Don’t cry over Stripped threads

We’ve all done it but wreck­ing a thread doesn’t need to be a costly disaster

Motorcycle News (UK) - - This Week -

Stripped? Don’t flip 1

There’s noth­ing worse than tight­en­ing a bolt and feel­ing it get­ting looser. When steel bolts go into al­loy threads, it’s of­ten the al­loy that fails. But it doesn’t mean disaster – stop, re­move the bolt and assess the dam­age. If the alu­minium threads have failed they of­ten stick to the bolt. Firstly, make sure the bolt is the cor­rect one by check­ing the threads are the right pitch and the bolt is the right length.

File away the de­cay 2

You can clean up the bolt us­ing a thread file (th­ese can be bought from any good tool shop for around £15). A thread file usu­ally has a choice of eight pitches, four on each end. With the cor­rect pitch se­lected, place the bolt in a vice and slowly draw the file across the threads, each stroke clears and re­vives the threads. You need to turn the bolt in the vice one bit at a time un­til all of the threads are clear.

Tap into fixed threads 3

When try­ing to re­vive dam­aged al­loy threads you should only con­sider it a tem­po­rary fix; the fact that some of the thread ma­te­rial has al­ready been lost by trans­fer­ring to the bolt sug­gests the over­all strength of the fas­ten­ing has been com­pro­mised. Be­fore you start, blast away de­bris us­ing an air­line or aerosol cleaner, then use a ‘chaser’ or ‘form­ing’ tap to re­vive the threads.

Flirt with an in­sert 4

An in­sert kit is a worth­while pur­chase if you’re re­pair­ing dam­aged threads. The kit re­places the orig­i­nal threads with a threaded steel in­sert, and com­prises a drill bit, shoul­der cut­ting tool, tap, form­ing tap, and se­lec­tion of in­serts in var­i­ous sizes. In many cases the steel in­sert pro­vides a su­pe­rior fas­ten­ing than the orig­i­nal al­loy threads.

Get some shoul­der room 6

The in­sert has a shoul­der at the top, this pre­vents it from be­ing over-tight­ened and sink­ing to the bot­tom of the hole. But first you need to cut some space fit for the shoul­der and for that you’ll need the shoul­der cut­ting tool. The tool is used in con­junc­tion with a tap wrench, and the shoul­der needs to be cut flush or slightly lower than the sur­face.

In­sert for strength 8

Next, screw the in­sert on to the form­ing tap. Ap­ply a per­ma­nent thread lock such as Loc­tite to the hole and wind the in­sert into the new threads us­ing the tap wrench. The form­ing die will start to give a bit of re­sis­tance as the in­sert’s shoul­der tight­ens against the sur­face. Keep wind­ing the tap in and it will press the threads on the ex­te­rior of the in­sert into the al­loy threads of the hole.

Drill be­fore you fill 5

First, you need to drill out the worn threads us­ing the drill bit in the in­sert kit. The hole needs to be over­size in or­der to both drill out the old threads and ac­com­mo­date the steel in­sert. Make sure the hole is at least as deep as the in­sert. Ide­ally you need to drill a bit deeper so the form­ing tap can run through the in­sert.

Cut some new threads 7

With the tap in the tap wrench, start to cut new threads in the al­loy us­ing a cut­ting fluid or light oil to help lu­bri­cate things as you go. It’s im­por­tant to make sure the tap is per­fectly level. Work the tap back­wards and for­wards pro­gres­sively, clean­ing out swarf as needed. The new threads need to be a lit­tle deeper than the length of the in­sert.

Re­paired and ready for use 9

With the in­sert now in place the hole is fixed and ready to take a bolt. Ide­ally you should use a new bolt with a bit of light oil or grease ap­plied. This will not only pre­vent cor­ro­sion, but will also give bet­ter feel when you torque up the bolt. If the new in­sert is a re­pair on a com­po­nent that has many fas­ten­ers, check the work­shop man­ual for spe­cific tight­en­ing se­quences and torque val­ues.

Newspapers in English

Newspapers from UK

© PressReader. All rights reserved.