Stainless Steel Bolts

[Spy]

I am currently contemplating changing out my stock 996 Turbo exhaust for a sportier sounding model.

From much reading, I know it is recommended to change the bolts for the exhaust and other bits (eg turbo bolts etc) for stainless steel bolts seeing as the exhaust is off.

I had a few questions:
- I believe that Stainless Steel does not have the tensile strength of the OEM steel bolts. Is this an issue or is there a specific type of stainless steel bolts I should be looking for ?

- Where, and which, Stainless Steel bolts are recommended ?

- Which are the ones I should be looking to change, what are their sizes and how many of each ?

Thanks for your help

[chriscoates81]

I wouldn't have thought your exhaust would be under much tension at all.

[anonymous-user]

SS bolts have significantly lower strength than carbon steel. There is also the risk of bimetallic corrosion if a SS bolt is fastened to a carbon steel fixture, no problem if exhaust is also SS.

[EvoSlayer]

REALIST123 said:

SS bolts have significantly lower strength than carbon steel. There is also the risk of bimetallic corrosion if a SS bolt is fastened to a carbon steel fixture, no problem if exhaust is also SS.

This^^^
There are only 8 studs and nuts (4 studs in each turbocharger) the nuts will most probably be knackered and would be replaced anyway. Don't bother fannying around removing the studs if they're usable, you'll only end up snapping them.

[phelix]

SS bolts on an exhaust are a good idea - they will last significantly longer than standard bolts. They're relatively unstressed. It's a good idea to put some grease or oil on the threads to prevent galling as you tighten the bolts down as SS is a little softer.

Bimetallic corrosion between stainless and non-stainless steel shouldn't be much of an issue in an automotive environment.

[FarQue]

Back in my motorcycle days I swapped a lot of steel bolts and screws for stainless. A2 grade was always used and I never had problems. I wouldn't use them to hold brake calipers on, but they were fine everywhere else...

[Spy]

OK, looking at getting this done in the next couple of weeks.

Can someone confirm the following:

- Are A2 Stainless Steel bolts OK to fix the Manifold to the Engine ?

- Are A2 Stainless steel nuts OK to connect the Turbo to Cats using the existing carbon steel studs ?

Thanks

[996TT02]

Spy said:

OK, looking at getting this done in the next couple of weeks.

Can someone confirm the following:

- Are A2 Stainless Steel bolts OK to fix the Manifold to the Engine ?

- Are A2 Stainless steel nuts OK to connect the Turbo to Cats using the existing carbon steel studs ?

Thanks

The manifold bolts were very (very) tightly done up on mine. They are high tensile bolts, IIRC 10.8 grade.

I could not source alternatives and just re-used the old ones, but backed off the torque.

I would not use SS here, there seems to be little point and if of insufficient strength may well shear when torqued to spec.

If you need to, buy new OEM ones, or if you manage to, equivalent replacements.

The the turbo nuts - I would (and did) use copper coated steel nuts. I don't like the idea of SS nuts/carbon steel studs but that's just me. Probably is OK however but I preferred the "copper" nuts, plus these latter can be bought / usually are specifically for exhausts and are of the locking type, whereas I have not seen SS lockers, except for nylocs, which of course don't need mentioning here.

If not mentioned already - get yourself a splitter as you may need it to get the old nuts off, and also buy the turbo gaskets too.

[fioran0]

I always just stud the heads for the exhausts using regular carbon steel studs with the aluminium heads and then use copper or brass nuts to secure the manifolds to the studs. Not on a turbo but the same OEM bolt is used across all models. The nuts become throwaways.
Following that line I would also use brass or copper nuts on your existing carbon steel studs.

[Pugley]

As stated by several people already.

The nuts and bolts used in the exhaust system are not safety critical and you are likely to hear something before anything actually dropped off.

For track focused cars that are inspected frequently and are unlikely to suffer being covered in salt normal OEM fastners would seem to be the best bet.

