Exhaust Studs Broken.., need suggestions. Options

[DougC]

OK, I have 3 broken exhaust studs on my 2.7 six. All but these three came out easily but these 3 were never going to move! I spray (for several days) with PB blaster, used a torch and nothing worked. Finally I bent one on purpose because I was at my wit's end and eventually broke it. I went ahead and cut the other two off in preparation for drilling. I have drilled out the originally broken one and tried using an "ease-out" but no luck (of course). I'm at the point where I can actually tap the hole for the original thread size. What size tap do I need to buy?

Doug C

[Joe Bob]

Don't know if the motor is out...but EDM works...some areas have guys that do it onsite. Drilling is a bitch.....

[Jake Raby]

Send them to Jerry's Broken drill and tap... Do a search for them...

Those guys have saved MANY pieces for me..

[dmenche914]

Go to the next biggest size EZ out if possible, if you drill on center, you should be able to drill just to the edge of hitting the threads, by then if should be lossened up enough.

what sized hole did you drill? What size EZ out are you using?

The correct hole (ie biggestt that will work)and EZ-out with a little heat ought to break about any stud out.

EZ out is the way to go, I have always had success with them on exhaust studs.

[lapuwali]

Conversely, I've never had ANY luck with an EZ out on any stud on the exhaust side of any engine. 100% failure rate here. I've resorted to EDM a couple of times, and drilled out and helicoil'd a couple of times. On the intake side of a couple of engines, I've been luckier and never even needed an EZ out. The stud usually just spun out on it's own, or succumbed to the "cut a slot and use a screwdriver" trick.

All the more reason I'm getting a stub-tubed header for my /4 ASAP...

[ArtechnikA]

go to Sears and get a set of these:
Screw-Ups(OK, they actually call them "screw-Outs and Drill-Out" but we all really understand...

left-handed hardened (carbide?) drill bit cores the stud, the left-hand spiral threads grab and extract.

911 exhaust studs are M8x1,25 (i think. might be M8x1,50. take one with you to the FLAPS to match...)

[DougC]

I've used the EZ-outs on other engines, hit or miss results. But will someone explain what EDM is? I've never heard of it. Oh, I did mean to mention that the heads are mounted to the engine, the engine is installed but there are no oil tubes in place. So I have fairly good access, all be it upside down on my back under the engine. Where to get heli-coils or time-certs, what size (stock and one spot larger than stock)?

Doug C

[DougC]

Rich thanks for the link, but man I'd like to accomplish this task without spending ANOTHER $70 (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif) . I know It would be an investment for the future but I have too many of these unexpected expenses already. With that said, I may have to get it anyway. Thanks.

Doug C

[Sammy]

Two ways to do it, one is electronic discharge machining as mentioned.
The other is to make a machining fixture that guides the drill perfectly.
A jig like that is darn near fool proof and even allows drilling out the broken stud with the engine in the car.
John Walker up in Washington does it that way, I think TRE in Hollywood does too.
The trick is to machine almost all of the bolt out getting as close to the root diameter as possible without going into the aluminium. Then it is just a matter of peeling the threads out of the hole with a pick or something.
Don't try it freehand or you may be in the market for a rebuilt head.

Might want to do a search on the pelican 911 technical board, maybe even post the question. There are several guys on that board who have done it correctly and successfully, they may even have a sketch of the jig. Lots of very experienced helpful folks over there. They may be able to save you a lot of money, time and aggravation.
Just don't mention anything about car wax, CWs, or small winkies. They don't like people who ask for advice and insult them at the same time.

[Sammy]

EDM (electronic discharge machining) is a process where an electrode is lowered into place slightly away from the broken bolt. An electronic charge like an arc is introduced, and the offending metal is blasted away. They usually have a stream of water directed onto the bolt also. Kind of a fancy air-arc system but much more controlled. Not something that can easily be done without taking the engine apart, plus it is labor intensive and the machinery isn't cheap, plan to spend at least $100 per bolt abd a minimum set up fee. that's at least what I pay at my shop, usually more.

[ArtechnikA]

if you happen to have (or borrow) a copy of Pelican Wayne's "101 Projects" book, he shows the process being done in-situ on a 911 at a shop. there are services that will do it onsite (at least in SoCal).

there *are* (or were...) "stepped studs" or "repair studs" that are M9 on one end and M8 on the other for exactly this application, but i had no luck actually finding them the last time i looked.

i understand your desire to have it done now, for no additional cost, but it has to be dealt with, and done right. it might cost a couple hundred bucks to have a qualified machine shop extract the studs. people *have* done this job in-place, from under the car, with a proper drill jig (i've seen them on the Birdie board too...) i'd think your chances of success would be better if you had the engine out, flipped over, working from the top on a rigid bench...

