Stainless steel screws into aluminium block

[strath44]

Hi folks, I’m working on my 996 and a lot of the screws and bolts are in a real mess.
Is there any reason for not using stainless steel other than increased cost?
I’m looking at replacing with stainless a lot of them as I plan have the car a while.
I assume the originals are zinc coated steel.
Thanks

[NMNeil]

Tensile strength?
https://www.boat-renovation.com/high-tensile-steel...

[gazza285]

Galvanic corrosion, so a decent anti seize compound would be a good idea, and one designed for the job, not copperslip.

Edited by gazza285 on Tuesday 8th March 07:08

[105.4]

gazza285 said:

Galvanic corrosion, so a decent anti seize compound wouls be a good idea, and one designed for the job, not copperslip.

Could you recommend better alternatives than generic Copperslip?

Cheers

[gazza285]

105.4 said:

gazza285 said:

Galvanic corrosion, so a decent anti seize compound wouls be a good idea, and one designed for the job, not copperslip.

Could you recommend better alternatives than generic Copperslip?

Cheers

A metal free compound would be better, we use Molykote at work. Not cheap though.

Edited by gazza285 on Tuesday 8th March 07:35

[dontlookdown]

The main advantage of using stainless fixings - corrosion resistance - is negated if you are screwing them into aluminium, because of the galvanic effect. Plus depending on the grade of stainless, bolts can have up to 75% less tensile strength than high tensile steel. That's why mfr default is HTS.

I'd replace like with like in your position.

[Polly Grigora]

Could be fun calculating torque figures, recently used some and they felt like they were going to snap rather than stretch, am no expert though

[blueST]

105.4 said:

gazza285 said:

Galvanic corrosion, so a decent anti seize compound wouls be a good idea, and one designed for the job, not copperslip.

Could you recommend better alternatives than generic Copperslip?

Cheers

I live in the Land Rover world where this topic s a regular discussion, I think generally folk conclude using stainless against aluminium is more trouble than it’s worth. If the 2 metals aren’t properly isolated the aluminium with start dissolve in double quick time. Stainless is much worse in this regard than mild steel. And as mentioned, for structural applications you need to be careful with the strength of the stainless fixings.

If you do go-ahead, Weicon paste is highly recommended as anti-seize to prevent corrosion. Much better than copper-slip. I’ve used ceramic brake grease with success too.

[strath44]

Thanks all I really appreciate all the replies, I think I will go the safe route and avoid S/S apart from on the exhaust maybe!?

Can anyone recommend online suppliers for bolts etc in lower quantities please?

[CrutyRammers]

Worth using ss in non stressed applications where it's not direct into ally though, especially in mucky areas.
I normally use eBay for bolts. Kay's fasteners are a good one.

[E-bmw]

Contrary to what the above posts have said, I would not use SS anywhere that didn't come with SS as standard.

The manufacturers invest millions in the product as it is sold & will only use the right thing for the task.

SS in ally will result in the ally falling apart well before its time.

SS in steel will result in the steel corroding far quicker that in should.

Stick with the right bolt/nut in the right material & grease it with the correct grease from new & it will last pretty much for the life of the vehicle.

[strath44]

Thanks I’ve gone zinc in anything going into the block and I’m using SS for the exhaust parts all off which are SS anyway.

I used Accu.com and found them excellent!!

[105.4]

gazza285 said:

A metal free compound would be better, we use Molykote at work. Not cheap though.

Edited by gazza285 on Tuesday 8th March 07:35

Thanks Gaz

[105.4]

blueST said:

I live in the Land Rover world where this topic s a regular discussion, I think generally folk conclude using stainless against aluminium is more trouble than it’s worth. If the 2 metals aren’t properly isolated the aluminium with start dissolve in double quick time. Stainless is much worse in this regard than mild steel. And as mentioned, for structural applications you need to be careful with the strength of the stainless fixings.

If you do go-ahead, Weicon paste is highly recommended as anti-seize to prevent corrosion. Much better than copper-slip. I’ve used ceramic brake grease with success too.

Ah, the LR world. Been there, done that, improved my metal fab & welding skills as a result

Cheers for the tip