Trek 4300 problem: Crank bolt keeps coming loose - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 07-10-2006, 09:46 PM   #1 (permalink)
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Trek 4300 problem: Crank bolt keeps coming loose

I've got a Trek 4300 that's about 2 years old now, and has been ridden more on the street than the trail, so it hasn't seen much serious abuse.

The problem is just recently, the crank bolt on the left-hand pedal keeps coming loose. I can go about 10 miles before needing to tighten this bolt. I cleaned out the threads as best I could and used red locktite on it, but still today it came loose again.

Is there anything I can do myself to fix this?
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Old 07-10-2006, 11:27 PM   #2 (permalink)
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new bolt? i would say blue locktight, if you don't mind the crank never coming off again. will you trash the bottom bracket before your trash the rest of the bike?

or TIG that fawker on there and grind it off if need be. come on, you asked this question on a booty fab 4x4 BBS.
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Old 07-11-2006, 04:01 AM   #3 (permalink)
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Try a new bolt first, and then a new bottom bracket.
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Old 07-11-2006, 06:59 AM   #4 (permalink)
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Quote:
Originally Posted by SeanP
new bolt? i would say blue locktight, if you don't mind the crank never coming off again. will you trash the bottom bracket before your trash the rest of the bike?

or TIG that fawker on there and grind it off if need be. come on, you asked this question on a booty fab 4x4 BBS.


Yeah I thought about tacking it with the welder

or possibly JB weld, but figured I'd find out how to *correctly* fix it before getting too ghetto with it...
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Old 07-11-2006, 07:24 AM   #5 (permalink)
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Quote:
Originally Posted by Fool
Try a new bolt first, and then a new bottom bracket.
Appropriate user name. The bottom bracket is much harder than the crank arm. Once the bike is ridden for a while with the bolt loose, the splines in the crank arm get wallowed out slightly and you loose the fit. With the old square taper brackets, tightening the bolt would compensate for the wear. With a splined crank, tightening will not take up the wear. JB weld would be a booty fab repair but the only way to solve the problem is a new crank arm. As for the welding suggestions, aluminum to steel, I'd be impressed.
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Old 07-11-2006, 02:53 PM   #6 (permalink)
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what kinda crank is it? like mentioned before riding the bike with the crank loose will wear out the splines and it usually trashes both the crank arm and the bb. i would try finding the torque specs and giving that a shot. some people will tell you that it doesnt matter but it does. loc tight prolly wont help to much but you can put some on there. also grease the shoulder of the bolts so you dont get a false reading on the torque.
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Old 07-11-2006, 07:43 PM   #7 (permalink)
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It's a square crank. I don't really know what the torque settings for this bolt is, but I've been using the "tighter than a motherfucker" setting on my allen wrench and it still has come loose, even after red locktite.
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Old 07-11-2006, 08:12 PM   #8 (permalink)
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I hate to say it but your tighter than a motherfucker technic is probably what squashed the shape out of you crank arm. You're lookin at pulling aluminum against tempered steel. Get a new crank arm and learn what the recommended torque setting is. when you tighten to the max at the start, you have no room for correction.
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Old 07-11-2006, 08:58 PM   #9 (permalink)
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Quote:
Originally Posted by Fisheadgib
I hate to say it but your tighter than a motherfucker technic is probably what squashed the shape out of you crank arm. You're lookin at pulling aluminum against tempered steel. Get a new crank arm and learn what the recommended torque setting is. when you tighten to the max at the start, you have no room for correction.

That may very well be the case. I'm curious to know what would cause it to come loose in the first place though. I guess it has something to do with being aluminum?


After getting some time to search a bit, it seems that others have had similar issues with their cranks bending, then causing the bolts to come loose. Seems like it would be better to use a left-hand thread on that bolt to keep it from coming loose as easily... I really don't know.

Are there any recommended cranks on the market that are decent, and affordable? I don't know too much about this sort of thing, since this has been my first mtn bike. It's all been a learning experience...


edit: the tighter than a motherfucker technique was implemented in order to get home with both pedals after it came loose 10 miles into a 30 mile trip. It went for another 100 or so miles before needing to be tightened again. But now it's loose after every 10-20 miles.
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Last edited by animator; 07-11-2006 at 09:22 PM.
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Old 07-12-2006, 02:23 AM   #10 (permalink)
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You might try a fresh lockwasher on the crankbolt first. (always start with cheapest and simplest)You never mentioned your size and riding style. Most bikes seem to be designed for people that weigh about 140# with legs the size of my wrists.A heavier rider who stomps hard on the pedals can eat a crank up pretty quick. The 4300 is an entry level bike and consequently does not come with a high end crank. I forgot to mention that the bottom bracket and crankarm should both be clean and dry before assembling. Grease on the mating surface will give a false torque and can cause it to loosen.
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Old 07-12-2006, 05:29 AM   #11 (permalink)
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Quote:
Originally Posted by Fisheadgib
You might try a fresh lockwasher on the crankbolt first. (always start with cheapest and simplest)You never mentioned your size and riding style. Most bikes seem to be designed for people that weigh about 140# with legs the size of my wrists.A heavier rider who stomps hard on the pedals can eat a crank up pretty quick. The 4300 is an entry level bike and consequently does not come with a high end crank. I forgot to mention that the bottom bracket and crankarm should both be clean and dry before assembling. Grease on the mating surface will give a false torque and can cause it to loosen.


I am 6'-4" or so, and in the 200-210 lb range. The bike's been on one serious trail, otherwise it sees mostly street or light trails.

I took everything apart and cleaned it as best I could before putting back together. Right now it's locktited, but I will give the washer consideration as well.

Or I'll just look into getting a new crank arm.
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Old 07-12-2006, 01:49 PM   #12 (permalink)
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Originally Posted by animator
That may very well be the case. I'm curious to know what would cause it to come loose in the first place though. I guess it has something to do with being aluminum?


