For my sins I've been using a Cagiva V- Raptor as my daily driver & commuting buddy - the one with a Suzuki TL 1000 V Twin motor. It does boff along the road quite nicely mind and can be a giggle when required. Anyhow some time back I replaced the stator cover due to some quite spectacular corrosion and dang me if it isn't happening again. I initially thought it might be due to salt but as you can see the majority appears to start on the cover to engine case union in which one of those real thin metal gaskets that has an outer 'paper' layer is used. So any ideas as to what may be causing this? could it be the two different metals of the gasket & cover reacting? You can also see the same happening around the inspection plug at the top which also uses a metal gasket/washer. I believe the cover is magnesium which is the same as the rocker covers but they show absolutely no corrosion. Even the one on the front pot which is in the teeth of the road muck but they don't have a 'metal' gasket.
When you place magnesium in contact with any dissimilar metal, the magnesium will suffer from galvanic corrosion. The gasket material contacting the magnesium should be non-metallic to electrically isolate the magnesium from other engine parts and fasteners. https://en.wikipedia.org/wiki/Galvanic_corrosion Even if the two dissimilar metals are separated with a thin non-metallic gasket or paint film, if the gap is bridged by water — or god forbid highly conductive salt water — then magnesium corrosion will still be likely.
Looks like galvanic corrosion to me, dissimilar metals together. I use magnesium anodes on my boat and they get eaten away just like that.
Thanks guys... rs. And thinking about it the rocker covers are separated from the head by quite a thick rubber gasket. Double rs... so three winters worth of riding isn't recommended then... ho hum Or riding in any rain unless, perhaps, I dry it out each time.
If you can isolate it by using another type of gasket then it will be ok as you have seen with the other Mg covers, make a paper gasket with some gasket paper and see if that solves it.
Many thanks, all really good suggestions guys but Shazaam!'s comment is the worrying one. I think perhaps a combination of all of them and perhaps a Cerakote rather than powder coat.
Hmmm.... so why are some gaskets made of thin metal with a 'paper' cover on either side? It would surely have been cheaper for Suzuki to use a standard paper/card gasket. It can't be there to prevent galvanic corrosion so is it anything to do with the massive dynamic electromagnetic field created by the stator or perhaps the heat it produces? The cover does get really hot.
The paper cover on both sides of the gasket is likely Suzuki's attempt to mitigate galvanic corrosion of the magnesium cover. I assume that the gasket edge is exposed metal, however. Looking at the picture, it appears that the cover surface that is touching the gasket paper has not corroded first. The corrosion appears to be primarily on the exposed cover surface adjacent to the gasket. I think that because the gasket is SO THIN, that the salt water is bridging the small distance across the gasket and completing the electrical circuit to the dissimilar metal — both in the engine casing, and/or the gasket material. The same condition exists at the inspection plug. It only takes having a pinhole or nick in the cover paint to start the corrosion locally, and it will then start its travel both ways adjacent to the gasket interface. Magnesium, unfortunately, is just not a good candidate for use in wet environments. Except of course, when purposely used in boating as a sacrificial anode to protect other metals against corrosion.
You have that exactly right Shazaam! that is how I remember first noticing it and during the winter washing it down then drying after every commute isn't a viable option... And after a little research on the web it appears to use of such thin metal gaskets is in areas of high heat which is exactly what occurs with the stator. Suzuki must have been on a right weight saving exercise because as mentioned the rocket covers are magnesium and the clutch cover is er... plastic... yes plastic! Which over time warps and becomes a right old pain to keep oil tight.
I happened to be talking to a retired metallurgist about this and he said the reason they use magnesium is.... who'd have thought, cost. It's evidently much cheaper and easier to cast complex shapes than with aluminium.
