Case saver and stud question

[my1st911]

I did use the search function, but didn't find what I was looking for. I have enjoyed this forum for about a year, and even though I don't contribute as much as I would like, I read and read and read. My 76 911s had low compression when I got the car, and had the psst psst sound when you first started it. My assumption was that the case had pulled studs, and without investigating further, I dropped the engine, and took it all apart last week.

As it turns out, I did a leak down test just before unbolting the heads, because I couldn't find any pulled studs, and cylinder number 5 just needed to be torqued down a bit, and all was sealed. So now I'm stumped.

I bought the car from the second owner. He didn't have any service records, but for the price, I didn't care. I drove the car all summer, and I am looking forward to my next warm summer cruise as soon as engine is back together. So here is my problem. The case was replaced at some time, as it has no serial number on it. It does not have the case savers in the case, and I think it would be wise to installl them. I'm in the Norther NJ area, and the machine shop that I was referred to by Pcar people I know wants 35 dollars for each one. Thats 24 head studs, plus the one through case bolt at 35 each. Thats about 900 each. Has anyone done his themselves with a drill press. This isn't rocket science, and 900 dollars is crazy in my opinion. Also I would like to know if I can reuse my head studs, or if I should replace.

Just to give everyone some background on myself, I am very handy, have great common sense, and I am an auto tech by trade. 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

[4sd911]

German Precision on the west coast charges $285 to timesert the head studs. You will need new studs, not metal, either 993 DILAVAR or Race Wear. If you try to use a drill press the drill needs to be able to operate at a very slow speed to thread for the serts. Best off having this done by someone that has experience with Porsche mag. cases.

[gsmith660]

There used to be a jig you could use to drill the case for the case savers but I haven't seen it advertised for a while.

[Walter_Middie]

My1st911,

Yes it is costly to replace all the threads. However, I think the stock studs are OK. I had all my threads replaced, and I bought ARP studs, but I didn't have to. Getting it done right is not always the cheapest way. Besides, if you mess this up, you are pulling the motor again, and the block may be junk. Pay once for good service and be done with it.

[my1st911]

So I have yes for using old studs, and yes for replacing. I am trying to do this right the first time, but I'm not the type of person who says while I was in there". I am doing thisrebuild on th cheap. No new bearings, just a reseal and inserts. If you secure the case halves on the drill press platform, and center it perfect, then drilling them myself should be easy. I realize the risks, but the machine shop take the same risks as well. Has anyone done there own inserts?

[cgarr]

We do a lot of 2.7 cases on our mill, you can use a good sturdy drill press. Its not just drilling the hole out but its making sure the tap is perfectly square or your studs are going to have the porcupine look. Make an install tool too: You also might want to use an 8x1.25 insert at the layshaft stud too, those often pull too:

[my1st911]

Originally Posted by cgarr

We do a lot of 2.7 cases on our mill, you can use a good sturdy drill press. Its not just drilling the hole out but its making sure the tap is perfectly square or your studs are going to have the porcupine look. Make an install tool too: You also might want to use an 8x1.25 insert at the layshaft stud too, those often pull too:

That is exactly my intention. I figured that if i clamped down the case and inserted a drill bit that is exactly the same size as the original hole, that it would center it perfectly, then take the correct drill bit, and enlarge. Whats your take on the original studs

[gsmith660]

You might contact enginetech at 1-800-869-8711 and ask them if they have a jig they are the ones I get timeserts from.

[jjrowe]

I think you can reuse the old studs, the original steel studs did not have a tendency to break only to pull the threads out. You will be solving that issue with the case savers. Since you are doing this on the cheap as you say, I don't think the studs breaking will be any more of a risk than the other items you will be skipping. Make sure the studs are the original steel type though and not dilavar, those did have a tendency to break. I believe you can use a magnet to check, dilavar studs won't attract it (search on this, I'm not 100% sure). As far as drilling your own case savers, I think its too risky. You really can't afford to make a mistake. You can probably find a VW machine shop that will be less expensive.

Jesse
1976 911S

[4sd911]

Using steel studs in a 2.7 magneseum case is asking for trouble. The old dilavar studs do break, the 993's are much better, if you don't trust those then go with Racewear.

[Walter_Middie]

My1st911,

Reading back in this thread, you don't mention having any machine work done on the case anywhere. Once the two case halves are separated, they twist like a pretzel. You have to have some machining done to the case.

