964 - Repeat of Head Stud Woes

[sms1305]

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!

[cstreit]

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.

[sms1305]

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:

Broken Head Bolt on C4- & in denial...

Thanks!

[sms1305]

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?

[briankeithsmith]

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...

[Eagledriver]

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

[Steve@Rennsport]

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.

[briankeithsmith]

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

Go with what Steve says

Brian

[sms1305]

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!!

[Groesbeck Hurricane]

Steve,

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

[Steve@Rennsport]

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)

[sms1305]

Originally posted by Steve@Rennsport
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.

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!

[cstreit]

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...

[Candelaria]

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

[Twystd1]

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

[sms1305]

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!

[sms1305]

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.

[sms1305]

... and here's what the wire looked like.

[Wayne 962]

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

[sms1305]

But how do you get the stud back in??