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Cranks going...

Old 06-08-11, 05:40 PM
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shooter5635
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Cranks going...

Hey all! I'm new here, and unfortunately i come with a problem...

I bought a '07 Diamondback Response Sport when i graduated 8th grade, and even though i barely ride it anymore i am taking it with me to college in the fall and i want it in top riding condition.

Now, i haven't ridden the bike in about a year, but the problem i was having was the crank would slowly come loose. If i remember correctly, i only tightened it up once or maybe twice, but im unsure. (I'm kicking myself in the butt because this started after i took the bike in for service, but i didnt know any better to take it back since it was the kids fault who took the crank apart and didnt tighten it enough... so its long out of warranty)

Now i've read that once it comes loose once, your pretty much SOL and your on your way to having to buy a new crank.

I dont need a $200 crank, but i dont want another piece of garbage that the same thing will happen with. I use the bike on mild trails, street riding, and regular everyday use. Im looking for some suggestions, since i know nothing about bikes and i dont trust my local shop.

Also, all the terminology is still very new to me, I work on cars not bikes lol so if you could do a little explaining along the way that would be excellent.

Much appreciated!
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Old 06-08-11, 06:23 PM
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First, there is no harm in really cranking down on the crank arm bolt to see if it will tighten up. If not, then you need to decide if you want to change it yourself or pay to have it done. You'll need a crank arm puller ($10 or so) and, assuming you'll do the bottom bracket as well, you'll need the apporpriate tool for that (again, around $10). You'll also have to do some minor adjustments to the front derailure once you get it all together but it shouldn't be a big deal.

There are a few important numbers for cranksets. Number of chain rings (assume yours has three so it is a triple), number of teeth on each ring (Bikepedia shows yours as 42/32/22 but that's easy to count or look for it stamped on the rings) and crank arm length (distance from center of spindle to center of pedal shaft - typically 170mm or 175mm on MTBs like yours).

The crankset determines the length of bottom bracket spindle needed so you'll probably need to replace that as well. If you went with a Shimano Alivio crankset it would be in line with the stock components on your bike and should be well under $50. I'd look for a crankset with removable rings (that usually eliminates the really cheap ones) and match up the other numbers to what you have.
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Old 06-08-11, 06:32 PM
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Originally Posted by CACycling View Post
First, there is no harm in really cranking down on the crank arm bolt to see if it will tighten up. If not, then you need to decide if you want to change it yourself or pay to have it done. You'll need a crank arm puller ($10 or so) and, assuming you'll do the bottom bracket as well, you'll need the apporpriate tool for that (again, around $10). You'll also have to do some minor adjustments to the front derailure once you get it all together but it shouldn't be a big deal.

There are a few important numbers for cranksets. Number of chain rings (assume yours has three so it is a triple), number of teeth on each ring (Bikepedia shows yours as 42/32/22 but that's easy to count or look for it stamped on the rings) and crank arm length (distance from center of spindle to center of pedal shaft - typically 170mm or 175mm on MTBs like yours).

The crankset determines the length of bottom bracket spindle needed so you'll probably need to replace that as well. If you went with a Shimano Alivio crankset it would be in line with the stock components on your bike and should be well under $50. I'd look for a crankset with removable rings (that usually eliminates the really cheap ones) and match up the other numbers to what you have.

Is the shimano Alivio crankset reliable enough to where im not going to need to check it every time i go to get on the bike/ potentially have this happen again? Im willing to spend as much as $100 to get a decent enough crankset. I am rough on my bikes....

I'm seeing that bottom brackets generally do not come with the crank set. How much/what brand are decent?

Where do you recommend getting parts online?

I really do appreciate all the help.

Last edited by shooter5635; 06-08-11 at 06:35 PM.
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Old 06-08-11, 07:01 PM
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The info I could find calls for a 110mm - 113mm spindle length so check to see what you have before ordering a new one. I'd go with the square taper instead of the splined. And you should have a 70mm English BB shell. Here is a crankset and BB for a decent price. If properly installed, they should do the job for a long time.

https://www.jensonusa.com/store/produ...Crank+Set.aspx
https://www.jensonusa.com/store/produ...m+Bracket.aspx
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Old 06-08-11, 07:07 PM
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Appreciate it.

Is the square taper stronger than the splined? Seems like it would be the other way around.
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Old 06-08-11, 07:29 PM
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Square taper has worked fine for me. Only one crank has come loose and rounded out on me in 25-ish years of riding square taper 3-pc cranks.

You don't need to check them every ride. You need to torque them down properly in the first place. I think 300 ft-lbs is a typical required torque and many people don't get those crank arm bolts that tight.

I don't think I'd let the interface make my choice for me. If you can source the exact same crank then you won't need a new BB, though.

Cranks sold with bottom brackets are much more common now than they were 20 years ago.

Last edited by LesterOfPuppets; 06-08-11 at 07:33 PM.
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Old 06-09-11, 09:55 AM
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Originally Posted by shooter5635 View Post
Appreciate it.

Is the square taper stronger than the splined? Seems like it would be the other way around.
Square taper has been around for decades and I'm sure will be around for decades to come. Splined wasn't really around too long before external bearing BBs took over. Just not as much splined stuff out there as square taper. Properly installed, either will do the job.
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Old 06-09-11, 12:56 PM
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He meant 30ft/lbs, not 300.

Of the few bikes I've dealt with, most needed re-torqued after a few hours of riding, then never needed it again.

Be sure to follow a decent guide. There's places thread lube goes, and thread lube should never touch. Doing that right is pretty critical.
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