explained I was still having the problem. He had a good look, was pretty sure he could do something, and so Wednesday I went back in with the bike & bag of bits (the roller kit device I got from Gaerlan- which another LBS had fitted incorrectly last year, and which Velocity then removed when they did the transmission, plus the FD off my old hybrid). Their fix: the roller device slightly modded and mounted to the two lugs on the back of the seatpost (why they were there in the first place, no idea, they aren't on subsequent model year Jetstreams, but they now have a use), so the roller sits just behind the chainring, plus they turned the bolts on the chainguides so the inner guard ring is much closer to the chainring (it's never fallen outside, so the increased gap there won't be a problem).
End result, touch wood- fixed. I did 20 or so miles today, up and down multiple climbs with umpteen gearchanges. And not one drop. Further intensive testing will hopefully confirm the death of the chain drop fairy!
My compliments to the LBS chap. Experts like such are to be appreciated.
Glad you got it fixed.
It's helpful to understand the reason for chain drop:
When shifting gears, especially in the direction where the derailer goes towards the more relaxed position (outwards for most high-normal derailers and inwards for low-normal ones), the sideways movement of the chain can be quite sudden/crisp. When the chain tension is on the low side such as when spinning faster with not too much force on the pedals, the chain gets this sideways snaky movement, a wave, just like when giving a stretched string a sideways jerk.
This sideways wave can be enough to make the chain climb on the chainring's teeth and fall off.
The cure is to arrest the sideways wave before it gets to the chainring. This is not so easy since the chain angle changes with gears at the back. What I did to cure the Swift's problem, was a little pipe that sits around the chain, with a widening taper towards the back to prevent the chain rubbing against that pipe in lowest or highest gears. So the wave moves forwards in the chain and bumps against the pipe, arresting it. Never had another chain drop since.
Chain guards will work if they are close enough to the chain without rubbing in low or high gears, close enough for the wave to bump against the guard to arrest the wave. If the guard is too far, the wave will pass the guard and the chain will still climb off.
A worn chain will be worse than a new chain since the sideways freedom is bigger in a worn chain.
Front derailers also arrest the wave.
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