Case saver and stud question

[my1st911]

Originally Posted by john walker's workshop

you won't be able to thread the drilled holes with the drill press. too fast. you need a jig or a mill. try it by hand and you will get them porcupined. the cylinder bases will be worn. they need to be trued on a mill or the cylinders won't sit on the same plane. there are 8mm studs around the intermediate shaft that need to be inserted also, especially that long one. the mainline bore in the case will be warped. it may mic out ok when you measure the individual bores, but they are not in line with each other. it needs to be align bored. if you try to use new bearings without an align bore, the crank will bind. if you really want a nice job, all these things would be done after the case mating surfaces are milled flat and the case align bored at both the crank line and the intermediate line. steel studs are generally fine, even used ones, but consider this.., mag cases are soft. that's why the studs pull. personally, i think that 24 new dilivars is the better choice with a 2.7 case, as they are designed to expand close to the expansion rate of mag/aluminum and would be easier on the case than steel. just my opinion. the heads will need a flycut and if you reuse the cylinders, they need to be trued at the head contact surface. the idea is to have all the components parallel to the crank centerline.

I have talked to many Pcar people, and have yet to get a definete answer. Some say raceware, some say steel is fine, and some insist on dilavar. Point being is I want the car to start, and be my sunday cruise, as well as not leak oil. If my steel studs do the trick, than steel it is

[john walker's workshop]

some people read stuff and relate it as knowledge, some learn from hands on experience. you're going to get many opinions on just about everything in life.

[my1st911]

[QUOTE=Peter Zimmermann;4504877]FYI: My book (The Used 911 Story - 8th edition) devotes about 11 pages to the engine repair issue, much of the discussion and photos apply to magnesium case-related issues. You might find the info helpful.

Also:

I've been working on a new book (title & publication date still unknown!), and I realized that one of the chapters fit this thread and might possibly provide some insight to head studs. Please consider that this information does not come from Porsche, it comes largely from my personal experience in the trenches working daily on 911 automobiles. I have done everything possible, using personal notes, etc., to insure accuracy, but the history of some things that Porsche has done can be considered murky at best. This chapter is not written in stone, and I'm open to knowledgeable discussion regarding its content. What you're going to read should be considered copyrighted material, so it may not be used or...blah, blah, blah. Enjoy!

Cylinder Head Studs

1977. Porsche was well aware of the problems associated with the 2.7 liter engine with its pulled cylinder head retaining studs following a repair that required cylinder head removal; sometimes the studs would pull without apparent reason. Porsche knew about thermal expansion, and had used, since the early ‘70s, in racing engines, a cylinder head stud made from an alloy called dilavar, while all street engines were assembled with steel head studs. Dilavar studs, first used in 930 Turbo Carrera engines, were found to have roughly the same thermal expansion properties as both aluminum and magnesium, which, in theory, would greatly reduce head stud stress at higher engine temperatures. It’s been written that steel studs, on the other hand, have an expansion rate roughly half that of the aluminum cylinders and cylinder heads that they hold together, which placed extreme loads on the crankcase and the studs themselves. Dilavar studs, a non-magnetic steel alloy, found their way into 911S production part way into the ’77 year, and the studs were only used in the bottom twelve, exhaust side, positions (each 911 engine uses 24 studs, 4 per cylinder head). A thoroughly tested no-brainer, or an experiment, I don’t think that anyone knows the answer to that except for a select few people at Porsche. The first dilavar studs were a shiny, brushed finish, similar to many modern kitchen cabinet and drawer pulls, with a color closer to silver than to light gold. Their purpose was to stabilize cylinder head torque through the temperature range that the typical 911 engine ran at. I’m sure that the factory hoped that Dilavar studs would also be the cure for pulled head studs in magnesium engine cases. Because the thermal expansion rate between early steel studs, and the alloys that they secured, was quite different, the change was made.

