Question about broken head studs...

[Wayne 962]

Got this question today in my email:

Hi wayne ,I have just received your Rebuild and Modify 911 book.So far ,It's great.I have a 1979 930 sold originally in Frankfort,and imported into the U.S. in 1995 to Naples ,Fl.with 12,000 miles on it. It now has 94,000. I have just bought it. Not much has been done ever to it.( Battery ,New Radio, New struts 3000 miles ago and an alternator, which was installed incorrectly and never really charged ,hence ,they put a new battery in it when I took delivery.This is my 2nd Porsche ,1st 911,I new when I bought it with this kind of mileage on a Turbo it would need a rebuild soon.I removed the alternator ,only to see 3 broken head studs ,2 on the # 2 cylinder and 1 on # 4. You make much reference to the bottom hd studs breaking ,but none to the top yet as far as I have read.Any ideas why this could happen other than extreme abuse. When I first tested the car ,I could hear the flap ,flap of an exhaust leak,but the car runs really good .I have stopped driving it ,since noticing the studs. I have been searching for tech manuals,but to no avail.I was very glad to find your book ,as I plan to rebuild the engine and transmission. Any comments on the upper hd. studs? Thank You

[Wayne 962]

Answer:

Porsche used Dilavar on the lower *and* upper studs for the 911 Turbo engines. So the problems that you normally see with the lower studs on the normally aspirated (NA) cars, also occur with the upper studs on Turbos (although it's not as common, since the lower studs are where the exhaust heat is, and thus where the most stress is located).

The flap-flap sound that you are talking about is a very bad sign, and one that probably would have been pointed out if you took it to a qualified mechanic for a prepurchase inspection. It's wise to have stopped driving the car in this condition, as you will probably cause damage to your heads and/or pistons and cylinders if you continue to drive it.

The solution is to tear down the top of the engine and replace the head studs. Unforunately, since three already broke, you will probably have a difficult time extracting the remaining ones. See "101 Projects for Your Porsche 911" for a project on stud extraction using EDM - which is what was needed on my 911SC engine.

-Wayne

[magic930]

My '87 turbo also had 1 intake side stud broken on the #5 cylinder. All the others were fine... But there were oil leaks at all cylinders except 2 and 3.

[cstreit]

I removed the alternator ,only to see 3 broken head studs

What I wanna know is how did removing the alternator reveal 3 broken head studs?

Good answer though. That flap flap sound is pretty common in motors I've heard with broken or pulled studs, usuallu means more than one is broken on a cylinder.

[magic930]

Once the alternator is out you can see under the shroud and with a flashlight see all the intake side studs.

[cstreit]

Good point... I was just being a wise guy anyway... ..that and it's usually the exhaust side tha breaks.