Torque Levels

[elliotsdaddy]

Evening all,

When playing around with your bikes do you adhere to the torque levels whenever possible?

I'm not talking about deep engine stuff...it's just that I am gonna change my fork seals and wondered if I should purchase a low value torque wrench or not as specific values are quoted.

Chris.

[robk]

Hi Chris

Torque settings are there for a reason as worked out by the manufacture so adhering to them is important. Also if you do have a failure you can rule out overt-tightening or under-tightening of a nut or bolt if the correct torque has been used. It is good practice so I would advise the purchase of a torque wrench that covers your needs.

regards Rob

[suzuki250]

Don’t buy one to cheap, better to go for a branded one

The cheap ones are not accurate

A good quality one will last a lifetime!

[mags]

I have been using torque wrenches for nearly 40 years and this is just my opinion... ( I still have one from my 17th birthday, in a wooden case made by my dad)

It is very difficult for the human hand to feel accurate torque hence the need for torque wrenches. The correct torque as specified by engineers is done to stop the plastic limit of fastener threads being exceeded and causing potential failure of the component or fastener. Thread deformation causes a stress riser at the thread root and allows far less load to be applied to the component before failure. Also, designed "cycles to failure" are severely reduced... if a brake caliper bolt is tested to 6,000,000 cycles of hard brake application before failure/no failure and the bolt thread is stretched beyond the plastic limit (by over-tightening) it may fail at 1,000,000 cycles shortening its design life by circumventing mechanical procedure.

I have met many people (especially motorcycle mechanics) who say "Don't tell me I need to use a torque wrench I've been doing up bolts for years , mate".

I say two things.... Why do you bother with a torque wrench for head studs or rod bolts but not worry for much else, is your hand NOT accurate for rod bolts only?

And.... I'll give you $1000 if you do that bolt up to 41 ft lbs with a ring spanner? MMMmmmmmm!

Using a torque wrench allows a fastener to be tightened and removed many times without stressing the threads of the fastener or the parent material.

It is also used to apply "even" pressure of one component to another with many fasteners... like, even pressure and no warpage of a crankcase cover for example.

This is achieved by applying the torque in stages and using the tightening pattern as laid down by the engineers that designed the component in the first place. Stages are used to NOT apply all the torque on one fastener at once leaving others undone. This can warp the component or attach the component in "cocked" or warped manner. Torque wrench convention usually has the torque applied in 3 stages. When doing up the side cover fasteners on Monty I use a centre/outside/criss-cross pattern and apply torque at 3Nm, then go around again at 6Nm and finish off at 10Nm (Montesa spec). A last run around at final torque to finish.

Correct torque also protects the component from failure via tension failure in the case of over-stressed threads or the component working loose from cyclic load, say, in the case of an under torqued fasteners on a front brake caliper or rear axle nut for example.

Torque patterns.... for example take the left side cover on my Montesa 4T, that has to be removed every time you want to change the oil filter. The case has many fasteners and a thin gasket. if the torque pattern or torque value is uneven the gasket is compressed unevenly and this will allow the best chance of a leak.

Also... holding the filter in (in the Monty) is a small tab held on by a small fastener. This tab holds the O ringed oil filter cover in position. If this fastener came out the motor would lose oil pressure and the fastener would be at the mercy of the rotating parts of the flywheel and stator magnetic pull... very costly and all down to one little bolt. I dont risk my idea of what I think the torque feels like, I torque the thing and dont take the risk of costing me mega bucks for repairs.

Granted there are some bolts that are not critical and experience over the years allows you to tighten these to "tight" and not have failures. Things that are not critical to rider safety are ok to snap or wear treads BUT... things like rotor bolts, brake components, steering/handlebar fasteners, axles, axle pinch bolts et cetera should be torqued to spec as a matter of good mechanical technique.

Torque wrenches come in "ranges" and are most accurate in the 20-80% of their range. For example... a 0-60 Nm torque wrench is most accurate doing fasteners up between values of around 10 and 50Nm. Torque wrenches mainly use springs (there are other types) and the springs under low tension and under high tension are the areas of least accuracy.

