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MTBR's I need your help

post #1 of 23
Thread Starter 
Yup so i messed up good this time.

First a story.

So i was ridin home from school one day (primary use of my bike, but i use it to go biking too, no one to ride with is the problem) and i see this rock boardering this guys drivway, and so i ride over it. problem was that i had my backpack on so i coudnt hop or anything. so i bent my front chain set thing (crankset right?) it had a bash guard, but it was a plastic POS and did nothing. TH bike still runs, it is just that the cranset rings are all out of alignment.

So i need a way to get them back into alignment. i have tried bending, but that didnt work. so i need suggestions.
(ok here come the part where I play helpless Nub)

my first thought was to buy a nice bashguard and scew that one and hope it straigtens it out, or keep trying to bend it straight.
ID buy anew one, but it has to be cheap, and good cause i have almost no $$$ (OK so im saving up to buy ski boots next year)
lets hear comments or suggestions
post #2 of 23
Gonzo will likely chime in soon! I have a feeling things get bent frequently on MTB's
post #3 of 23
a little more information on what type of crank and ring set up you are running would be helpful.
Usually, when you bend a ring it is the large one that is bent. Depending on the manufacturer this can be easily replaced.
In general, if indeed it is the the chain ring(s) that are bent. They can be straightened...they most likely will not be perfect...but you can get them very close.
The best thing to do would be to pull the crank off (you will need a crank puller...unless you have self extracting crank bolts). Then disassemble the chainrings. Take the bent ring and put it in a soft toothed vice...and gradually work it back to true......I find pump pliers to be very useful for this. If individual teeth are bent...you can try bending them back...but most likely they will snap off. If this does happen...just file the area smooth so the chain does not catch....a few missing teeth usually is not a huge deal.
If it is not a 'high end' crank and ring set....Cheap replacement rings can be found on many online retailers.
Mtbr.com has a drivetrain section. This will be a valuable site for further options on how to proceed.
Also parktool.com will give you clear directions on 'do it yourself' repair.
post #4 of 23
post #5 of 23
Thread Starter 
cranks: Giant, 22/32/42T

yup mine is a cheapy. it is riveted together it came with the bike, but he back is shimano 9 speed cassett, and sram x9. i got a 9 speed setup. if it matters

would it still be vialbe to take off the crank and bend it. when it is on its kinda hard to tell what is really straight. and how would i know if it was an easy off crank?
post #6 of 23
I would highly suggest going here:http://www.parktool.com/repair_help/...ttom%20bracket

and READING

If it is 'self extracting' the crank bolt itself will have a little cover nut of some kind on it...This will usually have small holes in it for a installing/removing with a pair of c-clip pliers......Without removing this....turn the bolt with the appropriate allen wrench....usually pretty big......and the crank will extract with it as the bolt unscrews. If the bolt comes out on its own with no crank ...then you need a puller.....
At that point...I would suggest trying to bend the rings back to shape on the bike.....Or you will either have to buy a puller....borrow a puller...or bring it to a shop.
Due to the nature of your questions ...a shop might be the best bet for you ....If you want to invest in the tools...go for it....Just make sure that you get the correct puller. Also if you are going to order new rings ...online...make sure that you are matching the bolt patterns....There are several options.
post #7 of 23
jeezus you people have him taking apart the whole BB/crankset.

TOTALLY unnecessary.

a bent chainring?

trash it. you'll never get it straight.

mounting a bash guard will not straighten it. it's bent.

chainrings are held by either 4 or 5 bolts. the majority on '04 and newer is a 4-bolt pattern, but some still have 5. either way that's how you remove the chainring, via the bolts that connect it to the crank arm.

there's a unique tool that holds the chainring nut, which is smooth for most of its circumference except two diametrically opposed square notches. the tool has a pair of diametrically opposed prongs that fit into the notches and hold the nut from rotating while you turn the chainring bolt with an allen key.

sometimes you can fake the nut into thinking you have a proper tool, if you can get a flat blade screwdriver of the same width and jam it against the nut... you'll see what I mean.

shen's suggestion of the Park Tools website is a good one, but he's sent you to the wrong spot. all you need to find is how to remove and install/replace a chain ring.

again, if it's bent, pitch it. new ones shouldn't be more than $25, which generally is cheaper than a bash guard (which will replace the outermost, largest chain ring). if you commute you probably don't want to lose your big ring.
post #8 of 23
to be more specific...my suggestions have him pulling the drive side arm which, as you know will have all the chainwheels connected. Keeping the whole unit together. This is the removal of one bolt.....(not the whole crank and bottom bracket unit)..... Putting in a vise to straighten it....You can get them close to true...depending on the severity of the bend.....I have done this plenty of times.
If it is severly bent...then certainly, replacement is necessary.

