This is exactly why I didnt want to get started, talk of fatigue will be superseeded by fatigue-corrosion and so the theory war escalates!
All totally irrelevent as every one agrees stainless steel unless you have an overiding obsession with weight.
Stainless bolts?
-
locum
Interesting discussion. I am looking at using mirror polished stainless bolts on my handlebar clamps, (both on my cycles and motorcycle as it happens). Is this an application for which high tensile carbon steel bolts (8.8 or higher) would be safer or would A4-80 stainless be, to all intents and purposes, just as good?
Unless your motorbike is over thirty years old, your bolts will be going into Aluminium (or rarely Magnesium) alloy. Then the strength, hardness, toughness of either bolt will be more than adequate.
The biggest dangers are overtightening and corrosion. The corrosion can be terrible causing the steel to weld to the alloy and then snapping the head off when you try to undo it. This is easily prevented by putting copper grease on the threads. I have had a few bumps and broken levers and mounts but never broken a bolt except by trying to undo it. These are ones that presumably other people put in without copper grease. None of the stainless steel bolts have rusted in at all but I have only been using them for 10 years and always with copper grease.
The polished ss will look much nicer and stay lookig nicer unless you ride a ratbike!
The biggest dangers are overtightening and corrosion. The corrosion can be terrible causing the steel to weld to the alloy and then snapping the head off when you try to undo it. This is easily prevented by putting copper grease on the threads. I have had a few bumps and broken levers and mounts but never broken a bolt except by trying to undo it. These are ones that presumably other people put in without copper grease. None of the stainless steel bolts have rusted in at all but I have only been using them for 10 years and always with copper grease.
The polished ss will look much nicer and stay lookig nicer unless you ride a ratbike!
I recall other discussions on this subject, with the outcome that copper is in the wrong place in the list of electrical potentials of various metals & actually increases the problem with electro-welding between aluminium and steel. I use lithium greases with minimal trouble. Unfortunately I can no longer find a source for the Century Oils greases formerly used in mining machinery. That stuff was totally corrosion proof!
If at first you don't succeed - cheat!!
Molyslip, the manufacturers of Coppaslip, now offer a product called Aluslip, which, as the name suggests, is a grease loaded with aluminium particles, specifically for use with aluminium. If it's as good as its older brother it should be very good...
Unfortunately the smallest pack size is a 500gm tin - a lifetimes supply for most of us!
Unfortunately the smallest pack size is a 500gm tin - a lifetimes supply for most of us!
Science is meant to help explain what happens in real life. If a scientific discussion of electrochemical potentials suggests that copper grease is ineffective, then that theory is ineffective and clashing with actual empirical data. Copper grease most definately works against the corrosion caused when steel and aluminium are mixed. I have completed dozens of scientific tests over 25 years of vehicle maintenance which prove that point. Copper grease is also effective where aluminium meets aluminium.
Ordinary grease possibly works as well except at high temperatures where copper grease really pays for itself.
Ordinary grease possibly works as well except at high temperatures where copper grease really pays for itself.
Pity about science,,, sometimes!
IMHO copper grease certainly overperforms against predictions.
Why?
My personal theory is that the finely divided copper particles form a natural fracture line in any corrosion that does form. In addition to that they also act as a filler, giving the grease more "body" than it would have otherwise, so helping it to stay in position and carry on doing what grease does best.
I do find myself wondering about this point though - electrochemical potentials are only realised in solution, aren't they?
So if the grease is keeping water off the surfaces, there isnt going to be any electrochemical activity, is there?
IMHO copper grease certainly overperforms against predictions.
Why?
My personal theory is that the finely divided copper particles form a natural fracture line in any corrosion that does form. In addition to that they also act as a filler, giving the grease more "body" than it would have otherwise, so helping it to stay in position and carry on doing what grease does best.
I do find myself wondering about this point though - electrochemical potentials are only realised in solution, aren't they?
So if the grease is keeping water off the surfaces, there isnt going to be any electrochemical activity, is there?
The water only has to come into contact with an exposed piece of each metal (eg bolt head and aluminium body surface) to create a potential.Then current can flow between the two bodies where they contact (at the threads). I cant remember if current flow will create solid state diffusion between the two metals or not.
Maybee they are replacing the copper slip with aluslip because the coppergrease is now known to be very carcinogenic.
My latest copper grease has graphite in it too. This would fit very well with your theory of a layer between the metals.
Maybee they are replacing the copper slip with aluslip because the coppergrease is now known to be very carcinogenic.
My latest copper grease has graphite in it too. This would fit very well with your theory of a layer between the metals.
-
George Riches
- Posts: 782
- Joined: 23 May 2007, 9:01am
- Location: Coventry
- Contact:
For me, it wasn't corrosion but the bolts coming out which was the problem!
The originals had slot heads, I thought it would be easier to apply more torque with allen key heads, as well as removing the need for a largish screwdriver in my on-board toolkit. I just went for stainless without much thought.
If they continue to loosen I suppose that adding some adhesive to the thread (possibly bostik or paint or even specialised stuff) will be a better bet than applying more torque.
The originals had slot heads, I thought it would be easier to apply more torque with allen key heads, as well as removing the need for a largish screwdriver in my on-board toolkit. I just went for stainless without much thought.
If they continue to loosen I suppose that adding some adhesive to the thread (possibly bostik or paint or even specialised stuff) will be a better bet than applying more torque.