kahn

Before loosening a bolt/screw is there a way to determine its torque value? In other words, in one example my saddle is mounted to a seat post by two bolts. But I was never informed of the value used to tighten the clamp on the rails. Steel rails by the way.

In another I have a motor in the front wheel of my bike. It is tightened pretty tight (vague) but if I get a flat I will have to loosen the bolts or nuts that hold the wheel on the fork. I'd like to know the value needed to affix the wheel back to the fork.

Is there a way of using a torque wrench by stepping through various torque values and seeing where it clicks to in tightening it.

Or another method?

Thanks in advance.

dedhed

https://www.fastenal.com/content/mer...ce%20Guide.pdf

Andrew R Stewart 

Yes but hat's assuming that the current torques are "proper" and there's no after the last tightening corrosion of other changes to the friction between the parts. A similar method is to note the wrench handle's "clocking", loosen the fastener and retighten to the same clocking angle but use a beam type of torque wrench.

There have been various charts of bike fittings and their torque ranges over the recent years, IIRC Park has one, None have motorized bikes that I know of...

Experienced mechanics tend to have a more trained "feel" for loosening and tightening levels then newbies do. This "feel" includes the understanding to materials and stresses each fitting has (or should have)

In the end torque levels used are more about having a fitting tight enough but not too much more. Published levels are more frequently about max levels especially when non metallic materials are at play. Andy

thook

@kahn i would imagine a motorized bike forum would be a good place for a recommendation, if they're of any salt like a good professional auto mechanic. iow's, certain auto repair jobs have a fairly standard "assumed" torque value to go by. wheel lug nuts, for example

mr. stewart makes very good points, though. torque values are meaningless if there's friction in the adjoining parts. to use automobiles as an example once again, one better be quite sure the head bolt bores in the engine block are free of ALL debris, rust, dirt, etc before torquing down. otherwise you'll get false torque readings from resistance and blow the gasket/s from uneven clamp force. so, with your case of attaining values with a clicker wrench, then no...it's not really a good idea to go by that. mr. stewart's "clocking" advice while noting the amount turns is a good idea. but, again, make sure threads are clean and you start from a point of hand tightening as far as it'll go.

as for saddles, meh...i've always just snugged them up real good without actually stripping hardware. i've also done a lot of wrenching, though. the feel thing, eh...

kahn

Thanks, ALL.

I will re-read this thread.

I recently discovered on my new bike (two and a half months old) that Torque Values are embossed on various parts (stem/seat tube). That is quite helpful. But I will take into consideration dirt/grit/corrosion when tightening various parts.

Iride01 

For things like a seat clamp, why not just tighten it to something more than snug. Then if your seat post slips, tighten it a little more.

If you do that several times and you break the clamp bolt, then you know something else is wrong that a known torque will have never fixed anyway.

dabac

Tightening nuts and bolts to a known torque is a shade better than guessing, but will still produce a considerable spread in actual result.
Disassembly torque spread so much as to be nearly useless.
If you’re trying to do something ”properly” w/o having an official torque number to aim for, you’re far better off chasing down a torque chart based on bolt size(and material) and use that.

Bill Kapaun

You simply can't tell because of the difference between sliding & static friction-
https://www.nextgurukul.in/questions...rictionf/16095

Sy Reene

If I understand the question correctly, i have a digital torque wrench that tells you the torque value you're at while you apply force. I suppose you could use something like this and try and carefully note at what reading the wrench starts to move the existing bolt tighter?

That said, I wouldn't bother. For seat rails, just start with something average like 6Nm, maybe using some assembly compound. If it doesn't slip, you're good.

pdlamb

What an insane idea, putting assembly specs or requirements where they'll be easily available when needed. How are repair people supposed to learn how to spend a half an hour doing a lookup for something that takes 30 seconds to do?

(What kind of bike is that? I want one!)

CliffordK

Many of the older torque wrenches have some kind of an analog indicator, so you wouldn't need to step through torque settings, just read the indicator.

But, if the piece has been assembled for more than a few months, and/or used, I would not consider such readings at all reliable.

I suppose a bit old fashioned, but I'd just go by what feels just about right. Perhaps that is one of the reasons for different wrench sizes. No 4 foot breaker bars on 4mm bolts.

If you're working on a vintage bike, it is quite possible that it wasn't ever assembled with torque specs anyway.

adipe

1. apply some waxy lube (beeswax is good enough - not needed to minimize friction but prevent wear and act as a light antiseize) on the seatpost - it will prevent clicking, creaking and if it happens that you have alum seatpost and steel frame then there would be the risk of them seizing up and you'll cursing and swearing when that happens. the lube you want put there does not need to work with friction but prevent movement. the static coefficient of friction is considerably greater than with movement and the pressure on the seatpost is not that great. the higher pressure and the higher sliding speed - the lower coefficient of friction for such substances like beeswax. straight paraffin is crap, avoid candle wax.

2. apply a bolt specific lubricant on the bolt thread. it will help the bolt reach a high enough tension without the threads being damaged and it will also prevent corrosion (stress corrosion is a real thing). apply lubricant on the bolt head so that the non-thread friction is lessened - so that the bolt does not give up as the torsional stress is added to the tensional stress.

3. if you don't trust yourself to go by feel (as only the bolt is vulnerable in this case) when tightening bolts and you don't want to risk having the bolt broken then tighten it to no more than 6Nm and if the seatpost slips (have something to mark it, like a zip tie - a few mm above the point where the seatpost enters the frame) then tighten it some more. usually seatpost clamp bolts take 8Nm torque. but it depends on what kind of lubricant is applied and the grade of the material.

DaveSSS 

I've never used a torque wrench on any M5 or M6 bolt. I still use one on cassette lock rings and my sram axs cassettes, but that's it.

SkinGriz

I would never trust the current torque to be correct. Hardened loctite, rust, galvanic corrosion, etc.

I remember seeing a chart that has all the proper torque values based on fastener size, material, tpi, and whether it’s a locking fastener or not.

Keep in mind that a thread lubricant will give you more clamping power for less torque than a nylock nut, so on something like a bike, the twisting torque to clamping force will not be as precise as a helicopter where the fasteners are getting replaced at overhaul or a wind turbine where the fasteners come pre lubricated and a hydraulic torque wrench is used.