Honda-SOHC
SOHC.co.uk Forums => CB500/550 => Topic started by: heliwilly on October 30, 2018, 07:24:06 AM
-
I have read on the .Net forum about the use of stainless bolts to replace various covers on the SOHC bikes causing problems with electrolytic action between the alloy and the stainless.
Have any of you had problem removing stainless bolts/screws that have been in situ for a long time.
If this is a problem, would a copper based grease prevent this happening.
On a personal note, I always fit dry to ensure the proper torque because of the alloy.
Bill W.
-
I have used many stainless bolts over the years. Copper-slip or similar is essential or over time the threads will almost always seize. I have so far not had a single seizure on threads that were coppered.
Sent from my Nexus 6 using Tapatalk
-
You're right to consider what's going to happen as you will be changing it.
Galvanic corrosion is the overall effect in operation, in which different metals appear on the "galvanic" scale, meaning that one is cathode and the other anode which given the right circumstances one will "plate" the other.
Usually they use zinc plated bolts so that the zinc is sacrificial, leaving both the aluminium and the steel more or less intact. That's what the white residue is, zinc oxide, I think. It also needs an electrolyte solution to make it happen generally, which is where salty water comes in to play it's part.
With plain stainless you've got no sacrificial material in the equation, so normally I think it'll start to "eat" the aluminium.
Any grease when filling the gaps around the bolt will exclude the electrolyte, if this is complete you'll probably be safe. But in marine application they've generally used one with zinc oxide included, that's normally the cream coloured greases that you can see used. It's this component that is then sacrificial.
Unless stated otherwise, most torque specification is given for dry threads. For using grease in that scenario, you'd expect to used a 10 to 15% reduction in torque to obtain the same clamping force.
-
There is a simple solution to avoid the problem....
Move to a hot dry country.
-
Graham absolutely despairs with some engines we have in where, in the past, SS bolts have been fitted dry and they have literally welded themselves to the alloy. They are a nightmare to remove with some causing quite destructive results to the alloy. If you must use SS bolts, they definitely need a barrier applied of some sort.
-
Thanks for the replies. I think in future I will be using a barrier grease. Which is the best to use. I have used copper based grease on somr car applications, but this is the first motorbike engine for 50 years. Thanks Bill.
-
I always use Stainless in non-load critical applications but I also always use copper based grease and so far I have never had a problem with seizure.
-
Same here