Chain Ring Buckle

[Trev Campbell]

Hi Guys, I've been having an issue with my chain falling off quit regularly when I'm on my Big chain ring and the outer 2 cassette rings. I've tried adjusting the front derailer and this has lessened the occurence, but I've noticed that there is a buckle of about 2mm in my big chain ring when I spin it. I was wondering if this could be part of the issue. I was thinking of taking the chainring off and putting it between 2 blocks of wood and whacking it with a hammer to see if I can straighten it. Is this a bad idea ?????

[Mustang]

"Well now" (as my grandson says) if its no good now what have you to loose? Why not get a new one & straighten the old for a spare?

[bychosis]

I had a bike shop, with reputable mechanic, straighten one for me using a soft (plastic) hammer. Couple of whacks, spin, repeat as necessary. Alternative might be using a shifter, close up the jaws and bend away, this apparently works ok on disc rotors.

[Wal42]

Please don't hit it with a hammer unless you want to make a saucer out of it.

As mentioned by bychosis, put a shifter on it, close the jaws so they're snug & bend a little, don't try to do it all in one go, just work your way around the 'dent', providing it isn't to badly bent (2mm should be ok, if it's a gentle curve), it's all about 'massaging' it back into shape not forcing.

You'll only straighten it once, everytime after that it'll get gradually weaker, generally you bang the chain ring in the same spot, so fix it, order another & keep that as a spare.

[Trev Campbell]

Thanks Guys, I'll give the shifter trick a go.

[toolonglegs]

It will already be weaker the first time you straighten it... that's alloy for you, likes to bend one way ok, doesn't like going back though.
On the hammer thing... I seem to recall the straightening alloy with a hammer was better than using a lever force?, something about the way it doesn't stress the material as much ( talking proper soft plastic and rubber hammers here, not your handy man claw hammers ) ... so not like correcting a steel disc rotor for example.
Long time since I have done such things though, but used to do a lot of alloy repairs on motorbikes during my apprenticeship.

[DentedHead]

... using a shifter, close up the jaws and bend away, this apparently works ok on disc rotors.

It worked on the rotors on my latest project. I used the same method to straighten a double chain ring, but never ended up using it, so while it straightens them OK, I can't vouch for the strength once it's done.


Dent.

[jules21]

On the hammer thing... I seem to recall the straightening alloy with a hammer was better than using a lever force?, something about the way it doesn't stress the material as much

same principle as cold forging - if you lever it, you tend to align the crystalline structure of the metal to allow it to bend - thus also allowing it to bend back. belting it causes a more amorphous (i.e. random) crystalline structure, which is stronger. it's been a while since i studied that so someone may provide a better explanation.

however, i have not found buckled chainrings to cause my chain to drop off. the key factor is adjusting the hi-stop screw so that the FD doesn't throw it off when you up-shift. if it's not falling off when you're up-shifting, then another check should be your chain - i recently had chain problems and if there are any damaged/broken links, that will tend to throw the chain off when they feed onto the chainring.

[Trev Campbell]

Jules thats the weird thing. It doesn't do it on the upshift. I'll get it in top gear and be powering along and then the chain just falls off !!!!! Which is why I thought it may be the buckle that is causing the issue, I'll have acheck of the chain like you suggest but what should I be looking for ????

[jules21]

Jules thats the weird thing. It doesn't do it on the upshift. I'll get it in top gear and be powering along and then the chain just falls off !!!!! Which is why I thought it may be the buckle that is causing the issue.

i can't say for sure, but check for problems with the chain - dislodged plates, maybe stiff links? the former had the same effect for me as what you're describing - when the damaged links feeds onto the ring, it spits it off.

[Trev Campbell]

Thanks will do.

[wqlava1]

"Well now" (as my grandson says) if its no good now what have you to loose? Why not get a new one & straighten the old for a spare?

Or (and it's late and I was very literal with the words of the topic in a different way) you could use the old one for a buckle. A bit too rodeo for my liking though, and a small 3rd ring would be better.

By the way, I buckled a chainring on a wombat recently (link below), and thought that the hastily fixed ring would drop the chain regularly. Not so. It's been fine for quite a few hundreds more km. I got a new one but there's no reason to change yet, except that it has a couple of extra teeth and I'm leaning towards raising my speed in all gears.
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