Stainless Steel Bolts for exhaust assembly

[Uwon]

I know that S/S bolts and nuts (A2-70) are not as hard as 10.9 steel, but they sure do not rust and break off after leaving them on for a season. Now that they are more available and reasonably priced, why not use them for the exhaust assembly, such as heat exchangers to crossover, etc. on a 911?

See Stainless Steel BASIC Information

Comments...

[afterburn 549]

the purest will say no for 3 reasons...just not correct
and dissimilar metals
3 expansion rate is wrong
How ever I use SS where I can with no adverse effects...works for me...every one is welcome to do as they want

[KTL]

I agree its a good choice to use stainless on the connection points like the crossover pipe and muffler/catalyst/cat bypass. Plain steel fasteners start rusting right away. Even quality plated bolts like the German Kamax stuff.

So it's going to corrode either way, be it with stainless (due to the dissimilarity issue) or regular 8.8 steel. I say go with the stainless because it'll be better over the long term. I've used stainless SAE 5/16" bolts with silicon-bronze nuts per the tip found on here years ago by Wil Ferch I believe. It's proven to work very good for me over the years. I think the reason the SAE hardware is chosen instead of metric is because SiBr nuts are not commonly available in metric.

That said, I have a ton of leftover SiBr nuts if anybody wants some. Buying them in packs of 50 tends to create a lot of extras in the inventory.....

[chris_seven]

Originally Posted by Uwon

Stainless Steel BASIC Information

Mostly sensible but stainless steel fasteners do need a little more care in assembly that conventional steel bolts.

All of the Austenitic Stainless Steel fasteners have a tendancy to gall sepecially if tightened quickly with air tools or ratchet spanners.

They have a higher coefficient of friction which makes them a bit stickier and a lower coefficient of heat transfer so high spots heat up more quickly.

In the limit galling can cause them to lock up completely and shear off heads.

On any application such as exhausts I would lubricate the threads with either a moly disulphide lubricant or boron nitride.

When lubricated reduce torque by 10% from the figures qoted in the article.

Mixing stainless steels also helps to reduce galling and would make diassembly easier.

We tend to use A2 -70 bolts and A4 -80 nuts.

The Silicon Bronze is a great idea especially on exhausts.

[Uwon]

Thanks all for your input. Never knew what galling meant so off to Wikipedia I went. I think that I'll use SS bolts and nuts per Chris with Wurth NI 2400 nickel anti-seize paste.

[burgermeister]

+1 on KTL / Walt's suggestion. I've always gotten the SiBr nuts off the SS bolts without issues (use a 6-point socket on the nuts!). I use plain hardware store 5/16" SS bolts.