R90S - Alloy on discs

G

ghwallice

Hero member
Location
Ipswich
I've asked this once before, but I can't find the thread....

BMW R90S. Front end was set up wrong, and the caliper holders on the fork boot rubbed on the disc. Disc now has alloy fused to it.

Is there an acid I can use to dissolve the alloy without too much impact on the disc? If not, how?

Regards, Greg
 
you could take the discs off and soak them in a bucket (plastic) of Caustic Soda to undertake a primitive caustic leach. You can buy a tub of drain cleaner crystals (NaOH) for a few bucks... Leave them to soak overnight and see how you go: rinse and repeat as necessary. Mind your fingers tho and be sure to wear some chemical resistant gloves... :o :o
 
Yep, caustic will dissolve the ali. Just ask my wife who used our aluminium stock pot for soap making  :LOL:
 
Highflyer said:
Caustic works fine .
Just remember to remove the carriers first.
Click to expand...

Didn't have any Caustic, so painted on Hydrocloric, being careful not to get any on the carriers...

Fascinating to watch. Heaps of little brown bubbles chewing away at tiny bits of alloy I couldn't even see or knew they were there. Took about 10 minutes!

Regards, Greg
 
Yep, hydrochloric acid is generally used to dissolve ferric iron (rust) and etch carbon steel. Wrong end of the pH scale: not sure hydrochloric attacks alloy appropriately well so best to buy some caustic soda crystals from any supermarket or hardware store.
 
Aluminium is amphoteric.
Just wash the disc with a lot of water (long soak) and it should be ok.
 
Grant said:
Aluminium is amphoteric.
Just wash the disc with a lot of water (long soak) and it should be ok.
Click to expand...

But the oxide is impermeable to water.

Otherwise minelaying ships and my fishing tinnie would have problems.

PS: If you wanted to dissolve the disc and leave the remaining aluminium then you could try nitric acid.
 
Wash it in water following the clean with Hydrochloric acid, to neutralise the effects on the iron disc.
 
ghwallice said:
I've asked this once before, but I can't find the thread....

BMW R90S. Front end was set up wrong, and the caliper holders on the fork boot rubbed on the disc. Disc now has alloy fused to it.

Is there an acid I can use to dissolve the alloy without too much impact on the disc? If not, how?

Regards, Greg
Click to expand...
hi Greg, are the disc's the standard S/S if so bin them and get some cast one's with pads to suit. That's what i did on mine and its changed the bike 🚲
Regards Andy
 
Plenty of water and scrubbing after the acid. Not mine. Just some bucket o.s i'm doing some work on for a mate.
 

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