Who's up on their metallurgy?

[earlyre]

Firstly, if in the wrong subforum please move.

Short version, dropped a bolt, couldn't find it, replaced with a stainless analog from Lowe's.( Different head, but right thread and length)

Do I need to worry about anything putting stainless fasteners into an Al housing?

Factory bolt is a flange bolt w/ an 8mm hex head, the ones I bought are cap screws, take a 5m Allen key...

 

[Kestas]

Any fasteners involving aluminum or stainless steel, whether it's the bolt or the hole, need antiseize applied to the threads before installation. Both of these materials are prone to galling, even in the absence of a corrosive environment.

Do you know if the original bolt had some sort of special grade to it?... and whether the replacement has at least the same grade?

Otherwise the fastener should be okay to use.

 

[racin4ds]

No issues at all, we used all SST fasteners into aluminum with my last military contract job. Very common thing. If you're worried put some anti-seize on the threads first.

 

[Michael_P]

Hardened stainless fasteners are much less likely to gall.

 

[Leo99]

Here is a nifty table:

 

[benjy]

be aware most 300 grades of stainless bolts are not very strong!!!

 

[kschachn]

Originally Posted By: Michael_P
Hardened stainless fasteners are much less likely to gall.

Where are you finding those?

 

[kschachn]

Originally Posted By: benjy
be aware most 300 grades of stainless bolts are not very strong!!!

Correct, and they cannot be heat treated to increase strength.

 

[earlyre]

Should have mentioned before, they're the two holding the two halves of the thermostat housing together on my sable, so I don't see temperature being much of an issue, nor really pressure, the cooling system is only 16psi, and didn't leak with just one holding the halves together.


The old ones are grade 8.8, pretty sure the new ones are as well( easy to check).
Plan on removing and doping with antiseize anyway, just wanted to make sure there's no long term issue with dissimilar metals.

 

[kschachn]

Originally Posted By: earlyre
The old ones are grade 8.8, pretty sure the new ones are as well( easy to check).
Plan on removing and doping with antiseize anyway, just wanted to make sure there's no long term issue with dissimilar metals.

Well you had dissimilar metals before unless the original bolts were aluminum. Antisieze is a good idea, cut your torque down about 10-15% so they don't strip the aluminum threads or snap.

I live in the rust and road salt zone like you do, so I often replace non-critical fasteners like that with stainless ones from the hardware store. I don't use them for suspension or critical engine bolts but most fasteners on the car are OK.

 

[earlyre]

Originally Posted By: kschachn
Well you had dissimilar metals before unless the original bolts were aluminum. Antisieze is a good idea, cut your torque down about 10-15% so they don't strip the aluminum threads or snap.

it looks at least to be AL plated/coated, whatever.
the spec is only 10 Nm(89 in-Lb/7.38 ft/lbs), aka just tight.
oh, and I mis spoke, since they're metric it's CLASS 8.8, not grade..

 

[853okg]

Half the parts on a modern bicycle have stainless fasteners into aluminum. There should be no issue.

 

[Kestas]

I stripped the threads on my bicycle when I tried to unscrew a pedal from the crank. I had to buy a new crank.

Half the transmission pan bolts on my 91 LeBaron were stripped when I bought it.

 

[Ducked]

Originally Posted By: Leo99
Here is a nifty table:

So maybe you shouldnt use copper-based antiseize.

 

[earlyre]

The stuff I have is nickel based.

 

[andyd]

I once used a normal 3/8 stainless bolt to hang an aluminum alt. I spent a couple painful hours drilling it when it sheared a yr or 2 later. No more stainless for Andy. Similar situation with M 20 alt pivot bolt. 8 x 100mm of good German steel. First go 'round resulted in a snapped mount. Further dealings led me to gooping the bolt in grease. I am painfully aware of dissimilar metals bonding. A thin layer of grease prevents it. No more stuck bolts and nothing has fallen off either

 

[Michael_P]

"Where are you finding those? "

Hardened Stainless Bolts

Hardened stainless nuts and bolts are commonplace on 2 piece brake rotors. I also always replace exhaust manifold bolts and studs with hardened stainless.

 

[Ducked]

Originally Posted By: earlyre
The stuff I have is nickel based.


In the red against both interfacing components in that chart, if I'm reading it right and for whatever its worth.

Aluminium base appears to be OK, as you'd expect.

 

[kschachn]

Originally Posted By: Michael_P
"Where are you finding those? "

Hardened Stainless Bolts

Hardened stainless nuts and bolts are commonplace on 2 piece brake rotors. I also always replace exhaust manifold bolts and studs with hardened stainless.

Thanks!

 

[earlyre]

Originally Posted By: Ducked
Originally Posted By: earlyre
The stuff I have is nickel based.


In the red against both interfacing components in that chart, if I'm reading it right and for whatever its worth.

Aluminium base appears to be OK, as you'd expect.


Nickel is in the green, but Nickel Alloys are in the red.