Ohlins fork leg corrosion

[68C]

Just stripped down my Ohlins forks to change the seals, had to drill out one of the bolts holding the mudgaurd. Thats when I found moderate corrosion on all four lugs that support the mudgaurd, thankfully once cleaned up and treated the fork seems usable although there is some material loss. Can't even begin to think how much Ohlins would charge for new lower legs.

 

I mention this as the corrosion was not obvious until dismantled, may be worth other folk with carbon bits taking a few minutes to remove the bolts to check.

 

An internet search shows carbon fibre is a problematical material within the aerospace and boating world, carbon fibre is a very good electrical conducter and when in contact with many metals in the presence of an electrolyte (dirty water ) will rapidly corrode due to galvanic action. Apparantly it is all to do with where the metals lie in the galvanic table, aluminium alloy in particular - but also stainless steel give problems. I have found that cheap stainless bolts will corrode in alloy unless well greased - had loads of fun drilling out the sheared stainless bolts I used to hold my old T3 exhausts pipes to the cylinder head.

 

The solution is to keep carbon fibre parts well insulated electrically from all metals, use thick paint, plastic washers, mylar film, jointing compounds even grease. Its carbon or graphite - not plastic!

 

 

http://www.eaa1000.av.org/technicl/corrosion/galvanic.htm

http://www.boeing.com/commercial/aeromagazine/aero_07/corrosn.html

http://www.corrosion-doctors.org/Aircraft/aircraft-design.htm

http://www.deskeng.com/articles/aaahzz.htm

[tikkanen]

Hmmm, sounds strange....

 

I changed my fork seals mid-September last year (also Öhlins with CF mudguard) and there wasn't any rust at all. Went like a doddle without drilling.

 

Any Öhlin owners who have experienced this?

 

BR

Søren

[Baldini]

Yeh. I found corrosion after first winter. I cleaned it up, think I put a bit of paint on the faces too & ever since have kept surfaces greased between mudguard & lower legs - no further problems, but then I don't go out in rain or when there's salt on the roads - not if I can help it anyhow.

 

I don't know anything about these characteristics in CF, thanks for the links, 68C.

 

KB

[belfastguzzi]

Interesting. I hadn't thought about that in regards CF. I do know that when I first went to remove the mudguard in order to take the Ohlins out, I had a horrible time because the alloy screws were so corroded. So I can see that the reaction could be a catalyst for the CF.

 

When I eventually got the bad stuff removed, I put in stainless items, with grease.

[belfastguzzi]

I've looked over the articles now. It's good reading, thanks. Very interesting for lots of reasons.

 

Something that strikes me are the references to water sitting in crevices being such a bad thing (even worse than one might naturally think). In relation to a Land Rover chassis for example, I have wondered if it's better to have holes i certain places that allow water to drain out, or better not to have them because they also may let water in

– but in relation to the V.11, I've posted pics before of the fairly large pools of water that sit inside sections of the V.11 spine. Perhaps a small drain hole, here and there, could be a good thing?

 

I don't know how thoroughly all the liquid is completely blown through the breather system, i.e. constantly being refreshed, or if the same water remains in some of the pools. One thing is for sure, the water in my V.11 hasn't gone anywhere in the past few years, as the thing hasn't moved. Time to get at it!

[68C]

Now you've got me worried, I started on a quick fork seal job to carry on riding in this unusually warm weather, without oil soaked brake pads! If I'm not carefull I will end up following minor defects along the bike to the tail light, don't want it to end another Great British Winter Rebuild with yet another dismantled bike in the shed. Yes, I know your in there Commando, Intercepter, kickstart Sportster, FZ750, BSA Sunbeam and the rest of you!

[belfastguzzi]

If I'm not carefull I will end up following minor defects along the bike to the tail light... with yet another dismantled bike [bike/car/speakers/radio/blahhhhhhhh] in the shed.

Yes, I know that story very well.

 

Have I told the story of how it all ended when the windscreen wiper fell off the car?

Yes, I have.

[Baldini]

Just build a bigger shed.

[belfastguzzi]

Just build a bigger shed.

Aye, that's where it all ends up.

 

 

 

And it's a fine thing too.

[68C]

Where did you get that photo of me?

[belfastguzzi]

Where did you get that photo of me?

erm, in your shed, of course

[68C]

Ah, I think I know where this going.

[grossohc]

I had to drill out 2 of the mudguard bolts on my bike a while back, seized solid, came out easy enough, but i was sweating thinking of the price if the lugs snapped off!!!. Went over the rest of the bike and lubricated each thread as i got the bolts out, i gave up on a few (oil cooler brackets and a couple of others) will worry about it when i need to take these parts off in the future, but i shouldnt have to it is after all a moto guzzi.

Gary

[gstallons]

I use either anti-sieze or loctite on all fasteners.

[PDoz]

G'day guys. I think you'll find the problem has more to do with using stainless bolts in alloy forks , ie it'll happen even without the carbon fibre bits. IN the boating world we use duralac between dissimilar metals to try and reduce the problem. Some genius put a stainless bolt into the alloy end of my yachts boom and it's never coming out! I've tried all the usual things- soaking with wd 40, heating and freezing it, impact driver...it's there to stay.

 

 

 

And off topic, since this is my first post, this site is an amazing resource! I'm up to page 40 so far and getting just a little paraniod about all the problems I'll be having in the next few weeks - having just picked up an 02 lemans with 5000 km on the clock. Surprisingly I've added 1000 km and nothing has happened in the last couple of weeks, so perhaps it's the honeymoon period?