Drilling out front header studs.....

978 Views 13 Replies 8 Participants Last post by stu_m, Oct 13, 2013

RichTLR

Discussion Starter · Oct 12, 2013

Mine have snapped, tried the mig weld a nut on fix to no avail, last resort now is grind them flush and drill them out. My question is - how deep are the threads in the head? I obviously don't want to drill too deep and buy a new head lol

Waiting for replies with drill in hand...

Rich

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The Chairman

· #2 · Oct 12, 2013

I'm guessing if you are doing this, you have replacement studs to put in. So all you need do is measure those to determine the depth.

Make sure you are using split point drill bits, so that they don't wander and help you to drill straight. Centre punch the stud before drilling, small pilot drill a few mm first.

Good luck!

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Angrywasp

· #3 · Oct 12, 2013

Use a small bit to drill out a pilot hole. The bolts don't go all the way to the head. There is a gap at the end of the bolt.

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Six5

· #4 · Oct 12, 2013

The exhaust bolt holes in the head are 24mm deep.

When you get the broken piece removed, replace them with stainless studs and brass nuts. This combination is much less likely to give you problems in the future. I used an 8 x 40mm stud.

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Rickysnicker

· #5 · Oct 12, 2013

Six, I'm just curious why you use brass and not stainless steel nuts?

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stu_m

· #6 · Oct 12, 2013

Rickysnicker said:
Six, I'm just curious why you use brass and not stainless steel nuts?

brass doesn't rust like other nuts

also I recon with them been the softer part its the nuts that will just snap off leaving the rest still useable

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The Ring-In

· #7 · Oct 12, 2013

if the mig didn't work then try a stick welder before you drill

use a much bigger nut

something with a 1/2 thread and hold it over the stub.

ive even built up stubs below the surface then welded the nut onto that.

let the heat out of the weld before you start to turn and turn back and forth in tiny movements as you go to break the scum off the threads.

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rushy

· #8 · Oct 12, 2013

this post by Sam seems a good option

http://www.tlzone.net/forums/frequent-tl-mods/126428-repairing-broken-exhaust-studs-bolts.html

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Six5

· #9 · Oct 12, 2013

Rickysnicker said:
Six, I'm just curious why you use brass and not stainless steel nuts?

See below.....

stu_m said:
brass doesn't rust like other nuts

also I recon with them been the softer part its the nuts that will just snap off leaving the rest still useable

Stu_m lists a couple good points to keep in mind, although a stainless stud shouldn't rust (unless you live in the UK :laugh). Also, some stainless steels can be rather "soft," so if it came down to one metal giving way to the other...:confused.... I can't say, because I don't know enough about it.

I'm not a metallurgist, but from what I've read so far, in the case of a stainless steel nut on a stainless steel stud, there is a great potential for galling to occur - especially in a high temperature, high vibration environment. The dissimilar metals (stainless and brass) prevent the galling issue.

I found this on an Alfa Romeo forum, and it encouraged me to look a little further. I'm not saying they are authorities on the subject, but if they are able to keep old Italian cars running, they are bound to have learned a few things along the way. :laugh

I would strongly discourage you from using stainless for both the nuts and bolts. Stainless bolts with brass nuts would be OK, and of course, conventional steel bolts & brass nuts like the factory used are fine.

When exposed to heat, stainless against stainless tends to "gall" (whatever that is - maybe some metallurgist can chime in). The long and short of it is that it will be impossible to remove the stainless nut from the stainless bolt after exposure to heat.

A little more surfing turned up this document from a somewhat authoritative source.

http://www.fastenal.com/content/feds/pdf/Article - Galling.pdf

While there is a potential for galvanic reaction between brass and stainless (certain types of SS more than others), it appears that the primary reason for using this metal combination on an exhaust stud application is to prevent galling. When it comes time to disassemble the parts, it is all nice and easy. No more broken bolts.

Stu (The Ring-In) has long recommended the brass nuts on exhaust studs, so I'm sure none of this is news to him. As for me, today I learned something. :coocoo

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The Ring-In

· #10 · Oct 12, 2013

cheers 6

I make the brass nuts at twice the bolt diameter

I also finish them with a solid carbide tap.

optimum torque to thread strength is achieved at 1.5 times thread diameter / length

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The Ring-In

· #11 · Oct 12, 2013

I use stainless for the studs because it resists degrading in the heat and hostile exposed environment.

and brass cos it wont gall onto the stainless.

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Rickysnicker

· #12 · Oct 12, 2013

Six5 said:
http://www.fastenal.com/content/feds/pdf/Article - Galling.pdf

As for me, today I learned something. :coocoo

So did I thank you!

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RichTLR

Discussion Starter · #13 · Oct 13, 2013

Thanks for all the advice, all drilled out and threads cleaned up ready for some stainless threaded bar that I'll get this week. Very, very nervy when I was drilling but it turned out ok

Thanks again guys

Rich

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stu_m

· #14 · Oct 13, 2013

I think I may do this while the engine is out over the winter just to save any future problems

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