Another victim to a broken head stud

[NaFe]

So I decided to service the SC engine last night and had all my parts and oil ready.  Hell, I even had a new rocker stud and Loctite to fix the one I'd lost. so I wasn't expecting to find this in the lower rocker cover when I removed it:

 

I'm trying to decipher whether the portion I have found is the head side or the case side. are the threaded lengths different for inner and outer?  As the broken stud would have been contained within the enclosed area of the rocker cover, and the fact I cannot find the allen bolt, I'm assuming its an old break that the Previous Owner would have encountered and not fixed?

Your thoughts are welcomed

 

Nath

 

[MFX]

They are threaded both ends, and that should be the outer part. It is strange that you can't find the allen nut though...

[NaFe]

I appreciate that both ends are threaded. I was wondering whether the length of thread on the inner and outer were different for me to establish is the bit I found was the inner or outer bit.

my guess is that I cant find the allen nut because the stud was snapped long ago and the outer part and the nut has been removed. and that what I have found is, in fact, the inner portion that's now come out.

[P-Kay]

interesting theory there @NaFe

I guess anything is possible, but these head studs are normally in there pretty tight. At the same time, you would wonder why you would sit the stud there for the sake of it and put the lid back on???

Guess you will only know which side it is by poking a wire down the hole to see how far down it goes.

Don't forget that one broken stud does not mean that a rebuild is in order. You can wait until you are ready Good luck with it all

[Mike D'Silva]

I think that is the outer part due to the length of the threaded section.. from memory, the threaded portion that is secured in the case, is much longer...

[NaFe]

Thanks @P-Kay. I just dont know where the allen head could have gone if its something thats just happened.  I'll have to have another good look around and see if I can find it.  I realise that it's still driveable as is, but i'm a little nervous of the ticking time bomb lol.

 

I think that is the outer part due to the length of the threaded section.. from memory, the threaded portion that is secured in the case, is much longer...

Thanks Mike, I was thinking that it looked quite short and therefore it may be the outer part.  I'll try the wire trick and see if it just keeps going

[MFX]

As Mike said, the top thread is the short one. I would also probably just use a screw driver, as the wire may slip past the top of the bolt. If it goes in around 200mm then it is probably all out, if it only goes 100, you have half still in there.

[Coastr]

Is this the first time you have had the valve covers off since purchase?  

Quite the gut punch.  No need to rush, start thinking about your options.  It is possible to just fix the studs without getting carried away.

[Harvs11]

Thanks @P-Kay. I just dont know where the allen head could have gone if its something thats just happened.  I'll have to have another good look around and see if I can find it.  I realise that it's still driveable as is, but i'm a little nervous of the ticking time bomb lol.

 

Thanks Mike, I was thinking that it looked quite short and therefore it may be the outer part.  I'll try the wire trick and see if it just keeps going

 

 

What's that round thing sitting below the adjacent head stud? (below / left of the broken one)   It looks like a barrel nut or at least a washer.  Strange that you only have a bare stud, the nut should stay attached.

The portion you have is the upper end and looks like there would be at least half a stud left behind.  This will make it easier to grip and remove when the time comes.  Your single broken stud is fortunately not one at the outer end of the heads.  The head will be well secured by the surrounding cam housing and shouldn't cause too much trouble.  If you have more than one broken stud on a head, or if it's at the end, you will definitely notice exhaust blow-by noise indicating a fix is required SOON.  

 It's easy to get sucked into a full rebuild when perhaps it's not yet required.  If the rest of the engine is in good condition this isn't such a big disaster and will only involve removal/refitting of the cam assembly, heads and barrels with replacement of the studs with new seals and gaskets.  Get some professional advice before committing too deeply.  Good luck. 

[Mike D'Silva]

I'd love to have a go at fixing this for you.. pull the motor out and ship it up to me. 

Yes, I am bored.. 

[Zelrik911]

Mike you wont ever be 'bored' again if you become the headstud guru.

Every 3.0 3.2 & Turbo has broken headstuds unless they have been recently replaced.

If you think your lucky & it hasn't happened to your 911, those dud studs are gunna break soon.

[Peter M]

Every 3.0 3.2 & Turbo has broken headstuds unless they have been recently replaced.

Every?  That's a big statement!

I don't believe 100% will suffer one or more broken head studs. 

Surely a couple of percent is closer to reality?