After getting some time to search a bit, it seems that others have had similar issues with their cranks bending, then causing the bolts to come loose. Seems like it would be better to use a left-hand thread on that bolt to keep it from coming loose as easily... I really don't know.

Are there any recommended cranks on the market that are decent, and affordable? I don't know too much about this sort of thing, since this has been my first mtn bike. It's all been a learning experience...


edit: the tighter than a motherfucker technique was implemented in order to get home with both pedals after it came loose 10 miles into a 30 mile trip. It went for another 100 or so miles before needing to be tightened again. But now it's loose after every 10-20 miles.
This is quite standard for square taper cranks. Most of the industry (bicycle that is) have converted to a spline system (ISIS, OCTALINK, etc.) or a 2 piece design where the cranks are attached to the spindle on one side and the other side a spline of some sort. The quality of the bike has something to do with it as well. Torque on crank bolts is between 25 to 30 ft/lbs depending on the manufacturer. A fresh lockwasher on the crankbolt first will NEVER work.

Replacement crank arms are avaiable for cheap. If you never want a issue again, buy a Shimano M440 crankset (or something similar) and possibily a new bb (if the bb you have is the right length you'll be 'ok').


Fisheadgib your full of shit. The industry does not see an 'average' rider at 140# with small legs. Legs are NEVER in consideration when a manufacturer is designing a bike. It is hard enough to find a women under 140# these days never mind a guy. I would say they see it as 165# these days. There are no weight limits on production bikes and if there were it would be noted all over the bike. 210# is nothing these days on the bikes. The frames can handle it easily. The 4300 is just an entry level bike, not a bad bike.

NEVER take your bike apart to wash it. Just use a damp cloth and wipe it down.

Last edited by XJCracker; 07-12-2006 at 01:50 PM.
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Old 07-12-2006, 03:54 PM   #13 (permalink)
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Originally Posted by XJCracker
This is quite standard for square taper cranks. Most of the industry (bicycle that is) have converted to a spline system (ISIS, OCTALINK, etc.) or a 2 piece design where the cranks are attached to the spindle on one side and the other side a spline of some sort. The quality of the bike has something to do with it as well. Torque on crank bolts is between 25 to 30 ft/lbs depending on the manufacturer. A fresh lockwasher on the crankbolt first will NEVER work.

Replacement crank arms are avaiable for cheap. If you never want a issue again, buy a Shimano M440 crankset (or something similar) and possibily a new bb (if the bb you have is the right length you'll be 'ok').


Fisheadgib your full of shit. The industry does not see an 'average' rider at 140# with small legs. Legs are NEVER in consideration when a manufacturer is designing a bike. It is hard enough to find a women under 140# these days never mind a guy. I would say they see it as 165# these days. There are no weight limits on production bikes and if there were it would be noted all over the bike. 210# is nothing these days on the bikes. The frames can handle it easily. The 4300 is just an entry level bike, not a bad bike.

NEVER take your bike apart to wash it. Just use a damp cloth and wipe it down.
Pack sand numbnuts. The 140# comment was tongue in cheek. I know most bikes are based on a 165# rider but thats only slightly more common than a 140# rider. Of my six bikes, four have suspension forks and two are full suspension. I've had to respring all of it. And I only weigh 195#. 210# is nothing on a frame but if you don't think a 210# guy can eat up a low end crank easily, than you're the one with brown eyes.

Last edited by Fisheadgib; 07-12-2006 at 03:55 PM.
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Old 07-12-2006, 04:11 PM   #14 (permalink)
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Quote:
Originally Posted by Fisheadgib
Pack sand numbnuts. The 140# comment was tongue in cheek. I know most bikes are based on a 165# rider but thats only slightly more common than a 140# rider. Of my six bikes, four have suspension forks and two are full suspension. I've had to respring all of it. And I only weigh 195#. 210# is nothing on a frame but if you don't think a 210# guy can eat up a low end crank easily, than you're the one with brown eyes.

210# is nothing for an entry level bike (Crank, frame, etc.) sure they exhibit more load on parts but manufacturers don't generally have issues with bike spec for people under 280#

You weigh 195? I wouldn't expect someone to be that fat with 6 bikes.
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Old 07-12-2006, 04:55 PM   #15 (permalink)
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You weigh 195? I wouldn't expect someone to be that fat with 6 bikes.
I didn't say I was fast, but I can trudge along all day long.( slow twitch and 11.5% bodyfat.)
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Old 07-14-2006, 10:16 AM   #16 (permalink)
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Swap it for a D60.....................................we're in what forum? Damn I got nothing then.
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Old 07-14-2006, 10:21 AM   #17 (permalink)
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Swap it for a D60.....................................we're in what forum? Damn I got nothing then.
Aren't Jokers supposed to be funny?
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Old 07-14-2006, 12:17 PM   #18 (permalink)
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Aren't Jokers supposed to be funny?
It was funny....................................in my head.
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Old 07-19-2006, 06:17 PM   #19 (permalink)
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I have a 4300 also and this crank is a piece of shit, very cheap riveted construction, and mine is missing a bunch of teeth. I just bought a better one and I'm converting to 9 speed.
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Old 07-22-2006, 01:49 PM   #20 (permalink)
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In my experience... Once a crank arm has come loose it is damaged and should be replaced. Ususally crank arms come loose because they were not properly torqued from the get go. When a bike gets its first tune up, which should be 30-60 days from when it was purchased, the crank bolts are suppose to be retorqued.

As far as missing teeth go. Manufactures make some teeth much shorter than others. This allows the chain to slide in and out during shifts. I have had customers notice it and complain that teeth are missing when in actuallity everthing is as it should be.
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