Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 09-05-06, 09:25 PM   #1
kidcharlamagne
muddy
Thread Starter
 
kidcharlamagne's Avatar
 
Join Date: May 2006
Location: biking the buffer
Bikes: Schwinn Mesa GS, Schwin World Sport, Schwinn Sierra Tandem, 3 Schwinn Homegrown HTs (frame only), Schwinn Moab III, Schwinn Sierra GSX, Specialized Crossroads (soon not to be mine)
Posts: 53
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
crank arm issues and creak

My non drivetrain side crank arm came loose and feel off during my last ride. I put it back on and within a few minutes of riding it was back off. I also have the most awful creak coming from the crank/BB area with each pedal. The bike is an 05 Schwinn Mesa and the crank & BB are Truvativ cheapos. Any thoughts?

Thanks so much for your expertise!
kidcharlamagne is offline   Reply With Quote
Old 09-05-06, 10:22 PM   #2
moxfyre
cyclist/gearhead/cycli...
 
moxfyre's Avatar
 
Join Date: Oct 2004
Location: DC / Maryland suburbs
Bikes: Homebuilt tourer/commuter, modified-beyond-recognition 1990 Trek 1100, reasonably stock 2002-ish Gary Fisher Hoo Koo E Koo
Posts: 4,166
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
The problem with a loose crankarm, especially square taper, is that it is likely to become permanently damaged and always loose. The BB spindle is steel, and the crank is aluminum, so if the crank is loose the harder spindle will gradually wear out and round the crank out, to the poitn where it can't be attached securely

The other thing is that your crank bolt may be stripped. Even if you crank is so worn that it wobbles around a lot, it should NOT be so loose that it falls off when the crank bolt is fully tightened. Can you check if the crank bolt is stripped?

Fortunately, you've hosed the LEFT crank, which is cheaper and can be replaced with practically any mismatched crank of the appropriate length. If the crank is the only damaged part, you can probably get a used one for $5 or maybe even free.
moxfyre is offline   Reply With Quote
Old 09-06-06, 12:44 AM   #3
DannoXYZ 
Senior Member
 
DannoXYZ's Avatar
 
Join Date: Jul 2005
Location: Saratoga, CA
Bikes:
Posts: 11,606
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Yeah, sounds like the crankarm is buggered. If you rode on it at all when it was loose and wobbling, most likely the spindle dug into the crank and the interface is no longer tight. ALWAYS make sure you tighten the crankarm bolts to spec with a TORQUE-WRENCH. About 30-35lb*ft is commonly quoted by the manufacturers. There's NO WAY you're gonna generate this kind of torque with the itty-bitty 6" double-sided Park wrench (at least without serious pain from the tool digging into your hand). You'll need an automotive-style 3/8" ratchet wrench with 10-12" handle and 14mm socket...
DannoXYZ is offline   Reply With Quote
Old 09-06-06, 01:00 AM   #4
moxfyre
cyclist/gearhead/cycli...
 
moxfyre's Avatar
 
Join Date: Oct 2004
Location: DC / Maryland suburbs
Bikes: Homebuilt tourer/commuter, modified-beyond-recognition 1990 Trek 1100, reasonably stock 2002-ish Gary Fisher Hoo Koo E Koo
Posts: 4,166
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by DannoXYZ
Yeah, sounds like the crankarm is buggered. If you rode on it at all when it was loose and wobbling, most likely the spindle dug into the crank and the interface is no longer tight. ALWAYS make sure you tighten the crankarm bolts to spec with a TORQUE-WRENCH. About 30-35lb*ft is commonly quoted by the manufacturers. There's NO WAY you're gonna generate this kind of torque with the itty-bitty 6" double-sided Park wrench (at least without serious pain from the tool digging into your hand). You'll need an automotive-style 3/8" ratchet wrench with 10-12" handle and 14mm socket...
I don't think a torque wrench is really needed. Basically, just tighten a crank bolt AS HARD AS YOU CAN. For me, 40 ft-lbs of torque means applying half my body weight (80 lbs) to a 6-inch wrench. I've never used a torque wrench, but have successfully installed cranks many, many times with no loose cranks. It also helps to clean and grease the threads of the crank bolts, as some cheap ones are quite ill-fitting and without grease you'll think the bolts are tighter than they really are.

With the older hex-head bolts, a 12" handle is definitely needed to prevent the tool from slipping. But with allen-head crank bolts, an ordinary 8mm allen wrench with 6" handle should be fine. One of the nice things about allen-head bolts is that the size of allen wrench needed usually tells you APPROXIMATELY how much torque to apply... most things should be torqued as much as is comfortable to apply with that size wrench
moxfyre is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 10:14 AM.