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Use of stainless steel bolts and copper slip in aluminium

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Alpine Daimler
Posts: 141
Joined: Thu Feb 18, 2016 2:17 pm
Location: Munich

Use of stainless steel bolts and copper slip in aluminium

Post by Alpine Daimler »

Hello Everyone

Any metallurgists out there?

I am completing the top end rebuild of my V8 and I have refitted the water manifold with thermostat housing connecting the 2 heads with new stainless steel bolts and the threads very lightly coated with copper slip grease I thought to help future removal.

I was admiring the finished job and thought it looked much better than the original partly damaged/rounded off and rusting original bolts when it occurred to me I may not be doing myself any failures due to the possibility of accelerated corrosion or difficult in future removal, with or without the copper slip, something I'm sure I either learnt years ago or read in the old forum which I cannot find anymore.

I have slaved on the inlet manifold with the old cleaned up bolts but also lightly coated with copper slip ....into the aluminium heads, upon reflection was that wise? if so its not too bad as I can take them out again and clean everything up and refit.

I've tried Google and the opinions there seem to be very mixed.

Regards

Rob C.
V8, its the only way forward, 1967 2.5 V8 Saloon LHD MAN/OD, DLOC member

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Vortex O'Plinth
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Joined: Fri Feb 12, 2016 8:15 pm
Location: Gloucestershire

Re: Use of stainless steel bolts and copper slip in aluminium

Post by Vortex O'Plinth »

Personally I would prefer to use Bright Zinc Plated steel fasteners when threaded into aluminium. Under conditions favourable to bimetallic corrosion - i.e. when immersed in an electrolyte - the high difference in potential between stainless steel and aluminium can cause the aluminium to act as a sacrificial anode to protect the stainless steel cathode. In theory this could mean deterioration of the female thread in the aluminium casting.

BZP or even plain carbon steel have a much lower difference in potential with aluminium and consequently any bimetallic corrosion would be less.

This all presumes that conditions for bimetallic corrosion in the joint are present, i.e there is an electrically conductive corrosive liquid present between the two metals. Whether the localised conditions of the bimetallic joint on a car engine can provide this electrolyte is doubtful if used with a lubricant/sealant such as Copaslip to exclude damp and in practice I'm not sure you would see any significant difference between the different combinations.
Nick

"Don't bother with the Air & Space Museum - there's nothing to see.......".

Stan Thomas
Posts: 647
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Use of stainless steel bolts and copper slip in aluminium

Post by Stan Thomas »

What Mr. O'Plinth is correctly saying in a word is that stainless steel in aluminium - especially of there is the likelihood of water being present coupled to thermal cycling, is a total no-no!

When you come to undo the stainless steel bolts they will probably bring the threads in the aluminium with them. Use bright zinc or brass bolts.

Chris_R
Posts: 554
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: Use of stainless steel bolts and copper slip in aluminium

Post by Chris_R »

I knew I'd read something about this and it's taken a few days to find what I was looking for.
Steel into aluminium can lead to Thread Galling; https://en.wikipedia.org/wiki/Galling and this is a good explanation: https://www.boltdepot.com/fastener-info ... lling.aspx

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Alpine Daimler
Posts: 141
Joined: Thu Feb 18, 2016 2:17 pm
Location: Munich

Re: Use of stainless steel bolts and copper slip in aluminium

Post by Alpine Daimler »

Thanks very much for your replies.

Suffice to say I have ordered some zinc plated bolts and the ones I have fitted will be replaced!!

I have ordered the bolts from here : https://www.westfieldfasteners.co.uk/BZ ... Rfull.html
I have used them before, they are reliable, reasonably priced and competant.

Regards
Rob C.
V8, its the only way forward, 1967 2.5 V8 Saloon LHD MAN/OD, DLOC member

saratim
Posts: 2
Joined: Wed Jul 15, 2020 3:37 pm
Location: Sayreville, United States

Re: Use of stainless steel bolts and copper slip in aluminium

Post by saratim »

You should consider Albany County Fasteners in case you need any kind of fasteners or tools in the future.
They are best in Sayreville, NJ.

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