Advice on removing a broken Exhaust stud.

[RSW]

I know there are a range of previos posts on this topic but I daren't do anything until I've taken stock of my own situation which is:

The PO must have snapped an exhaust stud. When I've removed my Heat Ex's the nuts I removed came off fine (following some good advice) I noticed one of the barrel studs to be missing and I couldn't see the tip of any thread. I'd hoped the stud was missing completely but unfortunatly it was simply snapped about 1mm below the level of the case.

So, this in mind I'd planned to drill the case and some how try to recover the thread. I've read the range of previous posts in which people take about stud extractors etc.. but I've also heard they aren't that good.

How deep is the stud hole? Has anyone thought about liquid metal'ing the new stud in place?
Of all the option - what is the best to use? Or should I just leave it?

Any and all advice is gratefully recieved.

Thanks
Richard

[kristian85]

You may need to EDM (don't remember what it stands for) it as described in our gracious host's Fine Book 101 Projects--as a last resort. I guess they're very difficult to get out by other means.

[Rot 911]

Liquid metal is not going to work. I've drilled out several exhaust studs before. Here is what I did. First get a set of high quality titanium coated drill bits for drilling metal. Second, get a set of left hand (reverse) drill bits. Next, using a very good punch, make a dimple in the center of the broken stud. This will insure that the drill bit will not wander when you start drilling. Start off using the 1/8" drill bit. If you start off using a smaller bit, be prepared for said bit to break off creating an even bigger problem. Use 3in1 oil, or similar oil, for lubricant while drilling. Make sure you drill down straight! This is probably the most difficult part. The length of the stud in the case is approximately 1" so drill down about 3/4". Keep using progressively larger bits until you have most of the stud drilled out. Now take your reverse drill bit (make sure you have a drill that has a reverse, counter clockwise, switch on it )and drill out the rest of the stud. Why the reverse? More than likely, when you start to use the reverse bit it will back out the rest of the stud leaving you good threads in the case. If you end up drilling out the stud and threads in case, use a timecert when installing the new stud.

[Nickshu]

Kurt is right on. I've been there on this one, snapped 4 of mine even with heat.

I drilled them out and tapped them and then installed new studs.
I cannot remember how far in they went, but I bought replacement studs (my local Porsche dealer had them in stock) and measured the length of the threads as a reference for how deep to drill. The threads (for your tap size) are 8mmx1.25. I believe (check on this one) the corresponding drill size is a letter size H. I had to go to an aircraft supply store to find letter size drill bits. All of them drilled out fine.
Have and assistant help give you and eyeball to ensure you drill straight. Go slow and measure continuously, you'll get it.

Hope this helps,
Nick.

[RSW]

It does help - thanks very much.
I'll get a new stud to examine and work from there.

Two questions -
1 - what's a timecert ? Is it a helicoil?
2 - if I cut a new thread, surely I need a wider replacement stud? or am I tapping the remnants of the old stud?

thanks again
Richard

[Rot 911]

Timecerts are a hollow piece of metal with inner and outer threads. Helicoils are what the name says, a coil of metal. Timecerts hold better. Pelican sells them. And yes, if you drill out the threads you will have to drill a bigger hole in the case for the timecert. Not a big deal. Done all the time.

[Nickshu]

Yes if you are just tapping you ARE in fact not on the same threadpath of the original threads. I weighted the benefits/costs of just tapping it (remember it only holds 16-18 ft lbs, and its only 1 of 12 studs), or drilling a larger 10-12mm equivalent hole for a Timecert.

So far 1 1/2 years and no problems. Retorqued several times just to check.

Nick.

[RSW]

It sounds like it's got 2 chances.
I'll have a look for these "timecerts" they sound just the job.

Thanks for the advice - it doesn't sound quite such a problem when you hear the solution.
Do you heat the case at all when using the reverse drill bit? or is it a case of - if it's gonna come out it will do it anyway?

RIchard

[Targa Dude]

Make a Tool.. Use as a Guide to drill out your stud..
then you can either use a easy out or keep step drilling until can be removed.

Good luck, Jorge (Targa Dude)

[Targa Dude]

Something like this will work....

[Bobboloo]

RSW,

You keep refering to the case but an exhaust stud does not go into the case. It goes into the head.
Also, you seem ready to buy a timesert when you aren't there yet because if the stud is drilled out without incidence then no time sert is needed. That's the idea behind the reverse bit. It backs out the stud leaving your hopefully undamaged threads ready to accept the new stud.

