Best bolts for going into aluminium?

[tux850]

I am replacing the timing belt on a 1L Ecoboost and in order to remove the sump had to first remove the aircon compressor. This resulted in one of the bolts snapping:



From what I can gather this is fairly commonplace - expected even - due to glavanic corrosion between the aluminimum sump and steel bolts, particularly on the lowest bolt presumably due to it being more exposed to the elements.

Removing the stud isn't an immediate concern as I have spare sump good to go, but I am wondering what bolts I should use for reinstallation? I need to check but I think they are M8x95mm and from a cursory check (for part code 1445777) they are around £7 each from Ford online (perhaps cheaper from a dealer but the nearest is some distance from me).



Cost aside (I need three as I wouldn't want to reuse even the ones that did come out in case they were seriously weakened during removal) I was wondering if I should just use 'non-Ford' bolts of a material of my choosing?

Looking at eBay I see that zinc-coated or stainless steel options are readily available and likely more besides. What would be best? Or would it suffice to put some copper grease on the threads of whatever bolt I can lay my hands on? I am hoping never to need to remove them again, but I might as well take a 'just in case' approach here.

Edited by tux850 on Tuesday 7th November 14:22

[GreenV8S]

Stainlesssteel in aluminium will corrode worse than mild steel as well as being more prone to galling and snapping.

The ideal would be mild steel bolts the appropriate grade which have been passivated. Zinc coating is one way to passivate them, but these days there are plenty of coatings which provide effective protection by sealing and isolating the metal.

[tux850]

GreenV8S said:

Stainlesssteel in aluminium will corrode worse than mild steel as well as being more prone to galling and snapping.

Ah, okay. Glad I asked! Thanks.

GreenV8S said:

The ideal would be mild steel bolts the appropriate grade which have been passivated. Zinc coating is one way to passivate them, but these days there are plenty of coatings which provide effective protection by sealing and isolating the metal.

I've just spotted the flanged head and that might limit my options. Need to check how the sits on/in the compressor as there's every chance a full-size head wouldn't allow me to fit a socket on.

Regardless which I go for, would you expect copper grease to help at all? I'm not just thinking on the thread but also around the mating faces to try and reduce the exposure to the elements?

[TwinKam]

Copper grease will be fine, but any grease will prevent it being a problem to you during your future ownership, or probably for the rest of its entire life... ie the car will cease to exist for any number of reasons before that bolt becomes an issue again.

[tux850]

TwinKam said:

Copper grease will be fine, but any grease will prevent it being a problem to you during your future ownership, or probably for the rest of its entire life... ie the car will cease to exist for any number of reasons before that bolt becomes an issue again.

Yeah that's true. This bolt is 10 years old and I can't see its replacement needing to be around for another 10.

(A big 'Hello!' to a future me that revisits this thread in 2033 moaning about a stuck bolt!)

[GreenV8S]

tux850 said:

Regardless which I go for, would you expect copper grease to help at all? I'm not just thinking on the thread but also around the mating faces to try and reduce the exposure to the elements?

Grease will help against corrosion, but when you torque the fitting make sure you know whether the figure you're torqueing to is for fitting dry or greased.

[tux850]

GreenV8S said:

Grease will help against corrosion, but when you torque the fitting make sure you know whether the figure you're torqueing to is for fitting dry or greased.

I am sure it'll be dry, but it is not that significant a fixing so I'd likely be doing it by feel anyway rather than using a torque wrench.

[GAjon]

Helicoil the aluminium.

[sospan]

Try a non copper grease. Copper and aluminium can set up a corrosion cell as with stainless. A small chance but worth considering as non copper grease ( as for brake pads) are available. Best option is surface treated steel ( passivated, zinc, others). Also check the torque needed.

[tux850]

sospan said:

Try a non copper grease. Copper and aluminium can set up a corrosion cell as with stainless. A small chance but worth considering as non copper grease ( as for brake pads) are available. Best option is surface treated steel ( passivated, zinc, others). Also check the torque needed.

Ah okay, it seems I'm making all the wrong stuff NG assumptions!

I've got various other greases available - 'universal', red rubber grease, and possibly a tube of 'brake' grease which I guess is just a another conventional grease in named packaging. The torque setting (dry) is 25Nm.

It turns out they are the same bolts used on the alternator and I've got a sst of those from a spare unit so maybe I'll just use them as they are to hand, perhaps with some grease or just dry given I can't see me waiting 10 years to remove them again (if I ever do at all).

[archie456]

Use a non-copper anti-seize compound such as this.

I was recommended this for putting stainless bolts into aluminium about 30 years ago and I've never had a problem.

[tux850]

archie456 said:

Use a non-copper anti-seize compound such as this.

I was recommended this for putting stainless bolts into aluminium about 30 years ago and I've never had a problem.

Okay thanks!

(And at the rate I'll use it I expect 500g will actually last me 30 years. Will report back then.)

[thegreenhell]

Get some Duralac. It's designed for exactly this issue.