The Triumph Dolomite Club - Discussion Forum

The Number One Club for owners of Triumph's range of small saloons from the 1960s and 1970s.
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PostPosted: Tue Mar 24, 2020 5:22 pm 
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Many years ago I remember from my Chemistry lessons at school of something called the Electrochemical series. It is a chart that relates different metals to their ability to produce a voltage in the presence of an electrolyte. i.e. a steel bolt in an aluminium casting in the presence of water. It is also related to how they corrode together.
So as an example Aluminium ( -1.66V ) and steel (=iron ) (-0.44V ) set up a voltage difference ( potential ) of 1.22V . But a zinc ( -0.76V ) plated steel bolt in aluminium only gives a potential of 0.90V.
So is my understanding correct that a zinc plated bolt in an aluminium casting is less likely to corrode that a plain steel bolt ?
Now I see that you can get nickel ( -0.25 V ) plated studs for the 1850.
This gives an electro-potential of 1.41 V for nickel and aluminium . Much worse that the 0.90 V of a zinc plated bolt in aluminium.
Is this how it works ?
If so, what is the advantage of nickel plated studs please ?
Thanks,
Tony.


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PostPosted: Tue Mar 24, 2020 7:53 pm 
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I think the same is also true of Stainless Steel bolts! I did raise this on a Stag Forum a while back. I do think you are right that the "least worst option" is zinc plated steel. Stainless Steel or Nickle Plated bolts, studs or what ever are potentially (pun intended :) ) more reactive/corrosive in my opinion. No one challenged my posting, but I would also be interested to hear what anyone with a chemistry/physics/metallurgy background thinks!

As to the advantages of Nickle Plate ......... not sure but they are shiny !!

For my money I use standard zinc plated studs and bolts. In the head I open the holes out slightly to ensure they are clean and have a smidge of clearance. I give the shanks a good smear of copperslip, I am aware that some differ on this and use a ceramic grease but it has always worked for me. I have an old Land Rover with an aluminium timing cover with several long thin bolts holing it. 20 odd years ago I removed it and when I replaced it Icleaned out the mounting holes and coated the zinc plated bolts with copper slip. I recently had the cover off again and had no trouble removing any of the bolts. Not quite the same as a Stag or Slant 4 cylinder head but similar - long steel bolts through an aluminium casting.

Roger

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PostPosted: Mon Mar 30, 2020 2:48 pm 
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This has always concerned me with Sprint (original-spec) alloy wheel nuts onto steel studs.

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