Loose Head Nuts

LynnsABCs · 09:04 AM

jpnovak · 06-03-2003, 09:37 AM

Glad to hear there was no damage or any broken or pulled (especially with a 2.7) studs. You sound ready to put some serious miles on the car.

Wayne 962 · Wayne 962's Garage

Uhhh, your mechanic doesn't sound too experienced in this problem. First off, an exhaust leak on a 911 2.7 is an easy thing to hear and diagnose - I can hear it when they are driving down the street. Blaming it on the muffler, well, perhaps it could have been true.

Not to rain on your parade, but there basically has to be a reason why the nuts on the studs came loose. On 2.7 engines, there's probably a 98% chance that they came loose because they have pulled head studs. If the studs were properly time-certed or had case-savers installed (preferred) then they should not pull and should not come loose.

It is possible that the previous rebuilder did not torque them properly, and they came loose. This however, is a very remote possibility. Having the head stud nuts fall off of the head studs is a pretty good bet that the head studs have pulled.

"But they tightened up when we retorqued them" you may say. This is indeed the case again with most of the pulled head studs. What happens is the stud pulls out when the engine is hot, reducing the stretch on the stud. When the engine cools again, the nut becomes loose and typically can be spun off with very little force. Heating/cooling over a few cycles of this (turning your engine on and off) will cause the nut to eventually rattle and fall off of the stud. When you go to retighten it, you will find often, that it does tighten up. This is because you are tightening them up on a cold engine and then "readjusting" for any distance that the stud may have pulled out of the head. Thus, they often can be retorqued.... for a short time.

" The mechanic assures me the case must have had case savers installed in the recent undocumented rebuild or the nuts would not hold the required torque value. "

Note that the above statement is not a good assumption.

Having the studs retorque is great if you are selling the car, but 99.9% of the time, once they start to pull, they will indeed pull out more (and quicker) after you tighten them. The material is weakened, and will not hold the stud as well. After the first time that they pull, it's only a matter of time (after 2-3 retorques) that the material will no longer grip the stud and will simply spin.

This is exactly what happened on my 2.7 when the fan belt snapped and the engine overheated. 400 miles or so later, the studs started to loosen, and then wouldn't take a retorque.

If the previous owner was savy (and slightly dishonest), he would have tightened up the head studs, let you drive it for a few miles, and all would have seemed well. A PPI may or may not have caught this problem, if the previous owner had just recently tightened up the studs. The best way to avoid this is to have documentation that case-savers have been installed in the engine (good to put it on the bill of sale, just in case you need to go to court).

beepbeep · 06-03-2003, 12:02 PM

Dunno anything about pulling studs but short rubber hose with one end in your ear and other on head/cylinder joint will revel if there is any exhaust leak.

Alan Cottrill · Alan Cottrill's Garage

can anyone describe the sound an engine makes with pulled/broken head studs?

would it be a low gurgling almost poping under acceleration when cold?

would it go away when warm?

I've been afraid to check the torque for fear of making things worse.

Rot 911 · 06-03-2003, 12:33 PM

Is this deja vu all over again? Didn't this conversation appear on a thread about a week ago?

Rot 911 · 06-03-2003, 12:38 PM

Ah here it is: Found my missing Horsepower!

It sucks having the ability to retain virtually useless knowledge. If only I could convert it to an income producing venture.

Wayne 962 · Wayne 962's Garage

It's possible that they are just loose, but it's also possible that I'll get struck by lightning today. The odds are with the first choice, by and far.

The sound the engine will make will be a phat-phat-phat type noise, especially on acceleration. Drive / accelerate next to a brick wall, and you will hear it easily.

"who assured us it was completely rebuilt by a reputable shop." What one person may think is a reputable shop, others might think are crooks. That statement doesn't really say anything...

Check the head stud nuts in about 150 miles. If any are loose, then you better prepare for a full rebuild within 1000 miles or so. After that, check them every 500 miles or so.