Are you sure you want to attempt this alone? It's an easy job for a shop. Just a suggestion.

Bobby

[82SC]

oops...I think he called it a case cuz I mistakenly refered to it as a case...yes the stud is in your head...not case

search the archives...I could have sworn someone offering me their drill jig incase I broke one...I didn't...

but the guys on the board are so good about helping out with advice and tools...

good luck

[RSW]

Maybe I have steamed in a little quick with a time-sert, its just good to know there is a solution out there to the problem.

I've heard of the jig before, it's something worth considering if I take the job on. The problem with taking it to a workshop is that I've got the car in bits at the moment and to be fair I think it's something I could tackle (famous last words)

I do accept the stud is actually screwed into the head - the word case just seemed appropriate to use at the time.

I think I have a plan of attack for the job and these reverse drill bits are high on my list - i've actually heard of folks having fair success with these bits as they just draw the stud from the head as they get deeper in - fingers crossed eh!
It's good to know there are few others that have done the job before.

Thanks
Richard

[island911]

Again, having a small Tungsten Carbide Cutter (#9910~$9) added to the ubquidious Dremel tool and you have a quick and easy solution.

If you drill, it *will* be off center. Use a drill bit close to the size of the stud, and this "off-center" will put your drill into the threads of the head. --NOT good--
This is where having a Dremel tool really helps out. It allows you to drill a pilot hole as a starting point, and clear out the remaning part of the stud with the Carbide Cutter.

If you're careful and take your time, it may seem slow going; but, will be much faster than getting someone to EDM the thing, or fixing the mess if you drill into the threads of the head.

[RSW]

The advice on the Dremel is greatly appreciated, I haven't yet got one but I'm deffinaty going to get one. The tungston carbide drill bits sound just the ticket - I guess they will have no problem boring into the snapped stud?

Like you say the art is getting it as central as possible.
All this said - would it be worth trying a stud extractor if all goes well? Should I heat the head with a propane blow lamp when trying to remove the stud? or is it best not to given the material it is made from?

Thanks
Richard

[Roy M]

Richard - It's never happened to me but I sympathise with your plight. Personally I would go the drill route but have a jig made up to provide a central hole. By careful measurement and location you should be able to either make yourself or get made something suitable - if you make it for a pilot hole the progressively bigger sizes will follow its path.

Sorry if this is obvious but when I was in engineering I always puished for a jig - the apparent extra effort always paid off and you're dealing with relatively expensive kit (your head) if it goes wrong!!

Good Luck

[island911]

Originally posted by RSW
. . .- I guess they will have no problem boring into the snapped stud?

As long as it's not a diamond stud, you should be fine It helps if you use cutting oil/fluid.

. . - would it be worth trying a stud extractor if all goes well? ..

Stud extractors are great when they work, but are a pain when they too snap off in the hole. Then you have to deal with cutting THAT thing out. . .and they are hard (read; slow cutting) Also, most stud extractors (easly found) are the tapered type. The idea is you tap the thing into the hole and the tapered edges bite into the stud. What often happens though, is they get "tapped" too far in, causing what's left of the stud to flair out and bind --then the stud extractor breaks.

. . Should I heat the head with a propane blow lamp . ..

No need -- it will only complicate things.

On jigs: I too would push for a jig if it were to be used many times over . . .and I would push for a jig if the guys doing the work were River-Dancers.

[RSW]

I spoke to some engineers today who had a good tool which might help me.

It looked and worked very much like a pop rivet gun but it inserted small hollow cylinders of brass which had a thread inside them.
As the gun is squeezed the pull this cylinder in the same fashion as a rivet and the displaced (compressed) coller then holds the item in place.

This looked like an ideal solution to the problem if all else fails.
My only concern is that the compressed item may crack the head as it bites. It doesn't seem to snap anything off like a rivet gun does - you just squeaze untill its tight so the risk is slight but never the less.
The engineers say I wouldn't crack the head no mater how hard i squeazed and told me not to worry but you can't blame me being concerned.

These look to me like time-serts (infact that was what I was asking about when they showed me this tool).
Has anyone used these before? are they any good?

Thanks again for all the feedback, all the opinons and advice realy helps.

Richard

[biggtbiggt]

I have 4 broken studs that i am working on right now! I got 4 out easy and 4 with heat and broke 4. I will let ya know how I make out.

[RSW]

Yes - Please do.
What is your plan of attack?