Do you still put grease on your nuts?

fastandfurryous · Post by **fastandfurryous** » 18 May 2005, 05:36

Ah yes, the galvanic series. The whole reason why bolting chunks of zinc to steel stops the steel from rusting.
Well. Aluminium and steel are fairly close to each other in the series, with aluminium slightly more reactive which means the aluminium will corrode preferentially, and very slowly. Unfortunately copper is a fair distance away, and is towards the "protected" end of the series, thus creating a larger electrolytic cell, and higher corrosion rates. The aluminium is still the preferential metal for corrosion, but theoretically it will disappear faster.
In the case of a steel bolt in an aluminium housing, Yes, you should probably avoid using copper based grease. (from a technical point of view, although in practical terms, I agree with andy above.)
But. If the bolt is a BZP (Bright Zinc Plated) then there is no need for concern, as Zinc is higher up the reactivity table than aluminium, and hence will be the preferential metal.
There is also the fact to consider that on order for the electrolytic cell to be set up, there has to be moisture present, in good contact with both metals, and both dissimilar metals need tobe in electrical contact with each other. This rarely occurs with coppergrease, as the fleks of copper are in suspension in a non-conductive grease.
Aluminium grease is indeed the spawn of satan when it comes to getting on EVERYTHING. Even trichloroethylene struggles to remove it. Horrid stuff. Worse even than graphite grease, and that's fairly horrible!

ActivaV6uk · Post by **ActivaV6uk** » 18 May 2005, 12:57

graphite grease oh god no! i hate that stuff its something we use to make when we had the machiene shop. the trick was that if you use to park in our carpark (privet) and you made it so that workers couldnt park you got a note, then you got a stronger worded note, then some one parked a pallet behind your car (and you had to come and apologise to management befor anyone would move it) then you got a note attached to your windscreen using graphite grease as the bonding agent, we never had to create a step after that...
Andy

j_roc · Post by **j_roc** » 20 May 2005, 01:04

Caution on using oil on threads as just in the hydraulic method when you put it under pressure it dont compress, so you think that a bolt is torqued up to the specs, and well it aint. Hope this helps

andycarter · Post by **andycarter** » 20 May 2005, 03:01

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by j_roc</i>

Caution on using oil on threads as just in the hydraulic method when you put it under pressure it dont compress, so you think that a bolt is torqued up to the specs, and well it aint. Hope this helps
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Presumably you mean a blind hole filled with oil creates a hydraulic lock situation, I suppose it could happen on things like cam bearing caps.
For plenty of good stuff go to http://www.boltscience.co.uk/
Andy

arry_b · Post by **arry_b** » 20 May 2005, 04:00

I've seen that crack an alloy crankcase on a Honda bike I once had. Ouch, expensive!