If I want to tighten a fastener to 60 Nm I wouldn't use my 0-60 and have it at 60Nm. I would use my next one up, 20-110Nm range (from memory) and set at 60Nm.

For the smaller fasteners I use an inch/pounds/Nm Its range is about 0-15Nm and the Monty case bolts are 10Nm.

I have 4 torque wrenches that I mainly use and are Norbar Aviation Quality that come with a test certificate. No need to go this far but I treasure them as they are very accurate and part of my tool collection.

There are also attachments that allow hard to get at fasteners to be done. Things like crows feet which give open enders on a torque wrench and you drop the value as calculated by the distance away from the torque wrench. Also... I have an attachment that can capture a ring spanner and attach it to the torque wrench... this come with a torque value table to calculate the altered torque values using the attachment.

If you dont have a torque wrench and everything you touch has been fine I dont have an issue with that but I use them to maintain accuracy as set by the design engineer and to not wear threads out on components that are removed over and over. Also gives the best chance of never having a failure of a component.

Mags

Edited November 10, 2014 by mags

[elliotsdaddy]

Thanks for the information all....torque wrench on order.

Found one that has a 5lbft-80lbft range for just under £30, so that'll do nicely.

Mags, cracking reply there mate, thanks very much, though I just wish you went into a bit more detail, hahaha.

Chris.

[mags]

G'day Chris,

Yeah mate! I thought I'd keep it short...

Mags

[dpyam]

One thing I've never found a definitive answer to - if you oil or copper grease a bolt thread, do you need to lower the torque figure used, as the friction will be less?

[mags]

dpyam,

The answer in for that still lies with the spec set down by design engineer/manufacturer.

Manufacturers in most cases specify a torque setting for the "assembled" parts fasteners (not all fasteners on bike, some you just use a recommended torque for the particular thread as set by the fastener maker) and if this part "assembly" specifies a compound applied (like in the case of rod bolts, usually a mineral motor oil) the torque setting is correct for the assembly with the compound applied.

In fact it might need the compound, in conjunction with the spec'd torque setting, to achieve the correct "tightness".

Here is another example....

My jet ski jet pump is under water and in a harsh environment. The 4, 10mm thread bolts holding the stator on corrode easy with no compound. Sea water wicks up the threads in a millisecond.

Yamaha specifies a Loctite compound to be applied to the threads and then torqued up to spec. This particular Loctite is a thread locker, anti-gall compound and a sealer (to stop salt water getting in to thread. Every year I disassemble the jet pump, check clearances and re-assemble, the bolts have been fine... 8 yrs now. Yamaha has spec'd a semi-slippery compound to be applied and then torqued to a spec.

Having said the above if I use an anti-seize type product where clean and dry is the norm I reduce the torque. I also reduce the torque if using full synthetic oil.... it is very slippery and a torqueing has to overcome friction.

If you think about it.... friction increases as you tighten the fastener, this friction applies load/pressure to the spring in the torque wrench. If you severely reduce this friction by applying a slippery compound more rotational force (applying pressure to the threads) is applied to reach the same friction point (more clamping force on bolt head to achieve same friction).... this can take the faster beyond the plastic limit.

I usually reduce from 10-20% in the case of anti-seize but I just do this from experience I dont have any set tables for different applied compounds... they may be around though. A mech engineer would be able to shed more light on the subject.

One thing I do if reducing torque because of slippery compounds applied where it is not spec'd is to drill and race wire the fasteners. An example is the 3 fasteners on the oil filter cover of my wife's Beta. One fastener was machined cocked from factory and the thread was stressed so I applied oil instead of "clean and dry" used 20% less torque and race wired the bolts. It was ok reducing cover sealing pressure in this instance as the cover has an O ring not a gasket so reduced pressure of less torque does not affect an O ring seal like gasket seal. An O ring seal just needs to be "home" a gasket seal needs a certain pressure to maintain seal and stop oil wicking and/or leaking.

