Stretch Bolts

I'm not minded to pay a fiver each for one inch, M12 bolts (so on this car 50 quid all told just for the brake calipers alone) when I cannot see
what's wrong with regular bolts just dabbed with Threadlock and done up a little tighter. Is there something I've overlooked? You will probably have guessed I'm old school and happy to be that way.
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On 17/01/2018 22:38, Cursitor Doom wrote:

There are various grades of high tensile steel. If you use a lower grade than specified, you either won't be able to do them up to the specified torque - or you will risk over-stressing them, with a risk that they will fail.
Not a good idea for a safety-related item.
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On 18/01/2018 11:38, Roger Mills wrote:

If they are stretch bolts then throw them away, they are one use only.
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On Thu, 18 Jan 2018 11:38:11 +0000, Roger Mills wrote:

Funny nobody worried about such details back in the old days - yet the world didn't end!

The alternative isn't a good idea from a wallet-related PoV, though.
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Cursitor Doom wrote:

I pay around a tenner for the crankshaft bolts on my old Fiesta, and they're tightened up to a mental torque. Big long breaker bar, socket extension pivoted on an axle stand, and lots of grunting. I suppose that tensile bolts are meant for critical applications.
The wheel bearing nuts are weird single-use laminated things, which are just bonkers.
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On 18/01/2018 12:09, Dan S. MacAbre wrote:

I have always received two of those bolts (different sizes) with a belt kit. I have got a half doazen or so new ones, I must put them on ebay.
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MrCheerful wrote:

I bought one recently because I have to change the front oil seal soon. Just waiting for a change in the weather :-) I only did the belt a couple of years ago, and I think I'll leave it in for a bit longer. The belt kits vary a bit. Some come with tensioner, bolt, and a water pump, since the job is such a pain. I remember doing the belt on a Capri - only took about half an hour. It had lost its teeth (harmlessly) on the way to my mum and dad's house. I just got the AA bloke to take us the rest of the way, and I changed it in the road outside their house - even had a spare belt in the boot. I wouldn't attempt that now :-)
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Is this on your 420G? Didn't think stretch bolts were common then. And I've never seen them used on an ordinary car callipers.
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On 18/01/2018 14:31, Dave Plowman (News) wrote:

and wouldn't they be UNF?
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On Thu, 18 Jan 2018 14:40:16 +0000, MrCheerful wrote:

No idea, but quite possibly. Dave seems to be having some problems keeping up with all the cars I encounter. The one in question here is a 2015 Merc. I very much doubt there were such things as stretch bolts at all back in the 1960s! :-)
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Cursitor Doom wrote:

My mother does this. Whitters on about one thing then changes the subject while carrying on just using he, she & it about the new topic. Put more details in and we won't be left guessing.
> The one in question here is a

What's the actual torque specification? Can't imagine they're actually specifying stretch bolts but they do tend to say "use new bolts" as they come pre-threadlocked.
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On 18/01/2018 19:51, Scott M wrote:

and new pads come with the bolts, and they are not M12 by 1 inch
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On Thu, 18 Jan 2018 21:07:11 +0000, MrCheerful wrote:

Why on earth would pads come with bolts?? These bolts are M12 thread and about an inch long (obvs not exactly one inch - I'm just trying to get across how little you get in exchange for your five quid).
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On 19/01/2018 00:18, Cursitor Doom wrote:

They do with some VWs if you buy genuine, OE pads. It's because these bolts have to come out to replace the pads and the official manual says to use new bolts, because they come coated with threadlock, AIUI.
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Stretch bolts are usually obvious by the tightening method given. Measured in degrees of rotation, rather than just a plain torque setting.
They are also rather obvious by comparing the lengths of new and old.
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On some types you have to unbolt the calliper to change the pads.

Is this some form of theoretical question?
Might help if you described the actual problem.
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On Fri, 19 Jan 2018 11:03:04 +0000, Dave Plowman (News) wrote:

Actually I think you've already assisted in that matter in one of your most recent comments, Dave. I'd forgotten about the different methodology between tightening stretchers and regulars. Seems like a perfectly good way to tell 'em apart.
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On 18/01/2018 19:51, Scott M wrote:

That's my understanding. I think it's just a play-it-safe way of ensuring threadlock (and the correct threadlock) is used.
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On Thu, 18 Jan 2018 19:51:56 +0000, Scott M wrote:

Can't say I've ever heard of pre-threadlocked bolts before. Another method they sometimes use is stainless steel wire woven though the bolt- heads. Bentley did that for all sorts of fixing points around the car where IMV it was totally unnecessary. But I'm no engineer....
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Lockwire? It's widely used in aviation.
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