Loctite advice please

General cycling advice ( NOT technical ! )
gerrymcm
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Joined: 30 Oct 2012, 2:52pm

Loctite advice please

Postby gerrymcm » 14 Oct 2016, 10:08pm

I'm in the process of building a new bike and want to buy a general purpose loctite for disc brakes etc.
Which "colour" should I go for please?
Thanks
Gerry

ThePinkOne
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Joined: 12 Jul 2007, 9:21pm

Re: Loctite advice please

Postby ThePinkOne » 14 Oct 2016, 10:28pm

Blue loctite for anything you might need to remove again.

TPO

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Loctite advice please

Postby Brucey » 14 Oct 2016, 11:22pm

....and red for stuff that will never move again, (or at least only with something of a struggle)

-well that is the simplified version, anyway... there are actually dozens of different grades with various highly specific properties.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

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Mick F
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Re: Loctite advice please

Postby Mick F » 15 Oct 2016, 5:30am

I concur with the BLUE. It works really well.

Can't imagine using red on a bike, though I have used it on my trailer stub axles. I even cross-drilled and bolted them too.
Long story!
Mick F. Cornwall

landsurfer
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Location: Rotherham

Re: Loctite advice please

Postby landsurfer » 15 Oct 2016, 8:19am

No loctite. Apply the correct / manufacturer approved torque load. "Glue" is for fixing broken things.
The Road Goes On Forever ...

hayers
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Re: Loctite advice please

Postby hayers » 15 Oct 2016, 8:24am

222 (pink) is good for general "shake proof" use - eg on musguard stays where you can't torque very high but going loose is really annoying.

Agree on brakes etc correct torque should avoid loosening, but as an additionsl measure won't do any harm, so long as it doesn't get jn the works...

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Mick F
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Re: Loctite advice please

Postby Mick F » 15 Oct 2016, 8:27am

If you look at any brand new component - brakes for instance - you'll find blue Loctite on the threads.
If the manufacturers put it on, it must be a Good Thing.
Mick F. Cornwall

mattsccm
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Re: Loctite advice please

Postby mattsccm » 15 Oct 2016, 9:35am

buttock covering maybe?
Never use the stuff. Never had anything rattle lose. Maybe lucky, maybe not but I wouldn't call the stuff essential.

Brucey
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Re: Loctite advice please

Postby Brucey » 15 Oct 2016, 10:28am

in terms of 'is it necessary?' the answer is 'not always'. But for manufacturers and riders alike there is a risk vs consequence calculation to be done. In this, the 'might do some good, won't do any harm' for modest outlay of time and effort seems persuasive.

It is as well to note that even in the days of nutted brakes, they were nearly always supplied with some kind of shakeproofing to the fasteners, be it special washers, crush nuts, or nylocks. Thus there is a precedent there, and (say) the use of blue Loctite on brake centrebolts is an equivalent measure that works easily with modern allen key fixings.

As to 'why do some fasteners come loose?' this ought not to happen if a connection is well designed, well manufactured, and well installed. However these things are by no means guaranteed; in particular there are a number of parts on a bicycle where there is likely to be an issue, e.g.

- the bolt cannot be torqued fully because the (lightweight) parts are not strong enough to sustain a full bolt load in that direction. Very many lightweight aluminium parts and carbon parts are like this.

- the nature of the service loads is such that a small (and rather likely from time to time) variation in tolerances means that at any given torque, loosening is likely in service unless threadlock is used. BB assemblies are a good case in point.

- the joint is liable to settle in service (for various reasons) and the length of the bolt is (unavoidably) insufficient to maintain tension should such settling occur.

The latter point applies to all kinds of things where the parts don't quite mate accurately or (say) there are liable to be burrs on the parts or the fasteners. If the parts are connected by a long bolt of some kind, the amount by which the bolts stretches when tight might easily exceed any reasonable amount of settling that may occur, and the connection will remain tight (car head gasket bolts often work this way). However the same parts, if connected by short bolts, cannot work the same way; any settling in the joint will more easily exceed the stretch in the bolts, and the connection will become loose.

