One Broken Stud

[DSPTurtle]

For close to eight years I have been watching this board dreaming of the day I would earn the opportunity to try my hand at rebuilding a 911 motor. Well... I am still waiting for that day. But at least now I have the car.
Last monday I took the day off to prep the 930S for an upcoming DE at Sebring. While changing the plugs I found a not so funny problem. Apparently the inboard intake stud on cylinder number 4 decided to split itself in half. After closer inspection I could tell that it broke from localized corrosion as described in Wayne's book. I pulled the remaining valve covers and the remaining studs appear to be okay. After consulting with a trusted advisor I have decided to attempt to repair only the one stud and be back on my way. Visions of cams and rods and pistons were in my head but I do not think I, nor the motor are quite ready for that yet.
Unfortunately the motor has to come out so the only "while you are in there" I am planning is to rebuild the tranny to replace all four sychros. (Yup, that is my plan right now).
For all the folks that say pulling the motor and trans are no big deal... I say up yours
I spent the better part of two days making that little project happen. Taking all this stuff off was a nightmare...



I had thought I could leave the exhaust in place since I am going to attempt to pull all three heads off as a unit using the manifold to hold them together. Well the first show stopper was the fact that the air injection was still attached to the heads and the only way I could figure out how to get to the 1-3 head mounting locations was to drop the manifold. Plus I noticed that when I reach into the hot side of the turbo I can move the shaft side to side ever so slightly so I figure I should either rebuild it or get a new one to install.
Fortunately the Porsche gods were smiling on me today and I did not snap any exhaust studs.



When I took the "helper spring off of the trans I almost killed myself. The spring went winging by my head and put a divot in the cement block wall. All the books and tech articles say that it is not a concern... hmm



With a little help from my wife, I was able to get the engine and trans out of the car finally. I have not been this dirty since I tore apart a junkyard 914.



Unfortunately it was 9pm by the time I had gotten everything tidied up a little bit so I was unable to pull anything apart just yet. But, my wife and I have an agreement... at least two of the "running" cars have to fit in the garage so I had to stuff everything under the 930S. I wonder if I leave it there long enough... will it reassemble itself???




Although I may not sound appropriately appreciative, I do realize that yes, this is what I dreamed about... be careful what you wish for.
By the way, any of you old hands ever seen a "Sperdiff" sticker on your trans when you pulled it out? Has "LEE" in red paint on the bellhousing. I am wondering what all of that is about... rebuilt diff maybe?
I look forward to hearing from you guys about your experience and thanks in advance for all the advice!!!

[Eagledriver]

Is your trusted advisor going to help you pull the motor again next year when you find 2 more broken studs? Do you know that the studs on your car are made of a material called Dilivar? If you replace the one stud and you use something other than dilivar you will have a leak at the cylinder to head junction. I don't blame you for not wanting to do more to the motor when it's apart but to not replace all the headstuds is silly. There is very little more expense to replace all the studs and you can use a better material. Search the engine forum on headstuds to get opinions on which ones to use.

-Andy

[Aurel]

+1
On a turbo, all the studs are divilar. They all need to be replaced. If you don`t want to replace the rings, keeps the P&Cs together. If the wrist pins don`t slide out easily, heat the rods. Use heat to remove all headstuds too.

Good luck,

Aurel

[DSPTurtle]

I hear you guys. But, the best advice I got was to pay attention to the motor as you take it apart. It will tell you a story of what it needs. The previous owner had it rebuilt about 40K miles ago. Looking very closely at the stud I can see exactly where the enamel was chipped and caused the corrosion.
I certainly plan on having to do this again in a year or two and at that point will tear it all the way down. For now I want to get it back on the road and have some more fun with it.
Who knows, as this gets further and further along I might get the bug and will ahve to listen to you guys talk me into splitting the case
As for now I think between the trans and the head stud and maybe a turbo rebuild or replace I have enough stuff on my plate that I don't want to scare the crap out of myself.

[Flieger]

Make sure you replace the Dilavar stud with a new Dilavar stud, not steel.

The expansion coefficient of Dilavar is about 20 x 10^-6 per degree Celsius

Steel: 11.5 x 10^-6 Aluminum/Magnesium: around 22 x 10^-6

(numbers from Porsche 917: The Undercover Story by Gordon Wingrove)

If you put steel in just that one head stud, it will warp the head as the engine heats because it will be clamping much harder than the Dilavar stud.

[DSPTurtle]

That is a really good point. Don't want one stud growing more or less then the rest. I wonder... since I will have the three heads off anyway, how much more work it woudl be to change the rest of the studs on that side. It seems like the new fully threaded studs from Porsche have the best reputation for not breaking or pulling. I would imagine that if all the studs on the one side were the same material I could still leave the other side alone???

[Flieger]

It all depends on how much you want to do before the real rebuild. You are planning on doing it right, at which point you will replace all studs with one type of metal. Some like Dilavar, when they are new they do a good job of not pinching heads. You can also get the "while I'm in there..."

I think 1 stud could hold you over until then. That way you would have all new studs along with a freshened engine.

[boeing 717]

Taking my engine out and doing a service was seriously the most fun, it was like an adventure seeing all these things that i had read about. Good luck. Just be careful the while your in there made me go WAY out of budget.
Good luck

JERRY