Last week I got the bad news....

[Chris79SC]

Had my 3.0 SC in my mechanic's shop to replace the stock exhaust system with a SSI/Dansk setup and we found a broken headstud. Talk about going from one extreme to another! One minute I'm anticipating an upgraded 911, next minute I'm comptemplating being out of the car for the next month.

SRC="http://www.pelicanparts.com/ultimate/image_uploads/headstud.jpg">


After reading all of the posts from Leland & others recently, I've certainly gotten much more up-to-speed with what's involved. My deepest thanks to all of the posters on this board.

My car has 270,000 miles on it, & a rebuild was done @ 165,000 (PO was my older brother who's now a Boxter S owner).

Prior to finding out this problem I had mistakenly assumed the noise I was hearing with the car at idle was an exhaust leak. Other than that, the car was recently backfiring & hesitating a bit when I was accelerating hard (100+ mph) but wasn't exhibiting any abnormal condition during regular driving (85mph). No real oil leaks to speak of...pretty much runs reliably & strong.

I'm leaning towards rebuilding the engine again, (1) since it has to be dropped to fix the headstud problem anyway, and (2) it has turned 105,000 miles since the last one. Its a little earlier than I would have choosen to do anything with the engine, but I'm looking at a top-end as a preventative measure with the car going on 22 years & over 100k mi. on this engine.

I guess the 3 questions I'm asking of you guys are:

1. Does the idea to rebuild again seem reasonable to you, or do you think I'm going a bit overboard...that its only been 100k & I should only fix the headstud problem?


2. If I rebuild, should I look to upgrade? Possibly bore the cylinders, JE pistons, & 964 profile the cams?


3. What's the feeling about JE pistons? Are they noisy?

[needlevalve]

Chris, sorry to hear about the head stud. Were they replaced during last rebuild? Your engine is going to be torn down anyway to repair the stud so all worn internal parts should be replaced while at it. As far as upgrading pistons etc. if you've got some extra bucks kicking around...why not!

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Matt Macpherson
1975 911 S
nvalve@yahoo.com

[Superman]

I'd agree with Matt. You will have the engine apart. You should at a minimum have a look at everything to see if the parts are all in good shape. Certainly replace parts that are not in good shape.

Upgrading parts that are still okay is another option. You might decide, before you even look, that you will replace everything with new. New P&Cs, new valves, etc. regardless of whether they are worn out.

At some point I will build a performance motor, and so I'll be choosing option #2. Right now I have a broken head stud as well and I plan to deal with it using option #1.

For example, someone might recommend that valves simply be replaced. But I am not finding a lot of wear on most of my valve guides, so I may feel that most valves are good to reuse. It's a judgment call.

I figure hey, it's a motor. Sometimes things wear out in motors, but all motors are running on used parts. And they're just parts.

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'83 SC

[pacmyster]

[Chris79SC]

Thanks Pac - You can see the broken stud in teh opening above the cover.

Yeah guys I'm pretty much already resigned to tearing it down for a rebuild. I guess after reading all of the info posted here, I was wondering about going to JE pistons and moving up to a 3.2L displacement. I wouldn't do it if their noiser, but I'm hunting for anybody that has 1st hand experience with them, or at least has heard an engine with JE's in it.

Anybody out there?

[Early_S_Man]

Chris,

Are you contemplating just replacing the bottom row of head studs as what you call the 'just fix the broken head stud' or are you argueing top-end refresh, i.e., valve guides and grind vs complete tear-down as the 'rebuild' option?

Your cylinders can't be bored much ... perhaps 1 mm, then there is the matter of replating with Nikasil, and add in the cost of JEs and you are close to $2000 for a minimal displacement increase! 98 mm P & C set gets you to 3.2 easy with no machine work to the case for not much more! Or if you split the case for a complete rebuild, you could have the cylinder spigot bores enlarged for 100 mm pistons, which cost essentially the same as the 98's.

From your picture post that was missing the leading '<' that Pete posted, it is clear you don't have the '84-up pressure-fed tensioners. That upgrade should be figured into your costs, too!

Another consideration ... do you know for certain whether your cylinders are Nikasil or Alusil?

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Warren Hall
1973 911S Targa

[Doug Zielke]

If that is a picture of your motor, all I see is a broken exhaust stud, not a head stud. So why would you have to tear the motor apart for this??
I think, one of our friends (Nickshu) even made a jig for drilling out these busted studs in place.

