head stud size?

[AlfredHitchcock]

Thanks for your help guys.

 

I will try counting the threads tomorrow and if its 13 tpi will buy a kit together with a long insert.

 

Whats pf wire Roger?

[RogerH]

If your stud hole is indeed a 1/2UNC helicoil tapped hole and is deeper than the deepest coil you can find then coils can be stacked.

 

I just had a play with some 3/8"UNF coils.

 

The tang in a blind hole can stay there, I would have thought, unless the bottom of the hole is a contact face.

 

Breaking the tang off is fun (I haven't a clue ). The insertion tool can't be used (as I first thought it could).

 

My kit has a flat ended prodder. I used this to push the tang downwards. I then used a piece of stiff wire with a hook on the end to pull it upwards.

To my surprise the tang broke off and I was left with a neat coil end. Long nosed pliers may help.

 

With a blind hole you would need to pull up first then push down etc.

Having put the first insert in I then inserted another coil. My first attemp had me winding the second coil OVER the top of the first - bad mistake.

 

Go #2 - I counted the threads above the inserted coil and wound the next coil down this distance minus 1/2 turn. I then gently edged the coil up to the lower coil.

When the tang was broken off there was apprx 1/3 circumference gap between the coils.

 

My test bolt ran perfectly down both coils - as it should do.

 

I'm sure a larger diameter hole would be easier as you can see the problems better.

 

So if you have a hole deeper than 3D then stacking the coils appears to work.

 

 

Carefully check your stud hole. What is the TPI - 13TPI = UNC 12TPI = BSW

 

If it coinicides with UNC 13TPI then your a lucky boy (had it got a BSW Helicoil why did the BSW stud not go in properly)

 

Obtain more coils than youn need and have a practice on some scrap material.

 

Roger

 

PS - you could PM Lord Flashart (Paul) in Canada as he did this early this year.

Edited August 1, 2013 by RogerH

[AlanT]

Now you know why I don't like Helicoils. Too easy to get in this mess.

 

This will probably wind up with a 14mm thread in it.

[RogerH]

I hope not.

 

If the hole is already tapped for the 1/2UNC helicoil then all should end well.

 

However if the hole needs more over sizing then anything could happen.

 

Roger

[AlanT]

Not much meat left in the wall is there!

 

Are the pictures showing two diferent holes? One looks to have not much thread depth, the other looks usable.

Maybe its just the light. Photos are difficult on this kind of stuff.

 

Not sure I buy this 12TPI stud thing. Measuring TPI without a gauge is confusing. Its the old fence-panels and posts thing.

Maybe the Helicoil thread cutting was poor some how. Knackered tap?

 

Then they find the stud wont go in so they shorten it. Getting a BSW stud from somewhere by accident seems unlikely.

Lots of Helicoil fixings I've come across dont let the bolt go to the end of the insert. Then they fail, then I see them.

[AlfredHitchcock]

Same hole Alan different zoom on my camera.

 

Does anyone have a 1/2 unc helicoil tap they can post me and I will gently try it in my hole please? I will of course pay postage and return it in same condition.

 

I'm working away atm so cant proceed with this but I intend to mark two graduations (inches apart) and count the tpi asap.

 

Thanks

 

Nick

[AlanT]

This is what you need:

 

http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=gauge%20thread&PN=DRAPER-30-Blade-4---42-tpi-UNF---UNC-Screwpitch-Gauge-Set-45440.html#SID=201

 

Al.

[BlueTR3A-5EKT]

Try one of the other (real) head studs in the thread that is visible. I know its the wrong diameter but the pitch is what we are concerned about. If it nestles snuggly the thing is tapped 13 tpi if it rocks it aint. Cheap version of a thread pitch gauge set.

Do the course threads of the real head studs snuggle nicely when placed against the rogue stud? If so it is 13 tpi.

 

Peter W

 

PS I too am watching this thread with great interest.

Edited August 1, 2013 by BlueTR3A-5EKT

[AlanT]

The gauges do a bit more than just measure pitch. In a good right you can see if the thread form is cut right.