[Mick]

I've seen this movie, you won't like the ending.

[Mike D'Silva]

I've seen this movie, you won't like the ending.

Yeah... but you aren't quite normal when it comes to these cars.. !!

[Russ]

at least the saviour of the 2.7 is that they'll pull studs before they break... and I agree with Peter M, I can't imagine every 3.0/3.2 having broken head studs.

I'd do a compression and leak down test on that cylinder and see what it says, then watch for oil leaks. Assuming they both come up okay I'd drive it while you think about if you want to rebuild it - don't rush into it as mentioned before.

If it's been running with the broken head stud at least it's hopeful that the allen head isn't floating around somewhere waiting to go into the combustion chamber

[NaFe]

Thanks for all of the feedback guys.  Much appreciated.  I've been moving house (albeit only 2km down the road) so this has occupied my time this week.  I put the rockers back on to move (tow) and when I get chance I'll take them back off again and hopefully retrieve the nut that Harv spotted.

I'll then do a compression test on all of the cylinders to check and try and do a leakdown test.  I've did a compression test back in 2011 after the engine had been sitting for 18months and found compression was down on cylinder 2.  If this is still the case now and i have the latest issue with cylinder 6's head stud it may be another good reason to start thinking of investigating properly.  These were the cold compression tests back in July 2011:

cylinder 1,3,4,5,6  all between 155-158psi and

cylinder 2 =105

[Buchanan Automotive]

Actually ,Zelrik911 statement is quite accurate , meaning that the older style "original"  Dilavar ( air cooled 911  ) head studs are very prone to breaking as they ( the older style studs )   will eventually fail

And to be even more accurate , you do not need more than one break per engine to realise that we have an issue , its quite common when one inspects ( say ) a 3.0L 911SC  engine ( with its original head studs) because the owner mentions a popping noise or similar not normal noise descriptions & we remove the lower rocker covers we see one , maybe two & sometimes three or more broken head studs , so naturally in this state this engine needs new head studs ( minimum ) 

So as we know , in the early days the first version of the Dilavar head studs were on the 1975 3.0L 911 turbo ( all 24 of them were Dilavar ) and Porsche then went on to use them on their NA 911 engines starting with the 1977 3.0L engines , but only on the lower row of head studs ( 12 ) , these early Dilavar head studs were a shiny brush finish & these often broke / snapped in the first few years from new ( particularly the Turbo )

Next version was about 1980 , these 2nd generation Dilavar head studs were "gold" like finish & like with the 3.0L 911 turbo, the 3,3L turbo received all 24 of them in Dilavar & the NA 911 ( 911Sc received them on the exhaust ( lower ) side only ( 12 )
These lasted on average a bit longer , but quite a few snapped . broke in the first 8 to 10 years from new ( particularly the 3.3 turbo )

Next version was the introduced late in the 1981 year model run ( for the 82> ) and this version was different to look at as it has a black painted on outer coating ( corrosion protection ), these were a bit better , but they still broke , but it took a little longer ( more heat cycles& kms ) etc , these are the ones fitted ( new ) to the 3.2NA ( bottom row ) & 964, and yes now in old age 964 engines do break head studs , its rare but does happen particularly in the last 10 years ( old age )

Last version from Porsche was developed for the 993 engine & these can be used in the older engines 

Note } from the beginning of the NON Magnesium crankcases , meaning 911SC etc , some people choose just straight steel head studs ( 911 101 172 00 ) , or the very high quality Raceway head studs or there stick with the Dilavar studs ( 993 101 170 53 ) its all up the what the owner wants to use 

So to recap ,  very rare to see( these days ) the first version Dilavar head studs that were fitted by the factory from the late 1970's , because they have all broken decades ago & have been replaced with the next generation Dilavar or other head studs

Its getting rare to see the 2nd generation Dilavar studs( unless its a very very very low km car ) , because like the first version they broke decades ago 

Regards
Bruce Buchanan  
Buchanan Automotive   ( 40 + years working on Porsche cars )

[Zelrik911]

Actually ,Zelrik911 statement is quite accurate , meaning that the older style "original"  Dilavar ( air cooled 911  ) head studs are very prone to breaking as they ( the older style studs )   will eventually fail
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Last version from Porsche was developed for the 993 engine & these can be used in the older engines 

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Bruce Buchanan  
Buchanan Automotive   ( 40 + years working on Porsche cars )

Bruce - have you seen any 993 broken headstuds as yet?

