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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Joined: Sun Mar 16, 2008 2:52 pm
Posts: 2125
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 ?

PostPosted: Tue Mar 24, 2020 7:53 pm 
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Joined: Tue Oct 15, 2019 8:00 pm
Posts: 113
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.


1975 Sprint Man O/D in Honeysuckle Yellow
1971 Stag Auto White

Too many cars, too little time!

PostPosted: Mon Mar 30, 2020 2:48 pm 
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Joined: Tue Oct 03, 2006 6:38 pm
Posts: 2626
Location: Birmingham
This has always concerned me with Sprint (original-spec) alloy wheel nuts onto steel studs.

Vindicator Sprint, Honda Fireblade RRX 919cc, re-powered by AB Performance. Quick.
1995 Trusty Peugeot 306 XND, no turbine, 242K miles young.
1997 Trusty Peugeot 306 GLX TD, 90K miles and soon to ride again..
Alfa Romeo 147 1.9 JTD 150 Ti Lusso , no longer smoking.
Various other transient runners for selling.

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