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edlithgow
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PostSubject: Torque Wrench Technique Question   Sat Mar 15, 2014 11:12 am

Just used one on the gf's scooter head bolts, and realised I wasn't exactly sure how!  Embarassed 

(I've used one before but a long time ago, and maybe I didn't think of this before)

My uncertainty is with the interpretation of the standard "tighten nut until the specified torque is reached" instruction.

Just now, when I did that, the nut was still moving.

Should I stop at that point (as the standard instruction seems to imply), or hold the torque at that level until rotation stops?

The former seems likely to vary, depending on how fast you tighten the nut.

The latter seems likely to be more reproducible, but also likely to get the nut a lot tighter.

This is using a beam-deflection wrench.

I suppose, with the click-type, (which I don't have) you don't have the option of holding at the set torque value, but the rate at which you reach it must still influence the final tightness of the nut?
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Justwatching
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PostSubject: Re: Torque Wrench Technique Question   Sat Mar 15, 2014 6:18 pm

I'm not necessarily saying this is the correct way, but I have always continued to apply the specified amount of torque until the bolt stops moving (I also use the beam deflection type wrench).
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edlithgow
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PostSubject: Re: Torque Wrench Technique Question   Sun Mar 16, 2014 4:36 am

Yeh, that's what I did, and its probably what I did the several years ago that I last used one, since it makes more sense to me.

BUT, as I understand it, you can't do that with a click-type, and they are probably a lot commoner in general service (I couldn't find a beam-type at all here in Taiwan; "Too old-fashioned"  Rolling Eyes Got a Draper last time I was back in The Yook)

This implies that the effective torque settings from a beam-type, used the way I use it, are going to be greater than from the click-type, which is probably what the manual assumes.

Fairly academic in this case since I don't have the official torque specs anyway, so I was guessing (20 ft-lbs) and then adding a bit in the faint hope of stopping it leaking (30 ft-lbs).

Be nice to know The Correct Procedure though.
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edlithgow
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PostSubject: Re: Torque Wrench Technique Question   Sun Mar 16, 2014 10:39 am

The more I think on't, the more it seems likely I've been doing it wrong.
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edlithgow
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PostSubject: Re: Torque Wrench Technique Question   Mon Mar 17, 2014 10:00 am

Actually, the more I think on't, the dodgier the whole procedure seems.

As far as I can work out, my perceived problem still applies with the click-type wrench, its just less obvious.

If (say) I'm aiming at 30 ft-lbs and I hold it at 29 until it stops turning, then go to 30 and stop, (or click) its going to be tighter than if I go to 30 as fast as I can.

Same applies to the click-type. If the bolt is moving, there seems to be scope for a lot of variation due to technique.
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Justwatching
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PostSubject: Re: Torque Wrench Technique Question   Mon Mar 17, 2014 3:48 pm

Would have thought if you continue to apply turning force until the bolt stops, you'll have a more uniform stopping point (i.e. should be less acceleration based). Test-retest for extra reliability? I think being consistent is the best you can do. The rest is somewhat out of your control. I've used two different wrenches on the same bolt and got different readings (I think the clicker one was buggered though). Different technicians will use different torque wrenches and have different techniques, and yet magically, they all manage to rebuild stuff without it falling apart. This tells me there's probably more room for error than you think.
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edlithgow
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PostSubject: Re: Torque Wrench Technique Question   Tue Mar 18, 2014 12:17 am

Apparently, from a bit of reading, its generally acknowledged that torquing bolts is a very imprecise procedure, so I feel a bit better about it now.

I suppose if you increase the torque gradually, so movement has time to happen, and you approach the "click-point" slowly, that should reduce the variability.

The distinction between reaching, and holding at, the specified torque, while it is a real one, isn't one that's easy to make with a beam-indicating wrench, due to its wider range of reading precision, so it probably isn't worth worrying about.

Friction is probably a larger variable, and I'm generally working with oiled or greased bolts, (while dry is usually specified) so obsessing over fine points of technique probably doesn't make much sense.
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