I was thinking of getting a 3.6 from a 993 and thought that the dilavar problem had been replaced with something else - maybe not? 

Thanks

[Buchanan Automotive]

No , but remember , most 993 engines( if they were city /suburban cars from new ) are dismantled for oil leak reasons by 130,000kms anyway & we generally install new head studs then anyway , along with anything else it may need , like valve guides etc 

Regards
Bruce B

[bear924]

I remember the day I decided to check my valve gaps a few weeks prior to a trip away. After removing the camshaft cover I found three broken head studs. Having three chunks of metal in my hand without knowing what they were was not a great day.  I ended up taking the 924 for that trip away and then had my 911 engine sorted. If purchasing a 911SC now, I would budget for a head stud failure on any motor that I couldn't prove had replacement studs installed. I found my broken studs a little before 300 000 km, the surprising thing for me is that the rest of the engine was is very good condition after that many kms (top end had been worked on prior, however bottom end had never been cracked according to my mechanic). If it wasn't for the studs, I suspect it would still be going strong.

Final thing of interest in my journey is that my mechanic showed me one of my removed studs. He put it in a vice a gave it a decent hit with a hammer. The stud snapped in two as if it was a piece of dry spaghetti. After seeing that I was impressed I'd only had three broken studs. 

[NaFe]

Thanks for the very thorough and informative post Bruce.  I just looked up some of the prices for a full set of headstuds.  Wow! There's a bit of a difference between the standard steel and dilavar or Racware stud sets.

What would you recommend Bruce?

Final thing of interest in my journey is that my mechanic showed me one of my removed studs. He put it in a vice a gave it a decent hit with a hammer. The stud snapped in two as if it was a piece of dry spaghetti. After seeing that I was impressed I'd only had three broken studs. 

I wouldn't expect anything different to be honest. The bolts are not designed to be smacked with a hammer. The bolts are designed to be strong in axial tension.  similar things will happen if you hit window with a hammer

 

[Peter M]

What would you recommend Bruce?

Good question Nate, especially if we expand it to:

"Bruce, what do you recommend owners do when they bring in an otherwise well running car that just happens to have one broken stud like Nate's?"

 

As an aside, I'm expecting to rebuild my 3.2 next year and have bought 12 standard steel studs to pre-emptively replace the bottom row of Dilivar's while the engine is out and most importantly, it's convenient to do so.  I'll also replace any of the original top row studs if there is evidence of damage or corrosion as the steel replacements are cheap to buy.

As for the "100% breakage rate by now" hysteria, maybe my cars didn't see that on the forums as a "fact" so none of the 72 studs - in two 3.2's and a 993 - I've been responsible for have broken any to date.  Lucky, I don't really think so.  A risk? Certainly, but let's not lose sleep over this quirk.

thank you both.

 

[tazzieman]

As for the "100% breakage rate by now" hysteria, maybe my cars didn't see that on the forums as a "fact" so none of the 72 studs - in two 3.2's and a 993 - I've been responsible for have broken any to date.  

The boys at Hartech say "About one third of the 911 sc's we inspect/service (and an increasing number of 3.2's) - that have just been sold/bought - have a head stud broken and the nut has gone missing - meaning that this is why it was sold in the first place - buyer beware."

[Coastr]

Well, all engines have a 100% failure rate in the long term.  It's not surprising that lots of SC engines have suffered from broken head studs.  Many SCs have achieved mileages that would seem astronomical compared to similar 70s/80s sports cars.  They also spend long periods of time sitting and then get driven enthusiastically.

nobody collects data but those in the business of replacing them see quite a few.  Maybe it's a few percent chance that you'll do it in your cars ownership, but the percent chance increases over the entire cars lifetime of all owners.  The first SC will be 40 years old soon.  The number of cars with a no-pages-missing history file for every receipt is low.   You might think your SC has still got all the original studs, but that's a bit like taking a 40 year old out on a date and asking if there are any skeletons in the closet,and then believing them when they say 'no'.

[Peter M]

Did come across a post on Pelican where he claimed he had 10 broken studs in his SC but the car still ran fine.  Surely a statistical outlier and I'm wondering for how much longer!

My understanding is that Porsche designed these cars for 20 years/200,000km so I guess they are all on borrowed time now.