Replacing bolts with stainless steel ok?

[zed4]

Hi,

I'm in the process of repainting some of my chassis, so I have various items removed. Whilst I'm at it I am wondering about replacing some of the bolts with stainless steel versions.

I've already bought the correct wishbone bolt kit from RT Racing, so I know they're the correct high tensile rating. However, I also have the antiroll bar mounts removed and the power steering rack unbolted. I believe these bolts are high tensile, but do they need to be? The antiroll bar brackets simply bolt a bracket onto the chassis and the power steering rack doesn't look like it really requires high tensile bolts.

So would I be ok to replace these with stainless steel bolts?

Thanks,

Dan

[phillpot]

Anti-roll bar brackets I'd say yes, should anything brake it shouldn't be disastrous. Anti-roll bar does not actually locate any of the steering or suspension, car would work without it.



Steering rack mountings? more than likely ok...... but

Can't see a problem in normal use but should you wollop a kerb or something and give them a real "shock" could they/would they shear?

[zed4]

I'm not 100% sure they are high tensile as standard, I will have to check the bolt. I suppose I could find some new zinc coated bolts as they're metric, but I have a big stash of stainless bolts here so it's convenient to use them!

[portzi]

zed4 said:

I'm not 100% sure they are high tensile as standard, I will have to check the bolt. I suppose I could find some new zinc coated bolts as they're metric, but I have a big stash of stainless bolts here so it's convenient to use them!

What is the lettering or markings on the stainless steel bolt head, have they got any markings like these? They need to be grade 5 bolts at least.

[zed4]

portzi said:

zed4 said:

I'm not 100% sure they are high tensile as standard, I will have to check the bolt. I suppose I could find some new zinc coated bolts as they're metric, but I have a big stash of stainless bolts here so it's convenient to use them!

What is the lettering or markings on the stainless steel bolt head, have they got any markings like these? They need to be grade 5 bolts at least.

Ok, the bolts I've taken out are 8.8, so they are high tensile.

The stainless bolts I have are: M8 - A4-70, and the M10 - A4-70

[portzi]

The stainless bolts I have are: M8 - A4-70, and the M10 - A4-70

so M8 & M10 are the thread diameter whats the A4-70 have you goggled it?

[kris450]

If replacing with Stainless then the equivalent 8.8 grade is A4-80.

[davelittlewood]

As long as the replacement bolts have 0.2% proof >640 MPa and UTS >800 MPa then they are at least as strong as the 8.8 bolts.

[Steve_D]

The A4 part of the stainless spec is the material grade as in its corrosion resistance.
It is recommended that you should not use A4 bolts with A4 nuts as they can cold weld to each other (known as Galling). So A4 bolts and perhaps A2 nuts.
Next time you are in the workshop ask me to show you the samples we have and the metallurgical report carried out on some bolts we had seize.

Steve

[hidetheelephants]

It's advisable to lubricate stainless nuts and bolts to avoid galling; better quality fasteners are supplied waxed, but I've never seen waxed fasteners on ebay or other discount vendors. Antiseize of some kind would be ideal but any grease you have will do the job.

[zed4]

Steve_D said:

The A4 part of the stainless spec is the material grade as in its corrosion resistance.
It is recommended that you should not use A4 bolts with A4 nuts as they can cold weld to each other (known as Galling). So A4 bolts and perhaps A2 nuts.
Next time you are in the workshop ask me to show you the samples we have and the metallurgical report carried out on some bolts we had seize.

Steve

Yes, I realise what A4 denotes, and after some googling I now know what the tensile rating is too.

Not heard of the nuts and bolts welding themselves together before. We use all A4 stainless nuts and bolts at work, all of our boats are built with them, and we've never had a problem.

[zed4]

davelittlewood said:

As long as the replacement bolts have 0.2% proof >640 MPa and UTS >800 MPa then they are at least as strong as the 8.8 bolts.

It looks like A4-70 are 0.2% proof 450 MPa min and 700 MPa min tensile. So not equivalent to 8.8 tensile.

So I suppose my question is, will the 700 MPa be sufficient for securing a steering rack and antiroll bar mounts, or should I really be using the original 8.8 grade bolts?

Both sets of bolts thread into the chassis itself, no nuts.

[CHGRIFF]

This has been covererd many times previously,and could have serious consequences if incorrect bolts are fitted. Primary consideration is the function of the bolt. If it secures a safety item ie steering rack, suspension or brakes you must fit high tensile bolts as originally specified. Fitting an alternative puts yourself in unecessary danger and should a bolt fail with consequences to car or yourself, your insurance company will invalidate your insurance. It is certainly okey to fit SS bolts when securing non safety items ie securing the body to chassis, induction and cooling system fitment as an examlple. Why take the chance.

[zed4]

CHGRIFF said:

This has been covererd many times previously,and could have serious consequences if incorrect bolts are fitted. Primary consideration is the function of the bolt. If it secures a safety item ie steering rack, suspension or brakes you must fit high tensile bolts as originally specified. Fitting an alternative puts yourself in unecessary danger and should a bolt fail with consequences to car or yourself, your insurance company will invalidate your insurance. It is certainly okey to fit SS bolts when securing non safety items ie securing the body to chassis, induction and cooling system fitment as an examlple. Why take the chance.

Fair enough. I think I will find some new high tensile bolts, rather than reuse the old ones.

Edit: At least I've learnt something about the ratings of bolts and tensile strength. All very interesting and useful.