Wobbly cogs - how to true a crank?
- Thread starter Rusty Scrubber
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Had the same problem with an XT crankset.
Remove the chain so the crankset can spin freely at any speed.
Then you can use the front mech's cage as a visual aid to find the areas where the rings are bent, and use a universal plier or adjustable wrench to bend it back into shape.
Don't bend too much, and let the crankset spin after each attempt so you can see if there's any improvement or where the next problem lies.
For ripples, I'd suggest using 2 adjustable wrenches close to eachother. You'll never get it perfectly straight, but it doesn't have to be. As long as the chain can run smoothly, it's good enough. I'd still keep an eye on eBay to look for a good replacement though.
It'll take a while. I spent around 45 minutes on my big ring, and it's now less than 0.5mm out of true. I already had plenty of experience straightening discs, so expect to need a bit more time.
I did it with the bike standing on the ground, both wheels held by one of those bike stands that you see in LBS showrooms.
Ideally you'd use a proper workstand, so you don't have to sit on your knees for an hour or more.
Remove the chain so the crankset can spin freely at any speed.
Then you can use the front mech's cage as a visual aid to find the areas where the rings are bent, and use a universal plier or adjustable wrench to bend it back into shape.
Don't bend too much, and let the crankset spin after each attempt so you can see if there's any improvement or where the next problem lies.
For ripples, I'd suggest using 2 adjustable wrenches close to eachother. You'll never get it perfectly straight, but it doesn't have to be. As long as the chain can run smoothly, it's good enough. I'd still keep an eye on eBay to look for a good replacement though.
It'll take a while. I spent around 45 minutes on my big ring, and it's now less than 0.5mm out of true. I already had plenty of experience straightening discs, so expect to need a bit more time.
I did it with the bike standing on the ground, both wheels held by one of those bike stands that you see in LBS showrooms.
Ideally you'd use a proper workstand, so you don't have to sit on your knees for an hour or more.
Rusty Scrubber
Retro Guru
FairfaxPat
Senior Retro Guru
Like the other guys say-use an adjustable crescent wrench, but bend it slightly past where you want it, that should straighten it out.
Rusty Scrubber
Retro Guru
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