Retorquing headstud nuts on 86 carrera

[nene]

I was adjusting my valves today and found a weird nut that I could not remember taking off. I started looking around where it might fit, and found that it went to the #2 cylinder head, so I put it back and started tightening, but unsure of the required torque. It does not look like the stud is broken as it is tightening up. Your help would be appreciated.

Serge

[Bob Kontak]

Bottom or top. If bottom may be a partially sheared head stud.

My SC is 25 foot pounds.

[nene]

Bob, the bottom head. What do you mean by sheared?

[Bob Kontak]

I am not trying to freak you out but..........

In 1997 I got under my new to me 81 SC and was prepping to do my first valve adjustment.

Pulled the cover and plop went the bolt into the oil catching pan. Cylinder #5.

Called the Porsche dealer and asked what the torque settings were to put it back on and the service guy said, I will buy you a beer if it tightens back up. It did not.

Once close to 25 ft lbs were applied, the bolt finished shearing.

Shearing means corrosion on the shaft of the dilivar studs. A pit occurs. Heat cycling causes the bolt to shear across the stud. Not the long way, the short way. I think the term is axially.

Torque it up to 25 and prepare for the Right of Passage.

[nene]

What I don't understand, is why would the nut just come off by itself and not along with the stud?

[Bob Kontak]

If the stud partially shears - holding on by a tiny bit on the outer circumference - the torque has been released. Nut can vibrate off over time.

Torque it up and see if you have gotten lucky. Hope you have.

[nene]

I don't have a torque wrench, but borrowing one tomorrow. I will see. Now, if the stud has broken off or loosened, would my compression be much lower than my other cylinders?

[Bob Kontak]

Doubt it. Think about where the torque is. At the base. Three still holding it on. S/B ok for a while then (at some point in time) the cylinder starts to do it up and down clacking, pounding away at the case/cylinder interface.

Torque it up. Try it by feel 25 is a pretty decent squeeze but by no means a grunt tightening. You should know pretty quick. If you can over-torque it -and back it off tomorrow - you are golden.

[nene]

Well, if 25 equals a very good hand tightening, than I should be ok, but I wanna use the T wrench for sanity reasons. What's your take?

[Bob Kontak]

My take from a VERY conservative standpoint is that you have a broken head stud. Keep in mind, I do not want to pimp you. Right?

If you can snug it up reasonably tight, I am talking like an oil pan bolt on a 'merican car, which takes about 18-ish. If it holds, the gods are smiling on you.

Chill till you get your torque wrench and then do that one and if it holds at 25 do the others. Don't back them off, just tighten till 25.

The car is a squillion years old and who knows what hacks have worked on it.

If it holds at 25 you don't have a head stud problem. Frankly, at 18, you don't have a problem either.

[nene]

Just to shed some light on my car, supposedly the PO's PO (Porsche Master Mechanic) rebuilt the engine (whatever that means). I have pictures of the engine out and that's about it, so I am thinking, is it a wise decision to replace studs when the engine is taken apart? The engine has 199k and the engine does not leak, so it doesn't make sense to me that with this many miles, the mechanic didn't do some diligence. Bob, when you say 25, I assuming 25 lbs?

[IXjamesXI]

Everything Bob said is true, and it's happened to me.
Head Stud Nut Backed Off..Cyl 4

I hope that your stud isn't broken or pulled, but I would bet that its broken. Did they rebuild the engine using the stock exhaust studs that were there? The good news is there are some great books out there, one of particular merit written by our host... plus lots of folks willing to lend advice here.

[safe]

Originally Posted by nene

Just to shed some light on my car, supposedly the PO's PO (Porsche Master Mechanic) rebuilt the engine (whatever that means). I have pictures of the engine out and that's about it, so I am thinking, is it a wise decision to replace studs when the engine is taken apart? The engine has 199k and the engine does not leak, so it doesn't make sense to me that with this many miles, the mechanic didn't do some diligence. Bob, when you say 25, I assuming 25 lbs?

If it was recently rebuild you might be in luck. Stock bolts are supposed to be retorqued after a few hundred miles. It might have just lost torque.

Yes, its wise to replace those studs, almost mandatory.

[Bob Kontak]

Originally Posted by safe

If it was recently rebuild you might be in luck. Stock bolts are supposed to be retorqued after a few hundred miles. It might have just lost torque.

I like this idea. When factory new, the 911 has a 1000 mile service that definitely adjusts valves but I am not sure they check stud torque. Seems like a no brainer since all is opened up, though.

Yes - 25 ft lbs but do some checking to make sure on the exact amount.

I did a little checking and found this E Sully comment from 2009:

This has always bothered me. Waynes book states 23.5 ft-lbs, retorque after 500 miles. The Clymer book states 23 ft-lbs. No mention of retightening. Haynes book states 21 ft-lbs, no mention of retightening. Andersons Porsche 911 Performance Handbook states 25 ft-lbs for steel studs and 29 ft-lbs for Dilavar, no mention of retightening. The factory manual states 11 ft-lbs, then 90* turn, no mention of retightening. The local dealership tech believes Porsche manual should be followed, no retightening of nuts. I believe Porsche used some intelligent engineers over the years and might be the best route to take. Perhaps it is different for built engines pushed hard with higher horsepower, but can anyone give me a reason on a standard rebuild to use a different method than the factory manual?

I think I would be a little confused after reading this. However, you have Dilivar studs if original. I think 23-25 is perfectly safe. 21 like the Haynes book says should be plenty - if all the same - but I would defer to the 23-25 range as the 3.2 has a bit more compression than earlier models. The factory instructions sound like stretch bolt instructions and yours are not stretch bolts. Stretch bolts are never to be touched again without replacement.

[nene]

Thank you again for your suggestions and hope all goes well.......................we'll see! I guess I can always retighten if needed.

Serge

[nene]

Sigh of relief! I put back the stud nut that was loose and retightened to 23 ft/lb and it did not break! FEWWWWW!!! I also tightened the rest and did find that one or two were a little loose, but all went well. Thanx again to everyone for the info.

Serge

[JAR0023]

Awesome. Now go by a lottery ticket before your luck runs out. -J

[Canada Kev]

He probably used up already...

[nene]

Interesting, after inspecting some of the studs that you could see the top to, I noticed that they had the "yellowing" finish some parts are coated with. I think the previous, previous owner did install new studs.

[nene]

Update, I just started the car after tightening the Stud-nut and performing the valve adjustment ant they sound a little louder, but in looking at other thread, this appears to be normal.