 

This will help too:

 

http://www.chronos.ltd.uk/cgi-bin/sh000001.pl?WD=magnification&PN=Optical_Aids_and_Workshop_Lighting.html#aEYG_2e_2e

 

Sorry this is so expensive. Thet are good though.

Edited August 1, 2013 by AlanT

[AlfredHitchcock]

OK........I've tried my new long 1/2" unc tap, which has a threaded length of above 2 inches, and it seems to sit nicely all the way down the 4" deep stud hole. In fact I've held it gently against the side and screwed it down and it follows the thread to the bottom and locks itself.

 

Thinking positively I'm going to buy a kit and try to follow Rogers advice to stack the coils. I will report back on here of the outcome.

 

Thanks again guys for your help and advice. I hope I can reciprocate in some way in the future.

[AlanT]

Make sure to try the Helicoil tap in first.

 

If the previous guy did this with a worn out Helicoil set then the stud wont go in the Helicoils.

[AlfredHitchcock]

Make sure to try the Helicoil tap in first.

 

If the previous guy did this with a worn out Helicoil set then the stud wont go in the Helicoils.

Will do Alan

[AlanT]

One coil in. try the stud. Next coil in, try the stud etc.

 

By the way, how did you get the old Helicoil out?

[RogerH]

Good Luck Nick,

TRy and source a '3D' coil (3D = 3 x diameter = 1.5") That way you may only need one or two coils. The less coils the better.

 

Roger

[AlfredHitchcock]

 

By the way, how did you get the old Helicoil out?

I ran my 1/2" UNC tap down it until I came to what I now realise was the unbroken tang!

 

Thinking it was a lump of rusty gunk or something stuck to the wall I poked a screwdriver down and twisted back and forth to free it.

 

Eventually I ran a drill down what was left and it fell to pieces.

 

Now its all cleaned out along its 4" depth I think there was only ever one 1/2" helicoil holding the rogue bsw stud in!

 

Famous last words?

Edited August 2, 2013 by AlfredHitchcock

[AlanT]

Obviously this has been in the hands of a bodger. Now you must double-check everything.

 

There could easily be another helicoil down the bottom. Only proceed when you are utterly certain that the thread is clean and correct all the way down the hole.

 

I have a small torch with a right-angled light pipe:

 

http://www.professionalequipment.com/pelican-mitylite-2aaa-blue-mini-flashlight-1900-015-120/pelican-flashlights/

 

with this you can look down holes

[AlfredHitchcock]

Quick update for those interested.

 

Ive just returned from a weeks holiday and first job was to try the 1/2 unc helicoil tap from my new kit.

 

I'm mightily relieved to say it went all the way to the bottom of the hole without much persuasion .

 

Just need to clean the bottom out of the hole and wait for my new stud to get those coils in.

 

Thanks again for your help guys - I appreciate it.

[AlanT]

Thanks for the update . We have all been wondering how you got along with this.

[AlfredHitchcock]

Like I say.........two steps back.

 

Got the new stud today and what I didnt expect was only the bottom inch is threaded!!

 

The stud is 9" long and 4" stands above the block face, so 5" is in the block. My helicoil tap is only 4" long so I cant get to the bottom and theres some more **** in the bottom 1/2" of the hole! I cant cut the stud short because theres not enough threaded portion.

 

1) have I got the wrong stud?

 

2) if Ive got the right stud how can this fit a standard sized hole?

 

3) I think the next step for me is to get his stud threaded 3" more and cut the bottom inch off. I dont think its that hard so could run a 1/2" UNC die up it quite easily and get enough helicoils on.

 

What do you guys think to my plan C?

[AlanT]

Obviously check you got the right stud!

 

I considered the possibility of making some kind of extension for the Heicoil tap so you can get down another inch.

This might work but the risk is that something will go wrong and you will get the tap stuck in the hole.

I wouldn't take this risk myself.

 

So we are back to threading the stud, i'm afraid.

 

You dont need a whole 3in of thread on the stud. I'd guess your Helicoil inserts are 1/2in long.

Lets assume you need three of them. Two would do probably. Four if you like.

 

Lots of thread wont make it any stronger but will create extra work and increases the risk of the stud getting jammed halfway in.

