Stainless steel screws

[donporfi]

Porsches have a lot of screws, is it OK to change most of these screws with stainless steel screws? Or there is a problem with galvanic corrosion and the parts that hold these screws will begin to rust ?

[porwolf]

Good question! I use a lot of stainless steel screws and did not have a galvanic corrosion problems. After all, their composition is very similar to regular steel screws and must be on the same galvanic level as regular steel screws. So there should not be a problem when they contact regular steel parts. They sure are easier to take apart down the line!

[wildcat077]

No problem whatsoever using Stainless screws ... I replaced all my exaust bolts with stainless ones on my Porsche as well as my other vehicles.My boat has all stainless screws and if i have to replace any screws i will use stainless !

Cheers !
Phil

[IROC]

I would not use stainless fasteners in any application where strength is a requirement. 300 series stainless is very weak.

[porwolf]

As far as where strenght is needed I agree with IROC. Stick with the specified fasteners.

[wildcat077]

I think the OP is talking about scews ... not sure where strength comes into play here.As far as i know i 've never seen anybody torque a screw before

As far as MY preference for stainless bolts for my mufflers and exaust systems,i've been using them every time i've had to replace exaust parts on all my vehicles without issues ...

Cheers !
Phil

[euro911sc]

Stainless screws of the sheet metal kind are fine. Stainless machine screws, bolts, and nuts may be fine depending on the applications. Stainless is MUCH softer than the plain steel units as IROC has pointed out. So, things that require strength should not use stainless replacements. Things like holding your coil on or stuff like that its just fine. However, IMHO, best to find yellow zinc plated plain steel to correctly replace the HW if you can.

-Michael

[Schmierung]

Agree sheet metal screws just fine. I am a regular at Home Depot for stainless screws and non-critical bolting. Type 304 ot 316 is fine for this.

Critical bolting is another matter. Carbon steel has a relatively flat tensile strength up to 650 where it starts to decline, whereas stainless declines at 400 degrees F. For exhaust best to use Type 347 or 321 stainless for the higher temperatures. High chromium steel is stronger but expensive (and requires normalization if welded).

[Mitch Leland]

I use a lot of S.S screws and bolts for non-structural applications, however when you drop one into the bowels of the car your magnetic wand won't help...

What I like about the S.S. hardware is that it doesn't lose its luster/finish like type II cad does.

[proffighter]

When I re-assembled my car the first time from raw tube, I used almost everywhere SS bolts except for example lower rear damper (coil over) bolt that needs higher grade (10.9 or 12.9)

After ten years now I have a good amount of expierence over this:

The grade I use is A2-70 (don't know the US grade) and I used it where 8.8 bolts were used, but I also for engine and tranny mounting and suspension.

I do not used for:

-Brake calipers
-Clutch
-CV's

I had never a failure/ break, but there are some contact corrosion issues. I have to say, that I always used the recommended lub when mounting. Without they tend to seizure and corrosion would increase:

-Lot of corrosion where I used non-anodized aluminum spacers
-Little to no corrosion under the body where bolts mounted to the tub (suspension, etc...)
-No corrosion on engine and tranny housing
-No corrosion on exhaust/turbo/muffler (headers, muffler and brackets are SS)

BTW, on sheet metal, little stuff like valve covers I use aluminum bolts...

Conlusion:

SS bolts can be used almost everywhere, but the tendency to seizure made the standard steel bolts the better choice if this is on your focus. On the other side the bolts itself will not rust. So it's a matter of taste

[HawgRyder]

If you use stainless bolts with stainless nuts...you MUST use an anti-seize with them.
If you don't...they will be a total ***** to remove later...to the point of shearing before breaking loose.
Bob

[IROC]

Originally Posted by wildcat077

I think the OP is talking about scews ... not sure where strength comes into play here.As far as i know i 've never seen anybody torque a screw before

Just for fun, the difference between a "bolt" and a "screw" is that a bolt is installed with a nut and you tighten by torquing the nut. A screw is installed without a nut and you torque by tightening the head of the screw. So, technically our 911s have many "screws" installed in applications where I would not use stainless (fasteners that hold the calipers on, spring plate-to-banana arm attachment, etc.).

A2-70 is essentially 300 series and has a nominal tensile strength of 700 MPa (~102 ksi). While that might not sound as bad as an 8.8 bolt (with a nominal tensile strength of 800 MPa/116 ksi), the yield strength (the stress at which the bolt/screw permanently deforms) is 640 MPa/93 ksi for the 8.8 but is only around 30 ksi for the A2-70, so an 8.8 bolt is approximately 3 times stronger than an A2-70 (in yield).

A bit of useless info for a Friday morning...

[proffighter]

To add some more info, If you are unsure about usage on a certain application, you can switch from normal A2-70 to A4-80 which is has (depends on diameter, thread size etc) about 25% higher strength and is more acid-resistant

And if this is still too weak, use those:

[wildcat077]

Geez ... if you guys want to get technical about stainless screws i'll print the Boeing and Airbus Materials and Processes Manuals when i go to work Monday and post the properties and alloys of every stainless material used in the Aerospace industry ... lol

Although i think Home Depot has all the required screws needed for our cars

Cheers !
Phil

[proffighter]

Originally Posted by wildcat077

Geez ... if you guys want to get technical about stainless screws i'll print the Boeing and Airbus Materials and Processes Manuals when i go to work Monday and post the properties and alloys of every stainless material used in the Aerospace industry ...

Please don't forget the manual for the flux capacitor

[shbop]

Go stainless. The only downside for the applications you've mentioned is that if you drop one in a tough spot, your magnet isn't doing anything for you. Had them on muffler applications forever with absolutely no problems.

[IROC]

Originally Posted by shbop

Go stainless. The only downside for the applications you've mentioned is that if you drop one in a tough spot, your magnet isn't doing anything for you. Had them on muffler applications forever with absolutely no problems.

I'm replacing all my fasteners with Inconel 718 and MP35N.

[donporfi]

Thanks for all the answers.
I know I should not use stainless screws or bolts where Grade Bolts are used.

[Dublinoh]

M & K Mufflers are supplied with stainless bolts...just saying

[porwolf]

Good US source for screws and bolts, stainless and other materials, with very good material information:

McMaster-Carr

Plus they ship small quantities fast. Easy internet transaction! I have bought a lot of stainless steel fasteners and other materials from them over the years.