1980. The first improvement to dilavar studs was made for 1980 SCs, which proved that Porsche was committed to their use. The stud changed in appearance, to an almost jewelry gold finish. For this design change to happen so early into the use of dilavar, Porsche must have seen, and not liked, corrosive activity on the first generation stud. Factory literature states that Porsche’s original philosophy of using twelve upper studs made of conventional steel, and twelve lower studs made of dilavar, remained consistent beyond the 1980 models. At some point dilavar studs were again changed, and the newer version was coated with a gloss-black paint-like substance obviously designed to withstand corrosion. This change was thought to have been made during 1981 production, or at the outset of the 1982 build run.

OK, you’ve read the first part of this chapter and are probably wondering why. Well, if you own a ’77-81 SC the subject matter above could easily make you about $3K+ poorer. Head studs break. Some more often than others, but mostly the problem occurs with the uncoated, early studs, followed by the second generation, also uncoated, studs. The studs break about two inches from the end where the head nut screws on; they are obviously susceptible to corrosion at that point. A fastener such as a stud, or bolt, is under constant stress, from the time that it is tightened until the time that it’s loosened. The act of applying torque to a fastener is the actual stretching of, in this case, the stud. Enter corrosion, which attacks where it can, and begins to eat away at the metal. Remember, dilavar is a steel alloy, it is not immune to corrosion, actually far from it. At some point in its life, a corroded head stud will snap at its weakest point, and will no longer provide the fastened strength that a cylinder head requires at each of four corners.
Head studs break on low mileage cars; perhaps more often than on high mileage cars. “How can that be?” one might ask. No one knows the answer, but I know it to be true. I also know that it doesn’t happen to all cars, maybe even less than ten percent of each involved year. My shop replaced head studs on far more cars with less than 50K miles on the odometer, than with more than 100K miles. It can create a bit of a conundrum; the cars that can be considered garage queens, and are obviously the most desirable to find and buy, are the ones that have this potentially expensive time bomb lurking in the engine bay.

FAQs:
“How does one know when a head stud is broken?” All 911s built between 1977 and 1989 have the same maintenance requirement for what is normally referred to as a major service – typically required at about 15,000 miles. That service consists of a valve adjustment, oil and filter change, engine tune up and other items. In order to perform a valve adjustment, the valve covers, aka rocker covers or rocker arm covers, must be removed. There are four covers per engine, and are usually referred to as intake (upper) covers and exhaust (lower) covers. During removal of the lower covers I have been hit on the foot by a two inch long piece of a head stud, with the cylinder head retaining nut still on it. Sometimes the broken piece will fall out; sometimes it will hide in a recess in the camshaft housing casting. A normal major service inspection should include, especially on high-risk cars, a visual to verify that all of the studs/nuts are intact.

“What is the immediate symptom?” Usually there is no symptom, especially on conservatively used, commuter or weekend cars. I’m aware of cars that have been driven thousands of miles after a broken head stud was diagnosed, with no negative result.

“When does stud replacement become something more expensive?” If one or more broken studs are discovered during a major service and the needed repair is ignored, at some point a corner of a cylinder head, usually the corner with the broken stud, will work loose enough to leak combustion (the gases that are supposed to leave the combustion chamber via the exhaust valve). From the very moment exhaust gases begin to leak out between the cylinder and cylinder head the process of erosion begins. Eventually a cylinder, possibly even a cylinder head, will be damaged beyond repair.

“Is there a symptom when it’s almost too late to do the basic stud replacement without extra cost?” Yes, the driver will hear a distinct and rapid “pop, pop, pop…” during acceleration; louder with a cold engine than a warm engine.


“If my engine has broken studs can the job be done so the repaired engine is a long-life unit?” Going by everything that is known today, the current generation of cylinder head studs, developed for the 993, should be trouble free for at least the service life of the engine that they’re in.

