You need a torque wrench if you’re se­ri­ous about en­gine build­ing or the safety of key com­po­nents like brake caliper mount­ing bolts or spin­dle nuts

Practical Sportsbikes (UK) - - Contents - Words &Pic­tures: Alan See­ley

In­side Pa­trick Williamson’s den of ancient and mod­ern – and plenty of junk too

How tight is tight enough?there are those blessed with the touch of a con­cert pi­anist who have such in­built self-cal­i­bra­tion they never strip a thread or leave a fas­tener too loose. For ev­ery­one else there is the torque wrench.

Not that you need one for ev­ery job, al­though if you are par­tic­u­larly un­prac­tised or ham-fisted a torque wrench dis­penses with guess-work.af­ter time you will find your­self less re­liant on one as your feel im­proves.

Torque wrenches are indispensable for some tasks es­pe­cially where even tight­en­ing or safety are crit­i­cal; cylin­der heads and caliper bolts are ob­vi­ous can­di­dates here. When given torque val­ues are at

as­tro­nom­i­cal lev­els, for ex­am­ple crank­shaft gear and clutch cen­tre nuts, it’s hard to gauge if you’ve gone tight enough and a de­cent wrench is helpful there.at the other end of the spec­trum, those small fas­ten­ers some­times seem to go from loose to strip­ping the thread with the mer­est frac­tion of a turn.

Ac­cu­rate torquing re­lies on a prop­erly cal­i­brated quality wrench. Rather than a one-size fits all tool, you ide­ally want one for small torque fig­ures, one for medium and one for large.that’s be­cause typ­i­cally each of these will be more ac­cu­rate within their given ranges than one that at­tempts to span them all.ac­cu­racy also de­pends on clean threads, or in­deed greased or oiled threads if that’s what the man­ual spec­i­fies.

And what ex­actly is torque?

Torque is twist­ing force around a shaft. In the con­text of fas­ten­ers, the bolt, screw or stud is the shaft.when the amount of force ap­plied to the lever and its dis­tance of its end from the cen­tre of the fas­tener are mul­ti­plied, there’s your torque; dis­tance x force = torque.

Torque wrench types

The most ba­sic type of torque wrench and in­deed the cheap­est is the de­flec­tion beam type where the han­dle bends as pres­sure is ap­plied and a pointer aligns with a scale on the han­dle.then there are the ones where you pre­set the torque re­quired us­ing a mi­crom­e­ter type bar­rel. Once the de­sired torque is reached the wrench clicks and the ratchet mo­men­tar­ily lets go.there are also elec­tronic ones that beep when you hit op­ti­mum tight­ness.

Al­ways re­lease the spring pres­sure on a wrench where you pre­set the torque. Don’t use your torque wrench as a socket drive. For crit­i­cal ap­pli­ca­tion ac­cu­racy, some peo­ple have their torque wrenches prop­erly cal­i­brated. For our pur­poses this is need­less ex­pense. Most are only out by a few per­cent at the ex­treme ends of their ranges. Note that some torque wrenches have a marker on the han­dle where you should try to cen­tre the pres­sure you place upon it.

How much torque do I use?

This is dic­tated by the fas­tener size, its ma­te­rial, what it’s hold­ing to­gether or screw­ing into or onto and whether it’s com­press­ing a gas­ket or not.where a torque fig­ure is given, that’s the one you want to stick to.where there is a range of ac­cept­able torque, go with the num­ber in the mid­dle.

Be­fore get­ting the torque wrench out, fit the fas­ten­ers and get them handtight. Don’t

tighten one fully while leav­ing the oth­ers loose where you have more than one fas­tener se­cur­ing a com­po­nent, let’s say a cylin­der head for ex­am­ple.

Tighten evenly and work on di­ag­o­nal op­po­sites from the cen­tre out. Once a com­po­nent is handtight, break out the torque wrench, again stick­ing to the rule on di­ag­o­nal op­po­sites.

A bar­rel pre­set type torque wrench clicks or ‘lets go’ when the cor­rect torque is reached.there are two schools of thought on whether you should go around the fas­ten­ers with the torque wrench again af­ter it has clicked. Some say that to do so is to risk over­tight­en­ing, oth­ers say its a de­cent insurance pol­icy. In truth you will rarely find a fas­tener that takes fur­ther tight­en­ing with the torque wrench af­ter it’s been done once.

Un­less oth­er­wise stated, torque fig­ures given are for clean and dry threads in good con­di­tion.an oily bolt will be too tight or even snap if you use the dry torque fig­ure. Con­versely a rusty or dirty fas­tener or one with dam­aged threads will be too loose de­spite the torque wrench telling you it’s tight be­cause of the in­crease in fric­tion.

Ex­tend­ing your reach

Some­times you’ll need to use a crows foot or dog­bone ex­ten­sion to get onto a fas­tener. In these cases the fig­ure set on the wrench will no longer be the same as that ap­plied to the fas­tener.you have to do a lit­tle sum.

Mea­sure the nor­mal ef­fec­tive length of the wrench and the ex­tended ef­fec­tive length. Di­vide the first by the sec­ond (this will be less than one) then mul­ti­ply it by the de­sired torque to get the new fig­ure you should set the wrench to.

For ex­am­ple:you want 12Nm on a bolt. Your wrench’s nor­mal ef­fec­tive length is 300mm.the dog­bone adds an ef­fec­tive 80mm. 300 di­vided by 380 is 0.79. 12 mul­ti­plied by 0.79 is 9.48. So some­thing around 9.5Nm is what the wrench should be set to.

Windswept numpty in sleeve­less jerkin is here to help

Not a tricky tool to use. But a very nec­es­sary one

A torque wrench is re­ally no more than a big, ac­cu­rate span­ner

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.