Exhaust Studs

I am currenly replacing my heat exchangers on my 1987 930, I snapped 2 exhaust studs; what is the proper procedure to remove the protruding studs?
Iyad

I snapped an inner stud off of cyl #5. There was about a 1/2" showing. I borrowed a collet-type stud-remover made by Snap-on. It comes with a set of inserts. Using the M8x1.25 insert, you screw it onto the remaining threads and then tighten down the collar. I also heat-cycled the stud several times with a propane torch and then soaked with PB-Blaster. Used the stud-remover in the same way as trying to remove the original studs: tighten first, then loosen.

If you break an outside stud, the Snap-on tool won't work because the head is in the way. You would have to weld a nut onto the end of stud, or drill it out and insert a Time-Sert.

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Greg
72 911S

I don't know about the "proper" precedure but when I do the same thing I always have to drill them out (carefully) and use a stud remover. So far, I've always been lucky that I didn't have to add the Time-serts --- I get away with just tapping the threads til they're clean then add a new stud --- Pelican can get them for you.

In fact, in a few weeks I've got to get behind my heat exchangers to fix some oil leaks and while I'm in there I'm gonna be replacing all 12 of mine just for the heck (agony) of it cause they're all rusted. I expect to break more than one so I'm ready to use my "usual" method. But I'll have them both removed which makes working on it a lot easier than with them still on.

Ggalloway's method above is a bit more detailed than my description here --- but is essentially what I do.

[This message has been edited by tog (edited 11-09-2000).]

Got a tip for you. The 'easy out' stud remover your normally see for sale is not a good idea. This is a tool which looks a little like an arrow head. You drill a pilot hole and insert this thing, which has kind of reversed threads. It grabs the stud and backs it out.

The real tool to use if you have a stud that is broken off flush so you can't get another tool (or nut) on it, is also Snap-On. The Snap-On stud extractor is more blunt at the business end and I believe it has a hex end at the other end. Again, you drill a pilot hole (this is the critical part, take your time!!!!!!!!!!!!!), insert the tool and back out the stud.

Here's the really tough part: the stud you're trying to remove (and drill) is MUCH, MUCH harder than the aluminum case it is stuck in. It is VERY easy to mess up this aluminum case during the drilling process. Take your time and good luck.

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'83 SC

Maybe I'm asking a question to which the answer is obvious once I get started, but everyone advocates heating up the studs prior to any attempt to remove the nuts. My question is how do you get at the ones that you have to use the long allen wrench thru the heat exchanger? Can a propane torch reach them from the side?

On those thru-the-exchanger nuts/studs...

Personally, I wouldn't use a torch on something that I didn't have clear access to. Seems to me that if you set fire to excess old oil or similar you'd have a heck of a time trying to put it out at that point. If I couldn't get the nuts off successfully (stripped?) I'd doing anything but try to use a torch in there including cutting or breaking the bolt/stud and then fix when I could clearly access them to replace the stud. I might use the torch at that point on the studs.

There is at least a 1/2" gap between the sheetmetal of the heat exchangers and the Barrel or Allen nut ... and certainly enough room to get access to the area with propane or oxy-acetylene 'rosebud' tip, from both outboard or inboard ... but if you enjoy drilling ... take whatever chances you want!

And, there is NO official procedure for removing broken exhaust studs, but most experts like Bruce Anderson recommend EDM machining of studs broken flush with the mating surface. But, removal of the cylinder head from the engine is required to do that 'proper' method!

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Warren Hall
1973 911S Targa

Warren is still providing excellent hints. Please do everything in your power to avoid broken studs and the drilling that usually follows. Penetrant, like Matlby's Penetrating Oil (the best) works only so good. Heat is your best bet.

Warren gave an excellent brief description months ago of this process. Use oxy-acetylene as propane is simply not hot enough. Sorry, it just isn't.

Get the fastener CHERRY RED using the 'rosebud' tip. put the tool on it, tighten just slightly, then back it off gently, slowly, firmly, evenly. If it still breaks, you did everything you could do.

And yes, if you take your engine apart and take the pieces to a machine shop they will drill out the broken ones nicely. but if you're careful, you can do this at home witout removing the engine. Just be sure the drill bit never touches the case. Use a HARD awl punch to dimple the stud so you can get the drill bit started. I use reverse operating drill bits. they drill counterclockwise and sometimes they extract the screw nicely, without the special extractor.

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'83 SC

I followed Warren's advice to the letter and only broke one stud. It was the forth one I tried to get off. The other three came off so easily that I got over confident and didn't spend as much time heat cycling that stud as I did the rest. Lesson: Take your time. Heat cycle each stud several times. You can indeed get a torch on all of them.

After getting them off I had difficulting getting the new SSI's back on. I ended up calling the owner of SSI, John. Here is his advice:

The new SSI design does not have a pass-through hole on cyl #5 so you cannot use any barrel nuts on that cyl. You will need a total of 5 barrel nuts and 7 copper nuts. Unfortunately most vendors don't seem to know this yet so they sell you 6 of each. As a result, one of my cyl's has a plain old zinc-plated nut on one of the studs. The original nuts required a 13mm wrench. The new copper nuts require a 12mm. SSI includes a special 12mm wrench which John only intends you to use on the inner stud of cyl #5 (the one w/ the missing pass-through hole). On all of the other studs which require a copper nut he recommended using a low-profile 12mm pivoting socket w/ 1/4" drive, a long 1/4" extension, and a 3/8"-1/4" adapter for your torque wrench. He bought his socket for about $30 from Snap-On. I was able to find a 12 and a 13mm at Sears for about $7 each. They work great. You should definitely buy the 13mm socket to help get the old exchangers off, and the 12mm to get the new ones on. I was able to get by with a cheap 13mm flex wrench, but the low-profile pivoting sockets work much, much better. After getting the right tools, the new SSI's went on in about 15 minutes.

As far as replacing the studs... I had to replace 5 studs. One had broke and 4 had come out with the nuts. I bought a 8mmx1.25 tap and used it to chase the existing holes before installing the new studs. I was able to find studs at a local Ace hardware that worked fine.

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Greg
72 911S

If you haven't much experience drilling out studs like these then Warren and Superman are probably right that heating the studs is your better bet. (I don't have any oxy-acetylene and the engines I've worked on usually have too thick a layer of gook and not enough room to make me comfortable.) To drill out studs anywhere takes a real steady hand not to "wander". I've been doing it my way so long that I never "miss" even laying on my back with a hand drill, but, you need lots of this kind of practice or you probably will "miss" --- so go the heat route if you can unless they break too short to get a hold of. Then when you must drill out, my method is to stage the drill bit sizes --- using smaller ones first to make sure I'm centered then larger ones to make enough room for the extractor.... etc