Bicycle questions: Off-topic discussion forum: Grassroots Motorsports Magazine

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Jan. 22, 2012 3:08 p.m. Run_Away Reader

Morning all,

I've got a hardtail bike that I rode in highschool and am in the process of getting back into road-worthy shape. The front derailleur is seized and the bottom bracket bearings are toast, so I've replaced both of those. Sometime when I was still riding the bike I replaced the front crankset because I wore the teeth down on the original and the chain would skip. I now believe the replacement crankset had a different "offset" if you will (I don't know the correct bike terminology) which caused issues with my front derailleur's ability to shift onto the outer ring gear as it didn't have enough reach. If I put the chain onto the 3rd range by hand, it had enough travel to leave it there, but not enough to push the chain onto it.

The guy at the local bike shop told me it was because I didn't have the front derailleur adjusted properly when he sold me the new derailleur and bottom bracket but I have the same problem still, even with the adjustment on the derailleur maxed out. Can I fix this alignment issue with a narrower bottom bracket, or should i get a crankset that matches the original?

Also, is there any advantages to having a bottom bracket mounted front derailleur like the original versus the seat tube mounted style? I like the cleaner look of the original I had, but don't know if there's any other differences.

New versus old.

Alignment of crankset to derailleur. The crankset is not bolted on, just pushed on to the tapered peg as far as I can by hand.

Same view with the front derailleur extended as far as it can, "H" adjustment screw backed all the way out.

I suspected the issue was with my non-original crankset when things still wouldn't line up but didn't confirm it till I was digging around and found the old crankset off my fathers bike of the same brand.
Mine:

What I think it was originally:
Jan. 22, 2012 3:52 p.m. 02Pilot Reader

It looks like you should have enough travel in the FD to get the chain up to the big ring. How close to the big ring is the cage? It should be very close - like a couple millimeters. Have you tried rotating the FD ever so slightly to move the rear of the cage further toward the big ring?

IIRC, MTB cranksets have a little more offset than their road equivalents, which might be the issue here, but I still think you can get it shift with what you've got.
Jan. 22, 2012 4:04 p.m. robmillion New Reader

it looks to me like the new derailler may work. its close though. your new chainrings sit out a little further than the old ones. but check the shift cable: it may not be tight enough, so that even with the H screw backed all the way out the shifter just doesn't pull enough cable to get the derailler all the way to the outer chainring. make sure the cable pulls the derailler out as far as you can pull it by hand. if the cable is definitely tight enough, then the only solution is a different set of cranks or a different bottom bracket with a shorter spindle (or axle). maybe a different derailler could work, but thats harder to figure out without a little trial and error. i would go with trying to get the chainrings closer to the frame. (narrower bottom bracket or different cranks.)

as far as deraillers go, i worked at a bike shop for about 10 years as a mechanic and i hated the type you originally had on there. you can't adjust the height- you'll need to if you ever change to different size chainrings. and you can't the adjust the angle so you have to bend it (you shouldn't need to, but sometimes you do). and if you have to replace it, it means removing the cranks and bottom bracket as well.

hope this helps.
Jan. 22, 2012 4:30 p.m. Run_Away Reader

Thanks for the replies.

Here's a video of the reach and clearance:
http://www.youtube.com/watch?v=rBilo0jnO3c&hd=1

Here's the position my original, now seized FD sat in on the big ring gear; as you can see it's pretty much gone as far as it can reach.

Unfortunately I don't have a rear wheel as it's getting trued right now so I can't put things together to test out. I also don't have my new shift cables ran yet. If I can exchange the bottom bracket for a shorter one that would be ideal - no money spent and everything would work together nicely afterwards.

Good point on this style derailleur being okay with chainring size changes - that's something I was wanting to do so I'll stick with the clamp on for sure.
Jan. 22, 2012 6:06 p.m. Rad_Capz Reader

Had a bike shop for 25 years. Closed to move south and still liquidating the remains. If you decide to put it back to an original stock derailleur I have an NOS derailleur listed on Ebay for 4 bucks http://www.ebay.com/itm/260939716255?ssPageName=STRK:MESELX:IT&_trksid=p3984.m...