Left arm loose, new bike.

[Grievous Turian]

Hey guys this is my first post... so greetings.

I recently bought a new bike that appears to have a loose left crank arm. I believe that's the name of the part. Please forgive me as I'm probably not as bike savvy as many of you are. I'm unsure of what I should or can do. It makes pedaling very difficult as I'm pretty much doing so with just the right side. Any feedback would be great especially a solution. Also I can't take the bike back nor do I have anywhere in town to get it repaired.

Thanks so much!

[Grievous Turian]

The problem has now progressed and the whole arm has fallen off.

Here some pics that hopefully could help out. Extremely lost on what I can do. My bike is my only ride.

[haykong]

There should be a cover hiding the other side of the bolt of the left crank arm that fell off.... it's basically a bolt that screws on to the left side of the axle... sometimes the cover that hides the bolt can be pried off with a flat head screw driver that is thin enough... do you have a tool set? you might need a 14mm socket wrench to bolt back on the crank arm.. keeping tighting it til it stops sliding on which will require a bit.... However if it does not tighten at all.. either the bolt is striped or the axle.... check the bolt and see if the threads are stripped... then look at the inside of the axle threads...

good luck

[FredS]

How new is new? If it is only a few weeks or months I would talk to the bike shop and take it bike to the bike shop you got it from for warranty work.

[Grievous Turian]

Thanks for the help. Here is a pic of the other side that probably has to be popped off.

[DaveM]

Unfortunately, the crank arm is too damaged to use and needs to be replaced. On the inside of the crank arm, there should be a number like 170 or 175. That is the length you need to get. If you google "left crank arm 170" for instance, you should see lots of choice for purchase. Just about anything should work OK. You want an alloy arm of the right length. Sugino and Suntour are common brands.

You will need to take the pedal off the old crank. This takes a 15mm wrench. But unfortunately, a lot of standard wrenches are too wide to fit. If you have some tools, try what you've got. An adjustable wrench probably won't work and you can't get a good enough grip. NOTE - the threads on the left crank are backwards, so you turn clockwise to loosen the pedal. If you don't have a tool that will work, you'll need to buy a "pedal wrench" too.

You'll need a 14mm socket to tighten the bolt that holds the crank onto the bike's bottom bracket. It is likely fine to reuse the old bolt, but not a bad idea to replace it at the same time.

Most bike shops would have these in stock and it's a 5 min job to install, but if you're stuck...

For the future...riding the bike once the arm got loose is what destroyed it. They didn't get it tight enough when they built the bike so really their fault, but if you had caught it immediately, it may have been possible to save it. Crank arms and pedals should be checked for tightness occasionally and need to be addressed immediately if they loosen up.

[haykong]

(04-22-2013, 12:53 PM)Grievous Turian Wrote:  Thanks for the help. Here is a pic of the other side that probably has to be popped off.

Just note... it's a cheap bike right when it was new?.. the parts on it are not designed to last long especially if there is a bit of abuse of the bike while riding it.....

and if it's a new bike it looks like it has quite a bit of abuse already... true the crank arm looks a bit damaged at the mounting points... If you can't get it back on .. you might have to decided is it worth repairing it vs getting a quality bike that can last longer...

anyway you probably can get a cheap left crank arm if the old one does not work...... as Dave mentioned... check if there is a size... labeled on it...

[Grievous Turian]

So I took the cover off and the piece came right out as it seems it probably should.

Here are pics if needed:

[haykong]

(04-22-2013, 01:04 PM)Grievous Turian Wrote:  So I took the cover off and the piece came right out as it seems it probably should.

Here are pics if needed:

does the bolt seem ok? or is it bent to you? what about the threads?

[Grievous Turian]

(04-22-2013, 01:08 PM)haykong Wrote:  does the bolt seem ok? or is it bent to you? what about the threads?

Seems to be just fine. I tried to tighten just it into the bike with my fingers and I can easily do so. Granted it probably has to be cleaned to be easier.

I feel as though whoever assembled it did a very poor job in tightening this specific piece.

[FredS]

The bolt looks like it striped out the bottom bracket, note the silver metal on the end of the bolt. You need to take the bike back and have them repair it and make it right.

[Grievous Turian]

(04-22-2013, 01:00 PM)haykong Wrote:  Just note... it's a cheap bike right when it was new?.. the parts on it are not designed to last long especially if there is a bit of abuse of the bike while riding it.....

and if it's a new bike it looks like it has quite a bit of abuse already... true the crank arm looks a bit damaged at the mounting points... If you can't get it back on .. you might have to decided is it worth repairing it vs getting a quality bike that can last longer...

anyway you probably can get a cheap left crank arm if the old one does not work...... as Dave mentioned... check if there is a size... labeled on it...

The probable reason of it looking so beat up was taking advice from a friend who doesn't appear to be reliable in this department. Basically I used brute force and hammered it. It clearly did nothing but scratch up my pedal. The other one on the opposite side is in mint condition.

[Grievous Turian]

Got the socket and ratchet that fit and the problem has been resolved.

Thank you all for the help. I will be sticking around here for sure.

[DaveM]

(04-22-2013, 01:42 PM)Grievous Turian Wrote:  Got the socket and ratchet that fit and the problem has been resolved.

I'd carry the ratchet with you. You can see from your first picture that the square hole in the crank arm is very deformed. The arm may stay on for a while, but I bet it is going to loosen up again while you're riding.

If you ever do get a new crank arm, I'd get a new bolt as well. You want full engagement of the threads because tightening the bolt is what seats the crank on the axle (and not hammering it on... )

[haykong]

Dave is right.. that you might have to have the socket wrench with you.

However, you might consider getting a thread lock gel/compound to put it on the threads on the bolt so it doesn't come loose.

Make sure you get the blue color which is medium strength...
make sure you DO NOT get the red color one which is high strength.

threadlock gel/compound is available in any auto store or hardware store.

when you take off the bolt.. check if crank arm slides off .. if it does.. it either means crank socket is too damaged or you did not tighten the bolt tight enough. If the crank arm stays on firmly... then it might be ok, but still use the blue threadlock on that bolt.... Normally, if the crank arm is seated properly you would need the puller tool to get it off after removing the bolt.

[manocas]

Hello Everyone,

although I've already learned quite a bit from this forum, this is my first post.

I am afraid I may have a similar problem with my left crank arm, but would love to hear you opinion before buying a new one and necessary tools.

The left crank arm of my one year old single speed SE Bike came off a couple of months ago. A nice gentleman at my LBS applied some blue threadlock gel and it survived for a week or so and slowly it became loose again and until it came off completely last week. How true were some of the predictions in this thread!!

I have some photos of it which I would like to share with you.


This is a new bike and I cannot afford to buy another one at the moment. I am now carrying a ratchet with me every time I am on my bike.

I would appreciated very much your advice.

Many thanks,

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[attachment=4243]

[nfmisso]

you need a new crank arm. LBS sells them.

[manocas]

(06-14-2013, 07:22 PM)nfmisso Wrote:  you need a new crank arm. LBS sells them.

I will buy tomorrow a new crank arm. The damaged one is marked CW170. Does this mean that any 170 mm left crank arm will do it? I hope the axle that runs through the bottom bracket is still okay.

[nfmisso]

most likely. take the old one with you.