I apologize for the link not being specific...it is a general page for repair
post #9 of 23
shen you will most likely wear your chain prematurely with a hand-straightened chainring.

also it's a huge waste of time to pull the crankarm just for one chainring, ESPECIALLY because you have to use a torque wrench to reinstall it. I doubt Yukon has one that would be suitable.

with a handstraightened chainring that wears your chain prematurely, you end up spending the money either way. mechanically speaking it's sounder to spend it on a new chainring.

the only argument for bending it straight is that you don't use it ever, and it's functionally your bash ring.
post #10 of 23
Quote:
Originally Posted by gonzostrike
shen you will most likely wear your chain prematurely with a hand-straightened chainring.

also it's a huge waste of time to pull the crankarm just for one chainring, ESPECIALLY because you have to use a torque wrench to reinstall it. I doubt Yukon has one that would be suitable.

with a handstraightened chainring that wears your chain prematurely, you end up spending the money either way. mechanically speaking it's sounder to spend it on a new chainring.

the only argument for bending it straight is that you don't use it ever, and it's functionally your bash ring.
No doubt, Gonz, replacement certainly is sound advice to prevent any further issues.
post #11 of 23
His chainrings are riveted together. You don't get real cranks on bikes under $600 anymore. I think he hasn't got much money, maybe he should try to straighten it or buy a used crankset from a friendly local shop. The tools to do it yourself might cost as much as getting the mechanic to swap it out. You should buy the tool and do it yourself if you think you will use it again in the future. If you plan to be a long time biker, you should buy tools as you need them and learn how to use them.
post #12 of 23
Taking chainrings off the crank without pulling the crank is easy. I do it all the time on my road bike when I'm getting everything really clean. BUT Yukon's is a riveted-together cheapo. Replacing the whole crankset would probably cost more than the bike is worth, esp. if he has to take it to a shop, or has to buy the tools, even tho mail order closeout cranksets are cheap. Yukon: Just grab those puppies with a channellock and get em as straight as you can. With a bike like that, chainwear isn't a big issue. And ask for a real bike for Xmas or your b-day.
post #13 of 23
Thread Starter 
I decided some pictures were in order
bad quality sorry its overcast and raining.

Front view


Back view
post #14 of 23
can't tell what is bent from the picture.....Since it is already off......give the ole' vice method a shot....it will get you rollin' until you get some replacement parts......
Tell me which ring is bent...I may have some extra used stuff I can send you....I will have to check.....I will skiing for the next couple of days though...
post #15 of 23
It has the appearance of a real crank with replaceable chainrings, can you remove the bent ring?
post #16 of 23
Thread Starter 
Nope im pretty sure I cant take off the individual rings. they are riveted on, no allen or anything
post #17 of 23
Yukon: Take a look at Nashbar.com. They have a couple of Shimano mtb cranks with welded-on rings for $15-20. Since you have yours off already, you might be able to put one of them on.
post #18 of 23
those are allen (hex) key heads. no problem. I think Yukon's looking at the shift pins and rivets that are there for shifting and not integral to the mount.
post #19 of 23
Yukon,
From the pic those four bolts look like allen bolts to me. Why not take to a local bike shop and get a price for the replacement. It really is easy to replace though, just use an allen key on each side of the bolts (they may be difficult to shift at first). If you order from the internet you will have to state how many teeth (e.g 42T) and how many bolts (4 or 5). I always put super glue on the threads of the bolts to stop the bolts coming out.
post #20 of 23
Looks like a regular crank, get a 5mm allen wrench and remove the bent ring. Order replacement and re-install. You got the crank off, that is the hardest part. Those bolts might not be real, like the buttons on the sleeves of my cheap sportscoat, just for appearance or the rings might be riveted together in some way that is not evident from the photos but I think you are 1/2 way through the repair already. Gonzo mentioned that you need a tool or flat head screwdriver to hold the nut(?) behind the bolt sometimes to loosen and to tighten the chainring bolts.
post #21 of 23
Thread Starter 
Nope its all one piece. it looks like ill have to buy one or un bend.
Yup so now im lookin for a craqnk (yes?) that doesnt cost more the the whole bike (i got like 30-40 i want to spend if that. if i buy do i get tehe chain ring crank, and the crank for the other side?
post #22 of 23
Quote:
Originally Posted by evansilver
Yukon: Take a look at Nashbar.com. They have a couple of Shimano mtb cranks with welded-on rings for $15-20. Since you have yours off already, you might be able to put one of them on.
See if your local bike shop has something like this. If you mail order, it might not fit but if you don't scratch it, you can return it. You will get both crank arms and three rings.
post #23 of 23
If you buy a crankset, you get both arms. You can remove the left side one as you did the right side, but if you're sure the new right side arm is the same length as the left side, you can just leave the left side on.
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