Rant

[Bob Kontak]

Originally Posted by 930cabman

Still, why would the engineers simply have not used a mild steel??

What they used were meant to match the thermal expansion rates of the rest of the engine.

Dilivar were better at this but they can develop corrosion pits along the shaft and shear after many cycles.

[Matt Monson]

Sell the car. Repairing it correctly is a five figure repair. I'll give you $7500 for it.

[swbstudios]

Ha,ha-good one. Actually, it's forged and spins as high as the one in my 911.

[Bob Kontak]

Originally Posted by swbstudios

Ha,ha-good one. Actually, it's forged and spins as high as the one in my 911.

Looks cast. Just saying. Not trying to stir up trouble. (Nice car, Bro)

[impactbumper]

hey man, at 41 years of age, anything can snap....

[Rawknees'Turbo]

Originally Posted by wayner

Yes, but the crank fell out so the point is moot

Don't most cranks tend to fall with age (so I hear)?!?!?! Good thing there's magic pills for that!!!

[Rawknees'Turbo]

Originally Posted by Bob Kontak

What they used were meant to match the thermal expansion rates of the rest of the engine.

Dilivar were better at this but they can develop corrosion pits along the shaft and shear after many cycles.

Sir Bobasaurous Sugar Scoops is correct, and strangely enough, Porsche never got the alloy, and how to preserve it (what coating to put on), figured out until the 993TT, "all thread" studs. Prior to those, even brand new ones were known to occasionally snap upon assembly.

[Bob Kontak]

Originally Posted by Rawknees'Turbo

Porsche never got the alloy, and how to preserve it (what coating to put on), figured out until the 993TT, "all thread" studs.

And they are cheap compared to Raceware, ARP and Henry, the windbag's hardware.

[safe]

Not sure how the $47 (times 24) 993 studs are cheaper than, for example the supertec at $729....

[theiceman]

Originally Posted by Bob Kontak

And they are cheap compared to Raceware, ARP and Henry, the windbag's hardware.

uh oh ...... here we go

[Tippy]

Let's face it, they are all overpriced!

[unclebilly]

So lets get this straight... you are upset that your 41 year old engine needs a rebuild... and you want a recall.

Hmmm...

[chris_seven]

There are a number of different issues at stake here and from a design point of view some of the mistakes are understandable.

If you consider the basic design of an Aluminium Sand Cast Engine case and the standard steel stud then there are very few issues.

The design is robust, has a good service factor and engines with Biral Cylinders and steel studs have very few problems.

If we then move to Magnesium engines with Biral cylinders even the 2.4S has few issues and has worked well.

The 2.7 with Thermal Reactors started to be an issue as we had high forces generated by expansion combined with a material that was losing strength with age due to the temperature of the thermal reactor and its impact on the stress relaxation of the magnesium Alloy. This leads to studs pulling out of cases.large the engine beyond its basic capability whilst trying to reduce emissions.- just a step too far I am afraid.

As far as I know Dilavar was first used on Turbo Engines where peak cylinder pressures were higher and maybe expansion was greater due to higher temperatures but this is a guess on my part. It is surprising that Dilavar was selected with a Alusil Turbo case and again the mistake is probably due to a rushed effort to react to the thread 'pulling' of mag engines.

It is not surprising that this material was initially considered as a solution for the problem of expansion.

Dilavar almost certainly will reduce the forces generated by expansion but sadly Porsche did fail to recognise its susceptibility to stress corrosion cracking in the presence of chlorides.

Is this a surprise? We must remember that although the Academic World had some evidence of this type of mechanism back in the Sixites the first commonly available published guides began to see the light of day in the early Eighties following a significant amount of research and testing, particularly in the case of Austenitic materials.

In fact very few Undergraduate Metallurgy Courses were not teaching Fracture Mechanics until the mid to late Seventies and then only as an optional part of a course.

If we add that the fact that Germany/Switzerland and Austria apply salt to their roads in a very sparing fashion it is not surprising that this fact was simply overlooked.

The Northern States of the USA, however, use vast quantities of salt which has not only helped to break Dilavar head studs but has also destroyed huge numbers of road bridge decks.

It is an irritating problem but and it's solution, with hindsight, is straightforward particularly with an Aluminium case.

Dilavar studs are now coated and should last many years even in poor environments as the salt will not penetrate the coating. I would also say that standard steel studs in Aluminium cases seem to work well and are generally trouble free.

The comment about using SAE 1020 is interesting and although I agree in principle that many of the exotic materials being used are not really justified some basic calculation will show that this type of steel isn't up to the job.

The force applied to a typical steel stud fitted on a engine using a Nikasil cylinder is around 6500 lbs.

This works out to a stress of around 580MPa (84 000psi)

Sadly the tensile strength of SAE 1020 is only around 400MPa (58 000psi) as a guaranteed minimum.

It may just about survive being torqued to the initial preload but it just wouldn't manage to deal with the expansion of the cylinder.

If you increase the shank diameter of the stud to try to deal with the tensile stress you would be fighting a losing battle as the force due to expansion would increase in scale with the area and be much more likely to pull out of a magnesium case.

The Aluminium cases seem able to withstand the increased expansion forces of a larger diameter shank but I don't really see the benefit.