Side Note: It is important to remember that you *cannot* get an accurate torque on these bolts, except during the rebuild process (and shortly after, if you use anti-seize). The torque spec is for a lubricated joint (between the nut and washer) so if you torque them to spec dry, you will be under-torqueing them due to the increased friction. Is this bad? I don't know. But it will be under-torqued. Tigthen them more perhaps? With the head-stud breakage problem, I don't recommend this. There is no one answer to this question - Bruce and I disagree on the retorque issue. I say retighten at each valve adjustment - at least if they are loose, you will get back closer to original spec.

-Wayne

eurocarrera · 06-03-2003, 02:29 PM

Good advice. Looks like I will be checking my head studs every 6 months now (they are divilar on the bottom row). I plan to rebuild pretty soon anyway, and some ARP or raceware studs are going in.

Superman · 06-03-2003, 03:55 PM

I have been told that 2.7L engines often have this problem, even after a rebuild. You say the case has had case savers installed, and I cannot refute that. If it has case savers, then the head stud would not be 'pulling' out of the case, but rather, the nuts might simply be getting loose over time. Again, I have heard this is common.

What has happened is (possibly) that when the pre-rebuild engine pulled its head studs or broke them, the heads were allowed to bang against the cylinder tops. This deformed both the cylinder tops and the head mating surfaces ever so slightly. The seal between Porsche heads and cylinders is essentially a metal-to-metal seal. Flycutting heads is not commonly done during engine rebuilds, or at least it is easy to overlook. So, you may have head mating surfaces that are not flat. This allows the cylinder to rock back and forth enough to let the nuts get loose.

Again, apparently this is quite common after a 2.7 rebuild that did not include flycutting the heads.

Stacy R · 06-04-2003, 05:10 AM

Does the case have to be opened to determine if case savers were done or can a mechanic tell just by looking at it?

Superman · 06-04-2003, 06:13 AM

Good question. You know, I *think* you can see where the studs enter the case. That would mean that you can visually verify what's there. I also assume case savers or time certs have been installed. I just bet the flycutting step was skipped.

masraum · 06-04-2003, 07:00 AM

Did anyone besides me think this thread was the title of some sort of porn comedy??

masraum · 06-04-2003, 07:02 AM

Oops, maybe I said too much

Dan Owens · 06-04-2003, 07:04 AM

LynnsABCs,

If you or your son spoke with the previous owner recently to verify that the case savers were installed by his rebuild shop just call him back and ask him for the shop name and call them. I'm sure they have copies of the paperwork on what they did to the car and they may be happy to verify what they did. If the previous owner developes amnesia on who did the rebuild then I think it's a safe bet that his word isn't too credible. If that's the case then I'd be banking on starting a fund to pay for the rebuild.

1fastredsc · 06-04-2003, 07:06 AM

I don't think that the potentially installed case savers can be seen from the outside due to the those air flow deflectors around the base of the cylinders. But if they're missing from your motor then seeing these inserts should be easy.

SpeedracerIndy · 06-04-2003, 07:38 AM

Is this problem just with the 2.7s? I have noticed a loose head stud on my father's 88 when doing a valve adjustment. I also noticed one on my 81 (both on the exhaust side). Didn't the change to aluminum case in 78 solve this problem??

Superman · 06-04-2003, 08:05 AM

With the AL case, you should be able to just retorque them. On the other hand, what I'm saying is that if heads and cylinders have been spanking each other, then they will continue to rattle and loosen nuts until they are cut flat again.

Elombard · 06-04-2003, 09:19 AM

Lynn I dont think a PPI would have neccesarily caught this. I had one done one time and they were not interested in pulling the valve covers for it, because of the oil I guess. I know better now but I assumed a head stud check would be part of a PPI, in this case it was not. There was 2 pages of notes about little interior rattles and worn carpet that I could of cared less about and no info. on engine internals. Be careful out there folks!! Hope this works out, if not I have a good core 3.0 I will sell ya!!

Alan Cottrill · Alan Cottrill's Garage

back to tightening the head nuts.

i've seen many posts where people have found nuts floating arount unter their rocker covers. they simply put them back on torque the rest and away they go.

to achieve a proper torque is there any reason you couldn't remove each nut one at a time lubricate with anti seize torque it down and then go through the torque sequence again just to even everything out?