For road cars that cook in salt during winter months I would opt for as many stainless nuts and bolts as I could fit. If you have ever tried to remove an old 996 manifold you will understand just how much steel suffers around hot exhausts and salt! I have also used stainless on all of the under-tray fixings as well because the original tin clips are of very poor quality.

[mcdk2]

Spy said:

OK, looking at getting this done in the next couple of weeks.

Can someone confirm the following:

- Are A2 Stainless Steel bolts OK to fix the Manifold to the Engine ?

- Are A2 Stainless steel nuts OK to connect the Turbo to Cats using the existing carbon steel studs ?

Thanks

A2 or A4 refers to the corrosion protection levels and nothing to do with strength. A2 should be ok on a car but would be hopeless in a marine environment.

The strength is defined by the number following As or A4. It is usually 70 or 80. 80 are stronger and are comparible with 8.8 grade steel bolts, i.e. not particularly strong.

Basically, if the current bolt shows 8.8, you can use A2 or A4-80. If it shows 10.9 or 12.9 and is a structural application, stay well away from stainless bolts. There are higher strngth stainless steels available but not commonly for bolts.

Hope that clears things up.

[mcdk2]

mcdk2 said:

A2 or A4 refers to the corrosion protection levels and nothing to do with strength. A2 should be ok on a car but would be hopeless in a marine environment.

The strength is defined by the number following As or A4. It is usually 70 or 80. 80 are stronger and are comparible with 8.8 grade steel bolts, i.e. not particularly strong.

Basically, if the current bolt shows 8.8, you can use A2 or A4-80. If it shows 10.9 or 12.9 and is a structural application, stay well away from stainless bolts. There are higher strngth stainless steels available but not commonly for bolts.

Hope that clears things up.

Oh and fasteners are of all sorts of quality and are generally badly policed. Buy from a reputable source, not cheap ebay asian jobbies

[Spy]

Thanks guys, useful info. I will let you know how I get on.

[fioran0]

I am a big fan of fancy metals for any parts where it is suitable. Titanium, super alloys and stainless etc can all be great.
However, you need to always think beyond just the longevity of the fastener itself and about what job its doing and whats its relationship is with other metals its working with.

Stainless bolts in an aluminum head is worth some thought. Significant galvanic corrosion risk in the threads coupled to the relative ease with which they can be snapped increases potential for trouble. If you think its a PITA trying to drill out a snapped off nasty old oem bolts, try with a snapped stainless one.

Stainless studs can be made to work around these drawbacks. You can use high temp thread lock to create a barrier between the two metals as the studs should never need to come out. Using a soft metal nut in this combination is also a good idea as it protects the stud.

http://www.bssa.org.uk/topics.php?article=89
Article from british stainless steel association on the use of stainless steel with aluminum. For those too lazy to read. Stainless used to clamp aluminum sheets together - little risk of corrosion. Stainless bolts into aluminum materials - unwise combination.

Make your own call regarding what combination of parts you want to run. Everyones risk/benefit analysis differs. What should be clear is that there are better options available than just throwing in oem bolts.

Edited by fioran0 on Tuesday 3rd June 20:36

[Inline__engine]

back from the dead.

with stainless studs in aluminium is it recommended to use an anti sieze such as nickel to enable them to be remove at some future point?

ive got some stainless studs with the internal hex drive (couldnt find any high tensile ones unforyntetly with the hex drive) this is a street car with stainless manifold

[IMI A]

Fellow on 911UK who makes batches of these in titanium alloy.

http://911uk.com/viewtopic.php?t=110603&postda...

[rObArtes]

You can get hold of Copper Coated Stainless Bolts or PTFE Coated Mild Steel Bolts,

[AW10]

Not sure a PTFE coating will last long in an exhaust system, particularly on a rear engined car where even the tips can get quite hot.

[battered]

I would imagine that the copper coated versions would reduce your corrosion and be less prone to galling. Slather it all in Cppergrease for good measure. Brass nuts would seem to be wise too, on either SS or mild fasteners. As others say, you can treat a brass nut as a throwaway item when it comes to stripdown and at least hey will always come off.