Washers

[mgjParticipant @mgj]

Chris – for a proper job into ali you use a helicoil.

 

I agree about stainless on exhausts, but graphite powder is good – if messy!

 

I remember someone once forgot to tighten the gun lug nut on a 76 in a Scorpion. No it didn’t come undone, but the shock effect due to slackness introduced a fatigue effect.  with the result that on the last firing the gun sheared the recoil buffer. It stopped in the radios (the gun, not the recoil buffer, which was I suppose much of the problem). Caused a certain amount of alarm – difficult to find out exactly hat was happening too, because flat radios don’t work too well. Not that the crew hung about overmuch to explain.

 

Moral – tighten nuts up correctly, especially if they are of the Jesus variety.

Edited By meyrick griffith-jones on 14/12/2009 18:16:53

[chris stephensParticipant @chrisstephens63393]

Hi Meyrick, 

At last something we can disagree about, Helicoils are an abomination and should only be used as a last resort. I do speak from some experience in the matter, lost count of the hundreds that i fitted. The blurb makes them sound fine but every single one I fitted had to be modified so the the fitting tag would break off cleanly, if it doesn’t and the screw should go deeper than the coil, it jams and unscrews with the screw, which it bu**gers by the way. This can be a  problem with spark plug threads, where the coil can be forced further into the thread than desired and might cause pre-ignition by the “hot wire method”, if not trimmed properly in the combustion chamber. The first coil can also put out and cause a jam. 

There is a much better thread repair outfit made or at least marketed by Wurth. This does not use a coil but a  threaded tube, where the male and female threads form a corrugation. They also have an unthreaded ridge at the top which fits into a recess, this stops the insert going deeper. At the bottom of the threaded part there is area that is designed to deform into the base thread, which acts as a locking device to prevent the inset unscrewing, which is  a Helicoil problem even if the tag has broken off cleanly.

Graphite powder, I have suspicions that it wont stop the two parts corroding together in the hostile environment of an exhaust manifold. It does though make a truly excellent lock lubrication, my front door lock, a 54 year old Yale, was getting difficult to get the key in, so I puffed it with graphite, now as smooth as silk.

chriStephens

PS You might say that any problems with Helicoils are the fitters fault and you might be correct, but with all due modesty, if I can’t fit one properly what chance does a ham fisted grease monkey stand. No insult to the ham fisted grease monkey intended or implied.

[CirclipParticipant @circlip]

C’mon guys, when you start “Use Stainless” qualify which GRADE you are advocating, not all Stainlesses stay bright and shiny, H/T types rust like bu**ery.

 

  Had one or two Helicoils that didn’t go in properly Chris but in the main, I’ve never had hassle. Did ALL the threaded holes in me mates Chiwanese wood turning lathe (Soft Iron), most of the Metrics in me Guzzi (Alloy only slightly better than Riceburner products, probably used Bud cans) camshaft clamping bolt threads in bottom of VW Beetle heads and various rescues. Perhaps I’ve been lucky??

 

  Copperslip?? Lurv it, again perhaps lucky.

 

  Regards  Ian

[Ian S CParticipant @iansc]

Fitted dozens of Helicoils for exhaust studs on Continental O-470 and IO-470 and IO-520 the main types that I overhauled and inspected.Read a wee while ago of a Kiwi chap who stripped the plug thread on his ultralite,so he put,or had fitted a helicoil,shortly after a major engine failure,instead of fitting a bronze insert he fitted stainless,with reduced heat conduction the sparkplug went into melt-down.Ian S C

[chris stephensParticipant @chrisstephens63393]

Hi Circlip,

DIN933 A2/70 (304) the common or garden variety commercial grade fasteners will do a better job than standard mild steel in an exhaust pipe to manifold situation, as far as rusting is concerned. Copaslip works better on stainless, where it helps to stop galling. On mild steel it does not prevent the rusting, which makes the two components stick together. I do use the stuff on the exhaust rings on my BMWs, but then both head and ring are Aluminium alloy, again to stop any galling. 

Have you too noticed that Chinese tapped holes seem a little “Slack”!

Hi Ian SC,

I assume on your aero engines that they use studs in the manifold/head and have nuts to hold the pipe on. Helicoils will work better with this arrangement. They don’t work as well in a situation where a bolt or screw goes directly into a casting. The problem is the way the fitting tag, which is designed to break off once the coil is inserted, fails to break cleanly. With a stud application this flaw will help to lock in the said stud. 

You can specify which coil length you want, the standard one is 1 1/2 times diameter, but the holes they have to go in  may be restricted for length. If you wind the coil in too far , then you have the problem of the coil closing in on the screw due to the lead in on the tap.

I suppose in summery in the real world as opposed to an ideal situation, that they work best where the screwed part is meant to remain in place  They will work, but  less well, where the components have to be regularly unscrewed. 

chriStephens

[Ian S CParticipant @iansc]

Yes Chris Thats the general picture.When inserting Helicoils there are two different finishing taps,one gives a class3 fit for standard bolts,the other gives a class4 (tight) fit for standard studs.Before we fitted Helicoils there were three different over sizes for the studs.The inserting tool prevented the insert being put in too far.The coils had a Continental part number.They can be the means of saving some very expensive parts.We’re getting a wee bit off course from washers.I was looking in a home built aircraft site,and they recomend a plain washer under the bolt head and the nut,and if in doubt use slotted nuts and split pins.Ian S C

[mgjParticipant @mgj]

When I said helicoils, I used the term like we use “hoover”. Any of the good grade inserts. Granted in some applications like aircraft the manufacturer will specify which one, but for most applications, any insert is better than none.

