Head Stud Problem
 

I AM REBUILDING A 1983 SC 3.0. YESTERDAY, I MATED THE CAM HOUSING TO THE HEADS AND TORQUED ALL THE STUDS/BOLTS TO 80% THEN I WENT BACK AND TORQUED THEM TO SPEC. EVERYTHING WAS GOING GREAT: GOOD SEAL, A SMALL, UNINTERUPTED BEAD OF LOCKTITE SQUEEZED OUT OF ALL THE APPRORPAITE PLACES. BUT...WHEN I WENT TO FINAL TORQUE #17 NUT (OUT OF 18 IN THE SEQUENCR SUGGESTED WAYNE'S BOOK) IT WOULD NOT TORQUE DOWN! UPON INSPECTION, THE STUD WAS STRIPPED BELOW THE TOP 2-3 THREADS AND THE STUD WAS TURNING! I DON'T KNOW WHAT COULD HAVE CAUSED THIS. ANY SUGGESTION? WHAT IN THE WORLD DO I DO NOW? I HAD THE HEADS REFURBISHED BY OLLIE'S IN CALIFORNIA WHO SPECIALIZE IN PORSCHES...ANY SUGGESTIONS--I SURE WOUL DHATE TO HAVE TO TEAR DOWN 1/2 MY ENGINE, ETC...

What a *****. Sounds like you have stripped one of the head studs out. Maybe. It is not clear from your discription what exactly is going on. You say the stud itself is turning? You also say the the stud is stripped below the top 2-3 threads. This implys the nut is turning and the stud is fixed. Is it?

The heads are not a factor as they are only a spacer in the overall operation, ie bolting the heads and cylinders to the block. If you have had time serts or something equivalent installed in the case and are using good head studs and nuts there should be no problem. IF you did not have some kind of case saver/time serts installed in the case you are likely in for a more expensive education than you wanted. Also there is the possibilty that the studs broke. Again - oh well. SOrry.

I too am a little confused by your description of the problem, which threads are stripped? The ones on top? Maybe you could post a picture for us? :confused:

The case/motor that you are working on does not normally need case savers or time certs, it is the toughest case ever produced by Porsche for a 911. It's easily capable of handling the stress and heat of turbo motors putting out 500+hp, so the 180hp SC never wears it out. :cool:

THANK YOU ALL FOR YOUR CONCERNS, GENTLEMEN. THE UPPER LEFT STUD ON HEAD #1 WAS TURNING DEEPER INTO THE HEAD SO THAT EVENTUALLY IT IMPACTED ON THE COOLING FIN BELOW. WHEN IT IMPACTED, IT STOPPED (FORTUNATELY, IT DID NOT BREAK THE FIN) SO THE STUD AND NUT STRIPPED AS I CONTINUED TO TRY TO GET TO THE FINAL TORQUE VALUE BEFORE I REALIZED WHAT WAS HAPPENING. AGAIN, FORTUNATELY, I WAS ABLE TO BACK OFF THE NUT, REMOVE THE CAM HOUSING COMPLETELY AND INSPECT THE SITUATION. THE STUD ALSO BACKED OUT WITH NO PROBLEM. I'M TOLD INSTALLATION OF AN 8MM TIME-CERT, A NEW STUD/NUT, REASSEMBLY AND I'M OFF TO THE RACES AGAIN! IT SEEMS ANY QUALITY MACHINE SHOP CAN INSERT THE TIME-CERT. DOES THAT SOUND REASONABLE? OLLIE'S PORSCHE MACHINE SHOP IN CA HAD NEVER HEARD OF SUCH A THING HAPPENING. THE MYSTERY IS WHY THE STUD TURNED INTO THE HEAD BEYOND THE END OF THE THREADS. CIRCUMSTANTIALLY, THE THE FORCE OF THE 80% TORQUE WAS NOT ENOUGH TO TURN THE STUD, BUT THE FINAL TORQUE WAS. A SET-BACK FOR THE PROJECT BUT NOT THE DISASTER I HAD ORIGINALLY SURMISED.:)

Post a picture, dude. You are making no sense whatsoever. :cool:

Yes, need further clarification. It sounds like the head nut AND stud were rotating as a unit.

Sherwood
http://members.rennlist.org/911pcars

Was the washer, under the head nut, left off?

THANK YOU ALL FOR YOUR CONCERNS AND SORRY FOR THE CONFUSION BUT HERE GOES:

