Stupid question about checking crankbolt tightness...
01-27-16, 12:31 PM
#26
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Ben- Many wrenches will take issue with your method and description. To suggest that the crank arm will lever against the retaining bolt/nut and further move up the spindle is not what some feel is really happening.
Instead as the arm is worked over the spindle with pedaling forces the arm's hole slightly opens up. There is no driving force moving it up the taper of the spindle (other then over tightening, a different force then you focus on). But this slight molding of the arm's taper to that of the spindle's causes a possible slop to develop in time. It is this opening up of the arm's fit to the spindle that causes the arm to, in time and cycles of use, fall off. At no time does the arm want to move up the spindle's taper (unless the bolt/nut is further tightened).
So the need to re torque the retaining bolt/nut is an initial bedding in follow up. Once this initial break in is done and compensated for (by the small amount of re torqueing of the retaining bolt/nut) little later maintenance is needed.
It's common for the LH arm retaining bolt/nut to need more tightening after initial use then the RH side does. By a larger amount... Andy.
Instead as the arm is worked over the spindle with pedaling forces the arm's hole slightly opens up. There is no driving force moving it up the taper of the spindle (other then over tightening, a different force then you focus on). But this slight molding of the arm's taper to that of the spindle's causes a possible slop to develop in time. It is this opening up of the arm's fit to the spindle that causes the arm to, in time and cycles of use, fall off. At no time does the arm want to move up the spindle's taper (unless the bolt/nut is further tightened).
So the need to re torque the retaining bolt/nut is an initial bedding in follow up. Once this initial break in is done and compensated for (by the small amount of re torqueing of the retaining bolt/nut) little later maintenance is needed.
It's common for the LH arm retaining bolt/nut to need more tightening after initial use then the RH side does. By a larger amount... Andy.
Andrew, Jobst Brandt said the exact opposite of you. He claims, as 79pmooney does, that the arm drifts slightly farther onto the taper and the bolt looses some tension. He says re-torquing to spec will cause arm damage.
I have always wondered if, after an initial ride, I should just snug the bolt back up to the arm so that I don't lose the bolt, or if I should re-tighten all the way to spec'd torque. When I put a wrench on the bolt, it definitely moves easily, and not an insignificant amount.
Still confused......
Failure from "over-tightening" is caused by repeated re-tightening of properly installed cranks. In use, an aluminum crank squirms on its taper, and because the retaining bolt prevents it from moving off the taper, it elbows itself away from the bolt and up the taper ever so slightly. The resulting loss of preload, after hard riding, can be detected by how easily the bolt can be turned.
Snip/
Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.
Snip/
Mechanics, unaware of why crank bolts lose preload (and commensurate crank tightening), have re-tightened bolts until cranks split. No warnings against re-tightening properly installed cranks are evident although it is here where the warning should be directed rather than at lubrication.
01-27-16, 12:43 PM
#27
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When I originally tightened the cranks(with the socket wrench), the bike was laying on its side and I was sitting on the ground. I wasn't jumping up and down on the lever or anything like that.
01-27-16, 12:53 PM
#28
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01-27-16, 01:05 PM
#29
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Well, that changes everything, then. Is there a horizontal torque spec for that bolt?
01-27-16, 01:48 PM
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01-27-16, 03:29 PM
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You guys are both ignoring what happens if you jump or hop while putting pressure on the lever. I often do this to loosen lugnuts on cars. I generally have to do this when using any wrench/ratchet less than a foot. Put the socket on it, stand on the bar, then hop a bit. Works every time. (Yes, I'm a light person.)
Torque wrenches that short won't be calibrated up to 100 ft/lbs, though. The ones that are have much longer handles, more like 24". With those, 50lbs of hand pressure will get you 100ft/lbs of torque.
When you bounce on the handle or whack it, you exceed the force that simple pushing would exert. In our example, the wrench would read more than your weight if you bounced on the handle. That's why the stubborn lug nut either turns or the stud snaps.
We never got on the subject of lubing threads (to grease or not to grease: that is the question). Engineers tend to agree that you should lube them to avoid false torque readings when threads bind.