[michaelnk@excite.com]

If I was in your place I would spend the minimum to fix the problem only. Or I would buy a 3.2 motor and for much less than what it would cost to rebuild this one (properly) you can gain 25 HP or more with Porsche stock reliability and smoother DME engine management.
A friend just rebuilt his 3.0 for the same reason and buy the time he was done (springs, pistons, valve guides,
oil fed tenseners, 964 oil pump. . .) he spent $9500!!!!.
I bought a 3.2 with 915 trany (which you don't need) 2% leak down on all cylinders for $5,500 $1500 to put in a 73 911 (which you don't have to do)
And after 15 track week ends my motor is still at 2% leak down not a drop of oil and very fast. . .

[michaelnk@excite.com]

One small detail. .you can still sell you 3.0 for $2500.00!!!
No brainer.

[Wayne 962]

WARNING - MISINFORMATION HERE!!!

Ok, what is shown in the picture IS NOT A HEAD STUD. It's an exhaust stud. It's quite common for these to break, although not too easy to repair them:



This is not the head stud problem that you have (unless you haven't described it too well). What you were hearing was an exhaust leak.

If you did have a broken head stud - I would still recommend that you just drive with it. Probably about 20-30% of 911SCs have at least one broken head stud, and their owner's don't know. These studs break all the time, and the motor can run fine on three per cylinder. If you break both exhaust studs (the exhaust ones are the ones that break - they are the dilivar type) then you will have an exhaust leak at the cylinder to head mating surface. This will give you a pop-pop-pop on acceleration (car should idle fine). Then you need a rebuild.

If your mechanic is suggesting a rebuild, you should dump him immediately. Seems a bit opportunistic to me.

If you don't have access to an EDM machine (like the one in the picture), then you can have the broken stud drilled out, and a timesert or helicoil installed in its place. This is what I had to do with just about every stud on my 3.0L motor, although it was apart at the time, making the process much easier.

-Wayne

[Doug Zielke]

Wayne,
Your post shows a *portable* EDM machine??
Very cool! Is this someplace like Andial or the Factory?
I've had EDM performed on small m/c parts, but I had to take them to the machine shop to have it done.

------------------
Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

[Superman]

I guess that's been my feeling too. I'm trying to figure out how to cheaply get my motor in healthy shape. If I wanted to spend $3-4k or more, I'd probably get a 3.2 that's in good shape. Instead, I want to buy some time and consider my next motor. So I will take the motor apart, replace what seems prudent and try to keep the cost in the $1-1.5K range. Some folks probably think Neanderthals like me should not drive Porsches.

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'83 SC

[Wayne 962]

Yes, it's a portable EDM machine - very cool. The pic is from the 70's, and is going to be in my book. Here is the text from that chapter:

