Straighting bent bicycle center-sprockets.

[x88x]

Anyone done this before? I've got some aluminum sprockets on my bike that are bent just enough to throw the chain, but not enough to really show an obvious problem area. I'd rather not buy new ones, partly because these are still perfectly strong, partly because they're pretty rare. I took them to a local bike shop to see about finding replacements, and the guy looked at them like that were from another planet. :P They're off my old Jamis Lightfoot (c. mid-1970's).

I was thinking maybe sandwiching one between two sheets of plywood on a flat surface and taking a big hammer to the top sheet, but I'm not sure if that would work or if the aluminum would just eat into the wood.

Any ideas?

[msmrx57]

With the sprocket on the crank and the crank in the frame hold a marker again the frame upright point towards the sprocket. Spin the sprocket and slowly move the marker towards sprockets until it marks where it's out of true. Then you have a starting point for re-truing. As far as the re-truing a solid piece of wood and a dead-blow hammer work pretty well on aluminum.

[dr.walrus]

I like solutions that boil down to 'hit it with a hammer'.

[mDust]

Since aluminum is really soft, you could just put it in a bench vice and crank it shut REALLY hard. I'd imagine it would be straight after that. Some shims would help keep any grip marks off your sprocket but wood might be too soft to force the teeth into line so if you have any sheet metal or metal bar laying around...

[x88x]

Since aluminum is really soft, you could just put it in a bench vice and crank it shut REALLY hard. I'd imagine it would be straight after that. Some shims would help keep any grip marks off your sprocket but wood might be too soft to force the teeth into line so if you have any sheet metal or metal bar laying around...

Ooh! That's a really good idea! I'll have to try that.

[blaze15301]

i just took a hammer and gently tapped at the sprocket on my mini bike i know completely different but same concept.

[Ichbin]

I think it's HAMMERTIME! (Super old reference from something I said like...4 years ago lol)

[altec]

If you just hit it, or clamp it, it'll most likely just spring back. I'd take two pieces of 2x4 spaced enough apart on the ground that the sprocket will sit on the edge a little and bridge the gap. Then take either a rubber mallet, or another piece of board and tap the bent area. Just make sure the bent section is parallel with the 2x4's they are sitting on. do it a little at a time and check it with a straight edge until straight.

Hope that makes sense. Other wise I'll setup what I'm talking about and take a picture tomorrow.

[Konrad]

Hammering onto a true surface will work fine. You might want to heat the part a bit first to reduce chipping and fractures, though it's probably not necessary (the part didn't snap when it bent in the first place).

This assumes you have a normal (kinda cheap) bike like the rest of us. If you're one of those guys who worships a bike worth more than ten computers then perhaps take it to the pros.

[x88x]

This assumes you have a normal (kinda cheap) bike like the rest of us. If you're one of those guys who worships a bike worth more than ten computers then perhaps take it to the pros.

lol, inadvertently a bit of both, actually. :P It's an old Jamis Lightfoot (if anyone knows bikes..I didn't know wtf it was till I looked it up) that I got for, iirc, ~$40 at a yard sale many years ago. Apparently originally it was worth quite a lot, and it certainly has lasted a long time. I bought it I think around 10 years ago, but Jamis stopped making the lightfoot sometime in the early 80's, near as I can tell, so it's probably around 30 years old now. ...probably a big reason why the bike shop guy had no clue about the sprocket. :P But no, I don't really want to spend any money on it if I can help it. ..it does need new tires though..the sidewalls on the originals are cracking..

[x88x]

Took a deadblow hammer to them last night on a 1/4" steel plate. Worked like a charm. :D