Stainless exhaust studs???

DUK · 10-31-2006, 05:59 PM

Was wondering if anyone has used and/or found a source for stainless exhaust studs? I keep running into standard american but not metric. Thanx, Duke

NoEardGoat · 10-31-2006, 06:19 PM

I'm by far anything close to an expert, but I don't know if the heat expansion is going to be the same as the studs designed for the application. May break something worse than the suds.

slammed1000 · 10-31-2006, 06:30 PM

more than likely he is just worried about corrosion. i feel the same way, why not make it out of a high grade stainless that wont seize up,rust and then shear off when you try to remove....

911pcars · 10-31-2006, 06:43 PM

SS material shouldn't rust, but use A4 as it is higher quality for this location. If you can't locate a proper "stud", look for an M8 setscrew with an internal hex to install it. Length would be ?

Sherwood

74-911 · 10-31-2006, 06:45 PM

Stainless Steel may not rust but galvanic corrosion when in contact with dissimilar metals can be a real problem. Stainless Steel and Aluminum are a real problem in boats unless an anti-corrosion / anti-seize compound is used. The stainless basically oxidizes the aluminum turning it into aluminum oxide, a white powder. I assume it would do the same with magnesium.

klaucke · 10-31-2006, 08:07 PM

I wouldn't worry about galvanic corrosion in this instance, and anyways you can install them w/ an anti-seize compound, many of which are good for 1500+ degrees. There are plenty of instances (i.e. just about everything in a Mercruiser I/O outdrive) in a boat where stainless and Al are used together w/o issue as long as you have sacrificial diodes or don't moor the boat.

Pelican sells these "Non-Corrosive Exhaust Stud Hardware;" I'm not sure if they're a stainless alloy or not, but are perhaps worth looking into.
http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_ENGpis_pg6.htm#item24

You can get normal SS studs from McMaster-Carr for around $1 a piece, although judging by their online catalog they are only available fully threaded, which should'nt really be an issue. Check out PN 93805A355 at www.mcmastercarr.com You could even buy a 1m peice of threaded rod and cut your own for less than buying them individually, and you could make them exactly 22mm.

greglepore · 11-01-2006, 04:44 AM

I'd think long and hard about doing this. Stainless doesn't rust, but it does gall when exposed to hot exhaust. You can drill out mild steel with QuietBoom's jig fairly easily, not sure I'd want to try to drill out a broken stainless stud.

ficke · ficke's Garage

I second Greg comments. Galling is a real issue. I have personally ruined alot of expensive SS bolts and avoid them unless absolutely necessary.

Jim Sims · 11-01-2006, 11:20 AM

Commonly available metric stainless steel studs will almost certainly be weaker than the carbon steel studs (likely strength class 8.8) being considered for replacement.

See this thread for more discussion on metric stainless steel fasteners and alloys:

SAE vs. Metric bolt strength

911pcars · 11-01-2006, 12:57 PM

The idea is to use the correct fastener in the correct application. One wouldn't and shouldn't use high-tech ARP-type fasteners to clamp the valve covers in place or for any low-stress clamping unless there's an unlimited amount of budget available or some other demonstrable advantage (e.g. Ti for weight savings). I don't think even a McClaren Supercar or Bughatti Veyron goes to that extent.

That said, the fasteners required to hold the heat exchangers in place don't have to be as strong as fasteners for suspension pieces, roll cages or connecting rods. What's important in this application are properties that stress anti-corrosion and perhaps heat-strength. Grade 8.8 steel studs were probably installed at the factory and they last as long as the corrosive environment they live in allows it. I think a good grade of stainless steel is a pretty adequate substitute that won't corrode as fast.... and break.

I have a link on my web site to a fastener manual that tells all, if any are interested.

Sherwood
http://members.rennlist.org/911pcars/
(under "Related Links")

fred cook · fred cook's Garage

When I replaced the exhaust on my SC I had to replace several broken studs. I used stainless metric studs sourced from my local Ace hardware store. That was over a year ago and so far no problems.

Jim Sims · 11-01-2006, 01:24 PM

"a good grade of stainless steel"

Such as?

goldgunner · 11-01-2006, 01:30 PM

At a minimum use 316 stainless which is the 'A4' refered to.

Ferritic stainless steels (400 series) would be even better - the iron (heat treatable content) that makes them stronger wouldn't be sufficient to significantly effect corrosion resistance.

From there high temperature stainless steels would be the best (ASTM A286) but would be difficult to find in the required sizes.

Zeke · 11-01-2006, 01:30 PM

I'm not as smart as the others, but I've broken more SS than other types. I'm not too bad of a wrench. That tells me something only further verified here.

goldgunner · 11-01-2006, 01:36 PM

"Regular" 300 (martinsetic) series stainless steels are not very strong...
301/302/303/304 are about equivilant to Grade 2 and Class 4 tensile strengths.

316 stainless is about equal in tensile strength to Grade 5 and Class 8.8

400 series stainless that has been properly heat treated is about equal in tensile strength to Class 10.9, somewhat less tensile than Grade 8.

A286 stainless in it's usual heat treat condition is around 160,000 PSI UTS, approximately same as Grade 8, Class 12.9 and 'standard' heat treated alloy hex socket head cap screws.

Inconels, waspalloys, etc. can be heat treated up to around 220,000 PSI UTS.

Jim Sims · 03:19 PM

300 series stainless alloys are austenitic, 400 series alloys are either ferritic or martensitic. There are also precipitation-hardening alloys and multi-phase super alloys like MP35N that are corrosion resistant. A metric 316 stainless steel fastener unless marked A4-70 or A4-80 may be assumed to be the lowest property class (A4-50) with a minimum tensile strength of 500 MPa which is about a equal to a metric strength class 5.8, low or medium carbon, cold worked steel screw or somewhere between an SAE grade 2 and 3 in the US system. In terms of fastener alloys these strength levels are "like putty". High quality, high strength stainless steel fasteners are available but are not likely to be found at typical retail sources.

randywebb · 11-01-2006, 04:02 PM

MPa

M = Mega, 1e6

Pa = Pascals, the real (SI) unit of pressure

500 MPa = 5,000 bar = 72518.87 psi

Jim Sims · 11-01-2006, 04:19 PM

An 8 mm A4-50 (316 stainless steel) stud can begin to plastically yield (twist and stretch) somewhere around 7 ft-lbs which is half or less of the torque value of an 8 mm 8.8 strength class medium carbon steel stud. The yield strength of a A4-50 screw is allowed to be as low as 210 MPa or 30,500 psi. Putty.

DUK · 11-01-2006, 04:25 PM

So after all of that, has anyone used the "non-corrosive exhaust stud" available at our host? And will they fit a 3.2 SSI setup? BTW I was thinking of getting a set from ARP out of 400 series stainless, any problems with those?

911pcars · 11-01-2006, 04:48 PM

AS a point of reference, 316L fasteners are available in class 80 with a tensile strength of 800N/mm2 and class 100 with a tensile strength of 1000N/mm2. (145 ksi) equivalent to 10.9 steel.

Before purchasing, make sure you understand what you're buying. Lower grades of 316, like Jim says, can be like putty.

Sherwood