Most of us in our lives have been stuck in a situation that they wish they hadn’t been. It’s the same feeling that you get when you’re sitting on the side of the road waiting for the police officer to get off his motorcycle after he pulled you over. You keep thinking, “Maybe I wasn’t speeding, maybe my taillight is out or something.” That’s the same feeling that you get when you break off a stud in your very expensive Porsche 911 engine case. Or transmission case, or the rear calipers that aren’t made any more and took six months to find! Never fear, there is a solution to all these problems that most people haven’t even heard of.
My own personal dilemma occurred when I was removing the engineering marvels called Dilavar studs from my 3.0L engine case. See Project 12, engine teardown for a more detailed description of this laborious process which involved several specialized tools including a blowtorch! Regardless of how it happened, I was soon left with a broken stud in my engine case. Repeated attempts to grip it with a pair of vise grips proved fruitless. An attempt at welding a nut to the Dilavar studs also resulted in failure and a string of shouted obscenities.
All was not well in my world when I phoned Alex Wong of Precision Tech for advice. He promptly sympathized, and then proceeded to tell me that he had been in similar dire straits many times previous. His solution was to take the case to Tap-Ex, a company that I hadn’t really heard of before, but would come to be forever engrained in my mind.
Tap-Ex is owned by John Blackwell, who is probably regarded as one of the country’s premier experts at removing broken studs from just about anything. The tools he has in his arsenal are based around a set of machines called electrical discharge machines or EDM. These machines work by passing a large electrical current through metal, literally zapping away bits of material until nothing remains. The process is utterly fascinating to watch, as it’s something that you don’t normally see.
The beauty of John’s process is that it is only destructive to the bolt or stud being removed. A small electrode is used to literally burn away the stud, making it increasingly easier to remove with an extractor tool. With my 3.0L aluminum case, the Dilavar stud had broken off on one of the cylinders, and was very difficult to reach with normal tools. I could have opted for the traditional approach of having my machine shop drill out the hole, but if something went wrong, then the case might be permanently damaged. In addition, the Dilavar studs don’t make the best candidates for drilling.
The first step is to mount the case flat on the tool bed. It’s important to have a straight line down the hole for the machine to burn away the stud. A hollow copper tube that is smaller in diameter than the stud was used as the electrode in this case. The electrode burned away the middle part of the stud, leaving a core, and the outer threads. Because the electrode is disintegrated along with the stud, it’s quite difficult to figure out when the electrode has reached the bottom of the case. When operating the machine, John needs to be attentive for the one to two second delay that occurs as the tool pauses at the end of the hole.
The process begins literally with sparks flying. As the electrical current burns away the middle of the stud, sparks and small bits of metal are thrown out of the case. The coolant that is sprayed on the whole process serves a dual purpose – to cool the area and also to remove the little bits of metal that are burned off. John covered the case with a clear plastic sheet so that we could observe what was happening without getting hit by any flying debris or coolant.
When the electrode reaches the bottom of the case and the machine is stopped, the center core of the stud can easily be picked out of the hole using a pair of needle-nose pliers. At this point, only the thin outer edge of the stud remains in the case, and it can be easily removed with a simple extractor tool.
While a lifesaver, this process did have one major drawback. It was impossible to keep the coolant out of the inside of the case. Since the coolant was used to wash away all the small bits of metal from the process, the entire inside of the case became contaminated with a fine grit that you could feel with your fingers. That, of course, meant that the entire bottom end of the motor needed to be rebuilt – something I had hoped to avoid.
When I went back to pick up the case, John had a whole stack of cylinder heads from a manufacturer that he was working on. He routinely takes on jobs that are shipped from all around the country. If you have a tough job that needs the help of such a process, then John is your man. The tab for the process was about $160 for both the broken Dilavar stud and a small sheet metal screw that had been broken off as well in my engine case.

Contacts:

Tap-Ex
310-323-3834
1940 W. Rosecrans Ave.
Gardena, CA 90249

Picture 1: Your worst nightmare! This head stud has been broken off in the case. This particular stud was a Dilavar stud, which cannot be easily welded to, and has a real tendency to break. The 911 exhaust studs located in the cylinder heads in particular tend to shatter and break because they have been tempered repeatedly by the heat from the engine’s exhaust system.
Picture 2: As with any precision machining process, the setup process must be performed very carefully. The engine block must be placed exactly square to the disintegration tool, otherwise the electrode might wear away the inside threads of the hole instead of the broken stud.
Picture 3: The electrode is a hollow copper tube that is positioned carefully with respect to the broken stud. The electrode must be positioned square to the case, otherwise it might damage the threads as it wanders off course.
Picture 4: The engine block is covered with plastic in order to keep the coolant and lubricant from spraying around the shop. The coolant serves a dual purpose: to cool down the area that is being disintegrated, and also to carry away bits of metal from the area. In this case, we attempted to cover up the case so that the fine particles of metal wouldn’t find their way into the recesses of the engine. To put it mildly, we weren’t successful, and the engine case had to come apart to be cleaned.
Picture 5: Sparks fly from the stud as it is slowly disintegrated. As the machine automatically drives the electrode deeper into the case, the operator must be careful to watch for the point where the electrode hits the bottom of the stud. The machine will pause for a brief moment when the electrode is not contacting any metal, and then start eating into the case when the electrode hits the bottom of the hole.
Picture 6: The hollow electrode burns away the middle of the stud, leaving both the center core, and the outer threads in the case. When the electrode reaches the bottom of the case, the center core can be easily removed.
Picture 7: The outer threads that remain are now significantly weaker, and can be simply removed using a beveled tool inserted into the inner section of the threads. The hollowed out stud is then easily backed out of the case with an extractor tool.
Picture 8: The usefulness of this process is clearly shown by this photo that John had in his collection. Anyone who has worked extensively on older 911s knows that the machine is set up to remove an old broken exhaust stud. A job that would have been nearly impossible to do without removing and tearing down the engine is now completed in under an hour. $200 versus a complete engine rebuild? Kind of puts things in perspective.