DENIS: I DON'T HAVE A DIGITAL CAMERA, SO NO PICS;
SHERWOOD: THE NUT AND STUD WERE BOTH TURNING UNTIL THE STUD IMPACTED ON THE COOLING FIN BELOW AND STOPPED, THE NUT CONTINUED TO TURN, THUS THE STRIPPING;
JACK: THE WASHER WAS INSTALLED.
ALL ELSE WHO ARE INTERESTED IN THIS UNUSUAL CIRCUMSTANCE:
NORMALLY, WHEN A STUD (WHICH IS THREADED ON BOTH ENDS SEPARATED BY A SEGMENT WITHOUT THREADS) IS IMBEDDED INTO A PART, IN THIS CASE THE HEAD, IT WILL ONLY SCREW IN TO A CERTAIN POINT, THAT POINT BEING WHEN THE THREADS STOP. WHEN I TORQUED THE NUT TO 80% OR SO, THERE WAS NO PROBLEM. WHEN I TRIED TO TORQUE TO THE FINAL 100%, IT NEVER TORQUED, SOMEHOW. NOT HAVING SUCCESS REACHING THE TORQUE VALUE AS ONE WOULD HAVE EXPECTED, I BACKED OFF THE NUT, LOOKED AT THE STUD (APPEARED FINE), REINSTALLED AND AGAIN TORQUED THE NUT (W/ A SOCKET). THIS TIME, APPARENTLY, THE STUD TURNED RATHER THAN THAN THE NUT TIGHTENING. AS THE STUD TURNED (SOUNDS LIKE A SOAP OPERA), IT SCREWED INTO THE HEAD, UNTIL IT PROJECTED OUT THE UNDERSIDE AND IN CONTACT WITH THE COOLING FIN BELOW, THEN STOPPED. NOT KNOWING WHAT IN BLAZES WAS HAPPENING, I CONTINUED TORQUING IN UTTER PERPLEXITY. SAYING TO MYSELF, "WHAT, IN BLAZES, IS HAPPENING? (PARAPHRASED, OF COURSE) SOMETHING IS AMISS." AND SOMETHING WAS INDEED AMISS. I HAVE CONCLUDED THAT THE STUD FAIRY (NO PUN, HERE) INTERVENED AND SOMEDAMNEDHOW, THE TORQUE VALUE AT 80% WAS ENOUGH TO TIGHTEN THE NUT, BUT THE TORQUE VALUE AT 100% WAS JUST ENOUGH THAT THE STUD TURNED, NOT THE NUT (THE STEEL NUT, NOT THE NUT WITH THE TORQUE WRENCH, THAT NUT BEING MYSELF). MY NEXT QUESTION IS, "WHY DOES IT TAKE TWO PEOPLE TO SCREW IN A LIGHTBULB?"

The head studs on a 911 motor do not thread into the head, as you describe, but rather pass through the head(s) and cylinder jugs, where they thread into the engine crank case. The jugs and heads slip over the studs, (135mm long/exposed, installed), then 24 special flat washers and barrel nuts secure the heads/P&Cs to the case. The torque value for these fasteners is approx. 25lbs. (Don't have my books handy). You couldn't strip a stud w/ 25lbs. if you wanted to.

The cam towers do not need to be installed to attach heads. They use separate fasteners. See photo:
http://forums.pelicanparts.com/uploads/tysonrebldd.JPG

Once again, a photo would clear up the description, but if not possible, could you be referring to a cam tower/head stud, the small ones that protrude from heads to attach cam towers, (12 on each side of motor I think)? What torque value are you using on both sets of fasteners? Which books are you using? :cool:

I think that he is referring to a cylinder head stud that is other than what is typically called the cylinder head studs. The long studs that are threaded into the case are called cylinder head studs. However, the studs that hold the cam towers to the heads are also cylinder head studs (by definition). The exhaust studs that hold on the heat exchangers and the intake studs that hold on the manifolds are also called cylinder head studs.

If you read his post more carefully, you will see that he is talking about the studs in the heads that are used to hold on the cam towers. When he says he torqued 17 of 18 studs, it's a dead giveaway, because if he was talking about the head studs that mount in the case, he would have to torque 12 of them.

-Wayne

YEP, IT'S THE CAM TOWERS I'M REFERRING TO (DOH!). A NEW FOUND RESPECT FOR TECHNICAL WRITERS HAS EMERGED SUDDENLY. THERE ARE 18 STUDS PER SIDE (THREE USE BARREL NUTS) AND ALL USE THIN SPRING-TYPE (WAVY) WASHERS. OOH, WAIT..., PROFESSOR DEMPSEY HAS JOINED THE DISCUSSION AS I WRITE...

THANKS, PROFESSOR! NOW THAT THE LIGHTBULB HAS COME ON, IT USUALLY TAKES TWO PEOPLE TO SCREW IN A LIGHTBULB BECAUSE THAT'S ALL THAT CAN FIT IN THERE! (GROAN). BUT MORE SPECIFIC TO WE MOTORHEADS, CAN AN ORDINARY, RUN O' THE MILL MACHINE SHOP INSTALL AN 8MM TIME-CERT IN THE MANGLED HOLE OR DO I NEED TO SEND THE HEAD TO A SUPER-DUPER SPECIALTY SHOP THAT HAS MARBLE COUNTER TOPS AND A PLASMA TV IN THE BATHROOM? AND DOES PELICAN HAVE THE REPLACEMENT STUD I NEED? AND, HOW IN THE WORLD DO YOU GET THE SUPER THIN, ALMOST IMPERCEPTIBLE HARDENED FILM OF LOCKTITE B-52 OR WHATEVER (ORANGE JUNK) OFF THE CAM AND THE HEADS? HMM? P.S. SPEEDER-THANKS FOR YOUR INTEREST IN MY DILEMMA!

No problem, Jim, I've recieved immeasurable amounts of free help around here. And Wayne, you are right, it came to me actually as I was typing that last reply. :cool:

Yes, it makes sense now. You have damaged studs, causing the nuts to lock on them, before tightening down, causing the stud to turn in past where it should be and finally the damaged part giving way and threads stripping. Not a pretty picture as it will cost as much as head studs would. IN othe words the cam towers have to come off and be seperated from the heads. Good news is the cylinders. pistons and case halves stay intact.

What I suspect is that the studs were damaged somehow. The damage caused the nuts to sieze up on the stud causing the stud to turn. Removing the studs, re threading them and reinserting them, with red loctite will fix this problem. Studs that were stripped must be replaced. At least I suspect it will based on my assumptions on what is wrong.

Another shot of the cylinders with head studs protruding:

http://forums.pelicanparts.com/uploa...26AA_small.jpg

Yes, any normal shop should be able to do this. We do have this stud in our catalog:

http://www.pelicanparts.com/catalog/shopcart/911M/por_911M_enginB_main.htm

Go to clylinder heads - it's on the page after that...

-Wayne