[Wayne 962]

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).