964 - Repeat of Head Stud Woes
 

It's a sad tale, but here goes.

In about 2001, I found my '89 C4 (with only 37K miles) had a broken head stud. There was much discussion, and many thought and suggested that doing nothing was a viable option given the low miles. But, out of abundance of caution, I rebuilt it - ARP head studs & rod bolts; profiled cams; oil seals; clutch; oil lines . . . the works. She ran beautifully. Unfortunately I recently developed an annoying exhaust leak, or so I thought. (OK, it's been at least 6 months.) So...off to the p-shop, which I have never done before. I just don't have the time right now and was hoping to have someone else deal with some issues for once. It now has about 67K miles on it - still low by many measures.

Found: Exhaust leak was between cylinders and heads on left side. On driver's side, No. 2 torqued down nicely, but No. 1 & 3 had problems. The studs were pulling when torqued.

Shop recommendation: Complete tear down; change out the ARP with dilivar, and timecert the crank case. Their concern is that the ARP studs are useful primarily in race applications when frequently tearing down and rebuilding. Dilivar is not cheap either.

I remember actually trading emails with Bruce Adams, who seemed to think (at least at the time) that a broken head stud on a 964 was unusual, if not unheard of at the time. Now, I wonder if I am blessed with another "unique" situation.

Anyway, I'm mulling over my options and thinking about doing the job myself again, but I'm wondering if this has happened before to anyone? Any experience (bad as it is) out there?

All theories are welcome!

Thanks!

Steve,

It is rare for head studs to pull out in any aluminum cased engine such as yours. (Breaking ones also rare)... I suspect that these two events are unrelated.

I would also suspect that at some point they were overtorqued because that would be the one thing that would really induce them to pull. I do not agree with the ARP bolts being for race-only application. I have heard that their metalurgy is close to the expansion rates of the cylinders more so ,I believe, than the steel ones.

I replace every early dilivar stud I see because they do have a tendency to break. You're in for a top-end probably, and time-certs if they are really pulling out.

Thanks, Chris.

Have you seen other pulled studs from the '89 vintage 964s? Any other thoughts about WHY I would have this problem - all on the left side of the engine?

Don't pull any punches. Honestly, if I were reading this I would suspect installation error. Any other theories why this would happen?

Here's my 2001 thread:

http://forums.pelicanparts.com/showthread.php?s=&threadid=4832&perpage=20&pagenum ber=1

Thanks!

Picked up the car today. Time to survey my options.

P shop says that he has heard of lots of problems with ARP studs on other cars (hondas, etc) from his machine shop. He is adament that the right move is to install the 993 dilivar studs due to correct expansion with heat...

I'll be curious to see if the case threads are ruined.

Anyone out there ever have to timesert the case on a 964?

I'd definitely figure out a way to keep the ARP's.

I'm not a metallurgists, but ARP makes some almost fail-proof stuff it seems.

If its good enough for race stuff, then its definitely good enough for your engine. Just gotta figure out what the issue is at the case level...

Why not just do what your mechanic wants. 993 studs seem to be holding up ok and your mechanic could be right about the ARP studs putting too much stress on the case. You could probably sell your ARP studs to help recoupe the cost of the 993 studs.

-Andy

I'll offer another opinion here and express my strong preference for the latest 993TT dilavars,..:) :)

ARP studs, while quite strong and bulletproof, do NOT expand at the same rate as the cylinders and we've experienced everything from loosened head nuts to leakage at the junction of heads & cylinders from distortion when hot.

I'm a huge fan of ARP fasteners on other engines, but I'll only use their excellent rod bolts in 911's. :)

Small engines (2.4 & smaller) can safely use steel studs and mid-size (2.7-2.8) can use steel as long as Case-savers are installed and engine temperatures are well controlled. I really prefer the late 993 TT Dilavars for everything else. Porsche used these same items in all 3.8 RSR and GT-2 engines with no issues on these parts.

Just one man's opinion, of course so YMMV. :) :)

Well Steve, I'd definitely say you've got more experience!! :)

Go with what Steve says :)

Brian

Thanks, Steve.

Have you actually seen the ARPs pull out of an aluminum case in a 964 before? I'm just wondering if I'm the "only one."

Seems like mine was one of the first 964s known to have even broken one back in 2001. I really don't like being the first in this regard!

I just got Wayne's book in the mail today and have already read about half of it, but found a ton of references leading me to believe that Wayne HATES dilavar. I wish his 964 supplement were available.

Is it possible that the added HP from the modified cams contributed to this? Of course, the engine is still in the car and I won't really know until its out...

In the scheme of things, I'm not married to any particular fastener. I just don't want to have to build this again in another 30K miles!!

Steve,

What is the Part # for the 993TT Dilaver studs?

Steve:

I've only seen pulled studs on 964 cases where someone else had "been there" before. Never seen a stock, untouched 3.6 with pulled studs. :)

Based on seeing a lot of 350+ HP 3.6 & 3.8 motors (N/A & Turbo) with no stud issues, I don't think the added HP was a factor. Human factors, OTOH are the leading cause of such things.