A good example of this might be a comparison between an M5 threaded QR skewer and (say) an M5 threaded rack mounting bolt. The former is considerably stretched when the QR is tightened (by about 0.25-0.4mm), so that instances of decent internal cam QRs 'working loose mid ride' are (in the absence of thick powder coating on the dropouts or similar) almost unheard of. By contrast the mating faces in a rack mounting are very rarely perfectly flat and burr-free, and the bolt is very short, so cannot stretch much at all (eg a rack bolt might stretch elastically by 0.01 or 0.02mm, so will become completely loose if the joint settles by more than that). Thus most folk know very well to check their rack bolts after a short period of use, else run the risk that they may loosen and fall out or perhaps wear/break through being rattled about too much.

Note that threadlocking ought to prevent loss of a loose fastener in such cases but it certainly won't stop the joint itself from working loose in every case, and indeed it cannot be expected to. Devices such as spring washers etc can maintain a weak tension in a joint that settles but IME this is rarely enough to hold a bolted connection on a bicycle securely.

Needless to say bicycle parts are not usually overengineered in such a way as longer bolts and fancier spring washer systems (such as stacks of Belleville washers) can effectively mitigate against settling and loosening; more usually the bolts are made as short and lightweight as possible, and this nearly always increases their chances of working loose.

In my opinion very many joints on bicycles are commonly overtightened (i.e. so that the parts start to yield) and this provides some increased chance that the joint won't settle and loosen in service (whilst incurring a very real danger that the fastener might break if it is re-used). So for example when you fully tighten a rack mounting bolt, you might lose the (thick, soft) paint on the dropout. Losing the paint thus may be inevitable; if you tightened the bolt less to start with, the joint could repeatedly work loose until the paint was removed anyway.

So when choosing whether or not to use threadlocking, it is as well to ask yourself what it is you are hoping to achieve; not all bolted joints work the same way or derive the same benefits from threadlocking.

cheers
-------------------------------------------------------------------------------
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

gerrymcm
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Joined: 30 Oct 2012, 2:52pm

Re: Loctite advice please

Postby gerrymcm » 15 Oct 2016, 10:44am

Hmmmmm I thought this would be a simple one :)
I tend to agree with Mick F "If the manufacturers put it on, it must be a Good Thing" but also realise that manufacturers need to "cover" themselves against potential issues so maybe it's simply them being cautious.

I've never used loctite and never had issue with things working loose. Recently when building my new (to me) bike I realised that it was untouched from new and as such had lots of blue loctite in the torx for discs and the bolts holding the disc adaptors to the frame and it got me wondering.

I think I'll stick to copper grease and ensure I check them frequently.

Thanks all
Gerry

landsurfer
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Location: Rotherham

Re: Loctite advice please

Postby landsurfer » 15 Oct 2016, 2:12pm

we design and repair train dynamics. Loctite is banned. torque loading is the only way
The Road Goes On Forever ...

flat tyre
Posts: 463
Joined: 18 Jul 2008, 1:01pm

Re: Loctite advice please

Postby flat tyre » 15 Oct 2016, 3:01pm

I built up a bike earlier this year using new components. Some of the bolts in the group set (Shimano 105) came supplied with loctite compound already applied.

gerrymcm
Posts: 446
Joined: 30 Oct 2012, 2:52pm

Re: Loctite advice please

Postby gerrymcm » 15 Oct 2016, 5:27pm

Landsurfer, "Loctite is banned" is it seen as a bodge? I'm no engineer but wouldn't loctite and the correct torque be better then correct torque alone?

PDQ Mobile
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Re: Loctite advice please

Postby PDQ Mobile » 15 Oct 2016, 6:47pm

IMHO a very good idea on rack (and mudguard securing bolts), esp front lowriders.
I use Blue.

Brucey
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Joined: 4 Jan 2012, 6:25pm

Re: Loctite advice please

Postby Brucey » 15 Oct 2016, 7:16pm

one of the things claimed by the manufacturers of such products is that (when applied in liquid form) the uncured threadlock provides a consistent kind of lubrication to the threads, so that the torque setting vs bolt tension isn't so variable as it might be otherwise.

However, on the minus side, many torque settings are specified dry, and the use of any lubricant can result in excess tension in the fastener.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~