44
FEBRUARY 2022
MAINTENANCE CORNER
By Duncan Bennett, Member #4171
T
his is a bit of a “left field” maintenance topic, but if your non-negotiable goal or at least prayer is to maintain the overall look of your bike and prevent male bolts and screws welding themselves into their respective female counterparts like a [awesome analogy too risque to print here] you need to think metallurgy. Galvanic corrosion to be precise. What is galvanic corrosion, and what does it mean when you pull up in Surfers Paradise alongside a group of fit looking young men/ladies (strike out whichever not applicable to your situation) in the middle of a small underwear shoot? It means that the polished stainless steel fuel tank you just installed to impress young men/ladies (go again with the striking out) is sucking electrons from that small busted-arse high carbon steel bolt you fixed it on with like a Dyson in a ‘roid rage. Losing electrons means rusting if you are iron, and corroding if you are any other metal, but either way you are disappearing. So one day your small busted-arse high carbon steel bolt will literally do that, your fuel tank will come adrift while on the M1, and unfortunately smack your fit young man/lady (you know what to do) pillion in the face. You won’t see either again. So how do we stop galvanic corrosion, or at least slow it down? It isn’t always easy with a new bike because the manufacturer will have a parts list, but not what the parts are made from, so over time we just have to accept that rust will start to appear.... Mirror stems are a traditional rust hotspot on BMWs from the late 1990’s and early 2000’s. These are made from low quality steel and chromed, so the electrons are sucked out until the rust gets started and the chrome starts to flake off, no coincidence that it starts at the bottom near the couple between the low quality and higher quality metals. This is a classic cause of galvanic corrosion - a small low quality metal part is coupled to a large high quality metal part - most of the bike including the engine block. So that is rule No.1 - small parts that you need to undo should always be of higher quality than the large parts, think 316 stainless steel for fasteners. The large mass of lower quality metal has more than enough electrons to keep the small high quality fasteners happy for a very long time. Often we have no choice on small parts, think Bunnings who rarely seem to have the right fastener in the right quality and you end up with zinc