 

Grovelling apologies.

Exhausts – that graphite coated yarn stuff. Pretty good but messy. Now I’d use marine grade SS. Like Circlip says, its not the highest of HT, but it stays shiny and its very good for such non critical applications.

 

As for studs and dowels. Make sure you use 2 for location and they are of uneven length and longer than all the rest. That way you can get the component over one, over the other, and then it’ll drop on. Same length dowels are a PITA. Or is that a hint and tip. 

Edited By meyrick griffith-jones on 16/12/2009 10:38:18

Edited By meyrick griffith-jones on 16/12/2009 10:41:49

[CirclipParticipant @circlip]

Sorry, when I said Helicoils, I meant the ones made by Armstrong Patents G-E-N-U-I-N-E Helicoils.

 

  For Non rusting S/S you can also use A4 or if you want to go REALLY OTT Titani– Oh, not again

 

  Regards  Ian.

[chris stephensParticipant @chrisstephens63393]

Hi Circlip,

I was talking about Gen-u-ine Armstrong Helicoils. The other make (whose name I forgot, could even have been an up-grade of Armstrong’s) have a much better inserting tool. This tool completely prevents the coil cross threading as it goes in, but we always used the real coils.

Re your last sentence, why did you ask earlier which grade “Stainless” if you already knew the answer? Or were you just testing? Shame on you.

All the best.

chriStephens

[CirclipParticipant @circlip]

L’s bells, you getting paranoid??

 

  No, you know and I know and I know you know and I know you know that I know BUT some out there might not as Stainless to many is just that, bright an shiney so WE need to edificate as Frank stated earlier, an it costs bu**er all to qualify, RIGHT!

 

  Hope you’re getting plenty of mince pies.

 

  Regards  Ian.

[chris stephensParticipant @chrisstephens63393]

Hi Ian SC,

With the standard Helicoil kits you only get the one tap. What you have is clearly an engine manufacturers repair kit, with far higher specs than us poor grease monkeys had to play with.

Do you, or anyone else for that matter, think it odd that you wire nuts onto studs but the studs you wire nuts to are just screwed in. Bolts are wired in, if they are screwed into castings, to stop them coming undone, so what makes a stud and nut different from a bolt? 

chriStephens

PS just checked and they still only supply one tap per size.  H*ly Sh*t they are expensive and they don;t supply the superior inserting tool. If you want to make your own all you need is a bolt of the right size and a file and about three minutes of spare time.

[jonkettParticipant @jonkett]

Armstrong were the UK agents and manufacturers for for helicoil, this is no longer the case, so they make there own version.

 

Regards

John K

 

Consistency is the last resort of the unimaginative.

[Ian S CParticipant @iansc]

Chris,we only used the Class 4 tap as it was usualy only the exhaust that gave problems,ie broken studs,first get it out,the method to try first,splined type stud remover(Snap On Tools),these I find work better than easy outs(tapered LH threaded),if that does’t work drill to root dia-tapping size,pick the thread out check the thread OK,remedy if required,either oversize studs or Helicoil.With the supplied tap the stud was a nice tight fit.I’d have thought that auto engine overhaul shops might have close tollerence taps for fitting studs.Ian S C The nuts exhaust and inlet are brass,and squeak as you tighten them.

[Gordon WParticipant @gordonw]

I drive a 2CV as a daily driver, there I’ve said it, Copaslip is very good stopping corrosion under bonnet, even exaust nuts, which are copper plated. This like anything else washes off when exposed to weather, but the nuts are still protected, so we should protect the exposed thread, with tape or sim. On ex. systems I usually expect to cut them off, cheaper in the long run.

[Raymond AscroftParticipant @raymondascroft71629]

Hi Guys

 

To prevent damage when assembling parts made of anodised aluminium etc. with hex bolts where the corners of the hex digs in to part and damages the finish an alternative to washers is to turn a 15 degs chamfer to about .01″ below the a/f size on the mating face of the bolt head or instead to turn a washer face again .01″ below a/f size x .015″ deep. An areospace solution to prevent galling with combination of stainless nuts & bolts is to silver plate the male thread.

 

Merry Christmas

 

Ray

[Frank DolmanParticipant @frankdolman72357]

     I follow the chamfering Raymond but not, I’m afraid, the silver plating.

  Could you please expand a bit.

[Mark Smith 3Participant @marksmith3]

Gordon, You poor bugger…2cv? I drive a VW kombi I must be as sick as you.

Mark

[Ian S CParticipant @iansc]

Wish I had a 2cv or a vw used to have a fiat 500 Bambina but I’m stuck with a bike.Ian S C

[Gordon WParticipant @gordonw]

Only mentioned the 2cv to demonstrate my knowedge of corrosion, also had a 500 Fiat,didn’t get chance to stop that corroding. But mine is only thing moving in snowy N Scoland at the moment, sprayed underneath with old oil just last week.

[Ian S CParticipant @iansc]

My 500 didn’t rust,it blew away!!But it handled the snow as if it wasn’t there.Ian S C

[Frank DolmanParticipant @frankdolman72357]

        Don’t bother, Raymond.  I see it now, it’s just dissimilar metals. You

    must understand, I am a bit thick as well as knowing very little.

                                                   Regards
       

[Author]

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