Driving with 1 broken head stud

[Daviboy]

Guys I am so depressed right now. I got home last Thursday and took the car for a spin before doing the 500 mile valve adjust. Had a strange sound when accelerating under load, only under load not when free reving the engine. Thought it was the fan belt too tight was a kind of screeching sound, adjusted belt and sound still there but now a kind of rattle noise. So I drained the oil last night and today I have removed the valve covers to check things and do the adjust and guess what, the lower rear head stud on #4 is broken only that one.
It was sitting on the valve cover but obviously when driving it was being rattled around by the rocker arm, which is not damaged thankfully. I just rebuilt the engine with new head studs et al.
I dont have the strength to tear the engine down again so soon and just wondered if it will be ok to drive for a while till I get the energy to tear down and replace again. Or would you just bite the bullet and tear down now???

[Daviboy]

I am not going to drive her. Just finished buttoning everything up after the valve adjust and took her for a spin. The noise is still there and I now know what it is, blow by on #4 got to be only happens under load obviously the more stress on the cylinder when accelaerating is allowing some movement at either the head side or the bottom end. So I am off the road again till I get some new head studs going to redo them all as I dont trust the batch I got....

[billybek]

That sucks! (or blows....)
I followed your overhaul thread.
Did you replace the studs at that time?

[Flat6pac]

Davie, you should have used steel. As in the past you opened the engine several times to get everything right so at this point you need to replace with steel studs. The dilivars dont retorque well and survive, especially if they are old.

Bruce

[Daviboy]

I did replace them, was not going to but I did and yes they were steel...

[lindy 911]

Can you share what studs you used? Where did you get them and what brand are they? Where did the stud break, down by the case or somewhere else? Sorry to hear your troubles; we all have them. Don't let it get you too down though. My motors coming back out for the third time because of a persistent nose bearing leak. I have to split the cases.

FWIW, the second time is WAY easier than the first, you'll feel like an old pro.


Lindy

[brads911sc]

Use Supertec. One of the best $650 you will ever spend. Sorry to hear this. Good luck!

[4sd911]

If you drive it with a broken head stud the head will move a bit against the cylinder, over time it will mushroom both the head and cylinder.

[ALEX P]

Really sorry to hear that Davy, I feel for you - I'm in the middle of a full rebuild that started off as a single broken stud but not after I'd just rebuilt it.

Seems the best stud options are 993TT (expensive), Raceware (very expensive) or Supertec (reasonable) I went for Supertec.

As others have said, I'm sure it will be much quicker & easier second time around.

Good luck.

[Daviboy]

I bought them from the local Porsche dealership all steel OEM studs. They will be going back fo analysis once removed from the engine. The one which broke did so about 2 inches down from the head stud.

[Geronimo '74]

Man, that sucks.
I followed your build somewhat too and I think you can only contribute this to bad luck.
***** happens, and it's never pleasant.

+1 on the Supertec studs, they're cheap and plenty strong.

[roadster49]

Just got this 911 SC in December. The PO that did not maintain it very well, so I anticipated some $$.

I took the valve covers off to adjust the valves today.

On the passenger side, I got the cover off and then from somewhere this broken stud fell. Now I thought like Davy that it was a broken stud and would have to tear the engine down. But I counted the studs holding the heads. There were 3 of these per each upper bank, for a total of 6. Checked the rest of the stud nuts and there again were 3 per each upper bank total 6 so it seems that is OK! The lower bank had 6 stud nuts per side. So that seems ok.

Total 12 studs per side bolted down.

So any ideas what this is or from where it came? Could the PO's mechanic just left it in? Anyway I think since all the studs seem to be in place I will finish adjusting the valves unless anyone feels something else is going on.

As Always
Thanks

R 49

[Flat6pac]

Your count is flawed, each side has 6 studs with capnuts up and 6 under the exhaust valve cover each side. Except on a Turbo, only the bottom row is dilivar, top row is steel. 24 studs hold on the 6 heads.
Bruce

[roadster49]

Not sure what to say.

If this is a capnut there are 3 up and 3 that are just nuts.

The bottom is all nuts???

Does that mean the engine has the wrong nuts? can these be changed without dropping the engine?

[brads911sc]

Where you from Roadster?

IMHO it is best to buy the Bentley and the two books Wayne wrote and learn what the head studs look like and properly troubleshoot and repair if needed. Driving with a broken stud is turning a $700 repair (if you go 24 Supertec) into a repair that can run into the thousands if you damage others parts by driving it that way. Just my .02.

[roadster49]

I am in Troy Michigan and have the Bently. I am new to being a Porsche mechanic, so that is my concern. I will get the books you suggested. When I looked at pg 030-11 in Bently it appears that I am ok with the intakes as I have the cap nut and hex nut for each of the intake studs as in the picture. The exhaust is all hex nuts, 6 per side.
so I counted a total of 6 cap nuts and 18 hex nuts = 24.