I used a 24" torque wrench to fasten the 10 head bolts on a car engine to 100ft/lbs each. Not that hard to do, since I needed only 50 lbs of hand force. I also use a 3' pipe as a "cheater" (handle-extender) on a plumber's wrench to loosen steam pipes. In that case, 50lbs of hand force results in 150lbs of torque. If I stand on the cheater and bounce a little, I can exceed 500ft/lbs.
Last edited by habilis; 01-27-16 at 04:11 PM.
01-27-16, 04:50 PM
#32
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Just took it around the block for a couple of miles. The new bottom bracket is smooth and quiet. But I'm running into a recurring problem that cut my ride short. Let me explain...
On my last ride, before I changed the bottom bracket and re-installed the cranks, I noticed the chain/chainrings were moving side to side about 1/8-1/4". While seated and exerting power to the pedals, I could physically see the chain/rings moving laterally. So, if I put pressure on the right pedal, the chain/rings would move to the right, and pressure on the left pedal would make the chain/rings move left.
The old bottom bracket was creaking loudly and had thousands of miles on it. That prompted me to replace it. I thought that if installed a new one the problem would go away... but it's still there. I'm stumped!
What is happening?
On my last ride, before I changed the bottom bracket and re-installed the cranks, I noticed the chain/chainrings were moving side to side about 1/8-1/4". While seated and exerting power to the pedals, I could physically see the chain/rings moving laterally. So, if I put pressure on the right pedal, the chain/rings would move to the right, and pressure on the left pedal would make the chain/rings move left.
The old bottom bracket was creaking loudly and had thousands of miles on it. That prompted me to replace it. I thought that if installed a new one the problem would go away... but it's still there. I'm stumped!
What is happening?
Last edited by richeydog; 01-27-16 at 04:55 PM.
01-27-16, 05:01 PM
#33
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Just took it around the block for a couple of miles. The new bottom bracket is smooth and quiet. But I'm running into a recurring problem that cut my ride short. Let me explain...
On my last ride before I changed the bottom bracket and re-installed the cranks, I noticed the chain/chainrings were moving side to side about 1/8-1/4". While seated and exerting power to the pedals, I could physically see the chain/rings moving laterally. So, if I put pressure on the right pedal, the chain/rings would move to the right, and pressure on the left pedal would make the chain/rings move left.
The old bottom bracket was creaking loudly and had thousands of miles on it. That prompted me to replace it. I thought that if installed a new one the problem would go away... but it's still there. I'm stumped!
What is happening?
On my last ride before I changed the bottom bracket and re-installed the cranks, I noticed the chain/chainrings were moving side to side about 1/8-1/4". While seated and exerting power to the pedals, I could physically see the chain/rings moving laterally. So, if I put pressure on the right pedal, the chain/rings would move to the right, and pressure on the left pedal would make the chain/rings move left.
The old bottom bracket was creaking loudly and had thousands of miles on it. That prompted me to replace it. I thought that if installed a new one the problem would go away... but it's still there. I'm stumped!
What is happening?
01-27-16, 05:21 PM
#34
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The new BB is loose for some reason. If the chain ring moves when you step on the right pedal, the spindle is wobbling inside the shell. Did you install the BB exactly as the manufacturer recommends? If it's threadless, are the BB shell faces perfectly square to the shell and parallel to each other? Are the faces chamfered (if that's what the manufacturer calls for)?
01-27-16, 06:14 PM
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BTW, what kind of bike is it? Some have shells wider than 68mm, the size required for most sealed BBs.
01-27-16, 07:00 PM
#36
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Can you turn the ends of the BB by hand, or wiggle them? If so, the chasing may not have left enough thread in the shell for the BB to grab. If that happened, your only option may be to install a threadless unit. I'd ask the LBS for some store credit if the thread-chasing was unsuccessful, unless they warned you that the operation might not work. Maybe you could buy a threadless unit and ask them to install it at no charge?
BTW, what kind of bike is it? Some have shells wider than 68mm, the size required for most sealed BBs.
BTW, what kind of bike is it? Some have shells wider than 68mm, the size required for most sealed BBs.
I can't turn the ends of the BB unless I take the cranks off again. I'll have to do that later. The shop never told me that it wouldn't work. They just said that there was some rust in the bb shell with a few damaged threads. It had to be chased because he couldn't install the cartridge either.