JMHP, comparing the early 3.0-3.2-3.3-3.6 Dilavars to the 993 TT ones is a mistake,....:) :)


# 993.101.170.51; not cheap, but you get what you pay for (most of the time)

Well . . . I was there - and no ego here - what, specifically, are the human mistakes that could have been made? Some have suggested overtorquing is a possible cause (which I would deny). Anything else, or could it be related to other aspects?

Just looking to avoid a repeat!

Thanks!

No ones accusing you, but it's the easiest explanation. Ruling that out Steve Weiners explanation makes sense. I like the 993 steel studs on most engines (except Turbos), but I'm interested to hear more about the 993 dilivars as they are used more.

That was the original point of the dilivar stud, because it expanded at a very similar rate to the cylinders themselves...

The latest 993tt divalar, continous thread type, are bullet proof, I also like Neal Harvey (Performance Developments) studs, again bullet proof., cheers, Candy.

I just spent an hour with one of the PNA racing dyno guys. I posed this same question to him.

He said:

"The reason any stud pulls out on the early or late engines is because some idiot probably bottomed out the stud in the case when he installed them"

This assumes they were torqued to correct values.

So there is another option of why you may have pulled a stud. At least thats one mans opinion.

Clayton

Now that is a definitive (and truly helpful) opinion!!

I will search my memory to see if I can recall bottoming them out, which I don't think I did. I do know, however, that I didn't actually measure the height of the studs on installation. I'm guessing that is exactly what happened.

At this point, I just want to understand the potential reasons so that "some idiot" (like me) doesn't make the same mistake twice when I rebuild that which I have already done. ;)

I will definitely buy a quality ruler for this time.

Thanks!

Here's the status of my initial inspection.

No. 1. cylinder on the exhaust side - you might be able to see in the photo that the stud on the right has about 7 threads showing. This is what the p-shop tech observed as he tried to retorque the stud nut. He said that when tightening the nut, the stud started to pull back. I was able to remove the nut by hand with an extension on the socket. No wrench needed. After I got the nut off, I was able to wiggle the stud back and forth. All the others were tight.

Plus, the end of the ignition wire was ripped down the side in the vicinity of the top of the head. Lot of oil blow by, too.

Unless someone knows the secret for removing and replacing a stud in place I'm planning to remove the engine in the morning. I think I've seen enough.

http://forums.pelicanparts.com/uploa...1176006447.jpg

... and here's what the wire looked like.
http://forums.pelicanparts.com/uploa...1176007036.jpg

Sure, you can remove that stud if it's loose. I have a feeling they just vibrated loose from not being tightened down completely on installation...

-Wayne

But how do you get the stud back in??

I recently rebuilt my 90 C2 3.6 engine with arp head studs and rod bolts new mahl cylinders and pistons with the late model groove. When I installed the arp studs I put them in with permatex threadlocker red.I had Rich at Jacksic Racing do my heads and I also bothered him quite a bit with a lot of questions about these studs.Rich feels that the stock ones are fine for a stock motor.Me being overly cautious and nerotic I decided to put the arp studs in.That was no easy task.I broke one stud taking them all out.Again Rich had to save the day and remove the broken stud and put a time cert in.I used a generous amount of the permatex and I could not get the arp stud to turn in the crankcase.If I wanted to get them out for arguments sake I would have tyo put heat on the crankcase again.I dont know if you put threadlocker or what kind you used,seems to me that something to explore.I tell you this I only have about a thousand mile on my new engine but it is dry as bone and runs well.Hope I dont end up with the same problem as you.Many people swear by these studs.Captek

Use Loctite on the end of the stud, use a nyloc nut on the end of the stud. Screw down into the case, and let the Loctite harden, then remove the nyloc nut...

-Wayne

It sounds like Steve needs to get a timecert or case saver in there first if the observation of his mechanic is correct that the stud pulled out of the thread when torquing it. Not sure if Loctite will save the day here.

I doubt you can install a timecert proberly without tearing down the engine.....

You could try some of the epoxy thats out there some are excellent and once cured they can even be drilled and taped,not that you would want to tap it but rather coat the stud with the epoxy and screw it back into the case and put a heat lamp on and let it sit for a few hours.I,am only suggesting this as a last resort before you tear down the engine.Youve got nothing to loose at this point.captek

I've decided to drop the engine and take a closer look at things with it on a stand rather than in the car. Given the amount of oil blow-by that is concentrated in the vicinity of No. 1 & 2, the complete looseness of at least one stud on No. 1, the p-tech's testimony that several of the studs were loose, and the increasing sound the "exhaust leak," I won't feel confident in the engine unless put an eyeball on the crankcase and cylinder tops. Plus, the knot in my stomach about having to rebuild again, is giving way to the excitement that I "get to rebuild" it again! Kinda sick, but I'll bet some of you understand...

I have the original no gasket configuration. I think there was some sentiment during my last rebuild that there just wasn't enough meat on the cylinder tops to accommodate a gasket channel. Any experience or thought on that?

Thanks!

