Head stud failure.......

[scotsman60]

Hello!!!

I'm starting this thread in this forum 'cause it seems like the most appropriate place.

I have a '90 C2 with 74,000 miles and I've just found a broken head stud on the inlet side of cylinder number three.

My initial thoughts are that at the very least I'll have to remove the engine and strip the left bank off. I'm thinking that I should be able to remove the cam towers and heads as a single unit, pull out the cylinders, extract the broken stud, replace it and re-assemble.

Does this seem reasonable?

Should I replace all studs and if so why?

Should I do both banks? (Of course I'll check that I don't have any more broken studs)

Since I'll have the cylinders out I'll be able to check the rings and valves for detonation induced damage (I was having some detonation problems previously).

I'm planning on modifying this car with a new (used) twin turbo engine next year so I'm not motivated to do a full engine tear down and recondition at this time......

I've got Waynes Engine rebuild book and I'm reading it right now. I know that my engine isn't covered but I figure a lot of the stuff should still be relevant.

Any advice or experience gratefully received.....



Doug

[Bill Verburg]

Should I replace all studs and if so why?

Yes, if one is broken can the others be far behind?

[scotsman60]

Bill,


Thanx for the reply.

Would you extend your reasoning to replace the studs on both banks?

I'm not sure how valid it is to assume that the others are close behind - it depends on the failure mode. From the piece that i recovered I can't really see anything obvious. The break is relatively clean at an angle of about 30 degrees to the stud axis. There are striations on the fracture surface but they don't look like fatigue striations - it looks like a fairly fast fracture of a high tensile material to me. There are no obvious nicks in the outer surface that might act as stress concentrations - but I only have the one half to look at right now......



Doug

[Doug Steinel]

Is the stud made of dilavar? I would think about replacing any dilavar studs with steel ones.

[scotsman60]

Doug,



Looks like the stud is Dilivar - its non-magnetic and black coated.

Pelican doesn't list head studs for the 964 (1990 C2) but Vertex has Dilivar, Raceware and "Super Stud (VSST)".

Dilivar and Raceware I know about - any idea what the VSST variant is?



Doug

[Doug Steinel]

I have no idea what VSST is. Anyone?

[Bill Verburg]

Studs fail because of corrosion, stress risers caused by assembly insults, metalurgy issues. Porsche has used several generations of studs.

If one went then the others are likely to go as well the best currently available aare Raceware or Arp, they are also quite expensive.

The 993(993 101 172 02) are better than the old epoxy coated Carrera ones(also used on 964), the 993tt(993 101 170 51) are better than the 993 ones. They are factory developed for the al. cases w/ compatible expansion coefficients, plain steel does not have the correct coefficient of expansion and will corrode and snap. There are lots of imitation steel and Dilivar studs out there. Use only factory supplied studs(or the Raceware or Arp).

Prices a year ago were, for the 993 $8.15ea, for the 993tt $19.95ea. Often discounted.

[jgparker]

I want to point out that the 993 stud listed above (993 101 172 02) is steel, not Dilavar. My personal belief is that OEM steel has virtually no chance of breaking, and they are actually the least expensive option. I have a hard time trusting even the new Dilavar studs, given the huge number of broken Dilavar studs stories on this board lately.

There has been a lot of good info exchanged on this board on the subject, so rather than restate it all, here are the previous threads:

http://forums.pelicanparts.com/search.php?action=showresults&searchid=643682&sortby=lastpost&sortorder=descending

Good luck,

JP

[scotsman60]

JP,


Thanx for the links. I used the search too but restricted it to the 964 forum so I missed a lot of the discussions.

After reviewing the info I'm thinking that I'll use the latest 993 head studs that appear to be steel and not threaded all the way down. I don't think that stud pull-out should be an issue with my case even using the steel studs with the adverse theral expansion coefficient.

I will definitely replace all the studs on the affected side of the engine and very probably the other side too.

I plan on dismantling the cam tower and heads together and hopefully replacing them without dismantling to save time. Of course if I find problems at the cylinder/head interface then I'll have to reconsider.

I'm not sure if my motor has the head gasket update or not - I guess I'll find out when I take it apart....

Is it accepted practice to re-use the nuts/washers?




Doug

[markwemple]

From what I have been told it is at the builders discretion. I will be on some and not on opthers based upon appearance. Of course I will not be using the ones off the broken studs.