1979 911SC - Broken Head Stud - minimum scope?

[ammonman]

There is an exhaustive thread about this topic https://forums.pelicanparts.com/911-engine-rebuilding-forum/137346-re-ring-alusils.html. After reading through it along with several others and on the advice of the mechanic who reconditioned my heads I honed the cylinders with a silicon ball hone and put new Goetze rings on. The rings seated immediately and I get no smoke on startup other than the occasional time when the car has sat a while. The mechanic who gave me the recommendation said he got it from a friend in the trade who is a long-time mechanic for one of the very well recognized Porsche race teams. He said that before he got this advice he had re-used a set of Alusil P&C with new rings for his own SC. Told me it took a year for the rings to finally seat but eventually they did. Just my experience and YMMV.

[craig.wilson1]

So I think I've found another issue and I think it's probably the main cause of the loud noise and reduction in power. It looks like the threaded hole in one of my heads (originally for the SAI manifold injector) stripped out and I've lost the plug. So the broken head stud I found earlier probably wasn't the root cause. It doesn't change my plan to change out the exhaust head studs, just adds some scope to the head work.

[gsxrken]

Haha- very common issue. Grab 2 spares and keep them in the glovebox for insurance in case another one lets loose far from home.

[PeteKz]

Yup, common problem and it makes a lot of noise, but not likely responsible for a reduction in power.

After that happened to me a couple years ago, someone here said that a pipe thread plug (1/4" NPT) is almost the same pitch as the m8(?) plugs, and will tighten as it goes in, being a tapered thread. Yes, it will somewhat mess up the threads in the head, but it has stayed in, and I don't ever plan to put the air injection system back on.