I was concerned about the one item I showed in the picture as I don't know where that fell from.

A question, do you re-torque the studs each time you adjust the valves?

Thanks,

[Flat6pac]

The only place that nut and part of a stud comes from is the exhaust side of the head. The stud part will be non magnetic, dilivar. That is why I said your count is flawed. Nuts or cap nuts all the same things are done, it holds the heads on. The torque on an SC is 25#ft. Do not retorque because the dilivar is set in it way until it breaks. Do not change the nuts because dilival will not like the retorque.
Let me post a couple pics that show the broken studs in a 78 engine

Bruce

[cole930]

Davy,

Here is something you might consider trying. I have a 930 and have had it for over 20 years. Over that period of time I have had a few studs break. I was actually standing the garage one winter, the car had not been driven for a few months, I heard a sharp "Ping" and heard something bounce across the garage floor. #4 bottom stud broke while sitting.

I jacked the car up a couple weeks later and took a look. Stud broke up toward the nut. I took a dremel and cutting wheel and cut the stud off a couple inches above the case, then for the next week I squirted PB Blaster on the stud at the case. On the weekend, using the broken portion of the stud I had cut off, I found that a 5/16 - 1/4 in. drive - 6 point socket would almost slip onto the stud. Using a couple long 1/4" drive extensions, I stuck the extensions through the head and then put the socket between the bottom of the head and the broken stud and popped the socket onto the extension. With the socket now sitting on top the stud I took a hammer a tapped the socket down over the broken stud. Once I had driven the socket down as far as I could I used a heat gun on high for about 15 min. to heat the case at the stud boss. I put a wimpy little 1/4 drive breaker bar on the extension at the top and backed the stud out like it was butter. I thought I was just lucky but have actually used this method 3-4 times in the last 6-7 years. Always after I installed a new stud and torqued them I never had a problem. All these broken studs and replacements have been in the past 7 years or so. In Nov. I tore the top end off the motor to replace head studs and redo gaskets to seal up the usual leaks we get. The heads, pistons, valves, and cylinders looked fine and all the replacements studs were still fine.

Not what I would necessarily recommend as a preferred practice but It worked fine for me for several years.

Cole

[roadster49]

Well you were correct. I was looking at the wrong parts. Here is a pic.

So now what? Supertec studs? rebuild kit? any recommendations for how to go forward would be appreciated or where to get parts. Professional shop to rebuild or try to do it myself?

Michael

[Walt Fricke]

Roadster

Cole has given the first account I have seen of someone who was able to replace a broken stud without top end disassembly! A really good trick to have up one's sleeve for the right occasion.

However, no doubt your stud failed because of rust. These parts are highly, and cyclically, stressed, both by thermal expansion/contraction, and with each revolution of the motor. It appears that rust creates a "stress riser" which allows a crack to form where otherwise it might not. The crack then gets deeper, and deeper, and deeper until the rest breaks. You may even be able to see a sort of semi-circular tree ringish pattern on the broken end.

Where one stud rusted and then broke, can others be far behind? Your picture shows the barrel nut on the unbroken stud is equally rusted, so one might assume that some if not all of your lower studs have rust on them.

It appears that there are two choices where you can't really go wrong: the Supertec studs, or one of the late 993 studs (the turbo?), though those are even more expensive than the Supertec.

There are other options. I just reused the studs on my SC when I rebuilt it a dozen or so years ago. No problems. But you do have a problem. I've used some "fake" dilivars (magnet mildly attracted through a black epoxy-like coating) on my 2.7 liter race motor. It has seen a hard life, but never a stud issue. But then it doesn't get exposed to water and road salt and the like. The old factory steel studs are quite strong, too.

As always, balancing economy with certainty is an individual thing.

If you see yourself as mechanically inclined, like fixing things yourself, and have the time, you certainly can do this yourself. Many here have gone this route. You start with a good book on the subject. I'd start with our host Wayne Dempsey's book on 911 engine rebuilding - Pelican is more than happy to sell it to you. It is incomparably the best resource, as Wayne is a child of the digital age and provides lots of color pictures he took to show what he is talking about. Also, his book is only about the engine.

So buy it, read it, and then decide how to proceed. You will see that some specialized tools are needed. They are not exorbitantly expensive, but for someone contemplating a one time job they may be a cost problem, You may be able to borrow those. Local shade tree 911 mechanics may be willing to come help you with the tricky bits. And it is always possible to take a partially completed project to a shop - if you don't want to tackle cam timing, you could just pay someone to do that for you, and then you can complete the work.

Browse (and search) around on this forum and you'll see plenty about guys doing it themselves. There are discussions about just about every aspect of the job. You can also educate yourself about head studs - lots of long discussions of that, as it is a common worry - as witness two guys posting about it within a day or so of each other.

Oh - have you found the thick washer which resides between the head and the barrel nut? There is one per stud, and I don't see one on the stub of the stud in your picture.

Walt