Last edited by richeydog; 01-27-16 at 07:22 PM.
01-27-16, 07:45 PM
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The bike is a 1991 Specialized Rockhopper with a Shimano Exage 400lx square taper crank. The shell is 73mm, original spindle length is 121mm.
I can't turn the ends of the BB unless I take the cranks off again. I'll have to do that later. The shop never told me that it wouldn't work. They just said that there was some rust in the bb shell with a few damaged threads. It had to be chased because he couldn't install the cartridge either.
I can't turn the ends of the BB unless I take the cranks off again. I'll have to do that later. The shop never told me that it wouldn't work. They just said that there was some rust in the bb shell with a few damaged threads. It had to be chased because he couldn't install the cartridge either.
The BB has "collars" that extend slightly outside the ends of the shell. These act as clamps and hold the BB firmly in the shell. Can you see any movement in those? If those move, the whole unit is loose, suggesting the threads have failed. If the collars are firmly fixed and the spindle has some wiggle, the bearings have failed. Unlikely in a new unit, I would think.
If you tightened the unit in a shell with damaged threads, it could have hurt the BB threads, but I'm just speculating. Best to pull the unit and examine it. If that's all that's wrong, that could be the best scenario. Those units don't cost much, so you could just install a new one.
Last edited by habilis; 01-27-16 at 07:59 PM.
01-27-16, 08:24 PM
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Personally I think you should take the bike back to the shop that did the install. I bet they can diagnose the problem very quickly. The symptoms you're describing are hard to pin down without access to the bike, I dont think anyone here can diagnose the issue just from your description. Since the shop put the BB unit in for you, I'm sure they'll be willing to take a look if you feel it isnt performing correctly.
01-28-16, 05:19 AM
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Frame cracks ?
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01-28-16, 04:09 PM
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Yep.
Last night I went back into the garage to check out the bike. Brought a flashlight with me so it would be easier to see....the garage isn't well lit. I didn't see any movement in the bottom bracket while pushing/pulling on the crank arms. Everything seemed fine until I saw a reflection off the frame. Ran my finger across it and knew it wasn't good. All this time I thought it was a scratch.
You can't see it in the photo, but the crack circles around each tube, about 3/4 of the way. When I push the right crank outward, I can see the crack opening up until I release the pressure. That probably explains the wobbling effect when I pedal.
Last night I went back into the garage to check out the bike. Brought a flashlight with me so it would be easier to see....the garage isn't well lit. I didn't see any movement in the bottom bracket while pushing/pulling on the crank arms. Everything seemed fine until I saw a reflection off the frame. Ran my finger across it and knew it wasn't good. All this time I thought it was a scratch.
You can't see it in the photo, but the crack circles around each tube, about 3/4 of the way. When I push the right crank outward, I can see the crack opening up until I release the pressure. That probably explains the wobbling effect when I pedal.
Last edited by richeydog; 01-28-16 at 04:25 PM.
01-28-16, 04:15 PM
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01-28-16, 07:06 PM
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01-29-16, 12:30 PM
#44
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02-12-16, 10:04 PM
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Oh.. yeah. I missed the main point, the whole already tightened thing. Yes I agree it will be "at least that tight" if the torque wrench clicks before the bolt moves.
@KevinSingleton you're not reading closely either (so that's two of us). 200 lbs at 6 inches is 100 ft*lbs (not ft/lbs either for that matter, so call it three of us). Nobody is saying it's 100 lbs.
@KevinSingleton you're not reading closely either (so that's two of us). 200 lbs at 6 inches is 100 ft*lbs (not ft/lbs either for that matter, so call it three of us). Nobody is saying it's 100 lbs.
02-13-16, 09:28 AM
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Super pedantic I know, but if you're loosening to retorque, resist the urge to loosen with the torque wrench.
Your brother will thank you.
Your brother will thank you.
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02-13-16, 11:46 AM
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Maybe I'm just lucky, but never had a problem with new or in good shape square taper cranks, and I've worked on quite a few bikes. I grease the taper (I know the opinions are divided about this), tighten the bolts by feel, check them after a few rides, retighten if necessary, and leave them alone afterwards.
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04-20-16 12:28 PM
