911SC Head Stud Problem Cause

[Coloradocurt]

Sorry, but I did search, so..................
I recall MANY years ago when the common problem with the 1975-77 2.7L 911 engines was the lower head studs stretching due to the thermal reactors and the heat they produced. The standard remedy during a rebuild on those 2.7's was to replace the lower studs with Dilavar studs. Now in doing some research on typical engine-related problems on the 911SC I'm seeing that broken Dilavar studs is not uncommon.
Can someone point me to a good, authoritative technical discussion of the "why" these studs are having problems? I often see opinions that the 3.0L 911SC engines are good for 200K miles (and more) when properly cared for. So are there any tell-tale contributing factors causing these studs to fail? And re the 3.2L engine, does this issue carry on to that series of engines, or did the Porsche engineers solve the head stud problem when they did the 3.2L engine (and if so, is that solution now part of the remedy for 911SC engines that have broken studs?
In the hour (or so) of searching about this 911SC broken head stud problem all I was able to find typically focused on symptoms and procedures/costs for repairs.
Thanks,
Curt

[Reiver]

I'm no expert but here goes.
If a dilivar stud is compromised by a scratch etc. then it is open to rust and eventual fracturing as it is brittle.
911's driven conservatively on short rides, not brought up to proper temperature, will sweat and the moisture created will not be burnt off/ evaporated.
This can lead to head stud failure.
I had an '83 930-16 (US motor) with 230k miles on it and all the original studs after 30 years of use, never a top end either...ran great.
I've had wrenches tell me they see more head stud issues with garage queens that were driven as I described above.
The 930-10 I have in the car now was rebuilt at 67k miles because it had 3 broken head studs from being a garage queen (I'm glad it was as I got a terrific rebuilt motor out of the deal).
Don't take multiple short cold engine drives and then park it for days....warm it up to op temp. then drive the piss out of it as was intended.....they last longer that way.
3.2's can have the very same issue.

[Bob Kontak]

Originally Posted by Reiver

If a dilivar stud is compromised by a scratch etc. then it is open to rust and eventual fracturing as it is brittle......................
I had an '83 930-16 (US motor) with 230k miles on it and all the original studs after 30 years of use, never a top end either...ran great.

+1 on pitting on the shaft - then they shear - axially. On mine, one stud sheared but was still held together by a nib on the edge. Nut plopped into oil drain pan as torque was removed from shear and it vibrated off.

I bet Arizona is as good reason why you did not suffer the problem.

I bought Raceware back in the 90's to replace. That's a $$ owiee now. But they are not giving away ARP or Supertec either.

[Reiver]

Originally Posted by Bob Kontak

+1 on pitting on the shaft - then they shear - axially. On mine, one stud sheared but was still held together by a nib on the edge. Nut plopped into oil drain pan as torque was removed from shear and it vibrated off.

I bet Arizona is as good reason why you did not suffer the problem.

I bought Raceware back in the 90's to replace. That's a $$ owiee now. But they are not giving away ARP or Supertec either.

Probably right, the car stayed in the SW and dry areas all its life. The 930-10 doesn't have any dilivar in it.
The guy that built the row has 3 cars/engines in for broken studs...2 - 3.2's and a 964 with broken dilivar.

[SCadaddle]

Originally Posted by Reiver

The guy that built the row has 3 cars/engines in for broken studs...2 - 3.2's and a 964 with broken dilivar.

And a 930. Or 2. And I still can't beat him out of your old cat bypass pipe!