“If my engine was originally fitted with steel upper studs, and Dilavar lower studs, should all 24 studs be updated to Dilavar?” Porsche must have done temperature analysis regarding the required expansion of the upper and lower studs, but I’ve not seen a technical bulletin advising the correct way to handle this. My shop found evidence of corrosion on original, steel upper studs, so our policy was to install 24 new dilavar studs on those engines (the exception being engines that we repaired on which the upper steel studs were visually perfect). Follow up inspections showed no adverse results, including unusual loosening of head nuts which would require periodic re-torquing, regarding those repairs.



All great information. Thanks for the great read. I am not trying to ruffle anyones feathers in any way, because we are all here for the same reason. We all have a passion for these cars. But one thing that makes us all different is our financial situation. I am 32, work in the automotive field, and have a mortgage. I am also unmarried. Ihave alot of financial responsibilties that prevent me from maybe doing this job to everyones approval. If the money wasnt an issue, I'd get a 3.6 and tuck it in there. The point being is that I have a fun car that had low compression, and leaked a little oil. I openned it up to install case savers and a nice reseal. I know that many of you are betting against me, but I either try it my way, and have to do it again, or it sits. I want to do the job right the first time, trust me, but the funds are just not there. I appreciate all your advice and wisdom, and I know you all are correct to a point, but just feel that somethings can be over looked. And if I am wrong, it will make a great first chapter if ever I write my own book. Wish me all luck. I will keep you posted.

[john walker's workshop]

no ruffled feathers. we're just trying to save you some grief. you picked an engine ( a 2.7) that is almost always a can of worms, so research your repair ideas well and good luck.

[gsmith660]

I would at least have the line bore checked what John says has validity once the case relaxes it can flex I was told years ago rotating the crank while torquing would line things back up, John is this totally bullsh@t I would like to know because if I grenade my science project I have another motor sitting on the shelf to take its place.

[john walker's workshop]

yeah, i call BS on that theory. the main webs are not going to realign by rotating the crank.

[cgarr]

Yep, the only alignment points are the nose bearing and the rear main, everything in between is on its own.

[my1st911]

Just one last quick question before I attempt this project with the help of some very knowledgeable people who shall remain nameless, are the case savers sold by PP the correct size for the head studs, and the one stud under the intermediate shaft. I know case savers come in many sizes, and PP lists a 14 mm case saver. Just thought it was on the big side

[jjrowe]

Also while you are fixing threads you may want to helicoil the studs around the perimeter of the case. If these won't torque down when you put the case back together it may not seal properly. In my personal experience pretty much every stud on that case has a good chance of pulling out when you retorque it.

Good luck!

[gsmith660]

Wow the 2.7 has been very very bad to some of you guys I have had 2 2.7s in my car and they have both been very robust to date I know the motor has had its problems but that was mostly because of the thermal reactors am I wrong. I maen if it was such a POS then why did the best of the early racing 911's have mag cases.

[Peter Zimmermann]

Originally Posted by my1st911

Just one last quick question before I attempt this project with the help of some very knowledgeable people wo shall remain nameless, are the case savers sold by PP the correct size for the head studs, and the one stud under the intermediate shaft. I know case savers come in many sizes, and PP lists a 14 mm case saver. Just thought it was on the big side

You definitely want the 14mm case savers, their coarse threads grab on and hold far better than the smaller (1/2 x 20, 12mm, etc.) ones.

[jjrowe]

Wow the 2.7 has been very very bad to some of you guys I have had 2 2.7s in my car and they have both been very robust to date I know the motor has had its problems but that was mostly because of the thermal reactors am I wrong. I maen if it was such a POS then why did the best of the early racing 911's have mag cases.

Well, for one that was over 30 years ago. No one is saying they are a POS, mine has almost 300k miles and has been a daily driver most if its life. The material is soft and extra care must be taken when rebuilding. If done right, they are a great engine!

[jim72911t]

my1st911,

Couple of questions: What sort of machining experience do you have? Do you know the technique for tapping on a manual mill? (Bridgeport, etc.) Have you ever indicated a hole with a test indicator? Have you used ever used a Procunier or Tapmatic tapping head?