 

So you need to run the thread up the new stud so that it stops at the point on the stud which will be about 2in

below the surface of the block when its fully home. Cut threads on head-studs are not ideal. Helicoils are not ideal either.

 

Ensure you cut the new thread exactly the same depth as the existing thread. Cut with soluble oil using lots of backing off.

Will take three or four passes gradually squeezing up the die.

 

I'd slacken the die as I came to the end of the thread so as to taper it outwards. The die is cut on the taper so will naturally leave the thread a bit like this anyway.

 

Try not to leave a sharp corner where the thread stops. I would bring the thread dead to size with a "chaser".

A thread restoring file would do. But you have to spin the stud to do this.

 

Then put your three Helicoils in down as far as they will go and screw the new stud through them.

Just be sure the Helicoils dont tighten up and you get everything jammed.

 

The depth of the hole makes this quite tricky!

 

Oh and dont put any marks on the shank of the stud when threading, like from your vice-jaws.

Wrap it with alloy sheet and put it in the vice jaws horizontally, if you can. Better still use a lathe chuck!

 

If you get trouble with the stud slipping whilst threading put nuts on the other end and "help" it with a spanner.

Edited August 17, 2013 by AlanT

[Motorsport Mickey]

It's bollocks...as stated previously if you do it will but a stress raiser on the stud which will likely cause it to fail in the near future.

 

If you need a longer threaded stud go to ARP and check what they can offer off their shelf, I'd be surprised if they haven't got a stud which will suit with a rolled thread which will give good service.

 

Tomorrow morning I'll check in my "get you out of jail" draw and see if the last person to use my extended tap set to thread the block at this size has returned it. The taps have had extensions welded to them to allow threading at the bottom of these stud holes from when I last drilled out and tapped broken studs from some blocks. If I have them they will be in the post to you Monday morning.

 

Mick Richards

 

Sorry, Alan beat me to the post, if you prefer to use his method no problem, I'll still check and if you want the taps posting I will.

 

Mick Richards

Edited August 17, 2013 by Motorsport Mickey

[Bob Smith]

If I have identified the correct stud from your description the stud 106960 should measure as follows:-

9.06" overall length

UNC threaded portion 1.06" long

UNF threaded portion 1.00" long

Slot length in UNC thread 1.19" long x 1/64"to 1/16" wide x 0.070" deep

Stud should have been made from the modern equivalent of EN16 material and heat treated.

Hope that helps

[AlfredHitchcock]

If I have identified the correct stud from your description the stud 106960 should measure as follows:-

9.06" overall length

UNC threaded portion 1.06" long

UNF threaded portion 1.00" long

Slot length in UNC thread 1.19" long x 1/64"to 1/16" wide x 0.070" deep

Stud should have been made from the modern equivalent of EN16 material and heat treated.

Hope that helps

 

Thanks Bob. That describes exactly what I have.

 

So a standard hole must only be 1/2" unc threaded in the bottom 1". I'm surprised by that.

 

Ive run a file over it and it doesnt seem that hard so I'm sure I could run a die up it.

 

Mick thanks very much for your offer however I'm resigned to the new stud from ARP or the easier route of threading and shortening. I'm a bit concerned though that you think it may introduce weak points.

 

Nick

[AlanT]

Mick is right. If he has a long Helicoil tap then use it!

 

Cut threads on these studs really aren't what you want.

 

I just didn't think you would be able to get such a thing easily.

 

If you do decide to do any thread cutting and shortening, do it at the other end.

From memory this is UNF not UNC.

 

If you strip the thread at the top-end then it will be easy to get the stud out and not much harm will occur.

Edited August 18, 2013 by AlanT

[RogerH]

STOP

Before you start cutting/filing/bending whatever why not remove the other 9" stud from the block and compare items. This is the middle stud on the offside.

See what the holes are like etc.

Is the newly exposed hole threaded ALL the way.

How much is threaded.

Does the new stud fit the middle hole.

 

Establish as much info as possible before you attack anything.

 

It is quite possible that the helicoils are much stronger than the original thread.

The Helicoil shear strength is greater and due to the shape there is a component of the pulling force of the stud actually moving sideways into the block forcing its position.

TRy and put back as much thread as has been damaged previously.

 

Roger