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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.

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Old 04-10-13, 07:40 AM   #1
Sexy_Lugs
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Installing bottom bracket, is torque wrech really required?

So like the title says, I am installing a new crank set and the instructions state that it requires a specific amount of torque. I called my LBS and they gave me the old "oh yes, it is def needed." I am skeptical about how much it really matters, so I am turning to you oh faithful BF people, what are your thoughts?
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Old 04-10-13, 07:48 AM   #2
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I think that you should use a torque wrench.
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Old 04-10-13, 07:53 AM   #3
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Yes - it's *nice* to be able to use a TW on a BB, but it's not *really* necessary unless you're using some really exotic lightweight parts.

As a matter of interest, what BB and crankset are you installing, and on what bike?
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Old 04-10-13, 08:54 AM   #4
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ah yes, wrench, got it.

I am installing a fsa gossamer megaexo triple on my new soma smoothie es.

Last edited by Sexy_Lugs; 04-10-13 at 09:02 AM.
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Old 04-10-13, 08:58 AM   #5
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I think you should use a torque wrench as well -- they're not expensive, and if you haven't installed a bottom bracket before, you won't have any idea how tight it should be.
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Old 04-10-13, 09:15 AM   #6
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no. i've never had any problem at all with a BB and i've never used a torque wrench. of course if you've never tightened a nut before...

it's not as if would NEVER recommend using a torque wrench. i used it on the cylinder head bolts, connecting rod bolts, main bearing bolts and clutch plate bolts on my '61 MGA among other things, but never on a bicycle. it won't hurt though.

BTW, i use .75 Grunts with a 3/8 drive ratchet wrench. that's usually enough.

Last edited by hueyhoolihan; 04-10-13 at 09:18 AM.
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Old 04-10-13, 10:06 AM   #7
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Odds are that you will not tighten your BB enough without a torque wrench.

Get your LBS to install it for you if you're worried but you should really torque the cranks too... maybe you should just go buy a torque wrench. The kind with the deflection needle aren't terribly expensive.
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Old 04-10-13, 10:38 AM   #8
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Just invest the money in the tool. It's well worth the knowledge that your bike is in spec, and one less variable when you start hearing creaks, or components work their way loose, etc. You will find yourself using it on other areas too.
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Old 04-10-13, 10:40 AM   #9
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Yes, use a torque wrench - I know some people who do it all the time probably hit something kind of close and it works OK, I've seen many failed setups due to insufficient torque - it is much higher than you would pick just by feel. There will always be a crowd who feels like they don't need it, but engineers don't put torque specs on those parts just for the hell of it, but because it is important. You don't need a super-fancy torque wrench, northerntool.com has a variety of 3/8" torque wrenches for ~$50 that would be totally sufficient. Once you have it, you'll find yourself using it a lot, and breaking a lot fewer parts.

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Old 04-10-13, 11:53 AM   #10
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Yes, torque wrench. Make sure you get the right one for the torque needed. I have one for the Bottom Bracket and another for the bolts that hold on the left side crank arm. The torque values are very different.
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Old 04-10-13, 01:33 PM   #11
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Wow, well with an overwhelming agreement... it sounds as though I need to go invest in one. Thanks for all the help!
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Old 04-10-13, 01:43 PM   #12
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I had always used the 2-grunt or 3-grunt method of applying torque. Maybe good for getting both sides more or less the same, but no way of telling the absolute value of torque applied.
When I began using a torque wrench, I was surprised at how far off I had been! (On the low side.)
You can pick up a torque wrench at Harbor Freight for $10.00 on sale, even up to the 1/2" drive size.
Probably not uber precision enough for NASA, but close enough for me!
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Old 04-10-13, 02:27 PM   #13
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Quote:
Originally Posted by hueyhoolihan View Post
no. i've never had any problem at all with a BB and i've never used a torque wrench. of course if you've never tightened a nut before...

it's not as if would NEVER recommend using a torque wrench. i used it on the cylinder head bolts, connecting rod bolts, main bearing bolts and clutch plate bolts on my '61 MGA among other things, but never on a bicycle. it won't hurt though.

BTW, i use .75 Grunts with a 3/8 drive ratchet wrench. that's usually enough.
If it's good enough for an old car then it is more important for something as valuable as a bike.
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Old 04-10-13, 02:54 PM   #14
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Yea if you have done it often enough to not have to ask the question, probably don't need it.

but since you haven't , thus; You asked, so then I'd say Yes. BB 1/2" drive
[I peg the needle on 3/8" drive Beam Wrenches, to get things like theBB adequately tight ,
1/2" drive, the Ft/# value should be within that range]
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Old 04-10-13, 05:23 PM   #15
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Chances of getting a precise torque without a torque wrench are about as good as chances of getting a precise tire pressure without a pressure guage. Both of those little gadgets make life a whole lot easier by removing all the guesstimating.
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Old 04-10-13, 05:35 PM   #16
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I've done lots of bottom brackets without a torque wrench and I've installed plenty using one. Honestly, I've not had problems either way. If I were to install one tonight I'd use a torque wrench because - well - I own one so why not use it. If you don't own a torque wrench, here's how to estimate:
Most bottom brackets spec around 30 lb/ft. of torque. Try to imagine a 30 pound weight hanging on the very end of a foot long wrench. That's quite a bit. Use that much torque on your bottom bracket.

The next question is: "What are you going to use for a crankset?" That's another item that will come with a torque spec and I think it's more critical than your bottom bracket. If you use too little torque on a square taper crankset, the left crankarm will come loose and wallow out the square hole. If you use too much, it will crack at one of the corners of the square hole.
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Old 04-10-13, 07:46 PM   #17
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Here's a link to Shimano's torque reference 'cheat sheet'. There are different torque specs depending on the kind of bottom bracket and all of them are probably higher than you think.

http://bike.shimano.com/publish/cont...ue%20Specs.pdf
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Old 04-10-13, 07:51 PM   #18
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I've been doing BBs by seat-of-OOMPH torque for awhile. last one I did (un55 square taper), I torqued with my torque wrench because it was handy and I had hte number in front of me, and I was surprised at how much torque it was. I also discovered my 'clicker' torque wrench doesn't work on backwards threads. :-/
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Old 04-10-13, 10:17 PM   #19
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Newtons, inch or foot lbs ?
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Old 04-11-13, 02:22 AM   #20
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A trap to watch out for - if you're installing English threaded BBs then one side (drive side from memory) is left hand threaded.

Some torque wrenches (like my clicky one - grrrr) will only read in the right hand thread direction. A beam and pointer style wrench will read both ways for you.
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