Heard interesting story today. One local had heads of from his '84 S euro 16V. When he put them back on some head studs were stretching like crazy. So much so that when he desided to replace them it was very difficult to get heads off as engine was on the car, they were so much longer than before. It appears those that stretched didn't have light coat of engine oil on the threads like stated in WSM. This was only mistake it seems. Correct torque was used. When first one stretched he loaned other torque wrench and both appeared to work flawlessly. How can they stretch so much just because of missing drop of oil? Could understand wrong torque number for those but not stretching that much to interfere head removal even though it's close when done inside engine bay.

 

This is odd. Oil on the threads removes friction there ard results in more stretch. No oil, less stretch.

And to stretch them enough to be noticable and a problem in removing the heads would be hard to do. I'd think the stud would break before then.

Wrong studs replaced? How many threads were showing above the nuts?

 

All studs including those that stretched were all original. He tried to reuse them. Stretched ones were replaced by used taken from similar vintage 944. No problems on those or originals that didn't stretch at first try. Don't know how much thread was showing. Haven't seen them yet.

 

Years ago I rebuilt a 84S engine that had overheated blowing a head gasket and warping one head. On reassembly, if my memory serves me well, all the upper head studs got to about 3 pounds of being torqued when they all started to stretch. I had to replace all the upper studs. I think they must be susceptible to fatigue that is exaggerated by overheating.
Fred

 

Thanks Fred. Makes sense, blown head gasket was reason for head removal. Thing heads were straight though. Don't remember them needing work other than cleaning, new seals and gaskets. Hope it stays together even though all studs weren't renewed.

 

Once you torque a stretch stud to its limit, the next time you torque it down it will often 'go plastic'- basically stretch like metal silly putty - when you get close to the tightening torque that produced the stretch first time around.

Not unusal though. Sometimes you get away without replacing them, sometimes you don't.

Greg

 

I've had the heads of my Euro twice and had no problems. First time was for head gaskets but I never really boiled it.

When torqued down, only one or two threads of the bolts extend through the nuts.