I have been paying very close attention to the history of studs on Pelican. Most have agreed that the steel studs are fine. In the 3.0 motors, they recommend replacing just the dilivar studs with steel, and leaving the original steel studs alone. In the 2.7, once the block is strengthened, the steel studs are good to go. It's only the older dilivar studs that are a problem.

[gsmith660]

Originally Posted by Walter_Middie

My1st911,

Reading back in this thread, you don't mention having any machine work done on the case anywhere. Once the two case halves are separated, they twist like a pretzel. You have to have some machining done to the case.

I have been paying very close attention to the history of studs on Pelican. Most have agreed that the steel studs are fine. In the 3.0 motors, they recommend replacing just the dilivar studs with steel, and leaving the original steel studs alone. In the 2.7, once the block is strengthened, the steel studs are good to go. It's only the older dilivar studs that are a problem.

What machine work are you talking about (shuffle pinning?) I have a case that has been split for about 10 years and I just checked to see if it needed a line bore and it mic'd out just fine I am going to have it checked again but as I understand all you need to do when torqueing the throughbolts is have someone turn the crank slowly and all will come into alignment. +1 on the steel studs the reason they break is the different expansion rate for steel verses mag. and if you strengthen the case ie: case savers the studs will pop like a twig if you get the motor hot

[sc_rufctr]

I understand your desire to save some cash but maybe you should consider something before you make your decision.

Paying a professional to do the work means you hand over the case halves and then you get a result... Period... (hopefully a good one...lol)

The guys that do this for a living know how to do this tricky task with no guess work. Don't get me wrong. I do understand your desire to save money... or more to the point not pay for something you feel you could do yourself but at the end of the day you want a reliable motor that will stay together. What's that worth to you?

I think there are to many 911s sitting in peoples garages not being used because someone tried to cut corners or tried something cheaper when fixing their car.

The one thing I've learnt the hard way during 14 years of ownership (two different 911s) is that 911s are robust and reliable cars but when something needs to be fixed... Do it properly the first time.

Sorry about the rant but I really believe this is the best way to treat our cars.
Hope it works out OK

Peter

[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.

[yelcab1]

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.

In other words, you can't have it cheap.

[Peter Zimmermann]

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.

“Is there any way to ascertain the presence of a broken stud without hearing the popping noise, or removing the valve covers?” With the car raised up enough to see the bottom of the engine, a flashlight examination can be done of the areas where the cylinders and cylinder heads join. Those areas should be dry and clean. If there is a black, crusty layer that appears to be burned oil, there is a chance that the engine has one or more broken head studs where the buildup is the heaviest. However, a broken head stud is not always responsible for this condition, sometimes it is from a tiny imperfection in a machined surface, and no immediate repair is required.

“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.

“Are the black-coated generation of studs, used since late 1981, the latest generation Dilavar?” No, Porsche developed a new Dilavar stud for 993 models (1995-1998), and 993 studs should be used for all repairs.

“Can anyone do this repair?” Usually you’re better off with a seasoned professional when 911 engine repairs are needed. There are an assortment of special tools needed to perform stud replacement, and it always helps for your technician to have a set of factory repair manuals on hand as well. There is no really good answer for this question, because there are probably DIYers out there who are more competent than the available mechanic.

[haasad]

Just based on my opinion but I've gone with .

Remove all studs

Identify as steel ( magnet check)

Aqua blast each to spotless

Electromagnetic crack detection NDT

Thread profile inspection

Stud visual inspection for corrosion pitting.

Powder coat exposed diameter

Mill Tap and fit timeserts to all vulnerable threads in case (Bridgeport universal mill)

This all on a euro 75 S with Mag cases ( not an engine that ever had thermal reactors)

For the record none of the studs showed any sign of stress or corrosion beyond acceptable levels. The facilities I used for the NDT and visual are the metalurgical labs for very signifcant engineering installations.

BUT not everyone has access to such facilities and without the confidence such process can give frankly I would have bought new 993 studs.

Andy

[yelcab1]

The milling work should be left to a professional, or at least a capable neighbor with a Brideport mill like my neighbor.

The stud replacement can easily be done at home.

[john walker's workshop]

epoxy painting used dilivars is not a good idea. you can bead blast them clean so they look like new, but they can still have rust penetration at the area that lines up with the head to cylinder joint and where they are exposed at the bottom of the cylinder. this rust penetration can be seen if you scrutinize the broken ends of a dilivar stud. so toss them and buy new.

[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 just purchased a drill press, and will be changing the pulleys to slow the speed down. Drilling in mag should be quite easy (the material, not the task itself)