The best method for good mechanical technique is to follow the manufacturers specified setting and compounds whether it be simple mineral motor oil, EP grease, anti-seize/anti-gall or a locking compound. In any absence of compound spec I re-install as found and it can be as simple as "clean and dry".

One good practice is always assemble with threads cleaned of any debris, dirt, old compound et cetera. I use a simple can of brake cleaner with a long nozzle to clean internal blind threads and a whiff of compressed air. Clean bolt and install... torque up.

One tip I can offer as well... NEVER, EVER assemble 304 or 316 stainless fasteners (bolt and nuts) bolt and threaded hole "clean and dry" as stainless has great friction (galling) properties and it can/will gall (cold weld to itself) especially if the tolerances of thread spec are on the limits. Even just plain old wd-40 or clear machine oil will stop it galling. If using a clear machine oil normal torque values should suffice.

Mags

Edited November 12, 2014 by mags

[dadof2]

"A mech engineer would be able to shed more light on the subject"

Shedding more light on the subject only illuminates what a complex subject this is. Unfortunately fastener torque is quite an unreliable means of achieving the correct clamping force because of a large number of variables several of which are listed in previous posts.

The correct clamping force can only be consistently achieved by having thoroughly cleaned fasteners, correctly "lubricated", then torquing to a low value to take up slack, the turning the fastener the correct number of degrees to put the correct tension in the fastener.

​Motorcyclist have been killed and cars have crashed after wheels have come loose even when torqued correctly, because the fitter had applied grease or anti-seize compound

[axulsuv]

Most torque spec's are given for clean dry fasteners , unless specified ... (aka most auto head bolts )

Glenn

And some cases a quick cleaning of the threads involved , light tap or die run , will give a much more accurate torque reading and clamping force .

And yes my wrists click .....

Glenn

And Mags , added on edit , Your explanation was superb ! for explaining why guys like you , me and copey and lineaway have way to much money invested in tools ... Right the first time is all that works . And Dadof2 ... too

Edited November 13, 2014 by axulsuv

[slicktop]

One thing I've come across with correct torque values; Mainly concerning top end bolts while the motor is in the frame.

I have bought the smaller wrench but there are areas where to get on the fastener you need another attachment, whether its an extension, swivel, or crowfoot. In adding any of these items the value changes and the conversions are hard to find for a hillbilly. Luckily I have been ok with changing gaskets with no leaks but I would not know if I am over torqued.

[dadof2]

Anyone see the Guy Martin (road racer) program on rebuilding a Spitfire.

Tightening the prop on (not good if it falls off). No torque wrench used, just swing on a long bar and get it FT.

Back to main point of post, much fastening is not about needing a specific clamping force, its just about making sure the fastener is tight enough not to come loose.

[slicktop]

Anyone see the Guy Martin (road racer) program on rebuilding a Spitfire.

Tightening the prop on (not good if it falls off). No torque wrench used, just swing on a long bar and get it FT.

Back to main point of post, much fastening is not about needing a specific clamping force, its just about making sure the fastener is tight enough not to come loose.

What Spit are you talkin about? I have a 63spit4 and paid dearly for the engine build. They had better followed either triumph specs or Kastner. Proper specs are just that. As Kas would say, " Never get beat by your equipment."

[dadof2]

Spitfire as in "flown by the few"

http://en.wikipedia.org/wiki/Alan_Christopher_Deere

[axulsuv]

And if my memory works at all , most aircraft prop nuts tighten opposite the direction of rotation of the engine ... So centrifical force and inertia are always tightening the nut.... Just like most modern auto fan clutches ... And yeah , I've only been twisting wrenches about a week now , and I learned everything on the internet ....

Glenn

Completely irrelevant dd2

And my first car was a TRIUMPH SPITFIRE 1967 , not a fighter plane from WWII

Edited November 18, 2014 by axulsuv