I've been a machinist/manufacturing engineer for close to twenty years, have access to a very well equipped machine shop (including a Bridgeport in my garage), and chose to have a Porsche machinist do my case. I talked to him beforehand, explained my credentials, etc. He told me I could do the job, no problem.

I still had him do it. His years of experience made me realize that he might just know a thing or two that I didn't, and would have to learn the hard way.

I think you might be getting in over your head, but wish you the best of luck, regardless.

-Jim

[gsmith660]

Originally Posted by jjrowe

Well, for one that was over 30 years ago. No one is saying they are a POS, mine has almost 300k miles and has been a daily driver most if its life. The material is soft and extra care must be taken when rebuilding. If done right, they are a great engine!

Thats what I am saying exactly but all I ever hear is bad things about the motor when you get down to it they are a just as good as any other motor but I did read somewhere for the stresses without the mods that are done now the 2.7 is at the engineering limit for the case.

[DanielDudley]

[QUOTE=my1st911; I am sure I can drill these out and install the case savers, but it's definitely nice to put the liability on someone else. Thanks all[/QUOTE]



If I were getting open heart surgery, i would want a Doctor that has done the operation a thousand times, not the guy who stood by and watched it done once. If you were working for me as a tech, I would not let you do this to my engine.

You have to do this 24 times perfectly, with no practice. I beleive in theory that you can do this, but I do not know.

Best of luck. Prehaps someone could donate a ruined case for you to practice on. That way, at least you get to find out how hard it is and practice in a safe way.

[gsmith660]

Originally Posted by my1st911

Just one last quick question before I attempt this project with the help of some very knowledgeable people who shall remain nameless, are the case savers sold by PP the correct size for the head studs, and the one stud under the intermediate shaft. I know case savers come in many sizes, and PP lists a 14 mm case saver. Just thought it was on the big side

I am a great supporter of DIY in any way possible but without a milling machine and the proper jigs doing 24 studs and getting them all straight would be a monumental task for a DIYer you could probably get a package deal to put in the case savers and true up the case ready for reassembly all in one fell swoop also consider having the case shuffle pinned and the oil galleys flushed out. Good luck in whatever you decide to do.

[gsmith660]

Originally Posted by john walker's workshop

yeah, i call BS on that theory. the main webs are not going to realign by rotating the crank.

Hey John when I am done with this project I plan on getting my motor back to a long block and bag it up and store it. I will contact you to true it up and shuffle pin it

[haasad]

I don't know about powder coating dilvar. As I said my studs are all steel.

I don't really understand why proper NDT wouldn't identify faults in any material assuming a competent metallurgist does the work.

However only my opinion and the route I have taken... Time will tell

take care

andy

[my1st911]

[QUOTE=iIf you were working for me as a tech, I would not let you do this to my engine.

[/QUOTE]

I am a tech. I can also say that some of my best learning experiences has been doing things without prior knowledge, taking my time and researching, and being successful. If I were working on someone elses car, or for you, then obviously I wouldn't take trisk. Since it is my car, I am asking for guidence and support. I realize that it may not work out completely well, but I think a quite basement without distractions and patience will hopefully end up in success. If not I will be taking apart a spare 2.7 in the garage

[my1st911]

Originally Posted by gsmith660

I am a great supporter of DIY in any way possible but without a milling machine and the proper jigs doing 24 studs and getting them all straight would be a monumental task for a DIYer you could probably get a package deal to put in the case savers and true up the case ready for reassembly all in one fell swoop also consider having the case shuffle pinned and the oil galleys flushed out. Good luck in whatever you decide to do.

In waynes book on rebuilding, he suggests a drill press for the inserts. As longas I center each hole perfectly, secure the case down, and slow my bit and go slow and easy, I dont imagine a big problem. My case has been replaced at some time and never ran hot. The leaks all came from oil t-stat, breather cover, and temp sender from the top. I believe that she will seal up well without going crazy on extra expenses of line boring etc