Wayne was right! - more info for the great head stud debate

[pryord]

Some of you may remember my rantings about finding a broken head stud one month after buying my SC.

PPI gone bad! Always remove valve covers!

Well, I've finally gotten around to getting it repaired and, since I seen several debates about whether or not people should drive with a boken head stud, I thought I'd let you know what the mechanic found.

I've driven the car for 3k miles since knowing about the broken stud. No telling how long it's been broken. I never took the car to redline, but I took it over 5,000 RPMs practically every time I got the chance. The heads are now pulled off, and the machanic found no significant damage to the heads or pistons. The heads were sent to be machined to insure a precise fit, but over-all everything looked fine. Only 1 stud was found to be broken.

This was just my experience, so add it to the mix. I'm sure it could have been worse, so I consider myself lucky.

[911pcars]

From experience following this and other Porsche BBs for awhile, I sense most of the broken (not pulled) head studs occur on SC's and Carreras made prior to '85-86. Most of these would be the silver or gold-colored versions of the Dilavar studs (You don't state, but I assume the steel one isn't broken).

I installed 24 black, epoxy-coated studs on my 2.7 back in the late 80's. Car returned to street life 10 years later so I'm holding my breathe.

I'm glad you didn't find additional engine damage.

Regards,
Sherwood Lee
http://members.rennlist.org/911pcars

[Wayne 962]

With three studs, you *should* be okay, but there is always a risk of damaging your piston and cylinder. I shy away from recommending that you continue to drive in the new book, just because it really should be repaired. Plus if one is broken, you can rest assured the others are not too strong...

-Wayne

[nostatic]

Is there any correlation between geographic location and breakage? Mileage? Age? Does anyone have any decent data on this one? For instance, are broken studs more likely to be found on cars that live in higher humidity regions? Higher temperature?

[A Quiet Boom]

Originally posted by nostatic
Is there any correlation between geographic location and breakage? Mileage? Age? Does anyone have any decent data on this one? For instance, are broken studs more likely to be found on cars that live in higher humidity regions? Higher temperature?

Ummm yes, broken headstuds only occur on 79SC's in the SoCal region.

J/K actually if I had to hazard a guess I would think Northern climates would take a harder toll on the headstuds since the heat cycles are more harsh and if the car has ever seen snow corrosion could certainly be a factor. Just an educated guess from a guy who understand metal (and how to break it in increasingly new and fantastic ways LOL)

[Sean Hamilton]

and now, after reading
http://www.pelicanparts.com/techarticles/mult_Engine_Rebuild/mult_engine_rebuild-1.htm
every time I tear open a bag of potato chips, I'll be thinking about my head studs.

[Wayne 962]

My SC was from Long Island (like me), and had mucho corrosion on all of the head studs...

-Wayne

[Bobboloo]

Noah,

Didn't 76' S's come with steel studs?

Bobby

[pryord]

I remember someone once suggesting that cars that went through long periods without being driven might be more likely to have corroded head studs. My car fits this description, because the PO hardly drove it at all. My car has been in Oregon (mild climate) all it's life.

[jeff91C2T]

here's another data point...

I had a broken head stud on a 3.3 Turbo motor. Leak down results for that cylinder where 15%. While driving hard, there were no signs of "problems". After tear down, you could see some blow by at the cylinder head but no real damage. Keep in mind this motor was run at 1 bar and run hard. The head was cleaned up (machined flat) reinstalled.

[jeff91C2T]

Still trying to attach an image...

[jeff91C2T]

And my importantly, the cleaned up version...

[ronb]

My 79sc w 118,000 miles still has the original head studs. Do I replace them all now, which would be a major job (for me), or do I leave them alone? Local advice just received from a mechanic who only does Porsche work (and exclusively races SCs) is that "... around here, 90% of them seem to go...perhaps you're in that 10% that don't". Engine is really strong, no reason to touch it other than that. Used on a daily basis, except in winter - and contrary to advice here, I was told - specifically for the head studs - to run it every 10 days or so, up to operating temp, to keep the metal (ie the studs) "conditioned". Your thoughts?

[nostatic]

I'd say drive the car, don't worry about "conditioning" (but how can you *not* drive the car everyday?), and maybe just sock away some money to pay for stud replacement if some future valve adjustment gives you the bad news. It seems as if this isn't like tensioners...if a stud breaks, you can likely drive on for thousands of miles and not even notice.

[911pcars]

Metal conditioning? Uhh... I don't think so.

Do turbos of the same era have more of a problem with head studs? They should have more considering the increased pressures in the combustion chamber. B.Anderson claims corrosion is the culprit for the early Dilavar versions - the gold ones that replaced the silver ones didn't seem to make any impact in this regard.

Also not sure why the factory, in all its wisdom, installed steel studs in the upper row and Dilavars in the lower row on NA engines and Dilavars on all 24 with turbos. Cost savings? Seems to me different expansion rates = unequal cylinder clamping stress. According to B.A., the factory used Dilavar studs on their racing engines (sprint and endurance) beginning in the 70's and they seemed to have pretty good success. Maybe we should race our cars more often.

Sherwood Lee
http://members.rennlist.org/911pcars

[ronb]

Thanks - I do drive it every day, except in the winter (I'm in the Berkshires in Mass). I will be using it 12 - 20 times a year at the track (mostly Lime Rock). The stud issue does seem to be a wild card; so checking @ valve work seems a reasonable way to catch (every 15k miles). And I guess I will not change the tire prior to a puncture - well put.

I did find out - the hard way - that the oil pickup screen had not been replaced - the hard way being overheating at the track. This was an essential upgrade that did not happen (doesn't really come into play at street / highway use). Apparently this was a known fault (?) of the earlier SCs.

[Superman]

I can add something here. I had one broken stud. Three or more cylinders were leaking at the cylinder/head joint. Therefore, the need to retorque your heads occasionally is REAL. I don't think broken heads studs damage cylinders more than loose barrel nuts. Recently we have heard several stories of nuts simply falling off. So......

RETORQUE YOUR NUTS!

[Wayne 962]

There is much debate around the retorquing of head studs. Bruce (Anderson) and I discussed this over the weekend, and came to some conclusions.... which are docmented in my new book.

Noah is 100% right!

-Wayne

[ronb]

can you give the gist of it here, so I don't have too many more sleepless nights? I will purchase the book regardless...(and I have a signed copy of your other book; now annointed with a lot of oily handprints. Perhaps a separate thread on most used 101 projects, ie photos of their condition?

[DonNewton]

I'm guessing Wayne has a new book for sale, soon. . .