304 Stainless All Thread as a Head Stud

Groesbeck Hurricane · 12-28-2001, 12:48 PM

Has anyone had any success with 204 Stainless All Thread in place of standard headstuds? I was trying to find some metric 10.4 grade all thread, but could only come up with 8.8 grade, which lists below M8 in tensile strength. Anyone else with luck in this area? (M8, 10MM, 1.5 thread)

Early_S_Man · 12-28-2001, 02:16 PM

David,

What is wrong with the OEM steel studs that are on the top row of your engine? The 911.101.172.00 studs are around $10.25 each, which means around $126 for the set to replace you lower Dilivars ...

Your logic comparing strength is a bit fishy, and, besides ... ultimate tensile strength is not the issue with head studs! A normal grade 8.8 M10 fastener is rated for a tightening torque higher than a high-strength DIN 12.9 M8 CV-joint bolt ... 47 Nm vs 42 Nm, so what is your point? The head studs aren't being tightened anywhere near 'normal' torque specs for a 10 mm grade 8.8 fastener!

Superman · 12-28-2001, 03:18 PM

JW made the statement once that he has never seen a factory steel stud break. Even if that is an exaggeration, I'm sold. Factory steel studs are going on my engine. Heck, if I'm lucky, I'll get to take it apart again.

island911 · 12-28-2001, 05:03 PM

Quote:

Originally posted by Early_S_Man
David,

... ultimate tensile strength is not the issue with head studs! . . ..The head studs aren't being tightened anywhere near 'normal' torque specs for a 10 mm grade 8.8 fastener!

1) I thought the maximum stud loading came when the thermal expansion of the cylinders out paced that of the steel studs.
2)If ultimate tensile strength is not the issue then why do they break. Is pure corrosion to blame?

All Thread in place of standard headstuds? . . .Yikes! Porsche studs are engineered to do more than just bolt the heads in place. They need to be "really stiff springs;" Stiff enough to hold the combustion forces and springy enough to withstand thermal cycling loads induced by the cylinders "growing" faster than the studs.
All-Thread will not last long under those conditions.

'81 SC COUPE

stormcrow · stormcrow's Garage

I don't think the issue with the tensel strength of stainless steel is of concern but the expansion rate.

The dilavar studs were used because they have an expansion rate similar to the alumimum and magnesium that is used for the crankcase, cylinders and cylinder heads.

Steve

Groesbeck Hurricane · 12-30-2001, 05:54 AM

Actually, two of my top row and three of my bottom row are either broken or torquing when I attempt removal. I was looking at Racewear studs and gasping at the price. Just trying to find an alternative route. Thanks for the replies.

My understanding of the strength requirements is in the heat cycles and the stresses on the motor when running, not the initial installation torques.

Oh yea, and to support my rebuild, I am selling one of our mares. anyone interested in a Thoroughbred Mare? 7 years old, very quick, needs experienced rider only, not a kids horse, loves girls and women, great horse for weekend use/moderate to heavy requirements. $2,500.00 if anyone is interested...

island911 · 12-30-2001, 08:20 AM

One other thing about All-thread vs studs; Having the threads run the length is bad for fatigue strength. The valley of every thread is a place for a crack to start. . ..kind of like a rock chip in a window can start a crack that keeps growing.

$2,500.00 for one hp gain. . .sounds expensive

'81 SC COUPE

Groesbeck Hurricane · 01-02-2002, 05:18 AM

Didn't look at the all thread that way. OK, so basically, even stainless can rust, all thread gives the crevices to rust, even though studs basically start out like all thread, the machining gives less of a surface to attract and trap moisture. Suck it up and pay for the part intended to do the job.

Oh, and that one HP gets to top speed in an instant and has the fastest 1/4 mile of any of our hp's. And she is an all terrain HP, four hoof drive with an on board brain! Tough to beat for such a small price.

Zendalar · 01-02-2002, 05:31 AM

This is the thing I am wondering too. Why don't people fabricate the studs themselves?

Take a long round bar of stainless or normal steel and make the threads to the ends of the bar by yourself. Tools to fabricate the threads won't cost much. If you want to be certain about the threads you could make the DIY studs longer and add second nut on top of the other.

And to harden the DIY studs (if you think stainless steel will become longer in time) you could heat them up near redness and then put them to room temperature mineral oil. This will harden the material and make a protective (black) surface to prevent corrosion (if built from normal steel).

sammyg2 · 01-02-2002, 07:06 AM

All thread is usually made with cut threads, just like if someone made their own. A high quality head stud will have rolled threads which are much stronger. All metals have a grain, similar to that of a tree. If the threads are rolled into the O.D. of a rod, the grain is molded (pushed) into the rod. It is still intact, just deformed.
If the same rod is cut with threads, the entire depth of the thread is weaked by the cutting of the grain and is much more prone to tensile failure. You would have to do some research to determine the manufacturing process they used to make that particular all thread. The grade rating is one indicator of reduced strength.

I would also speculate that most all thread is not heat tempered to anywhere near the same standards of application specific head studs.
I have a reputation to be a cheap b*stard, but this is one place where we should not try to save money, IMO.
Hope this helps.

911pcars · 01-02-2002, 11:44 AM

Dilavar is the ideal material in this application since this steel alloy expands at about the same rate as the alloy parts it clamps together. I know this is not the prevailing thought at this time.

My theory is that Dilavar head stud failure is either due to a bad batch of studs (poor quality control) or susceptibility to corrosion (cited in many explanations for alternative materials). There have been three versions of the Dilavar studs, with the latest ones coated by a protective layer of paint. I wonder how many coated Dilavar studs have broken compared to to the early versions? Dilvar head studs are not that heavily stressed since torque specifications are only 30 ft.lbs. and they expand in length with the other parts.

Raceware and ARP take a different approach as the material they use, heat treatment and quality control as well as the use of Timecerts or strong threads in the aluminum crankcase reduces the chance of failure in this area, even if they don't expand at the same rate as the rest of the engine parts. The stock steel head studs should be equivalent provided they don't corrode and create a stress risor.

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