Marc Shaw

As I begin the process of the final re-assembly of my car after the winter "extreme make-over" (Don's words ), I am thinking about all the trouble rusted and frozen bolts have given me.

I am therefore considering replacing most, if not all, bolts that I use with stainless steel (small weight hit, I know).

While on some areas it will make no difference (ex. wheelwell covers, underbody panel covers, etc) while in other areas it might make more of a difference or be more of a concern (ex. brake calipers, front suspension, etc.).

Anyone with any bolt/fastener or metallurgical experience care to comment on the relative strengths of stainless fasteners versus the standard OE bolts that Porsche used?

Thanks. Marc

I am also really starting to doubt the "never winter driven" line from the original ad for my car.

Heirsh

Low strength steel hex head bolts (grade 2) are in the 60kpsi realm for tensile strength.
316 stainless is about 70kpsi
18-8 stainless is also about 70kpsi
Medium strength bolts (grade 5 or metric 8.8) are in the 120 kpsi realm.
High strength (grade 8 or metric 10.9) are int he 150 kpsi realm.

Another thing to remember is how soft most stainless is.
18-8 Rockwell B70 typical
Grade 5 C25-34 typical (equvalent of rockwell b100+)
Grade 8 C33-38 typical (equavalent of B 105-110)

Fatigue strength is also a big factor with fasteners and I dont have the data in front of me, but I don't think stainless is anywhere near as high as most alloy steel.

There are other materials that can work, but they are costly (Ti, High strength stainless, Beryllium Copper, etc.)

The above is facts that vary some from bolt to bolt. What follows is just my opinion, but I will offer it so long as you take it at that. Use stainless where the bolt isnt doing any real holding (or you know how much it is holding and stainless is fine or you are replacing a low stremgth fastener) and plated or coated high quality 10.9 stuff elsewhere. Most of the bolts I've pulled out of my car have been medium strength. I've replaced them with the same or a high strength equivalent. Zinc and yellow chromate is a typical coating to resist corrosion. There are others such as what McMaster calls ultra coated.

Hope this helps.

Oddjob

I agree with Heirsh.

As mentioned, stainless is not as strong as the graded carbon steel bolts, and because it is softer, also tends to gall up the threads when tightened to a high torque spec.

Do not use stainless bolts on anything that is important (suspension bolts, brake caliper bolts, engine studs, mounts, etc.) - probably anything that you want to (or should) use the factory torque spec on.

I only use stainless on exhaust systems (but not on the manifold to head bolts/studs/nuts), and some other misc. fasteners underneath the car that tend to corrode.

dougn

don't use stainless on structural stuff..... like they said

Bangkokian

Besides the structural issues, I've found that stainless bolt/nuts tend to freeze over time and become very difficult to undue/remove. As such don't recommend using them where removal is required.

JasonAndreas

For about $30USD you can replace 99% of the fasteners (bolts, washers, nuts, etc.) used on the 964 with an OEM equivalent. I used Metric Multistandard and Spaenaur up in Canada. For instance you can buy 100 M6 yellow-zinc plated hex nuts for $6.25USD, and the same quantity of all-metal locking nuts for $8.25USD. I no longer reuse any fasteners (so corrosion is not an issue) and I don't have to worry that my local hardware store might be selling me remarked chinese knockoff fasteners.

springer3

Something else to think about is corrosion of the metal that the bolt is clamping together. Steel bolts for outdoor use almost always have corrosion coatings. The corrosion coating also protects the metal parts being bolted together.

I don't recommend stainless except where the OEM fastener is stainless (like some on the exhaust system). Save some money and use good quality steel fasteners with a gold or silver chromate coating. They last a long time. Spray a little cold galvanizing or chromate paint on bolts used in areas prone to rust. You don't need stainless. Stainless will not protect the other metal parts unless you spray it with paint containing metallic zinc or chromate compounds.

Indycam

For the man ....
http://www.racebolts.com/store/Metri...teners-C2.aspx
http://mdmetric.com/titanium.htm
http://www.mettec.com/metric.htm

hjcarlin72

From my experience with Aviation, most structural bolts used are cadmium plated. This give the bolt a gold color. This could be the "yellow zinc" that is being refered to> Zinc is never yellow, always silver in color. Suggest you use cadmium plated aircarft bolts. You can purchase these at Aircraft Spruce & Supply of Wicks Aircraft supply. Hope this helps.

Marc Shaw

Thanks all. That is kind of what I had suspected.

I will plan to use stainless where it does not matter and new OE plated bolts elsewhere.

Marc

Heirsh

Cadmium is a different plating than the zinc yellow chromate stuff I was talking about.

http://nepp.nasa.gov/WHISKER/photos/bus_rail/index.html

The above link provides a nice picture of the plating and its color.

Cadmium is a more resistant finish than this type of zinc, but it is more costly (and apparently toxic which I just learned). Probably why I see a lot more of the yellow zinc stuff.

http://www.stanleyind.com/finfo/plating.html

Above is a link to some finishes.

Calvaire

www.italbolt.it

the best