I had the same deal on my 964 engine.I got a great deal on the cylinders and pistons with the gasket late style.I bought them from EBS Racing in Nevada.Paid about 1,800.00 for new mahl cylinders.and pistons.If your going to rebuild again I would go for the late model cylinders.I agree it is some what interesting doing a porsche engine.Its complicated and at the same time its simple. Its still a lot of work and time.I would want to be certain that there are no kinks this time around.Also I used the dow corning aviation sealer for the crankcase and I put orange silicone around the nose bearing and the braether.I got this tip from Rich over at Jacksic Racing.The loctite seems to thin even though people swear by it.Good luck

First time I have heard of this. What exact type/number are these?

The dow corning is # 730 and the orange silicone is just a 3m silicone sealer.These are good products.The 730 is what they use to seal the aircraft engines,you know its got to be good if its flying.captek

Findings!
 

Engine is out . . . inspection of No. 1 cylinder stud (exhaust/forwrd). The nut was easily removed, but I needed to use a stud remover to get the stud out. Here's what the stud looks like.
http://forums.pelicanparts.com/uploa...1176689976.jpg

I thought the threads were just full of junk, but when I started cleaning the threads - I found a helicoil!! I had no idea.
http://forums.pelicanparts.com/uploa...1176690100.jpg

Here's a better picture of the POS helicoil.

http://forums.pelicanparts.com/uploa...1176690146.jpg

On the exhaust side of the head, you can see discoloration at 2:00 and 5:00.


http://forums.pelicanparts.com/uploa...1176690266.jpg

At least now I know what I'm dealing with.

So assuming I need to put inserts into the case,

1. should all of them be done or only the "bad" ones?

2. case savers or timeserts?

Thanks!

First off was the stud really hard to remove?Second was the nut torqed?I would ask Rich over at Jacksic Racing he is in new jersey but you can ship the case to him,very easy to deal with 908-362-8163.You are running the old style cylinders correct?No gasket maybe thats part of your problem.The picture looks like an heil-coil are you sure its not the aluminum threads?Did you remove all of the studs?Do they all look the same?Depending on how the threads look and how easy they go back in its hard to say to do all of them.But for my pieace of mind I would do all of them and go to the late cylinders,but again ask Rich he will know the guy knows porsches been doing them for about 40 years.Hope this helpsCaptek

that doesnt look like a helicoil, if you look at a cross section of that it is triangle shaped a helicoil is diamond shaped. looks more like pulled threads. as for overtorqueing has your torque wrench been calibrated the click kind are notorious for changing and causing overtourqe. all it would have taken would be to drop it in between doing the banks and both sides would be torqued differently

Steve, see here: http://forums.rennlist.com/rennforums/showthread.php?t=111791&highlight=gasket for some information about gaskets for the early-style 964 cylinders. I am running with this for about 18.000 miles and there is no sign of blow-by. Walt at Competion Engineering did an outstanding job. Cheers,
Ingo

I put a magnet on the "coil" - no attraction.

Thought (hoping) it might be a stainless coil, so I pinched a piece between my thumb and index finger and it crumbled easily. I'll take a close look at the case, but have to agree it certainly does look like pulled threads, though I've never actually seen one.

What next to repair, Timesert or Case Saver?

http://forums.pelicanparts.com/uploa...1176770406.jpg

Timecert for sure those things go in if there done right and you wont have to worry anymore.The case hole gets machined bigger and then rethreaded and then the timecert gets threaded in to the case,if my memeory serves me well.But somehow when yuo install the stud the timecert gets locked in the case.Again I always ask Rich at Jacksic,always quick to help and knowledgable.Captek

I'm betting that something weird happened to this engine case a long time ago before you were the owner. I don't see how you could have caused this to happen, from the events you describe...

-Wayne

Did you remove the studs yourself?How did you remove them?Did you put heat on the base of the stud hole?Captek

Thanks for the vote of confidence, Wayne! The only good thing to happen yet.

Captek: Thanks for your interest on this, too!

Did you remove the studs yourself?
A: Yes, but I've only removed the one that was loosest.
How did you remove them?
A: I used a 10 mm collet style stud remover. (See pics)
Did you put heat on the base of the stud hole?
A: Didn't need any heat. I didn't use Loctite Red.

http://forums.pelicanparts.com/uploa...1176842851.gif http://forums.pelicanparts.com/uploa...1176842859.gif

I,am not sure I understand,you rebuilt this engine and put in the arp studs but when you removed the old ones how did they come out?And when you put in the arp studs you did not coat them with anything?

Got all the heads off today. Also was able to look at the two pulled stud holes - completely smooth... No. 4 head looks like it just came back from the machine shop. Also found wide variety of torques on the head studs on the right side. Some were less than 30 and some were more than 60. I know my torque wrench couldn't have been that inconsistent. I'll post my diagram later.

Captek - My memory is that the ARP studs came already coated on that end, but I might have put a Wurth sealant on, too. You can see what looks like remnants of sealant on some of the studs.

http://forums.pelicanparts.com/uploa...1177301922.jpg