cracks and pulled studs...how would you know the unthinkable has happened?

[Kaleid]

With engines in our cars becoming increasingly old and many made of more porous substances than others (like magnesium), I always wonder- are there viable options for repairing cracked cases and making them fully functional again? Moreover, can an engine run ok in the short-term if it has a crack? I've seen threads about ditching a damaged case and all these pedigree cars out there with "factory replacement cases", but then I hear about machine shops out there who do a good job at fixing them. Has technology come into play with respect to being able to save a case present day vs. say 20 years ago?

Pardon the ignorance but I've never delved this deep on functionality of old 911 engines when the wear and tear starts to take its toll. Even an issue like pulled studs- how would you know unless you took the engine apart or unless you had a blatantly visible issue? Things like case savers (among others out there) would be a potential fix for this issue- but without opening your engine, would you know? Would the engine function properly with pulled studs? Just curious about all this since the notion of a "matching numbers" engine has always been an aspect linked to a car's value, Porsche or not. Any preventative measures out there to consider for engine block protection, extreme or not?

[edmayo]

You might suspect a pulled stud if you hear a slight soft exhaust noise more so when the engine is cold. Then putting a torque wrench to the head nuts will tell you if a thread is going away. Sometimes you also will know if when removing the exhaust valve cover a head nut falls out!

[chris_seven]

If the threads have pulled out then it is likely that Timeserts or Case Savers will solve the problem and these are quite straightforward to fit.

If the case has cracked then the location and nature of the crack is quite important. If there is a fatigue crack in the case then it is quite likely to continue growing and eventually it will become unstable and fail in a catastophic manner which could wreck the complete engine and may be cause other damage if the failure results in trip off road.

If you weld up cracks then you will need to check the case for deformation and line bore if needed. I guess you would also need to check spigots and other critical faces.

I don't think that there is a general rule you just have to try to fix whichever problem you are faced with at the time.