I’ve been in the depths of thread repair for various projects lately. This job involves a 2.7-liter 911 engine we are rebuilding to modified street specifications. It is well known that Porsche’s 911 magnesium engine cases have a tendency for “pulled head studs.” The fix – precautionary or not – involves the installation of a Time-Sert (or, Casesaver) for each of the 24 head studs. There are many ways to approach this job. This one probably takes longest. Mainly, because a Blake co-axial indicator on a 10mm stud is used to locate true center of each hole. From there, I drill the engine case to an appropriate depth for the new insert.
With each stud hole aligned in the mill, I also counterbore the cylinder spigots and stud hole with an endmill. This can’t be accomplished with the supplied counterbore in the Time-Sert kit. The reason being that the cylinder spigots sit proud of the case and will deflect the supplied counterbore.
I skipped a few photos here. But, this is the counterbored and threaded cylinder stud hole ready to accept the Time- Sert.
Time-Sert installed and ready to accept the factory head studs. This process occasionally distorts the ID of the cylinder spigot. So… whenever we are faced with a full rebuild. We have the case spigots resurfaced, and also make a light pass on the ID of the spigots to ensure the factory tolerance of .003″ to 004″ clearance with the cylinder barrel is achieved.