[Chris79SC]

Noah - Your impression of JE's have been noted. If I have to go that route, I'll feel a little better knowing that you've installed them with no adverse side effects.



[This message has been edited by Chris79SC (edited 06-10-2001).]

[Chris79SC]

Wayne & Doug Z - Thanks, I hoped by posting the picture that someone would tell me if my mechanic is being up front with me.

The broken stud he showed me is highlighted. Is that an exhaust stud? I knew at the time he was showing me the problem I wouldn't be able to tell a broken head stud from an exhaust stud. So I took his word for it, until I could post a picture here to confirm.


Warren - I'm told that their Nikusil. My brother had told me that he had gotten the tensioner update done, I'll check on that also.

A beginner's Porsche engine class is on my immediate agenda. Until then, I'm going to look into finding a new wrench, as I wouldn't exactly trust this guy with my life, if you know what I mean.

Anybody know a good mechanic on Long Island?




[This message has been edited by Chris79SC (edited 06-10-2001).]

[Doug Zielke]

Chris,
I guess my eyes were just looking for the obvious, after viewing the first shot of your motor. All I saw was a broken exhaust stud. You do have one of those. But now, your highlighted area is another thing entirely. You can see a head stud there for sure. If you put your fingers on it and push it around, then it's broken. John Walker??

------------------
Doug
'81 SC Coupe (aka: "Blue Bomber")
Canada West Region PCA
members.home.net/zielke/911SC.htm

[Chris79SC]

Oh, I see where you were looking Doug...the studs pointing down towards the floor. I guess I feel a little bit better it that is indeed a head stud. Not that a broken headstud is a good thing but, I was beginning to question my trust of his inspection.

The stud I circled is VERY loose...its only a portion of the stud.

[Wayne 962]

Ditto - I see the broken exhaust stud, and now the head stud. It's not supposed to be there, it's just loose, and rattling around. Take off your valve covers, and check to see if anymore are broken. Let me see if I have a pic from MY UPCOMING BOOK <- Subtle Plug:



Perfect! Shows the stud, and the nut with even an arrow pointing to it. Note that this is the top of the motor.

Again, I would keep driving the car, unless you have more than one (two or more) broken studs on the same cylinder. A lot of people out there have broken studs, and they don't even know it. The motor will perform fine, and you will not do any damage if you are running on three. Chances are if you have one broken stud, you will have more too. If you break both bottoms (the bottoms are Dilvar, the type that break, the tops are pretty strong, and see less stress (heat) anyways), then you will need to rebuild. But you will hear the pop-pop-pop on acceleration that is characteristic of this.

Just drive the car - you can't do any damage to it. If you do break two studs on the same cylinder, then you can start to do damage when the pistons flap against the heads, etc. but it sounds like you do not have that problem yet...

-Wayne

[Early_S_Man]

Chris,

Sorry for the confusion, I had a bit of brain fade about the tiny 3 mm oil line to the left side tensioner! I was thinking it looped down below that horizontal rib that the engine tin bolts to, but it doesn't, so your pic doesn't provide any evidence one way or the other.

I do disagree with Wayne to a certain degree about continuing to drive the car, though! Engines can develop the banging/popping sound with only one broken stud, as Leland's did ... I suppose the head barrel/Allen nuts can loosen on their own, simulating more broken studs, at least in not restraining the head from banging. Flame-cutting of the cylinder and head can occur as hot gases leak past the sealing ring!

If you do continue to drive the car, I strongly recommend that you get a 3/8" drive torque wrench and 10 mm Allen drive bit, and check/tighten the cylinder head nuts to 25 lb-ft on a monthly basis! A regular compression check wouldn't be a bad idea, either. Good luck!

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Warren Hall
1973 911S Targa

[pbs911]

Sorry to hear this. My 3.0SC has 35K on it. When the time comes, I will definetly replace the motor with higher stock displacement. Prabably a 3.2 but the 3.6 looks very good. Depends on the deal you can get. You can probably get 2.5K or maybe even 3K (ebay does wonders) and invest in a strong used motor. Stock strong HP is key, unless you don't have to worry about smog.
-----------------------------------
Paul
78SC Targa