I would like to see a stud made from a material with a basic yield stress of at least 750MPa (110 000 psi)

[930cabman]

Many good points Chris, is road salt a major factor in the demise of the factory standard Dilvar? our '75 specimen appears to have never seen salt from any source.


How many guys are running with stock studs after ??? years.

Is it a given when having the engine in for rebuild to replace the studs?

After all this/that/whatever, the winning material for a stock or slightly modified engine is?

[impactbumper]

Chris wrote a novel , pretty good points though

[930cabman]

Originally Posted by Matt Monson

Sell the car. Repairing it correctly is a five figure repair. I'll give you $7500 for it.

Great, I enjoy having cars, women, stuff other guys want to have, but can't

[Bob Kontak]

Originally Posted by 930cabman

Great, I enjoy having cars, women, stuff other guys want to have, but can't

Be nice. Cripes, you live in Buffalo. No need to be snippy. There are dudes that bury you financially on this board that don't carry your tude. This is a warning. You will be gone if you keep it up. Gone because it will be painful to post. Mulligan granted.

Spent a lot of time at Carborundum in Niagara Falls. I remember the big TRICO sign driving thru Buffalo. 80's and 90's.

Be advised, lots of us are older than dirt. Even if we had hot women, we have to say "Can you wait 45 minutes while this pill kicks in". Just happened to me. She said "Whatever, that gives you 15 minutes to do your thing since we are on the clock.

[SOAZ]

Originally Posted by chris_seven

There are a number of different issues at stake here and from a design point of view some of the mistakes are understandable.

If you consider the basic design of an Aluminium Sand Cast Engine case and the standard steel stud then there are very few issues.

The design is robust, has a good service factor and engines with Biral Cylinders and steel studs have very few problems.

If we then move to Magnesium engines with Biral cylinders even the 2.4S has few issues and has worked well.

The 2.7 with Thermal Reactors started to be an issue as we had high forces generated by expansion combined with a material that was losing strength with age due to the temperature of the thermal reactor and its impact on the stress relaxation of the magnesium Alloy. This leads to studs pulling out of cases.large the engine beyond its basic capability whilst trying to reduce emissions.- just a step too far I am afraid.

As far as I know Dilavar was first used on Turbo Engines where peak cylinder pressures were higher and maybe expansion was greater due to higher temperatures but this is a guess on my part. It is surprising that Dilavar was selected with a Alusil Turbo case and again the mistake is probably due to a rushed effort to react to the thread 'pulling' of mag engines.

It is not surprising that this material was initially considered as a solution for the problem of expansion.

Dilavar almost certainly will reduce the forces generated by expansion but sadly Porsche did fail to recognise its susceptibility to stress corrosion cracking in the presence of chlorides.

Is this a surprise? We must remember that although the Academic World had some evidence of this type of mechanism back in the Sixites the first commonly available published guides began to see the light of day in the early Eighties following a significant amount of research and testing, particularly in the case of Austenitic materials.

In fact very few Undergraduate Metallurgy Courses were not teaching Fracture Mechanics until the mid to late Seventies and then only as an optional part of a course.

If we add that the fact that Germany/Switzerland and Austria apply salt to their roads in a very sparing fashion it is not surprising that this fact was simply overlooked.

The Northern States of the USA, however, use vast quantities of salt which has not only helped to break Dilavar head studs but has also destroyed huge numbers of road bridge decks.

It is an irritating problem but and it's solution, with hindsight, is straightforward particularly with an Aluminium case.

Dilavar studs are now coated and should last many years even in poor environments as the salt will not penetrate the coating. I would also say that standard steel studs in Aluminium cases seem to work well and are generally trouble free.

The comment about using SAE 1020 is interesting and although I agree in principle that many of the exotic materials being used are not really justified some basic calculation will show that this type of steel isn't up to the job.

The force applied to a typical steel stud fitted on a engine using a Nikasil cylinder is around 6500 lbs.

This works out to a stress of around 580MPa (84 000psi)

Sadly the tensile strength of SAE 1020 is only around 400MPa (58 000psi) as a guaranteed minimum.

It may just about survive being torqued to the initial preload but it just wouldn't manage to deal with the expansion of the cylinder.

If you increase the shank diameter of the stud to try to deal with the tensile stress you would be fighting a losing battle as the force due to expansion would increase in scale with the area and be much more likely to pull out of a magnesium case.

The Aluminium cases seem able to withstand the increased expansion forces of a larger diameter shank but I don't really see the benefit.

I would like to see a stud made from a material with a basic yield stress of at least 750MPa (110 000 psi)

You post makes me feel like Ralph...

[Rawknees'Turbo]

Originally Posted by Bob Kontak

Be advised, lots of us are older than dirt. Even if we had hot women, we have to say "Can you wait 45 minutes while this pill kicks in". Just happened to me. She said "Whatever, that gives you 15 minutes to do your thing since we are on the clock.

Bob, did that set you back a buck fiddy?!?!

[Bob Kontak]

Originally Posted by Rawknees'Turbo

Bob, did that set you back a buck fiddy?!?!

Just like in Buffalo, a buck and a half gets you all night in Akron.