new build numpty questions

[ElyDave]

I'm sure there's lots like me, want to build from scratch but lacking skills or experience. I've been doing more of my own maintenance and learning a lot in the process but still have more to learn.

My next challenge, bottom brackets. The one I have bought gives a torque range on it, 35-40Nm I think, but the bb tool is dumb. Cassette lockrings have similar torque but from what I have read are much more forgiving, I.e. just do them up tight.

So, any guidance on bb? I don't want to over tighten and damage threads, or is t a case of hand-tight only as I have read elsewhere?

Further questions likely to appear.

[Gattopardo]

Depnds on the type of bottom bracket.

[ElyDave]

SRAM external, threaded.

[David Martin]

1 kilo is 9.8N. A weight of 1 kilo on an arm 1m long will give you a torque of 9.8Nm
For a 30cm long spanner you will need 3 kilos to get the same torque. Multiply that by 4 to get nearer 40nM and you are looking at leaning gently on a long spanner - try this out on some bathroom scales so you know how much lean it takes to get 12 kg.

This will give you a feel for how much grunt you need for a given torque.

[Brucey]

the torque figure is for installing the cups. Use a torque wrench.

The 'hand tight' thing is for setting the preload on the bearings, which is a different thing entirely.

cheers

[trekker12]

Unless, like me you own a Halfords ring type spanner for the external cups a torque wrench isn't going to help. I lean on it until I feel it's tight enough but I've been building things since I was a teenager and have good idea when I'm overdoing something plus I have weedy arms which actually helps until something has to be FT (look that one up yourselves but the second word is tight) - which is rare on a bike.

I've never used a torque wrench on the recent three builds I've done (and many years of tinkering). If you under tighten the BB, you will soon know about it when it starts creaking. The BB thread should be softer than the thread in the frame (depending on material) so if you over tighten to the point of damage - which I would think is also unlikely - then damage should occur to the cheaper more disposable BB.

Torque settings are more critical on carbon where the carbon isn't designed to take load in a particular direction but then I don't own any carbon.

[ElyDave]

the torque figure is for installing the cups. Use a torque wrench.

The 'hand tight' thing is for setting the preload on the bearings, which is a different thing entirely.

cheers

It's one of those external toothed/notched jobs, have the special tool so a torque wrench is not really an option looking at it.

I think David's"get a feel for it" seems the best option .

[Brucey]

It's one of those external toothed/notched jobs, have the special tool so a torque wrench is not really an option looking at it.

just get a decent tool (not expensive) with a 1/2" square drive in it so that you can use a torque wrench.

If you don't, you need to be good or lucky;  modern frames have BB threads that are easily wrecked.

cheers

[Canardly]

Not too much concern with torque here!

https://www.youtube.com/watch?v=RB1wcwlmsRc

[caerau]

Being weedy certainly is a bonus in this respect.  I am far from weedy and my biggest issue in fettling of any kind is to not just bazooka things before I've even realised I'm trying.


It's also known as being a klutz of course 

[ElyDave]

It's one of those external toothed/notched jobs, have the special tool so a torque wrench is not really an option looking at it.

just get a decent tool (not expensive) with a 1/2" square drive in it so that you can use a torque wrench.

If you don't, you need to be good or lucky;  modern frames have BB threads that are easily wrecked.

cheers

I got the all-in one tool, rather than a socket drive one, didn't know the other type existed.

[Brucey]

there are a few different ones on this page

https://www.sjscycles.co.uk/tools-bottom-bracket/

I have a 'fat spanner' tool that has a handle and a 1/2" square drive on it, so you can have your choice of drive methods.

Flat spanners also have their place; using one of these you can usually check that a cup isn't loose in the frame without taking the cranks out. But not easy to attach a torque wrench to one of these....

cheers

[jsabine]

If you don't, you need to be good or lucky;  modern frames have BB threads that are easily wrecked.

Hmm. Not *yet* had a problem ensuring the BB threads are clean, chased and greased, and the shell faced, then starting the BB cups by hand and making sure they turn freely, before snugging them up then tightening with an appropriate tool to about one British Standard grunt.

I don't have especially modern frames mind, although the above does work for modern BBs.

[fruitcake]

Good luck with the build. I've found building bikes tremendously rewarding and informative. Now that I understand how the parts go together, I know straight away what needs adjusting/fixing/replacing when there's a problem, and am not reliant on bike shops. I think I understand the bike better too when I am riding - I have a feel for just how much I can ask of it.

It's been a process though. I have spent hours and hours learning by doing, and - particularly with parts for vintage bikes - geting a feel for the necessary adjustments. I have broken tools, stripped threads, and snapped parts. I've slipped and sworn. I have disassembled and reassembled a wheel five times trying to get it running smoothly. I've learnt to be analytical and methodical, to solve problems by changing one thing at a time. And I've spent far too much time looking at bike parts on ebay and at bike jumbles, when I should have been doing more important things!

[ElyDave]

Thanks Fruitcake,

that's kinda why I'm doing it. I've made a point of doing as much as I can lately and I think i'll learn loads from a build in terms of how things fit together, setting up, fettling etc. All skills that I can then transfer into the rest of the fleet.

I'm not sure if I should have a swear box in the workshop though

[ElyDave]

Another new build numpty question

Torque for chain ring bolts?  About 10Nm?

[Biggsy]

See manufacturer's instructions or www.parktool.com/blog/repair-help/torque-specifications-and-concepts for recommended torque values.

Don't be afraid to trust your own judgement, though.  The human torque wrench is all most of us use.

[ElyDave]

seems to be a range, 10 is within that range