[DougC]

So, my idea of just buying the appropriate size tap and rethreading the hole isn't realistic? I've done this before (a long time ago) on a type 4 engine, although it was upside down on the floor. I have drilled the 1 hole already and it looks like I got it very straight, so now the tap wouldn't have a problem - would it? ...man anything not to have to flip this thing over or ship off for repairs. I'm doing this work solo. A tap and cutting oil were going to be my plan of action.

Doug C

[ArtechnikA]

QUOTE (DougC @ Aug 9 2005, 03:56 PM)

So, my idea of just buying the appropriate size tap and rethreading the hole isn't realistic?... I have drilled the 1 hole already and it looks like I got it very straight, so now the tap wouldn't have a problem - would it?

depends what you're trying to do, and what you've already done.

exactly how big is this "the" hole you've drilled?

was it a very small hole, contained entirely within the steel stud, which you were then able to remove?
if so, in that case, you should only need the thread to chase the original M8x1,25mm threads, right? and you'd be good to go.

or was it bigger? did you make a new, bigger hole in the aluminum head, completely oblitering the old hole?
if so - is the new bigger hole *exactly* concentric and coaxial with the original hole?

if you were going to tap it - what size? do you already have a new stud lined up?

or were you going to HeliCoil/TimeSert your new bigger hole and use an original style M8 stud?

all those ways are plausible and possible, but i've lost track of exactly where you are and what you've already done.

so - original clean 8mm threaded hole, or something bigger, and what's yor plan exactly ?

[DougC]

OK, here's what I've done so far:
-drilled out (but not completely) one stud. I say not completely becuase I haven't been able to see the original threads when looking inside the hole and a stock stud is slightly too big to fit into this new hole. Also, the EZ-out that I've been trying to use won't budge anything.

By reading that one might think I just haven't drilled a hole large enough to see the stock threads yet, but it sure seems like if I go any bigger I'll have to use a larger stud.

I thought at this point I could just try tapping the hole since I'm already at a point that is close to the stock stud size.. Hell I might have already drilled away the stock threads but I don't think so. The inside of the hole just looks like smooth metal, and I've kept a close eye on it and went slowly.

Doug C

[DougC]

Rich, you asked me what size hole have I drilled and I actually didn't even look at the bit to see (last night). I wonder what the maximum size bit would be before you reached the (orig) threads? Thanks as usuall.

Doug C

[TimT]

As has been mentinioned, left hand drill bits are your friend.

I dont have pics to show, but on a 911 I owned years ago, a p/o had broke an exhaust stud, then broke the easy out. So the PO's repair was to sister the remains of the original stud with another stud, then he cut a slot in the exhaust flange and used a large fender washer to capture the flange..

This IS NOT THE WAY TO FIX THIS

What I ended up doing was having the head put in a mill, and had a 3/8 or so mill plunged into the head. I then took a bottoming tap and tapped the hole, then threaded a slug into the hole..

After I reassembled the engine bolted up the exhaust, and drilled and tapped my repaired head.

So I ended up saving a potentially ruined head.

If youve already drilled the stud out to almost take a tap, get some letter or number drills, and you will be able to gradually open the hole up until the exact size for the tap..

[ArtechnikA]

QUOTE (DougC @ Aug 9 2005, 04:34 PM)

I thought at this point I could just try tapping the hole since I'm already at a point that is close to the stock stud size.. ... The inside of the hole just looks like smooth metal

ok, cool.

first - another question, no response required:
smooth *what kind* of metal? does it look like you are looking at a steel sleeve, or an aluminum hole. i can't describe the difference in metal colors but i know you can see it...

if you're *sure* you've simply cored the steel, a left-handed drill - possibly operated by hand - might just grab the remains and pull them out. once the middle of a threaded fastener is removed there's nothing to tension the threads... or pretty gently, use a screw extractor. NOT a square "EZ-out" - those are pretty useless. screw extractors look like left-hand threaded VERY coarse spiral auger bits, and they're somewhat conical. those should grab the core and let you extract it without wedging it in harder like the square ones do.

or you can try gently running in a tap. with luck, you'll simply cut away the steel bits still left in the original threads.

the fact that an 8mm stud won't slip into the hole you've made is a good sign.

[TimT]

also get some pics( like dental pics), and make a good sharp point on them, you may be able to start pulling the remains of the original stud out of the head.

[DougC]

Hey guys those sound like great suggestions. The EZ-out that I was using last night did seem to wedge the thing more than help in any way, so I need to find some of those left hand bits that were mentioned..maybe I need to stop by Sears this evening and price that kit (above) too. Thanks again!

Doug C

[Jake Raby]

Just make sure that you don't snap off the EZE out. They are super hard and no drill bit will touch them.